Necessary Torque for RC Rover

Other Hardware Motors, Mechanics, Power and CNC
1

Hi I am planing on building a remote controlled rover/ robot. However I am having difficulty calculating the torque.

I get about 500 oz-in or about 3.5Nm, I am wonder if that is a reasonable number for a robot with these specs:

Weight - 40lb (weight per wheel 6.25lb)
Max incline - 15 degrees
Desired speed of 2 m/s (6.6 ft/s) -- at about 200 rpm
An acceleration time of 2 secs
A wheel radius of 4 inches
A rolling resistance on grass - about 0.08

I plan on having a 4 drive motor set up, one for each wheel, will a motor like this one work and be able to pull the load as well as have a fast enough rpm
http://www.omc-stepperonline.com/dual-shaft-cnc-stepper-motor-nema-24-100mm-4nm566-ozin-24hs393008d-p-388.html? Also are there any cheaper and lighter solutions for this? I want to use steppers to estimate the distance traveled but It seems as though half the robot's weight will end up being motors, just compounding the need for a greater torque.

Thanks for any advice it is greatly appreciated:)

2

I make it about 4.4Nm for 15 degree incline - total for all wheels, so 1.1Nm per wheel.

Multiply by a safety factor for friction/gears/rolling resistance, call it 2Nm per wheel

You don't want to use a stepper motor for traction, use standard DC gearmotors, otherwise
you'll have no efficiency to speak of and very short battery life.

With 20:1 reduction gearing that would be a 4000rpm motor with 0.1Nm torque per wheel,
ie about 40W per wheel.

3

Thanks for the help. However I am still having difficulty finding a motor, do you have any recommendations? I have spent an hour or so looking on eBay with no luck. What site can I find the motors on?

4

Cordless drill motors are about the right power level, but don't normally reduce as far as 200rpm.

Finding a cheap gear motor in that power range is tricky - it may be more economic to go
for 2 motors not 4.

I found this: http://www.ebay.co.uk/itm/DC-24V-200RPM-8mm-Shaft-High-Torque-Reversible-Turbine-Worm-Gear-Motor-Reduction-/121790433191?hash=item1c5b4687a7:g:x~IAAOSwYHxWIojL

[ Actually one possibility is aliexpress.com - bound to have something ]

5

Once again thanks :slight_smile:

I have looked around on Aliexpress and think I have had some success. If you wouldn't mind it would be a great assurance if any of these would work before I buy them.

http://www.aliexpress.com/item/Wholesales-A58SW31ZY-Geared-Motor-5-240rpm-Motor-DC-12v-High-Torque-DIY-Robot-Rotating-Lock-Self/32448831099.html?s=p&spm=2114.01020208.6.11.kqBeLb

http://www.aliexpress.com/item/Wholesale-JGY-2838-12v-24v-Worm-Motor-3-214rpm-High-Torque/32373872548.html?spm=2114.01020208.6.5.kqBeLb&s=p

http://www.aliexpress.com/item/NEW-HOT-12V-DC-200RPM-High-Torque-Electric-Motor-Low-Noise-Gear-Box-Reduction-Motor/32472651792.html?spm=2114.01020208.3.1.ydDNws&ws_ab_test=searchweb201556_4_79_78_77_80,searchweb201644_0,searchweb201560_9

6

First one - not enough power

Second one - even less power

Third one - 30W continuous electrical power in. More like it.