775 pro performance and break in

[cmwilson13]

using a 775 pro for our shooter. we are getting poor performance out of it. pulling 40 amps at 11.5 volts(measured via pdp) and getting smoking hot just free spinning banebots 3 7/8 wheels with a 2 to 1 reduction via belts all running on thunder hex in vexpro bearings, belt center distance was set in cad so they are appropriate tightness. the wheels spin with little to no resistance by hand according to the spec sheet the motor should be somewhere around 12500 rpm, i did not have the ability to measure the rpm at the time but it was no where near that. we did no break in just straight to the shooter for test shots. can the lack of break in cause the poor performance or is there something i am missing.


also whats everyone's opinion on breaking them in. i know some rc people like to break in there 775s at 3v in water for 20 mins

[cmwilson13]

i have heard that high load full power runs on a new motor can pit the brushes, i wonder if that was our problem

[Sperkowsky]

We had issues with the 775pros so much so that we actually switched over to mini-cims.

Basically they were slipping from the versa planetary collar and we preferred to use an actual machine key.

[cmwilson13]

we dumped the versa in the first hr it pulled 60 amps using the versa 1 to 1.
we press fit a hex shaft onto the 775 and used the versa case to mount the motor with the guts removed. dropped to 40 amps just with that change

[Ether]

Originally Posted by cmwilson13

wheels spin with little to no resistance by hand

It can be deceiving. There may be more resistance than you imagine.

Can you remove the motor and run it with no load and see what the free current is?

[Doug G]

We too had some issues with our 775Pro motors and the versaplanetaries... Everything needs to be just right to get the free current down to 10 Amps or less. We are running dual vertical axis shooter, 3:1 with our VPs and dual 3.5 inch Colsons per axis. We had to really crank down on the clamp for the motor shaft to keep it from spinning.

[cmwilson13]

free current was somewhere around 1 to 1.5 if i remember right

[R.C.]

We are not using the VP's, using GT2 3mm belts and its fairly quiet with great performance atm. Also using press fit pulleys so no slippage!

[rahilm]

We're using 775pros with VersaPlaneteries in multiple places with no problem really (3:1, 30:1, and 100:1). The 3:1 goes into a 1:1.2 driving 4" AndyMark Stealth Wheels. At about 7k RPM (at the wheels), we're seeing about 10A current draw, which is right in line with the spec sheet. It gets pretty hot after 10 minutes of continuous usage, but that is completely reasonable. I can check with our students, but I don't think they did anything particularly special when putting together the planeteries.

[Ether]

Originally Posted by cmwilson13

free current was somewhere around 1 to 1.5 if i remember right

You probably have a lot more friction in your shooter setup than you realize.

40 amps @ 11.5 volts is 460 watts going into the motor, roughly 190 of which are being turned into heat.