Converting Invacare MK41 wheelchair to Remote Control

Thread Starter

timmyd-in-mississippi

Joined Feb 22, 2018
14
Alright! I followed Mark's article and I have all of my parts. I am going to convert my wheelchair base into RC so that I have an RC camera base. From reading his article I don't think I need to use the Arduino. I just need it to go and stop when I use my Flysky controller. This is new to me. Never messed with the Sabertooth controllers but it seems pretty straight forward.

I will include pics of my starting stuff.

My plan is to take the front tip wheels off and make a bar with some smaller tip wheels and this bar will slide into the foot rest mount. I will make a steel plate (to bolt down to the seat mount) with a 12" steel pipe welded to the base plate for my 3'-6' extension pole to slide down into (firm fit). I will probably mount the pole aft of center center by 6" or so to help keep it from tipping forward. If it still has a tendency to tip forward then I will add a weight bar across the back drag wheels.

Wheelchair RC Wiring 2x32 Controller.png
Invacare M41 wheelchair base.jpg
Conversion Parts.jpg
 

Thread Starter

timmyd-in-mississippi

Joined Feb 22, 2018
14
Hey Mark, I need your help. It is working like a champ. After getting dip switches set correctly I am good to go (using a single joy stick on controller).

I really need help with 2 things.
1. Slow down the ramp up speed so that it is MUCH slower to get to full speed. Right now I drives like I did 30 years ago :) I would like to maintain the ability to get to full speed but it would be nice that if I give it full throttle on RC stick, it takes 3-5 seconds to get to full speed.

2. I have not attached my emergency stop. The bottom has 2 poles on an orange side and 2 poles on the green side. I know wires are going from the ES to A2 and A1 but I don't know
a) which poles to connect to A2 and A1?
b) does the 5V power supply simply loop back to the 5V power supply (0V and 5V) ??

Afte this I am home free!! Very excited to say the least!!

Video link of first test run inside
 

Thread Starter

timmyd-in-mississippi

Joined Feb 22, 2018
14
@timmyd-in-mississippi ,
Looks like fun! What's the end goal for your robot?
Mark
It will have a pole mounted to the seat plate that will hold an Insta360 Pro 360 camera. The 360 camera will be mounted on a gimbal so that it never turns and always faces the same direction (very important when doing 360 video). I will use it to create tours of houses and well as outside venues.

I think I am going to put a "lazy susan" ring on the bottom so that my battery power that will be powering the camera will not get wrapped around the pole. since the robot will rotate and the camera will not, I need something on the bottom that can spin freely and keep the power cable from wrapping around the upright pole.

I just made a post prior to this one because I need your help solving two (correction 3) minor problems.
 
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Thread Starter

timmyd-in-mississippi

Joined Feb 22, 2018
14
Mark,
There is one other issue but I really don't think it is a problem for me.

3. When I have the brake lever locked, the unit will barely go. It is if the brakes are not being unlocked. I am sure that I used the correct wires but I will put a meter on them to verify that I did in fact select and use the correct brake wires coming thru the harness. I could visibly see them at the other end. If the wires are correct, then I have no idea what the problem is. I can hear the brakes clicking so they are releasing but it will barely move. However, when I have it in "free wheel" mode, it works perfectly and it comes to a stop pretty quickly.
 

Thread Starter

timmyd-in-mississippi

Joined Feb 22, 2018
14
I found best way to slow it down is to just simply set max speed on my FlySky controller :) I did not see that the EXP setting made any difference. It may be that the 2x32 does not read that EXP settings ?? Anyway, can save different modes (ie Planes) on the Flysky. that will allow me to have a baby crawl setting for indoors when needed and have saved profiles that get progressively faster and faster.
 

Mark Hughes

Joined Jun 14, 2016
404
1. Slow down the ramp up speed so that it is MUCH slower to get to full speed. Right now I drives like I did 30 years ago :) I would like to maintain the ability to get to full speed but it would be nice that if I give it full throttle on RC stick, it takes 3-5 seconds to get to full speed.
The way to do that is with Dimension Engineering's DEScribe software. It can get a bit complicated, but you'll want to create an exponential map that allows for whatever handling characteristics that you want. Then, you need to assign that map under the RC tab and assign a "fixed" calibration. To slow it down in the software, you should decrease "servo min" and increase "Servo Max" by say, 200 ms. You can drag the points around by hand and flatten out / ramp up the response. In your case, it sounds like you want to flatten it out.

2. I have not attached my emergency stop. The bottom has 2 poles on an orange side and 2 poles on the green side. I know wires are going from the ES to A2 and A1 but I don't know
a) which poles to connect to A2 and A1?
b) does the 5V power supply simply loop back to the 5V power supply (0V and 5V) ??
a) I'm hesitant to tell you to hook up to either one of those colors without a datasheet in front of me. But you can figure it out pretty quickly with a multimeter.
The switch starts out with two of those connectors connected, and the other two disconnected. When you push the e-stop button, the two that were connected disconnect, and the other two connect.
Use the multimeter in "resistance" or "Ω" setting. When you touch the multimeter leads to the connectors on the switch (two orange or two green), the connected ones will read <1 Ω. When you depress the e-stop, that value will go to >1 MΩ.
Let's pretend that the two green connectors are connected when the switch is "on". You'd connect one connector to 5V and the other to A1. Under normal conditions, 5V flows through the switch to A1. When the Estop button is activated, the connection is broken inside the switch. The hardware detects this and brakes the wheelchair.
 

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Mark Hughes

Joined Jun 14, 2016
404
I think I am going to put a "lazy susan" ring on the bottom so that my battery power that will be powering the camera will not get wrapped around the pole. since the robot will rotate and the camera will not, I need something on the bottom that can spin freely and keep the power cable from wrapping around the upright pole.
You might be interesting in obtaining a "Slip Ring" -- Similar to this: https://www.digikey.com/product-detail/en/sparkfun-electronics/ROB-13064/1568-1253-ND/5762403
 

Thread Starter

timmyd-in-mississippi

Joined Feb 22, 2018
14
Let's pretend that the two green connectors are connected when the switch is "on". You'd connect one connector to 5V and the other to A1. Under normal conditions, 5V flows through the switch to A1. When the Estop button is activated, the connection is broken inside the switch. The hardware detects this and brakes the wheelchair.
------------------------
Thanks Mark! Can I use the 5V out on the 2x32 board or do I have to use a separate 5V power supply to the Emergency Stop?
 

Mark Hughes

Joined Jun 14, 2016
404
Mark,
There is one other issue but I really don't think it is a problem for me.

3. When I have the brake lever locked, the unit will barely go. It is if the brakes are not being unlocked. I am sure that I used the correct wires but I will put a meter on them to verify that I did in fact select and use the correct brake wires coming thru the harness. I could visibly see them at the other end. If the wires are correct, then I have no idea what the problem is. I can hear the brakes clicking so they are releasing but it will barely move. However, when I have it in "free wheel" mode, it works perfectly and it comes to a stop pretty quickly.
Hmm....I really don't know what to tell you about that one. Perhaps there's a setting in the DEScribe software that hasn't been updated correctly? Check P1 and P2 under "Power Outputs" and then double check your dip-switch settings. Past that, if you've got the correct wires selected, I don't know what the issue might be. Maybe something didn't upload correctly. Verify settings and click "Upload Settings to Device" again.

BTW -- very cool video! Looks like you got that put together in short order. Next up -- adding the camera!
 

Mark Hughes

Joined Jun 14, 2016
404
I found best way to slow it down is to just simply set max speed on my FlySky controller :) I did not see that the EXP setting made any difference. It may be that the 2x32 does not read that EXP settings ?? Anyway, can save different modes (ie Planes) on the Flysky. that will allow me to have a baby crawl setting for indoors when needed and have saved profiles that get progressively faster and faster.
Oh that's pretty fancy. You might want to just do that then. BTW -- You can create several "maps" -- you have to assign the "maps" to the motors, otherwise it will stay with the default. Also make sure you "Upload Settings to Device" once done.
 

Thread Starter

timmyd-in-mississippi

Joined Feb 22, 2018
14
Mark, thanks for the very helpful answers to my many questions. I have now run into one more problem. Charging the batteries. The original XLR outlet is built into the control board with joystick. Do you know of an XLR port that I can buy to mount on the shroud that will wire directly to the batteries? Then I could charge my robot with the charger that came with it :)
 

Mark Hughes

Joined Jun 14, 2016
404
@timmyd-in-mississippi,
That looks like it will work out -- but the price is about 3-10x what I'd expect them to run. Something else to keep in mind -- you can cut the end off of your charger and reterminate it with anything you want. I'd recommend keeping a polarized connector so you don't accidentally hook it up incorrectly somewhere down the road. Just remember to keep positive to positive and negative to negative and you should be fine.
This was a very fast project from start to finish -- good job! My projects rarely go that smoothly.
Mark
 

Thread Starter

timmyd-in-mississippi

Joined Feb 22, 2018
14
@timmyd-in-mississippi,
That looks like it will work out -- but the price is about 3-10x what I'd expect them to run. Something else to keep in mind -- you can cut the end off of your charger and reterminate it with anything you want. I'd recommend keeping a polarized connector so you don't accidentally hook it up incorrectly somewhere down the road. Just remember to keep positive to positive and negative to negative and you should be fine.
This was a very fast project from start to finish -- good job! My projects rarely go that smoothly.
Mark
When hooking up the charger to 24v system, do I do positive and negative to one single battery or do I go to Positve on on battery and negative on the other battery? I would think it is option A, but I have never charged a 24v setup.
 

Mark Hughes

Joined Jun 14, 2016
404
@timmyd-in-mississippi,
Provided that there is 24V coming out of that charger, you'd connect the positive lead from the charger to the positive lead of the first battery, and the negative lead of the charger to the negative lead of the second battery.
I'm by no means an expert in battery charge circuitry, but I believe the ideal situation would be to get a 12V charger and charge each battery individually. My other concern is that I don't know what is in your charger -- is it a really a charger with charge control circuitry or is it simply a 24V power supply? (with the old wheelchair controller providing the control circuitry). It might be worth looking for a manufacturers mark / model number on the charger and googling it to confirm.
Best,
Mark
 

Thread Starter

timmyd-in-mississippi

Joined Feb 22, 2018
14
@timmyd-in-mississippi,
Provided that there is 24V coming out of that charger, you'd connect the positive lead from the charger to the positive lead of the first battery, and the negative lead of the charger to the negative lead of the second battery.
I'm by no means an expert in battery charge circuitry, but I believe the ideal situation would be to get a 12V charger and charge each battery individually. My other concern is that I don't know what is in your charger -- is it a really a charger with charge control circuitry or is it simply a 24V power supply? (with the old wheelchair controller providing the control circuitry). It might be worth looking for a manufacturers mark / model number on the charger and googling it to confirm.
Best,
Mark
This is the charger that came with the wheelchair. It originally plugged into the plug up on the controller (joy stick module). So it is definitely a 24v charger. My goal now is to just make it an onboard charger. I will wire it as you described (postive to battery 1, negative to battery 2. the charger will stay mounted to the robot and I will unwrap the cord and plug it into the wall to charge it :)

So when you charge an electric wheelchair normally, charging it will kill the functionality. this is done by wiring the #2 pin to negative (I looked up the XLR pinout). So I have no idea how I would set this up to "stop" the 2x32 controller while it was charging. I am sure there is a way to do that but it is not mission critical. I will have my FPV camera on it tonight and take a video of the completed robot ready for action :)

I am very happy with this and it would not have been possible without your writeup!!
 

Thread Starter

timmyd-in-mississippi

Joined Feb 22, 2018
14
@timmyd-in-mississippi,
Provided that there is 24V coming out of that charger, you'd connect the positive lead from the charger to the positive lead of the first battery, and the negative lead of the charger to the negative lead of the second battery.
I'm by no means an expert in battery charge circuitry, but I believe the ideal situation would be to get a 12V charger and charge each battery individually. My other concern is that I don't know what is in your charger -- is it a really a charger with charge control circuitry or is it simply a 24V power supply? (with the old wheelchair controller providing the control circuitry). It might be worth looking for a manufacturers mark / model number on the charger and googling it to confirm.
Best,
Mark
I found a really helpful link for anyone else who may have questions on how to direct wire a 24 charger, etc. Very very simple and easy to understand.
https://www.nyc-arecs.org/batt1.pdf
 
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