Legality of purchasing Planetary Gearboxes from alternative sources.

[GeeTwo]

Originally Posted by pilleya

For teams wanting to do this or something similiar, make sure you only use the low-power RS775-125 that Andymark sells. If you try to hook up a 775pro or 775-18 it is not going to end well for you. Andymark says on their website that if the pg27 with a 9015 is stalled then the gearbox will break. So even a reduction as low as probably 10-15ish:1 with a decent 775 will cause failure of the gearbox. In comparison the Versa-Planetary is rated up to 210:1 for the 775pro. So the gearbox can only handle 1/20th of the torque.

Check that again:

Originally Posted by PG27 web page on AndyMark

Performance Specs:

• Gearbox Reduction: 26.9:1
• Voltage: 12 volt DC
• Dyno Tested No Load Free Speed: 512.4 rpm
• No Load Current: 1.2 amps
• Gearbox Output Power: XX Watts
• Dyno Tested Stall Torque: 3.55 ft-lbf
• Stall Current: 63 amps
• Minimum torque needed to back drive a non-powered PG27: 0.3ft-lbs
• Maximum torque applied at shaft which breaks gearbox: 39 ft-lbs (breakage point is shearing of shaft)

There's another factor of ten in torque before breakage. Using the PG-188 with a higher torque motor is certainly subject to a sheared shaft, as stall torque with the 9015 motor is listed as 33 ft-lb, on the same output shaft.

[pilleya]

This is what is stated on the website for PG27 with 9015:

Originally Posted by Andymark Website

Be careful though, as the maximum torque the gearbox can handle is lower than the stall torque of the motor, be sure to limit it's output force

The description implies otherwise.

I'm not really sure if the Dyno testing results are correct( or maybe they are the 775-125 results), surely if the 9015 has a stall torque of 0.36 N.m( from motors.vex) with a 27:1 reduction the stall torque should be around 9.72 N.m( less due to frictional losses) rather 4.8N.m(using online calc from 3.55 ft-lbf)

If the stall torque measurement was correct it points to the gearbox having an output power of 65watts, which doesn't seem correct considering that from the VEX testing the 9015 is capable of 134watts.