G+_Michael J. Champ Jr. Posted April 13, 2016 Share Posted April 13, 2016 Hi guys, I am a disabled geek and enjoy hacking stuff to expand their uses. I have a retired power wheelchair I'd like to convert into a big RC car. My vision is to strip off the chair parts and extend the wheelbase so a child's battery powered toy car can be used as a body. The chair has a Invacare MK5 controller that has 3 speed settings. I am due for another wheelchair upgrade so I will have a second chair retiring soon that has the Invacare MK6i controller that will drive linear actuators as well. They are used in the chair to recline, tilt the seat and raise the leg-rests. This one would make a cool RC robot. I'd like to know how to unplug the joystick from the wheelchair's computer and plug it into a transmitter that will transmit the signals to a receiver plugged into the computer. The transmitter / receiver needs to interpret the joystick impulses, transmit, then convert them back into commands the wheelchair's computer understands to drive the chair/car remotely. Link to comment Share on other sites More sharing options...
G+_Quadflyingmedic Posted April 13, 2016 Share Posted April 13, 2016 If the chairs computer can interpret pwm then it should be pretty strait forward. I would get a cheap rc car remote and receiver that would be much simpler than trying to use the joystick from the chair. But I have no idea what the computer uses for input Link to comment Share on other sites More sharing options...
G+_Eddie Foy Posted April 13, 2016 Share Posted April 13, 2016 I think the easiest would be just use normal hobby servos to move the chair's joystick. I seriously don't think the chair uses RC ppm signals. (RCs don't really do PWM, its PPM, there is a big difference) Now if you want to go the hard way, this is another perfect spot for an o'scope. to read the voltage and signal from the joystick, then probably toss on an arduino as the RC to chair converter with a front end to to be a 'digital joystick' Link to comment Share on other sites More sharing options...
G+_Ben Reese Posted April 13, 2016 Share Posted April 13, 2016 I'm sure others have better ideas, but this is what's going through my head... Just spit balling... Not knowing the operating voltages of the control makes it a bit difficult (though a quick Google search would probably bring up a manual or a simple volt meter could be used to check it directly). You mentioned 3 speeds... Is the joystick gradually variable as you move it, or does it sorts jolt between speeds? If smoothly variable, it's probably acting as a potentiometer. If it jolts, I'd suspect multiple switches through its cycle being tuned on or off. That would tell you what type of signal the controller is expecting, but be careful too because it may be passing the full battery voltage through the controller instead of a lower 5v. Then there's replicating those controls... If it's multiple wires/switches turning on/off, you can probably get by with relays connected to an Arduino. If it's expecting variable voltage (like from a potentiometer - and assuming 3.3-5v), you could probably use PWM from the Arduino (maybe with a capacitor to smooth out the voltage? Not sure if that works or not) to send signals to the controller. Then theres the issue of remote control. You could use NRF24L01 chips (or Bluetooth, Zigbee, etc) and another Arduino (or Pi) to send signals to the driving Arduino, or you could get a cheap RC car and use the conrols from that or you could use a flight controller somehow, I'm sure... Again, I don't have any experience with most of this, but it seems like it should work and the project sounds awesome. Really, it might be easier to bypass the factory controller and drive the motors directly.... ? Link to comment Share on other sites More sharing options...
G+_Quadflyingmedic Posted April 13, 2016 Share Posted April 13, 2016 Eddie Foy I have recovers that do both pwm and ppm. Ppm is all the channels in one stream, pwm is individual wire for each channel. Most multirotors with flight boards use Ppm stream for the info, all of my planes use pwm one output for each servo Link to comment Share on other sites More sharing options...
G+_Quadflyingmedic Posted April 13, 2016 Share Posted April 13, 2016 Ben Reese I would think the control signals would be 3.3 or 5 volts Max into the computer, if that is the case I think you could use and arduino to do the conversion from a digital to analog signal. You could use a servo to drive the joystick you would need to fabricate something to give you the proper movement of the joystick. I would look into the motor drivers and see if those could be hacked to accept the signal directly, then if you have access to a good programmable radio you could make it do anything you want Link to comment Share on other sites More sharing options...
G+_Nick david (nickathome) Posted April 13, 2016 Share Posted April 13, 2016 This is a simple way to go. Explains in detail how to remote control a chair. Link to comment Share on other sites More sharing options...
G+_Michael J. Champ Jr. Posted April 14, 2016 Author Share Posted April 14, 2016 the 3 speeds are selected using a momentary switch on the joystick. It changes the mode settings that are programmed into the controller computer. A programmer is used to interface the computer and set the sensitivity and power settings of each mode. Link to comment Share on other sites More sharing options...
G+_Michael J. Champ Jr. Posted April 14, 2016 Author Share Posted April 14, 2016 I prefer to use the joystick from the chair if possible. I dont have the ability to use my hands to hold a RC controller. Link to comment Share on other sites More sharing options...
G+_Michael J. Champ Jr. Posted April 14, 2016 Author Share Posted April 14, 2016 I found this forum, but the technical jargon confuses me. http://www.wheelchairdriver.com/board/viewforum.php?f=2 I downloaded 2 pdfs with info abt my chairs, maybe someone more knowledgeable can assist me? https://onedrive.live.com/redir?resid=A4DF30B4B065CACF!42079&authkey=!AFx-I8g_oygr3IY&ithint=file%2cpdf https://onedrive.live.com/redir?resid=A4DF30B4B065CACF!42078&authkey=!AF-eSPpRZQUq7NQ&ithint=file%2cpdf Link to comment Share on other sites More sharing options...
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