GWS Top Electric Flight FAQ

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What does gearing do for you?

Gearing allows a motor to turn a larger prop at a lower rpm. This allows the system to produce more thrust while drawing the same number of amps. The trade-off is that top speed is reduced, which makes gearing suitable mostly for slow-flying aircraft. Sport electric planes are usually run with a direct drive system.


 How do I compare an electric motor to an ic engine?

If you are looking for a watts to horsepower conversion, then the formula is: 1 brake horsepower = 750 watts. The problem is that electric motors have many more variables than ic engines. In order to determine the performance of an electric motor, you must first answer questions such as how much duration you want, how much power you need, etc. Gearing also heavily influences the comparison.


How much heat can our motors dissipate?

At room temperature, according to the industry standard is 1 watt per square inch for continuous operation (24 hours).

It’s about 3 watts for ours for as long as a NiCad pack can run it


How do I keep my motors clean?

If commutator has deposits of carbon and gunk on it you can clean it with scotch rite or a com stick. Very light polishing action. You can also clean off gunk when motor is running by a few drops of alcohol.

If com is pitted or shows brush skipping and chattering your com has been overheated and needs to be returned. It is out of round. polishing will not cure out of round.

You need a lathe with a ball bearing in the tail stock and a diamond tool..or at least a sharp cutting tool.


How do I measure motor constants?
Of the 3 motor constants Kv and Io are much easier to measure.

Kv: With the motor shaft in a drill press running at a known speed measure the voltage at the motor terminals. Kv = speed / voltage i.e. if the speed is 6000 rpm and the voltage is 3V
Kv = 6000/3 = 2000 rpm/V

Io: Simply run the motor with no load (no propeller)and measure the current taken. That's Io. You can use almost any voltage because the current does not vary with voltage. However the motor will still be turning at the rpms defined by V x Kv so don't go too mad. I usually use 5V.

Both Kv and Io should be measured with the motor neutral timed. For most can-type motors this is what they are fixed at. If you do have a motor with adjustable timing then you can try (carefully) adjusting it as you measure Io. It will be neutral timed when Io is at its lowest value.

Rm: this takes a little more work. The motor and shaft must be held so that neither can move i.e. the motor is stalled. You then need to apply a voltage through a limiting resistor and measure the current through the motor and the voltage at the motor terminals. Note it must be directly at the motor terminals NOT the power supply. You will need to do this very quickly as the current will be high and the motor will quickly get very hot. Rm is voltage / current.

E.g. if you measure 5A and 1.2V then
Rm = 1.2 /5 = 0.24 ohm, a typical value for a Speed 400.


 How many capacitors do I need on the motor and what values ?
It is a good idea to fit at least 2 capacitors to most brushed motors to cut down on the radio interference which the motor may generate. The same capacitors can be used for all brushed motors, the value does not change with the size or power of the motor. The capacitors should be soldered from each motor terminal to the motor case. For extra security against interference you can also fit a third capacitor between the 2 motor terminals.