I have a similar weight problem.
I am trying to move 22 lbs. around at very slow speed and potential 27 degree slopes
and I come up with a requirement of two 5 kg-m torque motors (7000 oz-in.).
That is twenty times more torque than those servos.
None of the hobby robot shops have any motor like that, geared down to slow speed.
I am looking at this car air-conditioning baffle mover as a possibility:
It has no torque specifications. Five RPM gear down sounds promising, though.
Plus the reviews mention somebody needing 15 lb-ft. That is 2880 oz-in.. He got the units wrong.
So maybe he has no clue.
I'm guessing it is in the ball park, but maybe under powered.http://www.allelectronics.com/make-a-store/item/DCM-276/5-RPM-GEAR-MOTOR-12VDC/-/1.html
If anybody has a suggestion, please contribute.
Reducing weight is not an option.
I just thought of a radical idea.
I built a solar panel rotation device using a satellite linear actuator.
It runs very slowly on low voltage and low current.
I imagine it has a very long threaded rod down the centre.
I could attach a threaded rod to each wheel through a nut and turn the wheels like an old fashioned steam locomotive
by powering a DC motor, that switches polarity at the two extreme positions of the rod.
Direction and torque control without momentum would be difficult. This gets complex. I could make a career out of it.
Locomotive engines are more intricate than what meets the eye, now that I think about it.
Ok ... back to searching for gear boxes and motors.
Getting back to ridiculous ... I could push my robot with a linear actuator acting like a pogo stick. Bwahahaha.
Don't laugh too hard. That is how babies get around crawling on the floor. They don't have wheels, you know.
I read this link:http://www.societyofrobots.com/robotforum/index.php?topic=7927.0
and all my torque calculations look too high compared to their discussion.
But I used this page:http://www.societyofrobots.com/RMF_calculator.shtml
Mass 10 Kg
Desired Velocity 0.01 m/s
Desired Acceleration 0.001 m/s/s
Expected Efficiency 80 %
Incline Angle 27 degrees
Wheel Diameter 0.22 m
# of Powered Wheels 2 wheels
RMF Results: 0.145
I did find bike motors and planetary gears in this thread,
which might suit my use. Wheel chair motors are obviously too strong.
I wonder if I can match that 5 rpm air-conditioner component to the 4.5:1 planetary gear down ?http://endless-sphere.com/forums/viewtopic.php?f=28&t=9604
I stared at the planetary gear long enough to figure the 12mm (almost 1/2") shaft size is turning the 0.32" shaft 4.5 times faster.
So the gearing is in the wrong direction (speeding up), as far as my idea of matching it up with that 5 rpm motor.
Drop that idea and start looking for 0.32" motor shafts. Those bore sizes are all actually metric: 8mm and 12mm.
edit: Now I understand why they have two gear ratios for that planetary gear.
If I mount the wheel right through those planetary gear assembly holes, using it like a wheel hub, and ignore the 12 mm bore hole,
and mount a 8mm shafted motor to that smaller bore, I think I get that slower ratio.
I've never used planetary gears. I'm thinking out loud.