Problems replacing Hall joystick with Hall pedal in electric wheelchair control

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PushToClose

Joined Aug 5, 2021
10
Hello,

I am trying to build an electric toy car for my children, using the drivetrain from an electric wheelchair. The wheelchair is called a Kymco K-Activ, it is controlled by a joystick, and has a motor attached to each rear wheel. The front wheels castor, so differential drive of the motors allows the chair to turn. Below is a (very) basic schematic of how the controls and motors are connected to each other.
Screenshot 2021-08-16 at 17.26.10.png
I am trying to remove the joystick, and replace it with a pedal and a forwards/reverse switch. The idea is that the differential drive ability of the motors is not used, and that they only drive both forward, or both backward, at the same speed. I've done some testing to see what signals the joystick is sending to the Controller PCB, and think I know what I need to do to mimic its inputs. However, I've run into problems with simply removing the joystick from the Controller circuit.

I believe the joystick operates using Hall effect. It has eight pins, and is wired to the Controller PCB via an 8-way ribbon cable. I crimped an additional connector to the ribbon cable, so that I could read the voltages across the pins while operating the joystick. This has allowed me to find the GND and +5V pins, and shown that five of the pins hold 2.5V when the stick is not deflected. The remaining pin seems to do nothing. When the stick is moved, four of the pins vary between 1.1V and 3.9V, depending on the magnitude and direction of deflection. For example, full forward stick causes two of the pins to register 3.9V. The same two read 1.1V in full reverse. It would seem that I could create a circuit to mimic this input, but I am running into a problem before I can try to do this.

There are a series of safety nets that the Controller has, for fairly obvious reasons. You can't turn the chair on with the joystick deflected. However, you also can't turn it on with the joystick disconnected. This makes it impossible for me to start trying to feed the circuit my "dummy" inputs. I don't understand how to fool the Controller into thinking the stick is still connected. I've measured the resistances across the eight pins of the joystick when the stick is disconnected and receiving no power, and then wired up resistors to try to emulate the stick in the circuit. This returns an error when the Controller is turned on.

Does anyone have experience of a joystick or controller like this, and know how I might be able to get the controller to turn on without the original joystick?

If it helps, the person in this video dismantles the joystick for repair, which shows what the inside of the joystick looks like (I haven't done this because a replacement is expensive if I damage it):

Here are some photos of the controller and joystick:
IMG_2454.JPG
IMG_2458.JPG
IMG_2459.JPG
IMG_2461.JPG

Thanks for any suggestions or help.
 

drc_567

Joined Dec 29, 2008
1,156
... I converted a hardwired mouse controller to a trackball, basically a joystick without the stick ... several years ago.
The main difference between the two was that the mouse controller obtained variable voltages by utilizing the center tap of a potentiometer to position the screen icon, whereas the trackball required a current input to move the screen icon. So by converting the mouse potentiometers to variable shunt resistors, ... disconnecting one end of the potentiometers and using the center tap, everything worked as it should.
... I cannot say if this scheme will work in your case. ... Just my experience.
 

Irving

Joined Jan 30, 2016
2,188
Go search/ask on the forum at wheelchairdriver.com; there's a range of ways to do this with VR2 controller and it's been done before to add remote control to a wheelchair.
 
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