DPRG mailing list archives: DPRG: Wheelchair info.

Sat Feb 15 19:46:14 CST 1997

Dear DPRGers:

James Vroman called me a little while ago about the wheelchair.
Talk about getting me excited about robotics!  Even though I don't want
to distract anyone from the robotics contest and getting your robots 
ready for the contest, I'd like to mention some of the things we discussed.

James tried to tell me everything he's found out about the wheelchair.
I'll try to convey what he told me as best as I can remember it.
He mapped out all of the wires and believes the following
information to be correct at this time.  The motors have multiple
windings so that they can run at different speeds.  The control box 
basically worked where if you pushed forward, both motors turned on 
forward, if backward, both motors turned backward.  If you turned to 
the left, only one wheel motor would turn on to make it turn left, 
and similar if you turned right, only one motor would be on to turn 
right.  It looks like the wheelchair was a 6V/12V setup.  So with the
multiple windings and the multiple voltages, the wheelchair base is
capable of 4 speeds (plus stop) without pwm.  He mentioned that it
looks like the controller box was set for stop to tie the motors to
ground for breaking.  He says that there's a motor engage lever that
engages the motors to the wheels.  Also he states that there are inner
shafts to the motors that we could connect sensors to for measuring
turn and then to the wheels for slippage or load sensing.  He mentioned
that the wires to the battery connector was burned out from someone
hooking up the battery backward.  He mentioned that he will document
the electrical schematic before we make any modifications to it.
He mentions that the tray for the battery was rusted out.  He mentioned
that he may be able to scrounge up some angle iron and build one for
us.

James made some recomendations to me on what we should do with
the wheelchair base.  He mentioned that first of all we should consider
making the wheel chair be only 24 inches wide so that it will be able
to go through most doors easily.  He says that the expanding frame can
be removed and horizontal framing could be welded or bolted in its place.
Another recomendation he made was to remove the top tubular frame.  He
says that by shrinking the width, we should drop the idea of having a
chair on top.  Since no one will be pushing the wheelchair anymore, the
back of the wheel chair could be used for rack mounting of hardware.
For now we should use a deep cycle 12v battery only, and possibly encase
it in a plastic case (such as those for boats) in case of acid spillage.

He states that he should have the motors tested out this week, and that
he has a battery that we can use for now.  He says that there is a medical
supply store close to his house that he can go to if we need parts.  He
said he may check in with them just to see if there's anything they'd
like to give us.

We spoke about having a PC main brain, and the RS485 to connect to
each module as the group spoke about before.  The motors of the wheelchair
could easily be controlled by relays or we could do some sort of DC
motor control.  The wheelchair can easily hold about 200 lbs of weight
so adding a bunch of stuff like arms and a huge computer and the like
should be no problem.  It seems like the ultimate platform!

Again, I don't want to distract anyone from the contest at this time, but
the decisions for welding and cutting on the thing and using the 12v only
system need to be decided if James is going to continue to work on it.
He's really put a lot of time in on it so far, and we should really commend
him for all of the things he getting done for the group and from Tech-Tools.
James says he's at home with the hardware stuff.  I mentioned to him that
it was good since so many of us are more software oriented.  He seemed 
to be in his element working on the wheelchair modifications.

If anyone has any objections to James doing some of the things mentioned
above, or if you have other ideas for the wheelchair, please speak up.
-------------------------------------------------------------------------
Jim Brown       jbrown at why.net  or  jbrown at spdmail.spd.dsccc.com 
                http://users.why.net/jbrown
                http://www.dprg.org (next meeting is March 22nd) Bring robots!
Rom 3:23,24     http://users.why.net/jbrown/pcb.htm