Open FFBoard (Former OHSC)

A modular and open source force feedback steering wheel interface and motor driver for racing simulators and robotics

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The goal of this project is to develop a simple and comparably cheap force feedback steering wheel interface for stepper motors and servos for hobbyists as an alternative to expensive commercial option.

This will make for an affordable direct drive wheel cheaper than most alternatives while retaining high accuracy and responsive force feedback.

While there are several commercial toy grade FFB steering wheels and some higher end simulator grade producs these are very expensive and and are often not moddable or come with their own expensive ecosystem.

It makes sense to focus this project on a simple open source force feedback interface as this is the part where the community lacks a good and open solution.

Therefore the main goal will be to develop a universal FFB controller (Open FFBoard).

It will provide a modular architecture with interchangable motor drivers (think about vesc and odrive compatibility) and a reference motor driver board based on the TMC4671 still usable on its own.
(If you were here because of the servo control aspect the previous prototype promised)

The FFBoard is just an interface for USB HID, encoders, buttons and pedals.
The software is modifiable for different motor drivers and control outputs (USB HID for most users. Could also be a PPM output).

OHSC Powerstep v1.1

Gerber files and eagle project for old version. Functional but will not be supported further

x-zip-compressed - 557.54 kB - 07/06/2019 at 18:28


  • 1 × Powerstep01 Power Management ICs / Motion, Motor and Servo Control
  • 1 × STM32F411RCT6 or STM32F103RCT6 Main Processor
  • 2 × DTSM-6 Switches and Relays / Switches
  • 1 × USB_MICRO-B Connector
  • 2 × 68µF Caps 100V

View all 20 components

  • Testing the TMC4671

    Yannick (Gigawipf)11/23/2019 at 11:56 0 comments

    As mentioned before the reference motor driver could be powered by a Trinamic TMC4671.
    This motor controller promises everything a universal torque mode motor driver should do while being compatible with 2 phase steppers, 3 phase servos and DC motors with the same power stage. Nice.

    Big thanks to Trinamic MC for sending me a TMC4671 Devkit. This way i can begin testing the features before the fixed chip is sold again and the final pcb is manufactured.

    I tested the chip with the TMC IDE Trinamic provides for this kit. This software nicely explains with wizards in the form of a tutorial how to setup the core parameters of the TMC4671.
    It also helps debugging with graphs and register browsers.
    I have made a setup with a 2 phase stepper, an 8192ppr encoder and torque mode to see how it responds and it pretty much does everything the old OHSC with the powerstep01 did but much better and in hardware. Nice.

    A modular design would also allow support for multiple TMC Motor Drivers on one SPI bus for 2 or 3 axis systems.

    Video of the TMC4671 running

    And if you perfectly align the encoder speeds impossible for normals stepper drivers can be achieved.

    The next step is to finish a pcb and wait until the TMC4671 is sold again. This might be the best solution fo a reference motor driver for this project.

    Trinamic said to me that the TMC4671 in the fixed version is planned to be released in march 2020.
    Until then the current version is sold that has a few hardware problems.
    This means that the next prototype will still have the old version of the chip.
    For SPI control and FFB the bugs should not be an issue apart from having to slow down the spi clock a bit for now to avoid a data corruption issue.

    The step/dir interface does not work and the adc and spi MSB might have sporadic glitches which fortunately did not affect the motor control in the tests.
    All known issues are listed in the errata of the datasheet.

  • Change of project direction. More FFB, more compatibility

    Yannick (Gigawipf)11/04/2019 at 11:29 0 comments

    The goal of this project was originally to create an open source motor driver focussed on racing simulation controls.

    There are many different motor drivers but not many of them were really suited for the task AND hobby budget friendly.

    It makes sense to focus this project on a simple open source force feedback interface as this is the part where the community lacks a good and open solution.

    Therefore the main goal will be to develop a universal FFB controller (Open FFBoard).

    While the first prototype (OHSC) did kind of accomplish this goal it was clear that for reliable use and high accuracy the powerstep01 was not suited. They sometimes locked up or died as they were not used as intended and only provided 7 bits of resolution. I realized there is no way to reach the goal of reliable and high fidelity torque control with this device and there is a reason servo drivers are expensive.

    I was pointed to the Trinamic TMC4671 motion controller which would do everything needed directly in hardware and can be configured for steppers, 3 phase servos and DC motors simply via spi with the same hardware. The TMC4671 had as few issues in the first revision but will be fixed soon Trinamic promised me. Therefore i am confident that it should make things more robust and simpler on the software side if the task of controlling the motors is completely done by a separate chip.

    Building an external 4 half bridge power stage is more complex and expensive but will allow for much better cooling and higher currents.
    The goal remains to create a budget friendly kit but it is clear that the motor driver will get more expensive. (Think ~30$ parts OHSC -> ~50$ BOM cost TMC board + more work. We need 10 mosfets and drivers... etc.). From my calculations it should still be possible to make a kit like this below 100$ :)

    The current idea for the project will split into two main parts:
    An open source Force Feedback interface board with an STM32F411 for usb communication and control.
    This will support different motor drivers and will be modular. You can use your own motor driver or control schemes by writing c++ classes for this controller. The main software parts will be the motor control part for encoder input or force output and the control interface which will be USB HID for most users but could also be changed into a class that outputs PPM values depending on the steering wheel position and receives force values back to pass to the motor interface.
    For example a VESC or a commercial servo driver could be made compatible.

    A reference motor driver based on the TMC4671. This will be the intended motor driver for a direct drive wheel but can also be used as a standalone motor driver or development board for arduinos and different purposes. The STM board will be optimized for this motor driver.

    The next step is to test if the TMC4671 fits this goal and which motor drivers are a good alternative.

    This will be interesting and i will keep you updated. The new boards are almost finished and i am waiting for Trinamic to release the chip soon.

  • Update on FFB

    Yannick (Gigawipf)06/09/2019 at 11:37 0 comments

    One main goal of this project is to make a force feedback wheel kit.
    Therefore usb HID gamepad and PID must be supported.
    Also a braking resistor to dissipate any generated power for quick movements was added with an anti backfeed circuit.

    Reports are sent at 1khz which makes for a very smooth steering experience. (Torque resolution still only 7 bits which makes ffb a bit less smooth...)

    Implementing a basic HID gamepad is relatively easy, making it FFB capable a whole other story. 
    At least with the ST HAL library it is for example not possible to even send HID feature get requests.
    This had to be patched in and the whole HID descriptor with PID is in the kilobyte range.

    After many days of studying the 20 year old specification and sparse examples about PID basic FFB is now supported.
    Strangely some programs and games seem to not send the "Actuators Enable" command after sending a reset but instead a stop. But some do send a more sensible "stop, reset, start" sequence.
    Well... thats a story for another time.

    The main part of the current log is that most games use constant force, friction and spring effects and these are currently implemented in a simple way and work for assetto corsa for example nicely.

    The motor driver of the current prototype is still the powerstep01 but sadly two of them burned out after locking up. SPI commands can not be sent too quickly and the current resolution is limited to 7 bits. This might be fine in a slow robotic arm but not that great for FFB and any quicker applications that require precise torque.
    Therefore the plan is to use a more capable motor drive solution. This will get more expensive but opens up some possibilities like the use of 3 phase servos and steppers with the same hardware and more accurate torque control and better heat dissipation when using external power mosfets.

    Here is a short video demo with a FFB test and a scene of me trying to drift in assetto corsa without a shifter:

    Additional analog axes and buttons can be added via the inputs. Up to 16 buttons and 6 additional analog inputs are present for shifters, pedals and other controls. Maybe even add a thrustmaster wheel with SPI buttons to the free SPI port?

    Compared to the Thrustmaster TX this has of course still lower torque resolution and fewer base effects, but feels much sharper and very strong if you turn up the power. I would say it comes close and should be able to surpass the consumer wheels later maybe even for a lower price.

    Next Steps: persistent user configuration, code cleanup, new motor driver.

  • Choice of processor and control

    Yannick (Gigawipf)04/17/2019 at 13:17 0 comments

    Of course we need some way to send data and control signals to the OHSC for setup and direct control of important parameters.

    A good option would be a serial port. This would make it usable in programs and in a terminal for human users.

    It already has a hardware uart interface planned that could always be used to control everything important. But this needs a uart interface so in normal operation it would be nice to just use one usb port.

    As it is planned that the device can also be used as a HID gamepad for FFB we need some way to control it when HID is active. One option would be to use a hardware uart for that or HID feature reports that would make it impossible for a human user to control without a pc application.

    The best option would be to have hardware uart pins open and in hid mode setup a composite usb device with HID and CDC com port at the same time and if you don' need HID it just enables the CDC part.

    This is pretty hard to do with STs HAL libraries but should be the most compatible and usable option.

    So this is what i tried to setup and kind of succeeded until i found the reason why it would never transmit via CDC or break the HID part depending on the used endpoints.

    It turns out that the F4 only has 4 usb endpoints and HID needs two, CDC needs two or 3 with CMD and then there is EP0... So i need at least 5 endpoints.
    I could have spotted this by reading the datasheet more carefully which advertises "4 bidirectional usb endpoints". I thought that meant 4 IN and 4 OUT each but that is ~~not~~ the case. *it is. i had the buffers set incorrectly.*

    Now there are some options for the next iteration:

    • Stay with F4 (Limited endpoints but should still work)
    • Hardware uart interface and have 2 usb ports and F4
    • STM32F103RC without HW float (not really needed but nice to have)
    • STM32F7 (much more expensive, way faster and generally overkill)
    • STM32F2? Still a cortex M3 like the F1 but a bit more capable in terms of usb and speed.

    At the moment i would probably try the slower and cheaper F1 to stay in budget and keep the board small as there are some more modifications needed for the next iteration like braking resistors and anti backfeed.

    The pinouts are compatible and only the usb resistors would have to be changed to switch to an F7 or stay with the F4. Everything else is software configuration.

    The F1 would cost around 4.50€ in single quantities and very easy to get, the F4 almost the same with 5€ and the F7 would be about 8€ and make the device a bit more expensive.

    The F411 has a usable clock speed of 96MHz and the F1 only 72MHz but that is still more than enough. The F7 clocks at over 200MHz and is pretty overkill for the rather slow usage as most of the time is already spent waiting on spi and usb and the encoder is managed by a HW timer.

    I chose the F103RC for the second version because of the usb features and low price.
    This allows for a more versatile and user friendly configuration. Hardware float is not strictly needed because most if not all calculations can be done in fixpoint.
    The second version still retained the possibility for both F1 and F4 but was built with the F1.
    The F1 also has separate ADCs which could provide some separation for voltage measurement and analog inputs for gamepad axes and control signals.

    The next version will feature separate control and motor driver boards. And i might get back to the F411 as it seems like the endpoints would be sufficient and it costs the same as the F103.

  • First PCB tested

    Yannick (Gigawipf)03/28/2019 at 19:32 3 comments

    Finally the first pcb arrived and is tested to find any errors in the design and see if there are any major issues.

    Soldering everything by hand takes some patience but everything works as it should.

    A few problems spotted in the first design:

    1. Vias under the current shunts are too close to the pads and can be bridged to the resistor while soldering and short out the shunt voltage.

    2. Pullups of encoder were connected to 5v instead of 3.3v. Easy to bodge for now and fixed in the next version.

    3. 3.5mm terminals might be too small for big motor wires. Maybe add a 5mm footprint and move the caps and buttons.

    4. USB footprint from eagle not exactly the correct one for the ports. Drilled holes are in slightly different spots.
    Strange as the part numbers were identical and can be fixed by bending the mounting pins of the port inwards but should be changed to the correct one.

    Apart from that the driver and processor work correctly. I chose the STM32F411 as the main processor running at 96MHz. 2 LEDs for status messages, one power led and one direct driver flag led for critical errors are present on the board.

    And of course the gamepad communication is working with 16 buttons and 8 analog inputs.
    The encoder input is correctly scaled to 1080° of rotation and perfectly matches the virtual wheel in project cars.

  • Designing a pcb prototype

    Yannick (Gigawipf)03/05/2019 at 16:28 0 comments

    While the current prototype shows promising results it is a mess of wires and many pins on the stm are already blocked by the discovery board. Other boards where the powerstep shield can be stacked onto often have no usb port or other issues.

    I spent quite a few days researching parts, designing a pcb and preparing the cubemx project for the new layout and chip.

    For the next prototype i chose the stm32f411RCT6. This processor has enough pins for 8 analog and 16 digital pins directly connected to the chip while still having usb, uart, internal spi for the powerstep and screw terminals for the encoder.

    Some space is available to allow for a larger heatsink if needed. In theory it should be able to handle 80V but in current mode the driver runs best at 12-20V and this is probably what most users will have available anyways. At higher voltages the driver get really hot. In voltage mode not that much but i find the torque reaction to be much smoother and quicker in current mode.

    Now i will wait for all the parts to arrive and hope that nothing blows up in the first test.

    One other thing still missing is a nice nema34 dual shaft motor. The 34HS59-5004D from stepperonline looks like a perfect match with pre cut keyway and smaller back shaft and mounting holes for the encoder. Sadly it is not available at the moment so i will need to wait more or find a different one.

    After a week my parts finally showed up except for the terminal blocks.
    Not the most pretty soldering but it was all hand soldered and that lqfp powerstep is a beast to hand solder. Cleanup will be done once the terminal blocks are here.

  • Prototyping and FOC

    Yannick (Gigawipf)02/15/2019 at 19:47 0 comments

    My prototype consists of a stm32f4 discovery board and a powerstep01 shield.
    The goal of this stage is to implement a stable FOC control loop using this standard stepper driver. I chose this driver because it allows for up to 10A of current in current and sine voltage mode and can be controlled via spi quickly and stepped in stepclock mode.

    The field oriented control like approach works by keeping track of the step positions and aligning bursts of microsteps less than one electrical rotation to the current position and making sure the stepper never skips a full step.

    This needs a high resolution encoder with sub microstep resolution. I chose a 10k count E6B2CWZ6C (clone) encoder for this prototype.
    Microstepping is set to 1/16 because this is the highest setting the driver supports in both current and voltage mode and current mode allows for higher holding power between steps.

    Perfect alignment of the shafts is crucial for smooth stepping so a sturdy adapter was printed.

    Yes it is messy but there is no other option to get the driver connected to this board. The end result will feature a custom pcb :)

    The FOC loop is pretty much working right now and can turn heavy loads at stall conditions without cogging and the feeling of skipped steps.

    This video was made with <0.4A of current and a Nema 24 motor. Imagine a Nema 36 or 42 at up to 10A.
    The feeling is smooth as butter when forcing the load away. Very unlike an open loop stepper.

    At the moment the position holding is done using a PID loop which has to be tuned for the specific load and torque profile needed. This creates some overshoot which has to be reduced for accurate applications. Of course in this video the overshoot is extremely exaggerated because of the heavy load but even with small loads about 1-5 microsteps of overshoot and offset can be observed when the loop is reasonably tuned but not perfect.

    Later a step/dir interface to use this closed loop controller as a replacement for open loop stepper drivers will be implemented and this will need at least near microstep accuracy to be usable but the main goal is to provide smooth torque at stalls for applications that would traditionally need servo motors like linear actuators, force feedback and robots.

View all 7 project logs

Enjoy this project?



julien.greffeuille wrote 7 days ago point

Hi Yannick, i'm looking to make a diy nema 34 based steering for over 2 years, i'm now in first year of electronic school (hopefully i would be able to created circuits like you one day :) ). I'm looking at your project for several months now and i would be glade to be one on the first to try this circuit when it will be finish.

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Yannick (Gigawipf) wrote 6 days ago point

The next motor driver board will probably be made soon once the pcb design is final.
Its pretty much almost finished. I will post a log once it runs and if you have any requests you can message me via PM or the group chat.

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Benjamin wrote 11/22/2019 at 21:27 point

It would be wonderful if you could add 2 axis/joystick force feedback to this project. An open source solution is much in demand.

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Yannick (Gigawipf) wrote 11/23/2019 at 18:24 point

Currently not the main goal as i am trying to get a reference motor driver finished and the boards done, but certainly possible to implement later.

The design will be modular with the ability to have up to 3 motor drivers on one bus. It should be possible to implement that in software.

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Dmitriy wrote 07/08/2019 at 10:30 point

Great project! Any chance you can show piece of code for maintaining constant torque while changing position? I'm just curious of powerstep01 capabilities

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Yannick (Gigawipf) wrote 11/23/2019 at 18:21 point

I have used a foc like control scheme by sending bursts of step pulses to align the measured encoder angle to the current phase of the powerstep. Crude but worked. The the motor current was changed to set the torque together with a 90° phase offset of these step bursts. The next version will feature a real FOC motor driver and should run much better.

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Daren Schwenke wrote 05/11/2019 at 19:35 point

I have always dreamed of a controller board which could handle both steppers and BLDC motors.  FOC applies to both in the realm of what you have done here.  The H-bridges required don't care if they are all bound to a single motor, so the same board could effectively handle both 3 stepper motors (6 H-bridges required), or 2 BLDC (3 phase delta wired) motors (6 H-bridges required) and use FOC control.  Just a thought...  :)

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