[Splint]

Hi all,
I've been researching some technical specs for some motors I bought second hand and Al_The_Man has been very helpful in providing some specs for some engines in the same family as what I have. Below are the specs which most resemble my servos. I see the amperage rating is listed as Max. Pulse Current, I'm curiuos to know if this means a safe continuous amperage, or an unsustainable "peak" amperage. I'll be looking into power supplies soon so I need to have a clear idea of my requirements but I couldn't find a definition for Max. Pulse Current so maybe someone here can tell me.

Electro-Craft servo motors
Cont. stall torque (oz-in) 50
Peak Torque(oz-in) 350
Max. voltage (V) 60
Max speed (rpm) 6000

Mechanical

oz-in-sec2 0.0062
kt Torque constant 11.8
Ke Voltage Constant 8.6
Winding resistance (OHM) RA 1.04
Max pulse current (A) 29
Armature Induct. (mH) 3.3
Body Length(inch) 5.0

Thanks
Splint

[Al_The_Man]

Splint, I looked through the two Electro-Craft Catalogs, which by-the-way have a whole raft of info. on motor sizing etc. And It would appear that the Pulse current or Peak current is a value that should be used in sizing the amplifiers, amplifiers are usually rated in continuous and peak current and this peak value allows for very momentary current peaks, which normally would not harm the motor or the amplifier.
Most amplifiers have a max current setting on them, and will shut down when this value is reached, they should be set to at, or just above the continuous rating of the motor.
Power supplies, should be sized with a good margin should be based on the total continuous current for all the axis. Power supplies usually have components in them which have more tolerance to overload for short periods. The bottom line is the motors and amplifiers should be protected from operating much more than the continuous current, by setting as above, and suitable fusing in the power supply. This is method has worked for me in the past.
Al

[Mariss Freimanis]

The specs are pretty typical for a motor of that size. Here's some key concepts on servos:

1) Continuous stall torque (50 oz-in). You don't go over this number except for very short periods of time. The Kt is 11.8 in-oz / Amp, the max continuous current thru the motor is 50 / 11.8 or about 4.25A.

2) Peak torque (350 oz-in). This is 7 times max cont torque. The motor will draw 7 times rated max current and dissipate about 50 times (7 squared) more heat than it can safely get rid of. The flip side is you can use this torque at a 2% duty cycle ( 1 / 50 = 2%). It is usable for acelleration and deceleration.

3) The motor Ke is 8.6V / 1,000RPM and has a max rated 6,000 RPM. The max supply voltage becomes about 52V (8.6 times 6 kRPM).

4) Motor power output is 50 in-oz times 6,000 RPM divided by 1351 or 222W (about 0.3 HP). This is more than you can get from the largest NEMA-34 step motor.

5) Really pay attention to (1).

Mariss

[Splint]

Thanks guys,
so it sounds like I need to get an amp which can supply for each axis 4.25 amps continuous and 29 amps peak current. The voltage I'm not entirely clear on as Marris has shown in point 3 that the voltage should theoretically be 52volts, where as the published spec is 60volts. Would this be because the windings are slightly heavier and capable of handling 60?
David