Twin engines (GWS Lightning)

[Tim Mackey]

It has been done yes. Castle Creations in the USA market an ESC which they claim is designed to perform happily with a particular pair of their motors. As I say, nigh on perfect matchimg of the 2 motors is the key, and budget motors are unlikely to have this. Well worth a dabble at the prices these days. Let us know how you get on Terry.

[Tim Mackey]

Not my original scribblings, lifted from elsewhere, but saves me a lot of typing

2 brushless motors on one controller doesn't work. You WILL see smoke. It may be today, the first throttle squeeze, or next week, but it absolutely will happen, and here's why:

A brushless ESC is looking at the motor electrically, and via it's software deciding how best to run it. When you have 2 motors coming into it, it's forced to "average" the signals coming in, and run what it sees as a strange single motor as best it can. It may not run them at all, but even under best case scenario of "matched" or "identical" motors, it's still running the entire system (motors, batteries, and itself) very hot, ineficiently (no power), and will simply not last very long.

Even two motors, two ESCs, and a single common battery pack (to make the voltage and thus motor rpms the same) run into a single spur gear (ala Emaxx) usually does not work. Very subtle differences in Kv make for one motor doing all the work and getting very hot, and eventually failing.
 

 Another view....

The motors must be very closely matched in order to get it to work at all. Even if you get it to work, the timing from the controller is averaged between the difference on the two motors. Back-EMF pulses average when the wires are paralleled on the motors. As a result the surge currents will tend to increase the temperature of the motor and controller you're using. If you run 2 motors on a single controller the controller should be derated by around 25-30% (making a 45A controller about a 30A controller). NEVER attempt a dual motor, single controller setup when you're going to have high inertia loads (example-large props/small motors w/gearboxes).

[shades]

Anyway, Michael, on your original post, I would be interested to see how you get on with the GWS Lightening. I too was looking for the same sort of thing back in the summer. I was going to buy the Eflite version but wasn't available at the time. If you read the spec, both models seem to be almost identical but the Eflite one is almost double the price of the GWS one. Is the Eflite twice as good as the GWS (I dought it)or is it just over priced. I have built a GWS corsair which was totally crap on original power train, but now with some mods and brushless power it is great to fly. See my vid. http://www.youtube.com/watch?v=zbpWYrRxgPs As I couldn't get the P38 I wanted, I got an Eflite mini pulse 3D, which is great to fly. I bought a slightly more powerful "MOTOR" (Timbo)than required with the view to using it for the P38 when available. I would love to know what the difference is between the two makes. My main concern, with both of them, is the fact they use hollow section foam wings. Not even Elapor. Very delicate. I can't see retracts working on such a light weight model. Besides, surely fitting them would weaken the structure too much.