Re: EV Warrior motor: stall torque of 691 oz-in = X operating torque ?


"pogo" <NOSPAMpogo@xxxxxxxxxxxxxxxxxx> wrote in message
news:ZMvlf.18610$Pc3.13992@xxxxxxxxxxxxxxxxxxxxxxxxx
> Specifications for clockwise rotation: Motor only performance.
> Typical system performance.
>
> Voltage: 12 V
>
> Angular-velocity constant: 229 rpm/V
>
> Torque constant: 5.91 ozf·in/A
>
> Termaina resistance: 0.121 ohm
>
> No-load current: 3.9 A
>
> Peak efficiency: 64.3 %
>
> Power source resistance: 0 ohm
> 0.121 ohm
>
> Peak power: 0.368 hp
>
> No-load angular velocity: 2640 rpm
> 2530 rpm
>
> Stall current: 99.2 A
>
> Stall torque: 563 ozf·in

Well, you don't really have enough here to calculate the motor's continuous
torque rating. A quick check shows that the "peak horsepower" they give was
just calculated as 0.25(stall_torque*no_load_rpm), which is a pretty good
estimate of the maximum power you'll be able to get with a 12V supply, but
is probably a lot more than you should run it at continuously.



One thing we can use to take a guess is peak efficiency. Since these motors
come from electric bikes with 12V batteries, it is reasonable to guess that
they are designed to be most efficient when delivering their rated
horsepower at 12V.



>From the stats given, we know that at 12V, with t=torque:



RPM = 2640-t*4.67



Current = 3.9A +t*0.17



Input power is current*12 watts:



Pin=(3.9+t*0.17)*12



Output power is torque * RPM oz-in-rpm, or torque * RPM/1350 watts:



Pout=(2640t-t*t*4.67)/1350



Efficiency = Pout/Pin, and it is maximized when t=93.2 oz-in.



Speed at that torque is 2205 RPM, and output power is 152W, or 1/5 hp.

Current draw at that torque is 19.7A and input power is 237W. That makes
efficiency 64%, which agrees with the number quoted in your specs (they will
have calculated it the same way).



Since 19.7 is close to 20, I'd guess that the motor's current rating is 20A,
which translates to 95oz-in continuous torque.



All of those guesses seem pretty reasonable to me, given the size of the
motor.



--

Matt





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