[Yaaarc] robotics - H-bridges -wheelchair motors

[Keith Mc. (Route-To YAR)]

Ran Ong <ongrb at msn.com> wrote:
> Any using Wheelchair motors for any kind of robotics application ?

Yes.  FIRST Team 1502 (in Chelsea MI) built a drivable powered 
cart for carrying the compeition robot to and from the field,
along with a standing cart operator. (It's a "Gondola" application.)

> What kind of motor controllers you are using.
> Thanks
> \ran

In our case, we built it by cannibalizing a powered wheelchair.
Therefore, we used the original controller that came with the chair.
We picked up two identical powered wheelchairs (one for conversion. 
one for spare parts to maintain it), WITH batteries, at UM Property 
Disposition for $50 each.  

(They were a part of a ten lot of "for parts" wheelchairs retired by 
the University, but all of the motors and controls were intact and 
fuctional. IOW, the seat hardware had problems, not the mobility parts.)

There are a lot of commercial H-bridges out there, and net groups 
discussing homebrew ones.  But, the different h-bridge kits and assmbled
units each typcially serve a specific (or narrow range) motor specs.

We really need to know more about what you have now, and what you 
are intending to do with it.  There are several power/scales of 
these things, and the specs matter greatly.

1) What's your application?  (What is it intended to do?)

2) Which is it: hobby/tinkering/cheap, or commercial/compeition/maintainable?
With hobby/tinkering/cheap you can often be flexible with sources, specs, 
and hacking old stuff you get your hands on for pennies per pound. 
They're often one-of machines, and you can "bend" something cheap 
to the task (vs designing it from scratch for one purpose).
OTOH, commercial/competition/maintainable requires much more stable 
spare part sources for replication and maintenance over the working 
lifespan of the machine.

3) What voltage/current/power "scale" are you expecting?
   12v / 24v /36v / other?    

4) Do you have the motors already?  If so, what are their specs?
(PM? nominal voltage? peak power at .5*freespeed? stall current? etc.)
The motor specs determine what you need to look for in a controller.

If you do NOT have your motors yet, I'd *highly* recommend searching 
for surplus or used motor&controller *SETS*, vs trying to piece together
subsystems. Also, if a hobby app, don't forget seeking out complete 
used powered wheelchairs like we did, and do the same conversion.  
(Try eBay, local papers, etc.)  I've bought motor/controller as sets 
before.  You can't beat the price!

- Keith Mc.
Chief Engineer, FIRST Team 1502 "Technical Difficulties", Chelsea MI