HV-Maxx motor thermal shutdown problem

[Toon]

Hi guys, this is my first post - sorry it's long! :D

After many months of waiting, I finally got my hands on a HV-Maxx brushless system (it's only recently been released here in the UK). Here's a few pics of if installed in my truck - I do plan to shorten the motor power wires, removing the excess length. Oh, and I also bought a nice matched pair of GP3700 1.19v 7-cell packs to go with it!





I am running the transmission the opposite way around to stock, because I am using a Torpedo chassis, and the motor power/sensor wires won't reach the ESC at the back of the truck if the transmission is in the stock orientation.


Now, Novak's recommended gearing for the HV-Maxx in the E-Maxx is 14-16/70, which equals 13-15/66 if using a stock 66T spur. So I started at the lower end of the gearing, 13/66, which I increased to 15/66 to compensate for the lower internal gearing of the UE Spyder diffs I have.


First impressions are very good, it has great torque, and plenty of speed (I will strap my Garmin Foretrex 101 GPS into it soon and get some speed figures). But then, after nearly 7 minutes of fairly hard running, the motor lost all drive. I still had steering though, so I brought the truck back over to me and removed the body. The blue & amber lights on the ESC were blinking, indicating 'motor thermal shut-down', according to the set-up guide. So I got out my IR temp gun and took some readings. The air temperature was 60*F. The cells were at around 100*F, the ESC heatsink was 120*F (the fan was running), but the motor heatsink was at 175*F!


I let everything cool down and recharged the packs. For the 2nd run, I dropped the gearing to 14/66 (12/66 stock equivalent), but that is the smallest 32DP pinion I have. I got 9 1/2 minutes running before the motor thermal shut-down kicked in again. The ambient temperature was a bit lower (50*F), the cells and ESC were at about the temps. as the on 1st run, and the motor heatsink was 165*F. It was a mixture of 1st & 2nd gear running, on mainly concrete and gravel.


There is no binding in the drivetrain that I am aware of. The truck does weigh 12 lb 9 ozs. RTR though, so maybe it's too much truck for the HV-Maxx? I know running it on 14 cells is at the ESC's limit, but I use the 7-cell packs in my brushless T4 as well, so want to continue using them if possible. Any advice from the brushless guru's? Continue lowering the gearing until I can go a full run without thermalling? Drop down to 12 cells? Try it without the motor heatsink? Install a motor fan?


Whilst waiting for the HV to be released, I did seriously think about getting a Feigao 9L/10L motor with a BK 9918 controller. That setup would undoubtedly have much more power, but I wanted to start with a lower-powered setup, that has a few advantages over the Feigao/BK setup in my opinion (sensored system, useable BEC, better warranty, motor heatsink & ESC fan as standard). Maybe I should have taken that route instead. If the HV motor gets this hot in mild Spring temperatures, it's surely going to be even more of a problem in the Summer... :M: