This proposed project has the goal to modify an electric wheelchair so, that it will be able to drive on its rear wheels like a segway. By constantly measuring the tilt angle, a PID loop has to regulate the speed of the wheels in a way that it will self balance. The segway works by speeding up while the center of mass is in front of the wheel axis and by slowing down and eventually driving reverse when the center of mass is behind the wheels. In this case the user can just lean forward and backwards to accelerate and decelerate.
In my case, it should be possible to also control the acceleration with a joystick, so the user can go forward and backwards without having to worry about the weight distribution. The left / right steering can be done by moving the left and right wheels with a different angular speed while keeping the average speed calculated by the PID loop. When the user accidentally moves his center of mass, the vehicle should detect that and drive back to the original position, so the vehicle will not drift away.
There should be a button that will start the balancing mode by powering the wheels with so much torque that the vehicle tilts backwards and to end the balancing mode. It should also possible to drive in a non-balancing mode, so on all 4 wheels.
Furthermore it should be possible to control the vehicle with WiFi with an mobile app or a webpage.
The hardware consists of a wheelchair with 2 24” BLDC geared hub motors on the rear axis,
An ESP32 processor should read the current tilt angle with an MPU6050 6-axis MEMS sensor and do all the necessary calculations. I chose it, because is has enough UART ports and WiFi onboard. It should connect to the internet using a battery powered LTE router mounted to the wheelchair. By mounting an additional IP camera, it should be possible to control the vehicle remotely.
Many wheelchair users are able to balance on their rear wheels but when they stop concentrating on balancing, they will fall forward or backward immediately. It is also quite difficult do drive on the rear wheels while holding balance.
The primary use case is to get over obstacles like tram rails, cables or small edges that are in the way and to reduce vibrations while driving over bad surfaces like cobblestones or gravel. Furthermore it looks cool, which alone should be enough motivation for the project.
There are some wheelchair users which are not able to tilt backwards and they always need external help to get over small edges. With such a system, it will be possible to get around without the need for additional help. This requirement also means that the balancing mode should be able to tilt the vehicle backwards without any user input other than the press of a button.
In an earlier project, I did try if this will be possible, and found out that the motors can approximately 600Nm of torque combined. This allows the wheelchair to accelerate from zero speed to the maximum speed of 12km/h in 200 Milliseconds, which is enough for tilting the vehicle backwards (actually the anti-tip protectors behind the wheelchair broke in this test due to the high load falling backwards).
Having the ability to control the vehicle remotely can help the wheelchair owner to move the vehicle to a comfortable position for getting in or parking it when he does not need it. Furthermore it will be a lot of fun driving around in remote controlled mode.
The development should be published on github to allow other wheelchair owners to modify their motors so, that they also have the possibility to.
For this proposal, I need 2 TAPAS boards, one for each motor, but it would be better to get 4 boards to be able to test the software on an unmanned demo vehicle before trying it on a real wheelchair with someone inside.
this idea will get 4 TAPAS dev kits