Heliguy Forum - RC heli forum

We've had loads of great weather, with very little wind... so guess what, I've been without a working main motor. The three rather well used motors I have were all too feeble to get out of ground effect for more than a minute or two... and my replacement was being rather tardy to arrive.

But today, I received an ESky 3100KV motor and ESC. The 3100KV has the same mounting screw positions as the standard motor, so it fits the CP2's frame. The first surprise is that it has an 11 tooth pinion rather than the 9 tooth one that comes attached to the brushed motor. The second surprise is how much smaller it is than the brushed motor. (It's no lighter of course - since you now have an ESC, which also has a big heavy toroidal choke to stop electrical hash feeding back into the receiver).

I have a spare 4-in-1 (it was my original, and the power transistors died in it - I did repair it, but by then I had another 4-in-1) - which is handy, because if I have a failure I can go back to the brushed motors and not be grounded. Fitting the brushless motor is a Some Soldering Required job: the ESC's inputs must be connected to channel 3 which has no header on the CP2's 4-in-1. Also the connectors for the power feed isn't the same - I spliced it into the power that's used for the 4-in-1 so the standard battery packs work.

The motor itself is much stiffer to turn when unpowered compared to the brushed motor, but I think that's all magnetic rather than mechanical. The other thing is that the windings stay stationary and the case revolves - so I'm going to have to do something different with the servo wires to keep them away from the spinning motor case. Also, the ESC and its associated choke, and very stiff wires really need a bigger canopy - I can barely get mine on! But the weight does help the heli's balance: I have the dual motor mod and normally have to shove the battery very far forward to get the heli correctly balanced.

The first thing you notice when you spin the heli up is how different it sounds. It's about half as loud as the brushed motor, and has a turbine like whine.

With the 11T pinion, the rotor head speed doesn't seem that different to the brushed motor from the sound of the blades beating the air into submission as I flew around my back garden. Collective responsiveness is better - it has much better power, so perhaps I can put the rather heavy HDX300 head back on the heli. However, it's not so powerful that it overcomes the tail rotor with the dual motors, the tail still seems perfectly controllable.

When the ESC decides the battery has had enough, it cuts the power rather sharply (so you better not be over something you don't want to land on, because you're coming down - not so fast you can't take some evasive action, but it's not that gentle slowdown you get with the brushed motor). However, you can anticipate the ESC cutting the power - as with the brushed motor, you can feel the tail go "soft" when the battery is starting to go weak, and the RPMs start to drop off a little, so you do get enough warning to get over a landing area before the ESC decides it's had enough.

After a full battery of flying, the ESC is cool and the motor is barely even warm - a complete contrast to the brushed motor that gets quite hot even with two heatsinks.

Verdict: so far, I like it a lot. However, you need to be able to solder to fit it! In the CP2 modifications forum, someone has posted some instructions (which to summarise are - ESC input connects to channel 3 - which you have to solder, and the power connector from the battery must be modified to feed both the 4-in-1 and ESC).