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Astroflight's new robot motors build on their already impressive products for model boats and airplanes. The robot-specific models feature larger brushes, different windings, and available planetary transmissions.
In the course of determining which motor would best meet the needs of a new Team Tentacle robot. Mr. Tentacle worked up a motor statistics spreadsheet for each of the new AstroFlight motors, the links to which appear below. Thanks to Derek Young, builder of Complete Control and Pressure Drop, for the original motor sheet (640.xls) that gave me the idea for these.
A few words of caution on the information in the spreadsheets:The values are calculated using standard motor formulae with information provided by AstroFlight. Bob Boucher (president of Astroflight) is very good about providing accurate figures. but the physics of electric motors is quite complex, so simple calculations can only approximate what behavior you will get in the "real world".
The computed stall values for the Astro motors is very high - the motors will actually overheat and fail long before the stall value is reached. In addition, the "real" stall value for a motor is determined by the complete system of motor, speed controller, and battery. Astroflight gives a "stated stall" of 100A for all their motors, because 100A is about the most you can expect to get out of a NiCD pack and speed controller connected to these motors. The "Max Amps" figure is the constant current you can expect to put through the motor without burning it up. As a motor heats up the resistance goes up, which brings the stall value down and reduces the power out, so a cool motor is a happy motor.
It is VERY IMPORTANT to not drive the Astro's at more than the Max Amps value for any length of time. If you add cooling fans you can push the motors a little harder, but don't expect to get anywhere near stall without making some very expensive magic smoke. All of these motors benefit from additional cooling - I recommend adding fans for forced air.
DON'T EVEN THINK ABOUT OVERVOLTING AN ASTRO MOTOR! The max voltage stated is the voltage to use. For 24v, use an Astro 40. If you want to run 36v, use an Astro 60 or 90. The 90 can take up to 48 volts.
Caution: the output shaft on the 915p motor is only 4mm in diameter. The 915p has more than enough torque to snap this shaft if you are not very careful about mounting it. It is critically important to avoid putting any lateral load on this shaft. One approach that has been used to good effect is to mount a 3/8" or larger shaft over the stock shaft, supported with bearings at both ends.
These motors deliver terrific power for their size and while they are not cheap, they are an excellent value in my opinion