Brushless Stuttering / Hesitating in One Car but Not Another – Please Help?

[mrki]

Hi Everyone,

I am new to these forums so please be gentle. After getting back into RC recently after several years away, I thought I would try brushless.

I picked up a Nosram Evil Power / Dragon 10.5T combo (sensored) a while ago to run in my Tamiya Blackfoot Xtreme and it has run flawlessly with no heat, cogging or stuttering issues. The ESC is an A.I. set up so no settings to play with.

I built up an Ansmann Macnum, ball raced it and transferred the Nosram Brushless combo into it and I get really bad hesitating when accelerating. I swapped the whole system over from my BFE (27mhz radio gear and all) so I know it all works fine in at least one car. I have swapped it between them a couple of times and it will run with no problems in the BFE but not in the Macnum.

I am using a new Vapextech 3700nimh pack but this performs brilliantly in the BFE, leading me to believe it is not the battery problem. It is using a standard Tamiya connector but nothing is getting that hot.

The symptoms in the Macnum are that when accelerating on 3/4 to full throttle, the car will slow / hesitate for a second almost like it was a nitro car changing gear and you can hear the motor revs drop. It does this through the acceleration not just at one point. I have tried it with 23T down to 16T pinions and it is exactly the same symptoms. The motor and ESC are not getting hot, so as far as I can tell it is not over geared.

I don’t think it is cogging and at low speed or part throttle its fine. It has no problem getting moving or driving around at low speeds.

I tried a brushed motor (Peak Racing 13T) with the Nosram ESC last night and got the same problem. So it is not exclusive to the Nosram Dragon motor.

I was wondering whether it could be the slipper clutch or something out of true in the gear box that is causing problems with the ESC / motor loading. Alternatively, could the drive train be slipping? I have tightened up the slipper and ball diff, loosened them and everything in between.

If you rotate the spur gear it doesn’t run in a true arc and you can see a slight bit of wobble, essentially a rise and fall or 0.5mm over the whole rotation as well as a small amount of back and forth play despite the ball racers.

As this works in my Blackfoot (ball raced and the gears run silky smooth), I know there is something in the Macnum set up causing it. Could it be the ESC responding to the loading on the motor and cutting out?

I would really appreciate some help on this.