Cox air-o-commander conversion

[Topcub]

Hey all, I just got a Cox Air-O-Commander, and used my Hi-tech radio to make it a three channel R/C airplane. Originally, it would have been controlled by vaying the speed of the motors. I hooked the motor leads together (solder) and plugged them into my speed control. I am using a Li-Poly 7.4 V, 720mAh battery. My question is this: When I advance the throttle, the engines speed up to a point, and then cut off, like a motor does when your battery is low. I cannot get full throttle out of this plane because of this. Do you think it is because my motors draw too much current for the battery? My speed control I do not think is the problem It is a JETI JES 110. I believe it is able to handle up to a speed 400, and I had no problems with Topcub's motor on it, either. I may try a Ni-cad pack, and see if there are any changes, but any help from here would be appreciated. By the way, it flies pretty well on 1/2 throttle, and I am using Elevator/Rudder controls. I think this plane will be a hoot when I get the kinks worked out! ------Bob

[Dave Robelen]

Hi,
I would take the motor leads apart and run them one at a time with the system. If this results in the individual motor responding properly, it could be a wiring problem (unlikely) or high current. If the Lipo pack cannot support the current and the voltage drops too much under load, this would cause the ESC to shut off the motor and leave you control over the servos. Depending on the brand and vintage of the lipo cells, some have a pretty limited max current.
Regards, Dave

[Topcub]

Dave, I tried a Ni-Cad pack with the same results today. I am thinking maybe my speed control may be the culprit? I checked the motor wiring, and it is correct. It flies ok at the throttle I have, but full throttle would make this a real performer, I believe.

[Dave Robelen]

Hi,
That does seem to leave the ESC as a major suspect. Can you bench run and duplicate this condition? If so, you might feel for heat in the ESC. Most of these are set up to shut down when overheated to protect the components. On other thing would be to check the settings if you have a computer transmitter. plus-minus 100% on the throw, zero on trim offset, and normal on the normal reverse settings. Other than that, the ESC may be bent.
Regards, Dave