Stuttering Motor

[Percymon]

I finished my Blitzer Beetle resto at the weekend, configured as follows..

Modelsport (mTroniks) RV-12 reverse ESC - 12 turn limit

Ansmann Launcher 17x2 motor

Hobbyking 2.4GHz radio system

so far run with a NiMH 1900mAh pack and a old Tamiya 1400mAh NiCd pack (7.2V)

both batteries were fully charged, and both exhibit the same issue.....

after installing batteries the car will run initial full throttle starts for a couple of minutes max, but then starts stuttering and cutting out thereafter. Reverse works fine, the ESC emits the reverse 'noise' and the car engages after the reverse dealy without issue. Once the car overcomes the stutter its blooming quick, i have lots of donut marks on my garage floor to verify it !

I've read the ESC instructions a few times - there is no lipo cut off feature, so its not a low voltage cut out. Other possibles from the ESC manual..

1. RX too close to motor power wires ? I have the RX located in the stock position in the bottom of the chassis tub, with the ESC located above it on the upper 'deck' - as Tamiya instructed originally. The only difference is i have the short (5") aerial from the RX in an arc from the RX to the rear body mount (ie inside the shell, not sticking out of the roof). I havent tried locating the ESC yet, although thinking about it the motor wires are pretty parallel to the RX aerial.

2. Battery unable to supply load - fit a 1000uF capacitor. I have some bigger capacity 5000mAh packs that i will try tonight, as i know these will happily power a EXRun 9T brushless set in my heavy 4wd Hotshot without issue.

I'm guessing my issue is the ESC / aerial proximity, but any other areas to check are welcome ?

Also, does anyone know what sort of current draw a 17x2 motor will be demanding of the battery ? (ESC, battery and motor are all stone cold after 7-8 minutes use).

[Backlash]

If the problem only occurrs when you go full throttle from a standing start, then I would say that your issue is current draw, or more to the point, your batteries inability to supply the current required by the motor at takeoff, thus causing the battery voltage to fall lower than the required minimum voltage for the radio gear, thus causing the stutter..

Motor current draw at startup can easily be 4 to 8 times that of the rated or normal running current draw..

I would try a better battery pack..

Adding a 1000uf 16 Volt electrolytic power capacitor to the main battery leads to the ESC may help a little.. You could also try a Stutter Stopper, which is basically a power capacitor that connects to the battery port or free channel in your receiver.. You could make one very easily by soldering the positive and negative wires from an old servo plug or battery box plug to a 1000uf cap, and plugging it into the receiver... REMEMBER, ELECTROLYTIC CAPACITORS ARE POLARITY CONSCIOUS, reverse connect them and they go pop..

To explain the theory or logic behind all of this.. A capacitor has the ability to hold or store a charge, and then discharge it very quickly.. As previously stated, when you takeoff from standstill, the 7.2V batteries voltage may / is falling below the minimum voltage required for the radio gear to work, causing a stutter.. But if you have a "stutter stopper" capacitor connected, it will charge up to the BEC voltage, (typically 5-6V) and then when the 7.2V batteries voltage drops below the minimum required for the radio gear to operate correctly, the capacitor will discharge, and hold the voltage to the radio gear at the BEC voltage, thus removing the stutter.. Hopefully this makes sense..

If it was interference, i.e. ESC too close to the receiver, the problem should be happening all the time, not just at take off..

cheers

[Percymon]

Swapped battery to a vapextech 5000mAh NiMH pack and no issues tonight, bar trying to keep speed down and ultra sensitive steering!

Thanks for the help Backlash