# Using clutch disc to measure torque



## Tesseract (Sep 27, 2008)

Ummm... did you not know that torque from a dc motor is very nearly directly proportional to current? All you need to measure is current and voltage (motor or battery side), and motor RPM, to determine torque in ft-lbs:

Torque = (current * voltage * 7) / RPM

For example, we crammed 1000A through a warp 9 motor with 105V across it (105kw or 140hp) and it was spinning at 2000 rpm. That works out to a monster torque value of 368 ft-lbs IF the motor is 100% efficient (which it obviously isn't).

For up to 500A motor current the WarP motors seem to be 85% efficient; dropping to, perhaps, 70-75% efficient at 1000A (dunno - NetGain doesn't provide actual test data at that high of a current so we are winging it over here).


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## iss407 (Dec 6, 2007)

Yes I knew that. That is why I am interested in comparing shaft horsepower to electrical input power: to calculate efficiency real-time. The WarP 7 is dual shaft. I have toyed with the idea of using an alternator on the tailshaft for regen braking. Knowing the output torque would help monitor that as well. I've even had the crazy thought of sticking a small (~250cc) 4-stroke motorcycle engine under the hood tied to the tailshaft. The motorcycle clutch would allow me to engage/disengage the motorcycle at any time and the motorcycle transmission gearing with the right ratio on the chain sprockets would allow me to find the best RPM range for the motorcycle. Knowing the difference between the output shaft HP and the input electric motor HP would let me calculate how much power I am getting from the motorcycle engine.


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## piotrsko (Dec 9, 2007)

How about just finding a DYNO set up for the drive wheels?


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## iss407 (Dec 6, 2007)

A dyno is expensive and inconvenient. This option would give real-world numbers: different weather, temps, road surfaces, etc. In an ICE system it would have the same benefits. I live in the corn belt and E10 is cheaper than straight gas. My car would run fine on regular 87 octane but I buy 89/90 octane E10 because it is cheaper. I know that I get more energy out of straight gas though. This kind of setup would let me calculate if it is worth paying the extra at the pump to get the extra distance before the next fill up.


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