[TowerTalk] Rotor specs, are they a bill of goods ??

[Pete Smith]

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 
without damage.

73, Pete N4ZR

The World Contest Station Database, updated daily at www.conteststations.com
The Reverse Beacon Network at http://reversebeacon.net, blog at reversebeacon.blogspot.com,
spots at telnet.reversebeacon.net, port 7000



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.
> _______________________________________________
>
>
>
> _______________________________________________
> TowerTalk mailing list
> TowerTalk at contesting.com
> http://lists.contesting.com/mailman/listinfo/towertalk
>
>