Sunday, May 11, 2014

Hacking electric wheelchair drive

While building some robots for a museum we came up with the idea of using an electric wheelchair as the base for the robot.
Not wanting to replace the electronics we gave it a shot to try to use the existing motor driver and control it from an Arduino. On inspection it turned out to be a very common Penny and Giles Pilot plus drive.
Very little technical information is available about the interface between the joystick- and motor unit of this system. So we started reverse engineering. Here is what we have found so far.

By opening up the joystick and probing connections inside we found that the joystick movement are communicated as serial data @19200BAUD, 8 databits and even parity. Apart from the driving data the joystick unit also emit an additional, and completely different, data stream for controlling various lights and actuators on the chair.
The physical connection is using a propitiatory 6 way connector.

I turns out that the joystick sends drive data packets with checksum roughly every 10mS. Immediately after the data line changes direction and the motor controller returns a packet of data, again with checksum.
Simultaneously but not in sync another data signal is sent to control lights and actuators.

The data format seem to be completely non-standard but relatively simple to encode.

Probably for safety reasons the system does not tolerate any signals being missing or corrupted without shutting down so a fair bit of probing and fiddling went in to eliminating the joystick and replacing it with an arduino.
Here is a rough cut first Arduino sketch that allowed us to drive the wheelchair motors actuators and lights.
Quick shaky video of it running.

We plan to turn out a easy-to-use Arduino library for controlling the PG Pilot Plus soon.


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21 comments:

  1. Ummey RezwanaJune 23, 2014 at 10:57 PM

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  2. dooglieMay 23, 2015 at 6:19 PM

    I have a Pride Mobility 40A GC2 controller with the 4 pin joystick pigtail. I've figured out GND, INH, JStick, 24V pins on the Joystick connector and tried your code removing the actuator messaging but can't get anything from the device. Is there a bootup sequence or required conditions which must be met to turn the controller on and start taking commands? Do you know if the Inhibit line needs to be pulled low initially and then pulled to 5V or can it float at 2.5V?

    I'm also wondering if you figured out any other message conditions like Drive_modes?
    Thanks.

    ReplyDelete
  3. dooglieMay 25, 2015 at 10:08 AM

    I noticed the example Arduino Sketch uses a 20mSec cycle for the motor control data yet it was mentioned that a ~10mSec cycle was expected by the controller. Which is correct or is 20mSec close enough that it still worked?

    I've not yet been successful talking to a PG GC2 controller. I will build a bidirectional cable and see if I can read back, or even see, the controller response packet.

    ReplyDelete
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  8. MichaelMarch 7, 2018 at 9:14 AM

    Hello,

    This information is very inspiring. I have a Qtronix Power Module and wish to control it using Arduino. Unfortunately, the link to the Arduino sketch seems to be broken. Would you please post the sketch again? Many thanks inadvance.

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  11. AnonymousJanuary 29, 2019 at 9:07 AM

    A very smart idea!

    Keep up your amazing work and interesting articles - can't wait for the next...

    Thanks!

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  14. UnknownApril 13, 2019 at 5:03 PM

    I realize this is an old post and you may have moved on, but I'm working on a similar situation -- a P+G Pilot+ driver, but no joystick to help me figure out the signals. I tried the link to your Arduino sketch and it went nowhere. Were you ever able to post the Arduino library for the PG+? Thanks!

    ReplyDelete
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  17. DLRJanuary 13, 2020 at 3:08 PM

    I'm seeking a source for the connector described in this post. A friend of mine has a motorized wheelchair with a critical seat-raising mechanism that no longer works apparently because two pins of the male side of this connector are missing. I'm wondering if there is any source for a replacement connector. The company that made the controller for the seat-raising mechanism is now out of business, I'm told.

    More specifically, I'm wondering how the male side of this connector is connected to the cable to which it is attached. Are the leads soldered to the pins or is there some sort of compression fitting or something else? I ask because my friend bought a replacement controller on ebay only to find that it wasn't quite the same as the one she had and it doesn't work to operate the seat-raising mechanism. It does, however, have a complete male side of that connector so if I could understand how to remove that connector from the cable of the controller that doesn't work and attach it to the cable of the controller that did work, she might be back in business.

    Thanks very much for any assistance you can offer.

    ReplyDelete
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  19. UnknownMarch 22, 2021 at 4:00 AM

    Merhaba.Oncelikle iyi günler.Tekerlekli sandalye kullanan bir arkadaşım var.Joystick kolu aruzalandi.Vsu modeli.5 kablo çıkışlı.Elimizde Vr2 8kabla çıkışlı gımbal var .bunu vsi modelinde nasıl kullana biliriz .Bize yardım ederseniz sevinirim.Tesekkurler.

    ReplyDelete
  20. Mihai-G.July 15, 2024 at 5:46 AM

    Hello. I'm in the same situation. I have only P&G driver and I wish to control with Arduino. Can you post arduino sketch again ? Thank you

    ReplyDelete
  21. AnonymousSeptember 28, 2024 at 4:12 AM

    Hacking an electric wheelchair drive requires deep technical knowledge of electronics and motor control systems. Interestingly, just as Cody Rhodes black attire represents strategy and control in the wrestling ring, modifying wheelchair systems can give users greater independence, symbolizing mastery and freedom over their mobility devices.






    ReplyDelete

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