Mechanics and Construction > Mechanics and Construction

First attempt at a RC bot, PLEASE help! :-)

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Nothing more until you get further into what you want to do, or get started.

If you're using the Sabertooth, you'll control your speed through software (somewhere). lol. The Sabertooth will work just will basically switch the power coming from your batteries into your motors. I'm not sure how it handles speed control. You'll have to look that up. I put a microcontroller into the joystick of my chair, and by varying the voltage I can change my speed. Other more experienced forum members can help you on the Sabertooth side of things.

You'll have to choose between using the Sabertooth and the stock electronics on the chair. I'm afraid it's an all or nothing choice when it comes to controlling the chair. Both have advantages and disadvantages. If you're planning remote control and already have the Sabertooth, that's the best/easiest way to go. How you deal with your brakes is going to be a choice you make.

If you think you might want to play with the stock chair electronics later, just remove them or disconnect them after taking pictures or making a drawing of the connections. Remove them without damaging them, and you can reuse them later. Or if you don't want them, sell them on Ebay to help finance your project.

If you can walk me through how to do it with the stock controller then I would be fine with that and will just use the Sabertooth on something else. I don't know enough about it to know WHAT choices I have. Thanks again!

Using the chair's controller is a lot more work, and a lot touchier, due to all the safety features built in for the wheelchair user. At a minimum, you'd have to use a microcontroller hacked into your joystick for proportional speed control, or on some controllers, there's an external 9pin connector you can use for simple on/off in each direction, but no speed control. But a simple variation in any of 3 simultaneous voltages can throw the chair into error mode and stop it dead.

Since you already have it, I'd really recommend starting with your Sabertooth, while leaving the original electronics untouched. Then re-use them later when you get bored, or sell them. You'll have better motor control from the Sabertooth, too.

Sounds good. What was the verdict on speed with the sabertooth? will it have them at wide open (would be fine)? I guess I need to ask....How does the chair controller vary the speed? Is it PWM or voltage, orrrr? Thanks again

Somebody else here will have to answer for the Sabertooth speed control. I've not worked with them. I like what I read about them, and they get great reviews, plus they feature an RC mode, so you should have no problems there. Hopefully someone here can chime in on how the speed control for them works.

As for the chair depends on your chair. I hacked into my joystick. At neutral, it throws 2.5 volts on both axis wires. I measured full forward, left, right, and reverse, and voltage was up as high as 4V and as low as .7V depending on position. I send the voltage I need across 2 wires depending on what direction and speed I want to go. One problem with this is that I need 2 wires at 2.5V for chair-neutral. If I shut off my controller card BEFORE I shut off the motors on the chair, the voltage drops to 0V and the chair starts to move. (See why I mentioned a kill switch? LOL). Some joysticks use 5 volts like mine. Some use 12. Some use 24.  :o Just make good friends with your multimeter.
Internally, wheelchair controllers have their own network protocol. Rnet is just one of them. Others use single wire serial communication, or just SP1 internally. It's a confusing mess, and most wheelchair manufactures don't play nice when it comes to sharing technical information.

Seriously though, if you just want to have fun, use the Sabertooth. Bypass the chair electronics completely. It will be much easier, and the speed control shouldn't be an issue. I just don't know how it's done on the RC circuit, but I'm sure someone here can help you with that. What took me a couple weeks of research to learn, and a couple of days to implement and test using the wheelchair controller, you can accomplish in a couple of hours by using the Sabertooth.

Good luck! And keep us posted!


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