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Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
Yeah, you need to build yourself a dyno rig and get some hard numbers.
Here's a tip, watch out for the temperature coefficient of resistance of copper. The efficiency numbers will drop as the motor heats up, and you'll need to account for that when taking data. Either by measuring the winding temp and correcting for it, or by blasting the motor with a high-powered fan so it stays nice and cool.
If you use a second motor as a brake (easy with a 3 phase bridge rectifier and dummy load bank) and use the electrical power output to infer the mechanical input, then the temperature of its windings will also affect the result. A good dyno has a way of measuring the actual mechanical torque input. On the ones I've used, the brake is mounted in trunnions with a spring balance to read the twisting force.
Registered Member #2431
Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
Dr. Slack wrote ...
... and if you set up a motor/brake combination to absorb X watts at Y RPM, does the $70 ESC draw less power than the $13 one? If so, how much? Without numbers, everybody is just shooting the breeze.
Now $13 and and $70 *are* solid numbers. Until you come up with some like-for-like power consumption figures, I have every sympathy with their cheapskate point of view.
i should have added....
only whieght and cost as a penalty as said before.
but i use the full-cased Castle ESCs Phoenix ICE 50's (50 amp, 75 peak), for little more than 20 amps. they are heavier, and specifically the castles are expensive.
But in the defense of hefty ESCs, I like to state that in: -- 200 moderate crashes, (1-3 hours of repair time, minor materials) -- 30 severe crashes, (major damage, 10-30 hours of repairs, with major new parts.) -- and 15 catastrophic prop-binding/breaking at full speed crashes... (nearly 100% loss of vehicle)
I have not had a single Castle ESC fail in Bicopter use. If these were Chinese cheap ones, or the properly sized ones, Im certain i would have replaced at least 20 ESCs by now.
-Patrick Coleman
the efficeiency point would also bolster the above point further. But I will fab a brake as you suggest, because emulation is better in this case than simulations. 20 x 13 = $260 vs $140
Steve Conner wrote ...
A good dyno has a way of measuring the actual mechanical torque input. On the ones I've used, the brake is mounted in trunnions with a spring balance to read the twisting force.
ive seen Ford GM and the US navy do the same, with a load cell attached in this way to the brake housing.
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Is a 3 phase electronic speed control for brushless motors, effectively a step down SMPS?
