0wn3d_will
1 µW
- Joined
- Aug 1, 2011
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Do you guys have any suggestions on how I can measure the torque produced by a hub motor? 
How to measure hub motor torque?
- Thread starter 0wn3d_will
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John in CR
100 TW
0wn3d_will said:Do you guys have any suggestions on how I can measure the torque produced by a hub motor?
I don't worry about the actual numbers, and instead just hammer the throttle with as much current as the motor can handle or the controller can reliably deliver, whichever is less. If it starts to wheelie with a normal riding position, then I'm happy. If it feels like it wants to lift the front wheel even leaning forward over the handlebars, then I'm in nirvana and need a 3spd switch for times that I don't want those scary takeoffs...slippery conditions or a child passenger.
dogman dan
1 PW
The crude and dirty way, you can compare two motors, or two voltages or whatever by comparing how they climb a hill. How fast can they climb different grades for instance. But you don't get numbers. Takes torque to climb, so you get to see the difference easier.
I would think only a dynamometer can tell you real world numbers.
Grin Cyclery has a great simulator though, that esimates torque for commonly avaliable hubmotors. It's pretty good, so you could just use that data for a ballpark idea what the numbers are.
Torque of course, varies with speed. Most torque is 0-1 mph. By top speed, it's very low, down to near 0 if the motor is running no load.
I would think only a dynamometer can tell you real world numbers.
Grin Cyclery has a great simulator though, that esimates torque for commonly avaliable hubmotors. It's pretty good, so you could just use that data for a ballpark idea what the numbers are.
Torque of course, varies with speed. Most torque is 0-1 mph. By top speed, it's very low, down to near 0 if the motor is running no load.
0wn3d_will
1 µW
- Joined
- Aug 1, 2011
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- 4
Hey guys, I need your help for a school project. We need to make "torque measurement rig" for a BLDC hubmotor. It need not be mounted on a bike so we could make our own mounting. Our problem is how to actually measure the torque generated by the hub motor.
Are there electronic torque sensors out there compatible with a hub motor?
Or is there some sort of equation we could use given the load weight on the hub motor or the angular velocity or something?
Thank you
Are there electronic torque sensors out there compatible with a hub motor?
Or is there some sort of equation we could use given the load weight on the hub motor or the angular velocity or something?
Thank you
bigmoose
1 MW
Now it would help the learning process a bunch to think through how you would do it. All of us here would be glad to help you refine it... and you may have a better idea than anyone before you!
Your basic goal is to load the wheel motor and then measure reaction torque. Do a bit of research, it is fun. Start with searching "pony brake" to understand the basic concept.
As your research progresses you will discover multiple ways to load the motor, and multiple ways to measure the torque. Start to rank them via pro's and con's, like accuracy, ease of fabrication, cost, etc. See which methods bubble to the top. Sketch some out and share your ideas here.
What is important is for you to learn the method of technical problem solving at this stage of life, not necessarily to solve the problem right away. That is a skill that will profit you for a lifetime! ... the joy is in the journey, not necessarily in the destination.
Edits:... Miles is of course right below, Thanks for the correction!
Here is a thread with a video of ebikes.ca hub motor dyno... but I encourage you to do your own design.
http://endless-sphere.com/forums/viewtopic.php?f=30&t=32165
Your basic goal is to load the wheel motor and then measure reaction torque. Do a bit of research, it is fun. Start with searching "pony brake" to understand the basic concept.
As your research progresses you will discover multiple ways to load the motor, and multiple ways to measure the torque. Start to rank them via pro's and con's, like accuracy, ease of fabrication, cost, etc. See which methods bubble to the top. Sketch some out and share your ideas here.
What is important is for you to learn the method of technical problem solving at this stage of life, not necessarily to solve the problem right away. That is a skill that will profit you for a lifetime! ... the joy is in the journey, not necessarily in the destination.
Edits:... Miles is of course right below, Thanks for the correction!
Here is a thread with a video of ebikes.ca hub motor dyno... but I encourage you to do your own design.
http://endless-sphere.com/forums/viewtopic.php?f=30&t=32165
John in CR
100 TW
Miles said:Or, "Prony brake".... Google is used to either.... "pony break" takes you in the wrong direction, thoughbigmoose said:
Nice educational tidbit there Miles, as usual. I wish I could hang out with you and Bigmoose in an alternating manner as long as each could put up with me, which might be long periods, since I'm alot nicer than comes across in my typed words.
itchynackers
100 kW
Couldn't you just use some formulae? Ride your bike through a fixed distance, starting at zero speed. Measure the final velocity, time, and et voila. Plug in the numbers.
Or, mount the motor on a pulley system and use it to lift a known heavy weight a certain distance for a certain time (same concept).
Or, mount the motor on a pulley system and use it to lift a known heavy weight a certain distance for a certain time (same concept).
Sure. You can calculate from the basic spec. without running the motor, even. Measuring the reaction torque, as bigmoose suggested, gives you a simple, accurate and variably controllable system to experiment with, find out the sustainable torque, thermal inertia, etc.itchynackers said:
That's reassuringJohn in CR said:I wish I could hang out with you and Bigmoose in an alternating manner as long as each could put up with me, which might be long periods, since I'm alot nicer than comes across in my typed words.
If you're ever in London, John, be sure to look me up. Lots of great riverside pubs to hang out in, here in Greenwich 8)
salty9
1 kW
Reading this thread reminded my of an old (circa 1960) joke from physics class http://www.snopes.com/college/exam/barometer.asp
