Need a diagnosis :(
 

Not sure if this is in the right section.

Car setup:
ST-RR conversion
Medusa 1600kv 80mm with RCM motor heat sink/clamp
MMM ESC
2x 4000mah 3s LiPos in 6s1p
50/16 spur/pinion

Hi all,
Racing season is back finally, so did my first weekends racing on Friday/Saturday. Had a few issues with my car tho :(. I was running Mech brakes on Friday, but something happened to the receiver and the 3rd channel stopped working, so I removed brake servo, brake calipers and pads etc for Saturday. I note this just incase somehow switching to motor brakes may have caused this problem, as I didn't take note of my motor temps on Friday.

Now, my problem was motor temp. I'm running the standard 50T spur and a 16T pinion, which I thought would put me right in a sweet spot in terms of runtime and heat with the 1600kv motor on 6s. Unfortunately, this was not the case, and after each race (races were 10min) my motor was 85+ degrees (Celsius). This is why I got the Medusa, so that I can not worry too much about higher temps, however to me this seems to indicate that the setup is fairly inefficient and the gearing is wrong. Assuming that the hot motor and fairly warm but not hot (45C) batts and motor meant that the setup was undergeared, I tried a 17t pinion, but it didn't make much change on the temp. Please note, these temps were also taken at night, ambient temp was around 28C so it wasn't hot at all.

With the current setup, I was easily making the 10min race + 1-2 min for prac before each race. The most I ever put back in was 3025mah, which is pretty good I guess.

I'm about to strip it all down and check diffs and bearings etc, just incase there is some binding somewhere, although I can't feel any, but does anyone have any suggestions as to what I could do to try and lower my motor heat issues?

I have 46T, 48T and 50T spur gears and 12-18T pinions.

Also, just to make sure I'm on the right track, please let me know if the following statements are true (if everything else in the system remains the same)

decrease size of spur = increase in top speed but decrease in torque
increase size of spur = increase torque but lower top speed

decrease size of pinion = decrease top speed
increase size of pinion = increase top speed

thanks :)

Bigger spur/smaller pinion: More torque, less speed
Smaller spur/bigger pinion: Less torque, more speed

Is the 85 degrees at the heatsink or motor can? At those temps it's possible that the rotor has started to demagnetize. If you unmesh the pinion from the spur and turn the motor by hand is it as stiff as it was when you got it? Motor braking adds heat to your system but with your setup you shouldn't be getting that hot. BL motors can generate too much heat by being under geared as well as over geared, so I'd try gearing down a bit to see if that helps and if not gear up a little to see if that does anything.

It was 85C on the can, didn't bother checking the heat sink. As for the magnets being demagnetized, I hope not as that's why I purchased a Medusa!

The motor feels fine and feels just as hard to turn as when I got it.

if the motor is still as hard to turn as when you got it, then it should be fine. just be sure to stop it around 70-75C from now on. is there any dirt or debris inside the motor? my 60mm medusa started running hotter when it was sucking in dirt after my makeshift vent cover fell off.