A Question About Hacking A Wheel Chair

Question

Has anyone ever hacked a wheel chair controller? it seems like it would make sense or is it better to use a bridge can anyone shed some lite on this ? 2 10 watt 24 vdc motors

bjf5051 · Answer

For a project in college I used an Arduino to emulate the joystick controls for an autonomous robot. The joystick was opened up and leads were attached to the 0-5V for forward/back and left/right. Forward/Back 0.1=Backwards 100% 2.5V=Neutral 5V=Forward 100% Left/Right 0.1=Left 100% 2.5V=Neutral 5V=Right 100% Obviously the direction of the wheelchair was controlled by varying the voltage to the joystick. This is definitely the way to go because it still allowed the joystick to be used when the robot was not driving around under autonomous .... Graduated from school for two years now I decided I wanted to continue working on a similar project. So i bought a EZ-B, invacare wheel chair and plan on hacking into the joystick to gain control of the robot. I have been reading that i can use the PWM output to control the wheel chair. First thing I need to do is see what the voltage range is an how the robot is controlled by the joystick (hopefully it is the same or similar to the first time i did this). When using a wheelchair hacking the joystick is the way to go. found it more difficult to control the motors directly just because they are 4 pole and have a bunch of safety features that you will have to avoid.

bjf5051 · Answer

I am currently working on getting a 0-5V output where 0= backward, 2.5= no motion, and 5V= forward. Am i correct in saying that using the PWM is the best way to do this? The PWM control window in EZ-B controls the duty cycle which can be related to the output voltage but i do not know if this is the most efficient way of doing this. wheelchair aside...I am essentially looking for a voltage output which can vary between 0-5v which could be used to control anything from dimming and led to controlling a motor controller.

Putt Putt · Answer

I played with the joystick input method for some time and finally after many frustrating attempts i just bought a SabreTooth 2x60 and my troubles were over. The chair i'm using is a Jazzy 1122 with 2 - 24 volt motors, i removed the electronic brakes which is simple and the Sabretooth can use PWM , RC and serial inputs to control the motors. You can make the joy control work but if your center voltage is off even the tiniest bit the chair either wont start or if initialized will drift ever so lightly and it is vary difficult to maintain the pure regulated voltage that the controller requires. I have accomplished the task with not so satisfying results, weeks even months of fiddling around with it plus various regulator boards, but in one day I had it going with the SabreTooth. Save yourself a headache and decide if you want a robot or a wheelchair.

Danger! · Answer

Putt Putt; I went through the same thing that you did. I have the "Pride Jet 3." If there is any fluctuation in the center voltage, it shuts down and flashes an error code until it is shut off and reset. I suspect that the older ones were easier to hack into, but like everything, the more advanced they get, the harder it is to modify them.

fert · Answer

Thanks I will order a sabretooth I don't need the head ache,this really helped!

nmsr1196 · Answer

Hello All. I'm new to the forum. I have a Jazzy GT power chair. I wanted to hack the joystick but, its proving to be somewhat of a chanllange. I wanted to replace the controller with a Vantec or Saber, but then the two motors have four wires. I know that the black and red wires are for battery, but I don't know what the other two wires are. My question is two-fold....Can I just use those motors with just the red/black? And....What are the other two wires for? Thanks (in advance), nmsr1196

Herr Ball · Answer

Yes, you use just the Red & Black wires. The two white wires go to the motor brake. If the motor does not have 12 to 24 volts applied to it then the brake stays on and will not allow the motor to turn. You can just remove the brake, plenty of places on the web that tells you how to do it. Good luck with your project.

nmsr1196 · Answer

@Herr Thanks for the response. Do the two wires connect together then connect to the brake connection on the controller? In other words one electrical point? Thanks (in advance)

nmsr1196 · Answer

i just viewed the video(s)...question(s) answered. thanks.

bjf5051 · Answer

I am seeing this same problem with trying to hack the joystick directly, I keep getting error readouts for anything other than neutral position 2.44V and 2.45V respectively. Two of the left bar lights stay on and then the next 5 flash about once every .5 seconds. Has anyone figured out how to work around this? Only thing I could think of was to let the wheelchair start up with the original joystick and then introduce the second signal but I have not been having any luck... I have the Invacare storm series arrow with the mkiv A joystick. I would like to get this working with the current hardware and to not have to purchase a sabertooth. Thanks!

bret.tallent · Answer

One ingenious fellow in Ireland just used servos to manually move the joystick and says it works quite well. Here is the link Linky

nmsr1196 · Answer

I have forgone trying to hack the joystick. I wasn't exactly sure to substitute. I removed the brakes clipped the wires put a connector on the brake wires on the brakes and motors. Since I wanted to keep the charger, I connect the brakes to the connectors and charge. I used the roboteq motor controller to make autonomous.

Putt Putt · Answer

@bjf5051 Lots of us here have tried to hack the various joysticks for wheelchairs and we know what is required but in the end result, thou you can hack the sticks, it is actually cheaper to buy the Sabre-tooth H-Bridge than it is to properly interface the joystick with other electronics. I spent hours days and weeks trying to interface the sticks without buying some good quality electronics and had some success but it was always glichy and i didn't want to take the chance that my 12 mph , 250 lb robot would just blastoff when ever it wanted too or not move at all! I bought the Sabre-tooth H-Bridge and with-in 15 minutes had a working bot with a wheel chair base under full control. But hey, go for it and hack that stick and when you get it perfect let the rest of us dummies know how you did it. The controllers are very high tech I even bought a programming cable for them, that alone was only $100.00 and a myriad of emails just to get it! and the cable itself is an electronics piece of rocket science with built in proprietary signals. They are NOT serial of any kind that I know of. But don't get me wrong , I'm not trying to discourage you but when do you want to have a working bot?

bjf5051 · Answer

Yea i am finding only a few people who have been successful with hacking the joystick, mainly due to the safety aspect the wheel chair has during start up. I have been able to replicate the 2.47V and 2.50 start up on my wheel chair with no error codes on an arduino uno (no on my ez bee :/ ) so now i am on to trying to make it move which has proven difficult so far. I have heard everyone just ends up buying the sabertooth to control it....i like the breaking feature and i really like not having to spend the extra money on it so ill prob grab an o scope and put in a few more hours. And for the servo idea to control the joystick, extremly dangerous especially with a robot of this weight. Even with smoothing servos can be wild. I'll keep everyone updated, let me know if you have any ideas!

nmsr1196 · Answer

@bj5051 What type of motor controller are you using?

bjf5051 · Answer

None, I'm emulating the joystick with an arduino and two xbees using direct io

nmsr1196 · Answer

nicccceee. that sounds challenging.

Herr Ball · Answer

@bjf5051 Send me a email, I have something that might help you a little. Old-FireFighter138(@)neo(dot)rr(dot)com

bjf5051 · Answer

Got it working whoo! Made an rc circuit to filter the pwm signal and connecting the wires to the joystick during the startup. I have the chair rolling forward, backward, and turning when connected directly to an arduino, not able to do this with ez board yet. Should I keep updating this forum since i am migrating twords using arduino for my project.

nmsr1196 · Answer

That's cool! How did you do it?

Robot Doc · Answer

I'm thinking that whatever you're doing with the arduino should be able to be done using the EZ-B. Keep posting on this thread so we all learn what you are doing and then try and replicate it.

Putt Putt · Answer

Pictures Please........

Putt Putt · Answer

Wiring diagram please.....

fert

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