# motors in robotics

Discussion in 'Electronic Basics' started by lerameur, Oct 2, 2006.

1. ### lerameurGuest

Hello,

I am not sure if its the right place for this but here goes. I am
constructing a line following robot. it is going to ba a wooden
platform 2x3 feet. I will be putting around 60lbs on it. Is there an
equation that will guide me to the right specification of a motor, (in
watt). I bought these geared motors:
http://www.skycraftsurplus.com/index.asp?PageAction=VIEWPROD&ProdID=443
but the motor turn bery slowly and I afraid they will heat up in time.
Plus the gearhead of one of the motors just stripped.
Is there a weight to motor power conversion ?
I guess the motors I have, ran at 24 v max, with a calculated 0.2 amp
max, so 4.8 watt?
Also those geared motors are hard to find, i did not want to go into
the trouble building my own gears, it probably would not be as precise
and strong.

thanks

ken O

2. ### BobGGuest

I go to skycraft every Saturday. Cool place. Get a spring scale and see
how many pounds it takes to pull the thing. Lets say 10 lbs. Now decide
how fast you want it to go. Lets say 10 ft/sec. So thats 100 ftlbs/sec.
A HP is 550ftlbs/sec, so you need one fifth of that...A HP is 746
watts... 746/5 is about 125 watts... 12V 10A or 24V 5A about. You can
compute rpm needed at the wheel if you know wheel diam. And torque
needed at the wheel.

3. ### Michael A. TerrellGuest

I used to go there once in a while, but I miss the real surplus
stores in Dayton, ohio.

--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

4. ### Guest

That's interesting, you make it sound simple. I wonder if it is
(simple) <g>

You mention torque and wheel diameter ... do those affect the selection
of motor size as well, or are they independent?

And I have a second question, about braking. Our robotics team uses
Victor speed controllers with a jumper that provides motor braking by
shorting the motor terminals. But given the momentum of the robot, it
still doesn't stop right away.

I know if we put the motors into reverse, it stops very suddenly but
puts great stress (and I imagine, current load) on the motors. If
instead we were to arrange to 'pulse' the speed controllers between
neutral(braking) and slightly reverse, would we be able to stop sooner
without tearing the motor out of the robot, overheating the Victors and
blowing breakers, or both?