0 Members and 1 Guest are viewing this topic.

#### bilalbajwa

• Beginner
• Posts: 4
##### Easy Question about Stall Torque.
« on: February 19, 2010, 02:09:53 PM »
Hi, I am building a two wheel robot with a ball caster at the back.

I am using a 50:1 Metal gear motors Qty: 2.

Q1. The weight of my robot is 12oz Total including everything (motors, battery etc etc). The stall torque of each motor is 15oz. As i am using two motors i think i should be ok. What you guys think?

Q2. Moreover, will i be right if i say i am using two motors so the weight of my robot will be equally distributed on the two motors and the ball caster. As the ball caster is only being dragged. So each motor will see the weight of the robot to be like approx 6oz?

Here are the specs of the motor:
Gear ratio:                     50:1
Free-run speed @ 6V:            630 rpm
Free-run current @ 6V:    100 mA
Stall current @ 6V:            1600 mA
Stall torque @ 6V:            15 oz·in

#### waltr

• Supreme Robot
• Posts: 1,905
##### Re: Easy Question about Stall Torque.
« Reply #1 on: February 19, 2010, 03:24:54 PM »
Q1: No, the stall torque is not 15oz it is 15oz-in, big difference.
Check what torque is here: http://en.wikipedia.org/wiki/Torque
Explained better than I could in a short post.

Q2: To the first approximation that could be correct if most of the weight is on the wheels and not the caster but is not the whole picture. Friction is really the biggest factor to determine what the motors can move around on a level surface.

Also the relationship of motor torque and robot weight is not straight forward.

SoR has a very nice Robot Motor Factor (RMF) Calculator in the tutorials. Go there and plug in the numbers for your motors and bot. Be careful as to not enter unrealistic speeds, accelerations or angles. For the maximum speed use a little less than the Free-running motor rpm and the tire circumference.  Then come back to this thread to ask more questions.

You will find that your motors have plenty of power. I an using the micro metal 100:1 motors (10 oz-in torque) for a 12oz bot and it'll climb a nice grade without slowing down.

Have fun