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Micromite-based 4DOF Simulator Seat Playing a car racing game (or if you prefer, a driving simulator) on a big screen can be thrilling. Plus it’s a lot cheaper and safer than taking your car to a racetrack! But it’s a lot more exciting if you can actually feel the motion and forces as you accelerate, brake, corner and drive up/ down hills or banked tracks. Build this four-degree-of-freedom racecar seat and experience that motion, without spending heaps! It works well with flight simulators, too. I f you’re really into racing games or driving simulators, you’ll want a seat like this, which moves to simulate the motion of the vehicle you’re ‘driving’. It can also give you some sensation of motion with a flight simulator, although obviously, it can’t quite simulate barrel rolls and loops! You can go out and buy one right now (or order it online), but you could easily spend thousands of dollars on a good one. If you have some mechanical and electronics skills, and are interested in a bit of a challenge, you can build your own for a fraction of the price. And in this article, we explain just how to do that. You can see the sort of results you can expect to get if you build this seat by watching the following short video: https://youtu.be/tn9LW758emc That video shows a racing simulation game called rFactor (available on https://store.steampowered.com), actuating the seat using the SimTools software (link at the end of this article). Micromite-based The electronics, whose job is to inter26 Silicon Chip by Gianni face with your PC, retrieve data from the simulation and then drive the motors in the seat to the required angles. It’s set up using a touchscreen interface. And it’s all based on a familiar module to SILICON CHIP readers: Geoff Graham’s Micromite processor. The electronics module can control the motors in the seat using off-theshelf motor driver boards, or even better (and much cheaper!) you can build your own, as described later. The seat itself is a bucket seat as installed in many race cars, or even street cars. They are widely available and not terribly expensive (try a wrecker who might have just what you want!). Of course, if you want to use a famous brand seat (like a Recaro) be prepared to pay just a little more! The seat’s supporting structure is built mainly from steel tubing, plates and MDF, with linear bearings to allow it to move forward and back and simple ‘bearings’ made from caster wheels and tubes to allow it to pitch forward and back, yaw from side to side and roll from side to side. Between two and four motors provide the motion, depending on how many ‘dePallotti grees of freedom’ (DoF) you want. Australia’s electronics magazine siliconchip.com.au MICROMITE 4DOF AXES CONTROLLER Roll Up POWER SUPPLY “Pitch” Down PIC32MX170F256D Yaw H-BRIDGE Forward “Surge” POLOLU 758 Back WIPER MOTOR WIPER MOTOR Fig.1: apart from the mechanical side, which we’ll get to shortly, here are the electrical components of the simulator seat and are described in the text. The motors are worm drive (12V or 24V wiper motors, for example) which can be obtained at low cost from an auto wrecking yard. The panel below shows and explains the six basic degrees of freedom, while Fig.2 shows those motions the most complicated version of the seat provides. With a driving simulation, turning the vehicle normally causes some degree of yaw, sway (pitching sideways) and possibly also roll (pitching forward/back). Acceleration and deceleration cause changes in pitch (to simulate suspension compression) and surge (forward/ back motion), while driving over bumps or elevation changes (ie, going up or down a hill) causes heave (up/down) movements. The use of a standard seat slider mechanism provides a reach adjustment for the pedals, steering and gear controls (slider frame), so that you can customize it to suit each individual driver. Additionally, the seat can be relocated forward or backwards through additional holes on the main frame. It also provides a reach adjustment for the pedals and other controls, so that you can customise it to suit each individual driver. WHAT IS DoF? The are actually six Degrees of Freedom, which allow you to experience just about any force you’re likely to encounter. All relate to the possible movement of a ship at sea or an aircraft/spacecraft in flight. These are: Roll Right Yaw Left Pitch SC 2019 Down siliconchip.com.au The seat assembly can be built in three different versions, with two, three or four degrees of freedom. The three DoF version cannot move forward or backward but can tilt forward, back, left, right and yaw. The two DoF version cannot yaw either, and can only tilt forward, back, left or right. Essentially, the two DoF seat is made into a three DoF seat by the addition of a “swivel/yaw frame”, including a third motor which causes the back of the seat to swing from side to side. The three DoF seat is turned into a four DoF seat by the addition of another base (made from MDF) DoF – Degrees of Freedom – refer to the directions you (or more properly, your craft) can move (in this case, simulated by our seat). Up Forward Fig.2: the four ‘degrees of freedom’ which allow you to experience just about any force you’re likely to encounter while in a moving vehicle. The seat described here can provide all degrees of freedom except for left/right and heave (although its up/down axis does provide some degree of heave motion). Move up and down (elevating/heaving); Move left and right (turning/swaying); Move forward and backward (accelerating/braking or ‘surging’); Swivel left and right (yawing); Back Tilt forward and backward (pitching); Pivot side to side (rolling). Our simulation seat has four of these motions: up/down (heave), forward/back (surge), swivel (yaw) and roll. The ‘heave’ motion is implemented by moving the front of the seat up and down on both sides at the same time, while roll is provided by the differential vertical motion of the front of the seat between the left and right sides. Australia’s electronics magazine September 2019  27 Fig.3: the four main subframes: from left to right, the yaw base/swivel frame (not required for the two-DoF version), the main frame, the seat frame and the slider/steering frame. The majority of mechanical construction work in building the seat involves fabricating these four sub-frames. They are made mostly from steel tubing, plates, angle, flat bar and a few brackets. You will need some welding skills to do a good job. with linear bearings and a motor, so that it can slide forwards and backwards. The two-DoF version is the easiest to build, especially if you omit the seat slider adjustment. It’s possible to upgrade a two-DoF version to the three-DoF version later, and similarly, to upgrade the three-DoF version to the four-DoF version. The four main subframes are shown in Fig.3. The yaw base (not required for the two-DoF version), the main frame, the seat frame and the slider/steering frame are arranged in a stack, with the bottom frame on top of the yaw base, the seat frame on top of the bottom frame and the slider frame hanging from the seat frame. Building the seat frame/assembly This is a job which requires some significant fabrication skills and tools. Most of the components are made from steel, which can be cut using a metal cut-off saw or manually (and slowly!), with a hacksaw. The 6mm plates used to attach the electric motors are the only plates requiring actual shaping. Any metal supplier The seat frame with the bucket seat removed 28 Silicon Chip can cut these. It can be done manually, but it’s hard work! The other mounting plates are either fabricated from blank metal plates or made up using standard off-the-shelf brackets. There is a need to machine special bushes and rods to suit the spherical bearing and universal joint unit. These should be made to fit the selected components. The two rear caster wheels on the swivel base are attached using spherical bearings to reduce friction, and the shaft holes must be re-drilled to keep the correct horizontal height of the frame. Nylon solid wheels (not rubber) can also be used, although this will increase the power demand from the motor. In this case, the two angle holes to the main frame wheel also need to be re-located to maintain the correct horizontal level of the main frame. For the simulator frame to swivel, the body of the larger caster swivel wheel base is used. The wheel housing needs to be cut and welded to the swivel base. To allow a smoother swivel movement, it would be better to remove the ball bearing from the large caster swivel A view of the universal joint connecting the seat frame to the main frame. Australia’s electronics magazine siliconchip.com.au C 120 16 7 24° A 300 800 SLIDER BASE C 205 395 380 A G C C C A H 300 340 H 1071 134 ALL DIMENSIONS ARE IN MM F 130° 518 SLIDER & STEERING FRAME B 72° 149 1 October 2019  29 185 282 12 H G A E 40° C 82 518 I 340 FOOT PLATE B E B E 340 F D 500 134 SC 2019 SLIDER STEERING D B F E 149 800 30 base and introduce a double raw-angular contact bearing or similar, with a dedicated spindle. But that would require a dedicated housing design. The caster swivel base used is the easiest solution and works well. Figs.4-7 show the details of how each subframe is made, while Fig.8 shows the MDF pieces which need to be cut and shaped for the table which holds the steering wheel and gearshift lever, and the floor base, which is only needed for the four-DoF version of the seat. Fig.9 shows the assembled seat (four-DoF version) from two different angles while Fig.10 shows a 3D view of the completed assembly (3 DoF). You can also refer back to Fig.3 and the photos throughout this article during construction in case you have trouble figuring out exactly how the various pieces fit together. We won’t go into exhaustive detail on the construction steps here, partly because there are various ways you can go about it, and partly because we expect constructors with the tools and skills to be able to do so should be able to figure it out from the CAD drawings and diagrams. Most parts will need to be welded, although some parts are bolted together, and generally, the holes which need to be drilled for these bolts are shown in the drawings. Drill 12mm holes for M10 bolts, 10mm holes for M8 and 8mm holes for M6. Once you have built the subframes, given them a good coat of black paint for rust prevention (and to make it look good), put them together and then you can start mounting up the motors and fabricating the linkages to attach them to the frame where required. If building the three-DoF version, it’s easiest to completely build and test the two-DoF version first, then add the yaw base, motor and linkages and test that separately. Similarly, to build the four-DoF version, build and test the three-DoF version and then add the floor base, linear bearings, forward/back motor and linkages, then wire that up and test the final product. Once you’ve built the frame and attached the motors, you will need to build the controller module and obtain a suitable power supply before you can wire up the motors and test it properly. Make sure you attach the punched angle rail to the slider frame (“foot plate retainer”), even if you aren’t using the chequerplate foot plate, as it adds needed rigidity. The CAD drawings do not show how this is mounted, but you can see it in the photos. J FOOT PLATE RETAINER (x2) Fig.4: the slider and steering frame provides a place to mount the steering wheel, gear shift lever and pedals, while allowing them to be moved forward and back, to suit users of different heights and sizes. It’s a good idea also to fit the foot plate, to give you somewhere to rest your feet (it looks nice, too). 583 SC Fig.5: the bucket seat is mounted on the 12 x 12mm diameter seat frame, and P 38 holes to attach seat can be moved forwards or K M backwards 4 x 8mm O into one of diameter three positions holes to L N L attach through extra slider O bolt holes. This frame also provides 280 K attachment points for the 320 P slider and          steering frame and also the caster wheels          which roll on the optional swivel frame. N 2019 152 K P siliconchip.com.au Australia’s electronics electronics magazine magazine Australia’s 524 95 380 The additional adjustment holes allow 25mm further movement of the seat frame assembly. 355 110 81 SSeptember eptember 2019  29 2019  29 200 You can cut the MDF components using a jigsaw and laminate the edges with PVC edge banding tape and a hot air gun. 225 W V U 70 108 T T U R Adjustment and weight handling Q There are two options to assemble the seat and slider frame, depending on whether a standard seat slider is used or not. If using a seat slider, this is bolted between the seat bottom and top of the slider/steering frames. Unlike in a vehicle, instead of moving the seat itself, it moves the sliding/steering frame back and forward. The seat frame/slider frame is bolted to the pedal frame, while the slider top rail is bolted to the seat frame. This allows the foot frame to move forward or back as needed, with minimal disturbance to weight ratio balance of the unit as the seat stays close to the universal joint pivot point. There is a further 25mm forward or backward step adjustment on the seat frame, as there are three sets of holes in the seat frame to which the seat can be bolted. This can be used to offset user size or weight differences. I have tested the rig with a 120kg, 1.75m tall individual, and both the frame and the motors were able to cope without any problems. S 765 W 300 U 123 V U T 61° V Q 510 U T T R 750 U 391 S 100 650 108 V Q W U Controller circuit U S SC V 2019 Fig.6: the seat frame mounts on top of this main frame, which provides attachment points for the two front motors and also the caster wheels, which roll on the optional yaw base below. <at> 185 2019 5 40 40 15 8 SC 113 2 6 40 <at> X 335 7 75 280 5 350 2 Y 305 Z $ X 200 120 <at> 12 30 8 <at> 755 40 RETAINING WHEEL 16 6 LINEAR BEARING BRACKET 7 45 700 R887 The controller circuit is shown in Fig.11. This excludes the four motor controllers, which will be described separately later. You have a couple of options when it comes to those motor controllers. The job of this circuit is to receive data from the simulation running on a PC via a USB port, then perform some calculations to determine how the motors need to be driven to move the seat appropriately. It must then produce the appropriate drive signals to send to those motor controllers. All of this work is done by the software running on IC1, a 44-pin SMD PIC32 processor programmed as a Micromite. The aforementioned software is therefore written in MMBasic. Data from the PC comes in via a USB/serial adaptor that is wired up to CON1. The data then goes from CON2 to CON4, via a pair of jumper wires (blue/green dashed lines). CON4 connects to pins 8 & 9 on IC1, which are configured as a second serial port (ie, not the same one used for the <at> 5 8 <at> Z 8 2 <at> Z WHEEL HOLDERS 3 25 30 Fig.7: the yaw base/swivel 3 frame allows the main 100 20 20 frame above to rotate around 146 the front pivot point made from a caster swivel wheel. 60 50 It rides on two caster wheels attached to the angle bar which roll on the angled metal plates at the back of the frame. This also provides a mounting point for the yaw motor. 30 30  S Silicon Chip A view of the typical linear bearings and shaft used for the forward/backward motions. Australia’s Australia’s electronics electronics magazine magazine siliconchip.com.au 280 225 $ $ 130 445 1100 340 450 % % Motor $ FLOOR BASE (FORWARD/BACK) % Fig.8: these pieces, cut % from 16mm MDF, provide a SC 2019for the steering wheel and gear table shift lever, and the optional floor base which is needed for the fourth (forward/back) degree of freedom. BUCKET SEAT GHEPARDO (ADJUSTABLE) A view of the aluminium plate used as a footrest, installed on the slider/steering frame. siliconchip.com.au 355 150 115 $ 200 200 STEERING & GEARSHIFT TABLE 470 Micromite console & programming). To program or reprogram the Micromite software, the jumper wires connecting CON2 to CON4 are changed to connect CON2 to CON3 instead, so that the USB serial port accesses the Micromite console. During regular operation, the software reads in and processes the data from the USB serial port on the PC. It then generates control signals on digital output pins 1-4, 15 and 21-23. Pins 15 and 21-23 carry PWM signals which determine the torque/speed for each motor, while pins 1-4 control the direction of motor rotation. These signals go to pin headers CON8a-d and header sockets CON9a-d – these interface to one of two types of motor controller. CON8a-d suit pre-built modules, the “Pololu High-Power Motor Driver 18v25” while CON9ad suit a module that you can build yourself, for considerably less than the Pololu modules cost, described later in this article. It’s a slightly revised version of my design published in the Circuit Notebook section of the November 2017 issue (page 80). The main difference is a slightly changed layout to better suit plugging into the controller board used for this project, plus a slight simplification which removes two redundant resistors. While not shown in Fig.11, the board has two two-way terminal blocks to feed +13.8V and 0V from a high current supply into the board, for distribution to these four motor controller modules (see Fig.13). The motors are wired directly to the output sockets on the motor driver modules. If using my motor drivers, because they have three control inputs, rather than the two of the Pololu modules, you need an extra inverter for each driver. This is provided by IC2, a 74LS14 hex inverter. It converts the direction signals (low for one direction, high for the other) into two signals, with one going high for rotation in one direction, and the other going high for rotation in the opposite direction. CON6 is a 14-way header to connect to a 2.4in or 2.8in touchscreen based on the ILI9341 controller chip, which is the same screen used in the Micromite LCD BackPack and V2 or V3 BackPack. This is used to set the unit up and to monitor its operation. See the screen grabs below to see how the screen is used. It’s critical to calibrate the motor control scheme properly. Australia’s electronics electronics magazine magazine Australia’s Fig.9 (below): when the four main frames, seat, table, steering wheel and pedals are all joined together, they should look something like this (4DoF version). LOGITECH G27 STEERING FRAME NOT SHOWN SSeptember eptember 2019  31 2019  31 Fig.10: here’s a 3D view of the four main frames (not including the floor base or motors) as they appear when fully built and assembled. Other connectors CON5 is an in-circuit serial programming header which is compatible with the Microchip PICkit 3 and PICkit 4, although you could also connect it to a Microbridge (see the May 2017 article; siliconchip.com.au/Article/10648). This is necessary if you purchase a blank PIC32 microcontroller. If you purchase a pre-programmed micro from the SILICON CHIP ONLINE SHOP, you can get away without this header. Power is fed into the unit via CON7. It must be a regulated 5V, and this supplies the LCD screen at CON6 directly, both for logic power and to run its backlighting LEDs. (Initially the plan was to supply power via CON1 from the PC’s USB port but we found that the voltage drop caused by the long cable between the rear end of the chair and the display (about 2m) caused the display to misbehave. So it is best fed in via CON7). The 5V rail is also regulated to 3.3V by LDO REG1, to power microcontroller IC1. CON10 allows a DS18B20 temperature sensor to be connected to the board, so that the unit can shut down if the board temperature gets too high. If you use one of the DS18B20 sensors on the end of a A view of one possible mechanical link between the front motor shaft and the positioning potentiometer. 32 Silicon Chip wire, you could mount it in or on the power supply, or one of the motors, if you want. But if anything is going to overheat, it will probably be the motor drivers, so the ideal location for this sensor is in the middle of the M1 and M2 driver boards as these are the most heavily used. The pins of CON11 can be shorted to reset microcontroller IC1. It could be wired to a momentary pushbutton reset switch. CON12a-d provide connection points for the four motor position feedback potentiometers. Basically, as the motors rotate, the voltage at pin 3 of each of these connectors varies between 0V and 3.3V, and this is fed to analog input pins 27-24 of IC1, so it can use its internal analog-to-digital converter (ADC) to sense the potentiometer positions and thus drive the motors to a particular angle, just like a servo motor. LED1 is a simple power indicator to show when the 5V supply is present. And finally, CON13 is an auxiliary header which breaks out connections to four spare Micromite pins plus +3.3V and GND, and could be used for future expansion (such as adding a fan to simulate wind!). Pololu motor drivers Note that the Pololu motor drivers now being sold are somewhat smaller and cheaper than the versions shown here, but they do the same job and are drop-in replacements. These drivers enable bidirectional control of the highpower DC brushed motors used. These motor driver boards support a wide range of motor voltages, from 6.5V to 30V DC, and can deliver a continuous 25A. You can get these modules in Australia from RobotGear (http://siliconchip.com.au/link/aats) or Core Electronics (http://siliconchip.com.au/link/aatt). Or you can build your own H-bridge drivers, which are almost as capable... H-bridge driver circuit My own H-bridge module design is shown in Fig.12, which is very similar to the circuit published in the Circuit Notebook section of November 2017. The H-bridge is formed from two CSD18534KCS high-current logic-level N-channel Mosfets (Q3 & Q5) and two IRF4905 P-channel high-current Mosfets, Q2 & Q4. The rear bearing assembly. The retaining centre bearing prevents the frame from over-tilting during strong changes of direction of the swivel frame. Australia’s electronics magazine siliconchip.com.au An overall view of the assembled unit. The positioning of the motor links on the two lower frames is best determined once assembly is complete. Schottky diodes D1-D4 parallel the Mosfet body diodes and absorb any back-EMF or motor braking energy. They dissipate a lot less heat than the Mosfet body diodes because of their lower forward voltages. There’s also a local 100µF bypass capacitor across the motor supply. Zener diodes ZD1-ZD4 protect the Mosfet gates from excessive voltages, clamping them to about -0.7V and +15V. AND gates IC1a & IC1b combine the PWM and directional input signals to generate the gate drive voltages, and their outputs directly drive the gates of Q3 and Q5. These signals also go to the bases of NPN transistors Q1 and Q6, which form inverters to generate the drive signals for the P-channel Mosfets. These also act as level-shifters, so that when the signal from IC1a/IC1b is low, the gate of the associated P-channel Mosfet is held at V+, around 13.8V, to keep that Mosfet switched off. When the signal from IC1a/IC1b goes high, the baseemitter junction of one of these NPN transistors is forward-biased, and current flows through its 3.6kΩ base current-limiting resistor, causing it to switch on and pull its collector down to just a volt or so. This is well below the 13.8V at the source of Q2 and Q4, so one of those Mosfets switches on. The 1.5kΩ base-emitter resistors for Q1 and Q6 ensure that they switch off when there is no drive voltage, and as a result, all four Mosfets are kept off if the 5V supply is absent, even if the 13.8V motor supply is present. The 160Ω emitter resistors for Q1 and Q6 prevent them from fully saturating when switched on, so that they switch off faster when the base drive is removed. The exposed seat frame. The full frame, without the seat in place. siliconchip.com.au Building the control module The control module is built on a single-sided PCB coded 11109191. Use the overlay diagram, Fig.13, as a guide during construction. You can etch this at home, as I did, or you can buy a commercially-made PCB from the SILICON CHIP ONLINE SHOP. That board will be double-sided, with copper tracks on the top layer replacing the wire links, saving you considerable effort in fitting those links. Australia’s electronics magazine September 2019  33 CON7 DC IN +5V + 470 – CIRCUITRY IN THIS SHADED AREA V+ FF2 FF1 RESET- 8 5V 7 PWM 6 DIR+ 5 DIR– 4 GND 5 GND 47 F  LED1 K 4 3 2 2 1 14 1 IC2a 3 PWM 2 DIR 1 GND CON 9 b CON8b V+ 5V(out) FF2 FF1 RESET- 8 5V 7 PWM 6 DIR+ 5 DIR– 4 GND 5 4 3 2 4 1 3 CON4 IC2b 1 TX 3 PWM GAME 2 RX 2 DIR CON10 1 GND CON 9 c CON8c V+ 5V(out) FF2 FF1 RESET- 8 5V 7 PWM 6 DIR+ 5 DIR– 4 GND IC2: 74LS14 5 4.7k 3 TEMP SENSOR IN +3.3V 2 1 4 3 2 6 1 5 IC2c 3 PWM ICSP 2 DIR CON5 1 GND MCLR Vcc 5V(out) FF2 FF1 RESET- GND CON 9 d CON8d V+ 8 5V 7 PWM 6 DIR+ 5 DIR– 4 GND 5 PGD 4 PCC 3 2 1 +3.3V 3 4 5 6 IC2d 8 1 2 9 7 3 PWM 2 DIR K A CON8a-9d: For Pololu Drivers CON9a-9d: For DIY drivers SC 20 1 9 LM3940IT LED 1 GND GND IN GND OUT FOUR DEGREES OF FREEDOM MICROMITE-BASED MOTOR CONTROLLER The only slightly tricky part to solder is SMD microcontroller IC1. But it isn’t a particularly fine-pitched device, so it is not too difficult. You will need some good flux paste and a roll of solder wick, though. Start by locating its pin 1 dot and line this up with the pin 1 indicator etched into the copper on the bottom side of the board. Tack one of the corner pins to the board, for example, by applying a little solder to one of the pads and then sliding the chip into position while heating that solder. Check that the chip is square and all the pins are lined 34 +3.3V OUT IN 100nF A CON 9 a CON8a 5V(out) NOT REQUIRED IF POLOLU IS USED REG1 LM3940IT-3.3 +5V Silicon Chip up with their pads. If not, re-heat that initial solder joint and gently nudge the chip in the right direction. Once it’s correctly aligned, apply flux paste to all the pins, then solder the diagonally opposite pin from the one you tacked. Apply solder to the remaining pins. You can do this by loading the iron tip with some solder, then gently dragging it along one edge of the chip. Repeat for the other edges, then check for solder bridges across pins. If you find any, apply extra flux paste and clean them up with solder wick. Then use pure alcohol or flux residue cleaning solution to remove flux residue and inspect Australia’s electronics magazine siliconchip.com.au 9 10 11 T_IRQ 8 T_DO 7 T_DIN T_CLK 6 T_CS 5 SDO 4 BKL 3 SDI 2 SCK 1 D/C RESET 1 18 CS 2 RESET CON11 1k +5V 50k +3.3V GND +5V 12 13 14 CON6 ILI9341 BASED LCD DISPLAY 47 F +3.3V 17 AVDD 28 VDD 40 VDD AUX1 MCLR 1 2 3 4 RPB 8/PMD4/RB 8 RB9/RPB 9/SDA1/PMD3 RPB 7/PMD5/RB 7 RC 6 /RPC 6/PMA1 PGEC 3/RPB 6/PMD6/RB 6 RC 7 /RPC 7/PMA0 PGED3/RPB5/PMD7/RB5 CON13 18 6 44 5 43 4 42 3 41 +3.3V 2 1 38 IC1 RPC 5/PMA3/RC 5 5 PIC32MX170F 2 MX170F 37 RC9/RPC9/PMA6 PIC3 RPC4/PMA4/RC4 –256D 8 9 10 11 12 13 14 15 19 20 21 22 RC8/RPC8/PMA5 RB 10/RPB 10/PMD2/PGED2 RB 11/RPB 11/PMD1/PGEC 2 RPC3/RC3 TDI/RPA9/PMA9/RA9 RB12/PMD0/AN12 SOSCO /RPA4/RA4 RB 1 3 /RPB 1 3 /AN 11 SOSCI/RPB4/RB4 RA10/PMA10/TMS/PGED4 RA7/PMA7/TCK/PGEC4 RB 1 4 /RPB 1 4 /AN 10 TDO /RPA8/PMA8/RA8 OSC 2/CLKO /RPA3/RA3 OSC 1/CLKI/RPA2/RA2 RB15/RPB15/AN9 AN 8/RPC 2/RC 2 RA0 /AN 0 /VREF+ AN 7/RPC 1/RC 1 RA1/AN1/VREF– AN6/RPC0/RC0 PGED1/AN 2 /RPB 0/RB 0 AN5/RPB3/RB3 PGEC1/AN3/RPB1 /RB1 AN4/RPB2/RB2 VCAP AVSS 16 VSS 6 VSS 29 VSS 39 JP1 34 RX 2 33 TX 1 GND CON1 +5V 1 CON3 CON2 PROGRAM 32 +3.3V USB-SERIAL INPUT 36 35 PWM2B IN/OUT 31 2 2 3 1 4 5 30 6 27 +5V GND TX RX DTR +3.3V CON 12 a 26 3 25 +3.3V 24 2 1 23 POT – M1 CON 12 b 7 3 +3.3V 47 F 2 1 TANT. POT – M2 CON 12 c 3 +3.3V 2 1 POT – M3 CON 12 d 3 Fig.11: the control board circuit is relatively simple, thanks to the use of a PIC32 Micromite microcontroller (IC1) and four separate motor driver H-bridge modules, which connect via CON8a-d or CON9a-d, depending on the type. Motor position feedback comes from attached potentiometers, which provide variable voltage signals at CON12a-d. The blue and green dotted lines (CON2 to CON3 or CON2 to CON4) are where jumper leads are fitted to select between programming mode and game mode. the solder joints under magnification to ensure they are all good. Fitting the remaining parts If you have a single-sided board, the next job is to fit the 27 wire links on the top side of the board. They are shown in red on Fig.13. Don’t miss any, and if you are using uninsulated wire, make sure the links are taut so that they can’t easily bend and short to each other, or to the leads of adjacent components. Now fit the five resistors in place where shown on the siliconchip.com.au +3.3V 2 1 POT – M4 overlay diagram. It’s best to check each one with a multimeter before soldering it; you can identify them by the colour bands, but they are easily mixed up. Next, solder IC2 in place, ensuring that its pin 1 dot is orientated correctly. You can use a socket if you want, but it shouldn’t be necessary. IC2 can be left out if you are using the Pololu motor drivers. Install LED2, with its longer lead towards the closest edge of the board (marked “A” for anode on the PCB). Follow by fitting all the standard pin headers. Depending on how you are building the unit, some can be left out, Australia’s electronics magazine September 2019  35 Fig.12: the circuit of the DIY version of the motor driver (H-bridge) module. It uses four Mosfets to drive the motor in either direction, controlled by two small-signal transistors and a 74HC08 quad 2-input AND gate. This is only slightly different than the version previously published in Circuit Notebook. but they’re quite cheap, so it’s easier just to fit them all. If using the Pololu motor drivers, you can also fit the four 8-way female header sockets now. Follow by mounting polarised header CON7, then the capacitors. The electrolytic capacitors are polarised and must be orientated as shown. You can identify the positive lead as it is the longer of the two. The tantalum capacitor should also have a “+” marking on its body, while the aluminium electrolytics will have a stripe on the can showing the negative lead. You can now install the two terminal blocks along the left edge, with their wide entry holes facing the edge of the PCB, then fit regulator REG1 with its metal tab orientated as shown in Fig.13. Your touchscreen module should have come with a 14pin header pre-soldered to it. You can now connect this up to CON6 on the controller PCB using fourteen femalefemale jumper wires. You can get such wires joined together in a single ribbon cable, which would make the job a little easier (and neater). Pin 1 of CON6 is as the bottom, so make sure this goes to pin 1 on the LCD (pin 1 is +5V, pin 2 is GND) and that each pin is wired up in sequence. Use the two shorter jumper wires to connect Tx on CON2 to Tx on CON3, and similarly, Rx to Rx. Fit the shorting block on JP1 only if the controller is driven via the USB and LCD display installed close by (see our earlier comments about the display misbehaving with a long cable). Do not connect any other power source to CON7 (the LED will not light up). Solder the six-pin female header to the bottom of your USB/serial adaptor, so that its pinout matches that of CON1. Then plug this adaptor into CON1. Programming IC1 If you’ve purchased a preprogrammed Micromite chip, you can skip this step. Connect a PIC32 programmer to CON5, ensuring the pinout is correct (for a PICkit, this will be the case as long as pin 1 is lined up correctly). If using a PICkit, use MPLAB X IPE to load the 44-pin Micromite Mk2 HEX file into the chip, which can be downloaded for free from either the SILICON CHIP website, or Geoff Graham’s website (geoffg.net). If using a Microbridge, follow the instructions in the Microbridge article on using pic32prog to load a HEX file into PIC32. The file is the same regardless of the programmer you’re using. Loading the BASIC code You are now ready to connect this adaptor to your PC via a USB cable. LED1 should light up. Fire up a terminal emulator (or MMedit) and connect to the serial port which Here are the two motor drivers which suit our controller: on the left is the commercial “Pololu” driver, while at right is our DIY version (see Fig. 12 above). The DIY version, however, does require that IC2 is fitted to the PCB (see text). 36 Silicon Chip Australia’s electronics magazine siliconchip.com.au Fig.13: use this PCB overlay diagram as a guide to building the controller PCB. If you’re using a single-sided board, fit the wire links where shown in red. Otherwise, if you’ve purchased a double-sided PCB, that is not necessary. Note that the motor drivers shown here are now obsolete; the new versions are pincompatible but a fair bit shorter, so the supply wires will need to be a little bit longer. Also note that while this diagram shows the Pololu modules fitted, it also shows IC2. As explained in the text, you do not need IC2 with the Pololu modules – the diagram simply shows where it would be fitted if you are using DIY H-bridge modules. has now appeared at 38,400 baud (check Device Manager to see the newly allocated COM port number). Once you’ve established communication, use XMODEM or MMedit’s upload function to load the BASIC source code for this project into the Micromite chip. As with the Micromite firmware, the BASIC code is a free download from the SILICON CHIP website. You will then need to configure the touchscreen and set up the code to run on power-up by issuing the following commands: OPTION LCDPANEL ILI9341,L,36,32,35 OPTION TOUCH 30,31 OPTION AUTORUN ON GUI CALIBRATE Once you’ve finished calibrating the touchscreen, you can use the GUI TEST TOUCH command to check that it’s correct (touching the screen should leave a trail of dots), then cycle power and check that the splash screen comes up (see Screen1) and by touching the screen, the main screen (Screen2). Building the H-bridge module If you aren’t using the Pololu modules, you can build your own H-bridges using the double-sided PCB coded 11109192. Use the PCB overlay diagram, Fig.14, as a guide. Start by fitting the resistors where shown, except (for the moment) for the two 2.2kΩ, followed by the zener diodes, with the cathode stripes all facing towards the bottom of the board as shown. Next, fit schottky diodes D1-D4. Note that D3 faces in the opposite direction to all the other diodes. Also, since the diode bodies are quite large, you will have to be careful in bending the leads to fit the closely spaced pads on the PCB. Now solder IC1 in place, ensuring its pin 1 is in the correct location. You can use a socket, although we suggest you Top and bottom sides of the controller PCB, before the H-bridge drivers are attached (they slot into the header pin sets on the top side). While this single-sided board is ideal for home PCB makers, a double-sided version, which has all the links already in place as the top side pattern, is available from the SILICON CHIP ONLINE SHOP. IC2 is not required if Pololu drivers are used. siliconchip.com.au Australia’s electronics magazine September 2019  37 Part list - seat frame Pedal frame / slider 2 800mm lengths 20x20x1.6mm square steel tubing (A) 2 520mm lengths 20x20x1.6mm square steel tubing (B) 4 300mm lengths 20x20x1.6mm square steel tubing (C) 1 320mm length 20x20x1.6mm square steel tubing (D) 2 150mm lengths 20x20x1.6mm square steel tubing (E) 1 135mm length 20x20x1.6mm square steel tubing (F) 1 400mm length 25x25x3mm steel angle (G) 2 25mm lengths 25x25x3mm steel angle (H) 1 500x340x1.6mm rectangle of aluminium chequer plate (I) 2 800mm lengths of 30x30mm punched steel single slot angle rail (J) 10 M6 x 30mm machine screws and hex nuts (for attaching J to the slider frame). Seat frame 2 583mm lengths of 25x25x3mm steel angle (K) 2 355mm lengths of 25x25x3mm steel angle (L) 1 75x145mm rectangle of 6mm steel plate (M) 1 524mm length of 25mm diameter steel tube (N) 2 280mm lengths of 30x5mm flat steel bar (O) 4 M10 x 25mm machine screws (to join O to L) 6 M10 hex nuts (P) Main frame 1 750mm length of 40x40x1.6mm square steel tubing (Q) 1 650mm length of 40x40x1.6mm square steel tubing (R) 2 762mm lengths of 25x25x1.6mm square steel tubing (S) 2 300mm lengths of 25x25x3mm steel angle (T) 4 123mm lengths of 25x25x3mm steel angle (U) 2 142x100mm rectangles of 6mm steel plate (V) 1 215x100mm rectangle of 6mm steel plate (W) | not needed for 2DoF or 3DoF versions ~ Silicon Chip Fasteners and Linkages 6 55mm lengths of M10 threaded rod (for casters) # 12 M10 domed-cap nuts # 16 M5 x 12mm machine screws (for linear bearings) | 2 M6 x 15mm self-tapping screws (for retaining wheel) # 1 150mm length of M10 threaded rod (to swivel base) # 1 140mm length of M10 threaded rod (to MDF base) | 2 130mm lengths of M10 threaded rod (to seat frame) Bearings/wheels 8 M10 female swivel-head ball bearings 3 spherical insert ball bearings [NBR-SB201/12-40-22] 2 50mm diameter caster wheels (8) 1 heavy-duty swivel caster, 65x95mm minimum base size (wheel removed) (9) # 1 steering universal joint or prop-shaft UJ (from any car scrap yard) (for connecting the seat frame to the main frame) 4 linear ball bearings with rails (SBR12UU [block] & SBR12250mm [rail]) (%) | 4 Carinya 40x40 zinc-plated brackets (Bunnings Cat 0046902)(<at>) | not needed for 2DoF version; one only needed for 3DoF version solder it directly as some pins are soldered on the top side. Next, install the two 2.2kΩ resistors, which are mounted vertically, followed by transistors Q1 and Q6, with their flat faces orientated as shown. Also, before soldering the diodes, test fit the nearby Mosfets to make sure they will not get in the way. You may need to bend the diode leads a little to get them into a favourable position, where they clear the Mosfet bodies. Now solder the two 2-way terminal blocks in place, with the wire entry holes facing towards the outside, followed by the four Mosfets. As there are two different types, be careful not to get them mixed up, and ensure their tabs face as shown in Fig.14. Before soldering them, it would be a good idea to attach each pair to its heatsink, to ensure they line up correctly. Insert the insulating layer between the two pairs, then push them down as far as they will go and solder and trim the pins. Finally, fit header socket CON1 to the underside of the board, and it is ready for testing. Once you’ve completed the modules (you will need one for each degree of freedom that you are building into the seat), plug them into the main board. Note that the power supply terminals for this module are reversed compared to the Pololu module, so you will have to cross the wires over when you wire them up. 38 Swivel frame (|) 2 755mm lengths of 25x25x1.6mm square steel tubing (X) 1 700mm length of 40x40x1.6mm square steel tubing (Y) 1 350mm length of 40x40x1.6mm square steel tubing (Z) 1 305mm length of 40x40x1.6mm steel angle (2) 2 146mm lengths of 40x40x1.6mm steel angle (3) 4 40mm lengths of 45x45x5mm steel angle (4) 1 75x113mm rectangle of 3mm steel plate (5) 2 75x200mm rectangles of 3mm steel plate (6) 1 30x120mm rectangle of 3mm steel plate (7) # not needed for 2DoF version Wiring it up Luckily, this part is pretty straightforward. As you can see from the photos, I mounted the power supply for my rig at the back. I suggest you do the same. You will then need to run some thick (~25A-rated) wires, or a similarly rated figure-8 cable, from the supply up to the motor power terminals on the control board. Next, run a set of 10A-rated (or more) figure-8 cable from each pair of motor controller outputs to the appropriate motor. Motors 1 & 2 are at front left and right respectively. Motor 3 (if fitted) is the yaw motor, and motor 4 is the Fig.14: here’s how to fit the components to the double-sided DIY H-bridge board. For clarity, the heatsinks, mounting screws and insulating layer between the two pairs of Mosfets are not shown here. Refer to the photos of the unit for details on the heatsink mounting. It’s a pretty packed board, so don’t be surprised if you have to bend a few component leads to get everything to fit. Australia’s electronics magazine siliconchip.com.au Parts list - controller module 1 Dunnings 100x100x140mm angle bracket (Bunnings 1076757) | Motors/power 2 12V DC Fiat X1/9 lights retractor motors with 40mm radius action (roll) 2 24V DC garage sliding door motor with 40mm radius action (surge/yaw) ~ (worm-drive motors can also be used but are more expensive) 1 13.8V DC 40A power supply (Jaycar Cat MP3089) 2-4 100kΩ potentiometers (see text) MDF pieces 1 445x225mm rectangle of 16mm MDF ($) 1 280x130mm rectangle of 16mm MDF ($) 1 150x200mm rectangle of 16mm MDF ($) 1 1100x800mm rectangle of 16mm MDF ($) (floor base) | Other 1 Ghepardo fixed-back, five-way adjustable racing bucket seat 1 standard car seat slider mechanism (optional – see text) 1 set of Logitech G27 force feedback steering wheel and pedals Several metres of heavy-duty figure-8 cable Several metres of medium or light-duty three-core (or more) cable Connectors, to suit motors Total lengths of tube/angle/bar/rod 40x40x1.6mm square steel tubing: 1.1m 20x20x1.6mm square steel tubing: 4.6m 40x40x1.6 steel angle: 0.65m 25x25x3mm steel angle: 3.5m 30x5mm flat steel bar: 0.6m M10 threaded rod: 1m forward/back motor. Each motor must be fitted with a potentiometer to sense its shaft position. You need to wire the three connections for each potentiometer back to CON12a-CON12d on the controller board, ie, from motor 1 back to CON12a, motor 2 to CON12b etc. There are many different ways to connect these pots to the motors. Some motors have an extended shaft (for example, the two garage door motors I used). This allows placing the pot on one side of the shaft and the lever on the other end. Note that the arm lever length should not exceed 4550mm pivot to pivot, or the motor torque requirements may be too high. The RPM of a typical wiper motor will be around 50 revs/min. Wiper motors usually have the shaft extending only one one side, which will require a different mounting. The wiper motors unit pot uses a fork and spindle (a slide type mechanism). This allows full 180° rotation. But to avoid possible damage to the pots, I recommend opening the pots and flattening the wiper arm stopper. (see Fig.15). Additionally, do not attach any mechanical links yet – this is to avoid sudden and dangerous movement of any one of the actual chair frames. In each case, the pot wiper is wired to the connector siliconchip.com.au 1 single-sided PCB, code 11109191, 133.5 x 96.5m 3 6-pin headers (CON1,CON5,CON13) 5 2-pin headers (CON2-CON4,CON11,JP1) 1 14-pin header (CON6) 1 2-pin polarised header (CON7) 4 8-pin header sockets (CON8a-d; optional – for Pololu motor drivers) 4 5-pin headers (CON9a-d; optional – for self-built motor drivers) 5 3-pin headers (CON10,CON12a-d) 1 jumper shunt (JP1) 1 USB/serial adaptor (eg, CP2102-based; SILICON CHIP ONLINE SHOP Cat SC3543) 1 6-pin female socket (for USB/serial adaptor) 2 2-way 5.08mm pitch screw terminal blocks [Altronics Cat P2040/P2040A] 1 2.4in or 2.8in ILI9341-based colour LCD touchscreen [SILICON CHIP ONLINE SHOP Cat SC3410] 2 short (~100mm) female-female jumper leads 14 long (~200mm) female-female jumper leads (for LCD screen) 1 1m length of Bell wire, tinned copper wire or light-duty hookup wire (not needed for double-sided PCB) Semiconductors 1 PIC32MX170F256D-I/PT microcontroller, QFP-44, programmed with Micromite V2 firmware (IC1) 1 74LS14 hex Schmitt trigger inverter, DIP-14 (IC2)^ 1 LM3940IT-3.3 3.3V 1A low-dropout regulator, TO-220 (REG1) [Jaycar Cat ZV1565] 1 5mm LED (LED1) ^Not needed with Pololu Capacitors motor drivers 1 47µF 6V tantalum electrolytic         2 47µF 16V aluminium electrolytic 1 100nF MKT or ceramic Resistors (all 1/4W 5%) 1 47kΩ 1 4.7kΩ 1 1kΩ 1 470Ω 1 18Ω Parts list – DIY H-bridge H-bri dge (per module, 2-4 required) 1 double-sided PCB, code 11109192, 54.5 x 23mm 1 5-pin header socket (CON1) 1 4-pin terminal block, or 2 2-pin terminal blocks (CON2) 2 small heatsinks (cut down from Jaycar HH8526) 1 piece of insulating material, 20 x 20mm (eg, presspahn or stiff plastic) 2 M3 x 16mm machine screws, shakeproof washers and nuts Semiconductors 1 74HC08 quad 2-input AND gate, DIP-14 (IC1) 2 BC546 100mA NPN transistors, TO-92 (Q1,Q6) 2 IRF4905 P-channel Mosfets, TO-220 (Q2,Q4) 2 CSD18534KCS N-channel Mosfets, TO-220 (Q3,Q5) [SC4177] 4 1N5819 40V 1A schottky diodes (D1-D4) 4 15V 1W zener diodes (ZD1-ZD4) Capacitors 1 100µF 25V low-ESR electrolytic Resistors (all 1/4W 5%) 2 3.6kΩ 2 2.2kΩ Australia’s electronics magazine 2 1.5kΩ 2 160Ω September 2019  39    Fig.15: to make the pot wipers    continuously variable, prise the lugs holding the rear cover on apart and remove the stoppers on both the pot cover and the internal workings. pin that’s closest to CON5, the ICSP header, while the opposite ends of the pot tracks go to the other two pins. But you need to be careful to connect these two connections with the correct polarity, or else the motor will bump into its end stops the first time it’s powered up. To get this right, disconnect the motor wiring one at a time and briefly power each from a 12V source so that they rotate fully clockwise, then measure the resistance from the wiper to each end. Find the end which gives the highest resistance when fully clockwise, and ensure that this end is wired to the ground pin on CON12a-d. The ground pin is the one centre pin of each header, while +5V is at the right-hand end. Also, make sure that you don’t get the motor wiring mixed up; the motor which is wired to CON12a should be powered from the M1 outputs (CON8a or CON9a) and so on. Wiper motors usually have a switch in the gearbox which need to be bypassed in this application. Wiring for all motors must be isolated from the motors and frames; you should also make necessary arrangements that take into accout that there are several parts which move and could cause chafing later on. The top side of the completed controller PCB with the four Pololu H-Bridge motor controllers in situ, with heatsinks (eg, Jaycar HH8526) attached. Set-up and testing You can now change the jumper leads from the Tx and Rx pins of CON2 to go to CON4 rather than CON3, then power the controller up by placing a shorting block on JP1 and plugging the USB cable into your PC. After the splash screen has been shown and you can see the main screen (shown in Screen2), briefly disconnect each motor from the power supply and apply 12V to Motor 1 should move anti-clockwise about 45°. This command should return it to centre: Screen1: the initial splash screen which appears on the LCD touchscreen when power is first applied, assuming that the Micromite firmware and BASIC code has been loaded onto the PIC32 chip. Screen2: this shows you the current motor positions (POTx) and desired motor positions (MOTx), along with the internal temperature reading. Touch the limit percentage bars to adjust the motor power for each axis. 40 Silicon Chip each motor in each direction. Check that as the motor rotates clockwise, the relevant POTx reading on the screen increases, and as it rotates anti-clockwise, the reading decreases. Check also that the temperature reading is correct. Set the roll, surge and sway limits low, then connect all the motors back to the main power supply and switch it on. The motors should all move towards the centre, then stop. If any of them are acting up, switch the power supply off and check their wiring, especially to CON12a-d. Now open a terminal emulator program and connect to the USB/serial port on your PC at 115,200 baud (or use MMedit chat facility), then type the following sequence and press Enter (you may need to copy and paste this text into some terminal programs for it to work): A<at>~~~Z (That’s a capital A, the at symbol, three tildes, and a capital Z). A~~~~Z  (That’s a capital A, four tildes, and a capital Z). Repeat these commands, moving the <at> (at symbol) to the right, to test the other motors, eg: Australia’s electronics magazine siliconchip.com.au Here’s the electronics “works” – the (commercial) power supply on the left and the H-brdge controller on the right. ing, flying and other simulators: A~<at>~~Z A~~<at>~Z • • • etc. www.x-sim.de www.xsimulator.net http://bffsimulation.com If that all works, then you’re ready to close the terminal emulator, turn up the settings on the touchscreen, fire up your simulator and give it a try! Once you’ve finished testing, it’s up to you whether you want to leave the controller board powered from the 5V USB supply, via JP1, or rig up a 5V regulator to run the controller off the 13.8V motor supply – or via some other arrangement, like a 5V DC regulated plugpack. To see just how expensive commercial equivalents of this project are, check out the following links: Useful links Further information regarding the actual seat development and construction can be viewed on the following link: The following websites are dedicated to simulations which have developed accessible programs to extract the physics data from many supported games, including driv- • • • • • • • www.pagnianimports.com.au https://simxperience.com www.inmotionsimulation.com www.atomicmotionsystems.com www.cxcsimulations.com www.vrx.ca www.xsimulator.net/community/marketplace/ 2dof-3dof-optional-descriptions.81/ Changing the software Screen3: this is the screen which allows you to save or load those presets, depicted as three different types of vehicle. siliconchip.com.au The BASIC code includes two variables called PotLimMax and PotLimMin which allow the motor potentiometers to work at the centre of their movement, taking account of any possible small ‘overrun’ past the +90° and -90° maximum angles. PotLimMax is the required travel angle of rotation of the pots (from 0 to 1), in this case, a full 180°, while PotLimMin is the value at the lowest point of the travel (-90° angle, again from 0 to 1). There are also offset variables (Brk1, Brk2, Brk3 and Brk4) are used to limit or remove any minute motor movements due to pot variation when standing still. These also assist in ‘powering-off’ the motors when movement is not required. You can control the most suitable axis strengths relating to the type of simulation being run, by limiting the PWM pulse width to a percentage of its maximum value, via the touchscreen. These can be saved and reloaded in three SC presets (Screen3). Australia’s electronics magazine September 2019  41