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Power wheelchair 4x 24volt actuator control with touch screen

Sun Sep 24, 2017 5:57 pm

hi there, I am looking in to the final stages of my wheelchair build, and I am getting close to the seat controls etc.,

I was thinking of using a raspberry pi as the main guts, I need to control at least 4 24volt actuators, and would like to be able to have a touch screen rather than buttons or switches, I would also like to be able to slide through pages of functions, so the main screen showing the (at present) 4 actuators main controls, being up down of the seat up down of leg rests, tilt in space, and recline.

I may want to add other things like curb climber (again via actuator) and other functions, but would also like to slide to the next page and have a load of pre-set positions, so if I press button one it moves 3 separate actuators at different speeds form their current positions so at the press of a button I am raised to the standing position, that would mean the back slowly reclines the foot rest lowers and the seat base it tilted forward, and clearly in reverse if I press button two, or press button 3 for the lie down sleep position, or home mode where I need to put all actuators down, and so on.

I would also like to have a screen that displays current speed, maybe GPS function, and or media player (no not that lazy just spend loads of time in the chair) I have a 3D printer so can build custom waterproof housing, but I just do not know if the raspberry pi is up to the job and if so how hard it would be, I have never programmed before and pain hinders learning to as it affects concentration so much.

I am OK with things like relay switches, so rather than the need to power the actuators I would think I would need to use relays and just use the raspberry pi to switch them, all the actuators being used are motor driven, so assume some sort of servo control is the way to go, also as new on the forum, do not know if I could ask if there is someone I could pay to do the programming of it. Any way any help advice would be very good.

Cheers. Mark.

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Re: Power wheelchair 4x 24volt actuator control with touch screen

Sun Sep 24, 2017 10:50 pm

Wall of text. Please add some paragraphs and other punctuation (some full stops would be good).

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Re: Power wheelchair 4x 24volt actuator control with touch screen

Fri Sep 29, 2017 12:16 am

post edited the original posters text to make it a bit more readable.
hope it helps.

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Re: Power wheelchair 4x 24volt actuator control with touch screen

Thu Oct 05, 2017 5:20 am

The actuators will probably need position feedback.
Controlling each of them would need something like an Arduino.
These Arduino's, (one or more) can be controlled via the touch screen Pi via i2c/uart/spi.

But you still need high current drivers ... al-servo-m

These days I use this for programming Pi
Similar to the Arduino method.
You could even use Zero's instead of Arduino per actuator so them only one piece of software needs to be learned.
Pi's only have 2 hardware PWM out, but that's enough for two actuators? More than that is tricky.

It would be hard to do everything with one Pi.
Doable if the smarts are on the Actuator driver.
Are you using worm drive DC motor actuators or linear?
I'm dancing on Rainbows.
Raspberries are not Apples or Oranges

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Re: Power wheelchair 4x 24volt actuator control with touch screen

Tue Dec 12, 2017 1:58 pm

I am half way through a similar project, it is turning out to be quite expensive, but reasonable. The motor controller of a midwheel drive powerchair is 100 Amps per channel, about 50Amps more than what is needed by the motors, so it can be rated medical. The standard medical rated motors are a max peak current of 1000W which is about 40 Amps at 24V for the drive wheels. Your motor controller needs to handle this amount of current or circuits can get very over heated an pop like popcorn.

I chose an MCP263 motor controller for my project, 2 channels. Each rated to 60Amps. This costs about $260 usd. I am trying to keep the project as open as I can, as in open hardware/software. I am documenting it at ... on-project. Each month I am buying what I need and it is working out much better than expected using an Raspberry Pi 3 as the brains. I will be using an Propeller micro-controller to read lots of sensors and GPS but I'm not quite that far yet.

For each actuator, I will be purchasing a suitable single channel motor controller that can handle the Amp/Watt rating of the motors. I may need to use a few Raspberry Pi's to keep everything running smoothly with all the motion control and sensing I need to do :)

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