Speaking of stalling, I don't think I've heard it mentioned here that
one of the advantages of the DC motors used in the Yaesu rotators is
that you can run them up against a mechanical stop (like a swinging gate
sidearm, for example) and leave them trying to turn literally for hours
73, Pete N4ZR
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On 1/4/2011 10:19 AM, jimlux wrote:
> Jim Thomson wrote:
>> OK, I see mentioned on most rotors... specs like "start up torque" and
>> "running torque" and also "stall torque"
> Because that's how motors and gearboxes are specified, in general?
> Stall torque is limited mostly by the winding resistance and the kind of
> motor. Running torque has to take into account the losses in the gear
> train. There will usually be some sort of time limit on how long you
> can run it stalled (for motor heating).. if the motor is internally fan
> cooled, spinning at all makes a big difference.
> By looking at the current draws at the different torques (if available)
> you can figure out how much of the power is going into the losses vs
> actually driving the load.
> For 3 phase AC induction motors, there's standard ratios that are used
> (Full Load Amps vs Locked Rotor Amps vs Normal Starting Amps). 7:1 is
> typical Locked Rotor vs Full Load. 3 or 4: 1 is typical for start vs run.
> (this is why a slow starting capacitor start motor cooks the start cap...)
> And, as you point out, there's also a "holding torque" for the brake.
> The other things that affect these specs are the kind of gear train. A
> spur or planetary gear set will usually allow the load to backdrive the
> motor. A worm gear drive won't.
> As for why inchpounds and not Newton-meters or ft pounds or other
> units.. tradition. Small sub-fractional HP motors are almost always
> specified in inch pounds.
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