View Full Version : Need brainstorming help

04-26-2009, 08:24 PM
I've been trying to figure out a couple of things recently. I thought I'd throw them out there in case anyone has any bright ideas...

1. I have a wheelchair base that I would like to radio control. It has a single motor forwards/reverse control based on a potentiometer.

At the moment I have a servo mechanically connected to it - this works OK, but I would prefer a more solid state approach. Does anyone know of a way to generate an isolated voltage from an RC/Servo style pulse?

2. Even though I have the biggest servo I can find to control steering (front wheel) it's not really enough. I need to replace this with a windshield wiper motor, and some kind of controller. Ideally I want to make a monster servo out of the wiper motor - is there a non microprocessor route to accomplish this?

I was thinking that maybe I could open up an old servo and somehow couple the innards to the motor - I'd need an amp of some kind...


04-27-2009, 01:45 AM
>> open up an old servo

Which is a microprocessor-route in itself actually.

Naw, you need an MC. Either reading a position sensor, or reading a potentiometer. Or a full fledged computer with an A->D, but that seems a bit overkill. ;)

Are you using one of the gigandoid 12v Vantec servos? They have more torque that just about any wiper motor...

04-27-2009, 12:28 PM
On 1, it almost sounds like an RC speed control would be the concept of something working, getting a voltage from an RC pulse. Trying to match a speed control to the wheelchair motors might be difficult. Some devices that are for bigger motors include the IFI controllers (http://www.ifirobotics.com/victor-884-speed-controller-robots.shtml), the Vantec stuff (http://www.vantec.com/products.htm), and the OSMC (http://www.robotpower.com/products/osmc_info.html), all of which might be capable of the wheelchair motors depending on motor specs.

For 2, there are the ServoCity power gearboxes (http://www.servocity.com/html/robotzone_servos.html) that add a gear train to a regular servo to get pretty high torque. They also have their linear servos (http://www.servocity.com/html/linear_servos.html) that look pretty strong.

04-28-2009, 06:13 PM
Thanks for the ideas. I looked into all the options regarding the 'monster servo' and I've ordered a 13:1 gear box for my titanium hitec servo.

I think this should give the best bang for the buck.

I'll follow up when it arrives with some pictures.


05-04-2009, 09:44 AM
OK, I got the gearbox - modding a 7955 servo is quite possible the hardest thing I've ever had to do. I would recommend getting the servo installed by the servocity.com techs.

YouTube - Dalek Steering Servo - revision 223 :-)

...and in the Dalek...

YouTube - Dalek Steering Servo Part 2