# What is the torque transmission efficiency using a bycicle chain/setup for robot?

For this robot the gear attached to the motor is linked to the gear attached to the wheels by a bicycle chain (I am using a bicycle wheel and transmission set as the parts for the robots movements).

How does using a bicycle chain affect the power transmission efficiency, how does this impact the torque?

I agree with @Andy 's answer, that chain efficiency is over 90%. I'll point out that your terminology is not quite right - using bicycle chain (or any other transmission) affects power transmission efficiency. It's a subtle but significant difference between what you said (torque transmission efficiency).

First, efficiency is defined as the ratio of output to input. With gearing, you could use a very inefficient transmission and still have a larger output torque than input torque. This would imply that your "torque transmission efficiency" is greater than one.

Second, in the case of zero/stall speed on the drive, the torque output should be nearly the same as the input torque.

Both of these cases are covered when you talk about power transmission efficiency.

• Thanks for the answer, you say the chain efficiency is above 90%. I have calculated the torque necessary to move the robot in the worst situation possible, since the chain is around 90% efficient, can I directly translate that to necessary torque and increase the torque value I calculated by 10% to compensate (this is why I put torque transmition efficiency instead of power)? Commented Aug 31, 2016 at 14:21
• @Square79 - Yes, you can do that, but it's an abuse of terminology that only works out due to the cancellation of the gear ratio in the output power equation. You can increase the input torque to increase the output torque enough to overcome the power loss, but like I mention above the "torque efficiency", output divided by input, can easily be greater than one if the gearing is setup that way.
– Chuck
Commented Aug 31, 2016 at 18:28
• Ok, thanks for clearing that up, I edited the question. Commented Sep 1, 2016 at 7:47

From a cyclists' perspective - a good modern bike chain transmission is very efficient - percentage efficiency is somewhere in the high 90s and has been for decades.

(From anecdotal evidence: endless debates in cycling over the years, about various inventors attempting to "improve" the design of the bike with belts/pulleys, conventional gears, even things like propshafts etc. Such alternative designs sometimes have useful features, but they haven't significantly improved overall on the strength, efficiency and light weight of the modern chain & sprocket.)

As far as application to robotics is concerned - it will help to make sure everything is mounted well, not in a flexible way so things cannot deflect under load, and the gears and chain are kept in a reasonably straight line. These are the way bike components are mounted too.