Electric Motor Accessories
The electric drive system for our trainer comprises a motor plus other electric motor accessories. Three principle components in the power train are:
1) Brushless Outrunner Motor
2) Electronic Speed Controller (ESC)
3) Lithium Ion Polymer Battery (LIPO)
Plus the following:-
5) Lipo Charger
Brushless Outrunner Motor
Our power setup is based around a 3548, 900kv motor from which we need to develop a maximum 600 watts of power to give our trainer adequate performance. We have looked at the possibility of using either a 3 cell lipo or a 4 cell lipo both of which will provide the power we require.
If we go back to motor choices where we demonstrated the calculations necessary to determine the current consumption of both options, we showed that a 3 cell lipo will need to deliver 54 Amps whereas a 4 cell lipo only needs to deliver 40.5 Amps.
Our Electronic Speed Controller (ESC) can be selected to cover either option. My own rule of thumb is to choose an ESC that is capable of handling at least 30% more current than our maximum demand. so if we go for the highest demand and add 30% we come up with a figure of 70.2Amps. We can round this down to 70Amps for our purposes.
If we select an ESC rated at 60 to 70Amps then we can use either a 3 cell or 4 cell lipo comfortably. Admittedly the 54Amps is fairly close to the continuous running rating of a 60Amp ESC but there is still a good margin above the maximum demand. Its worth mentioning at this point that it does not pay to buy an ESC that is only capable of the maximum demand required of it. Its life expectancy will be relatively short and it will run excessively hot.
What we have to consider now is a combination of current demand and flying time. basically, the more current you pull from your battery, the shorter the flight will be.
You only have two parameters to consider when selecting a propeller for your electric motor. These are:-
Diameter and Pitch.
Having said this, you must be certain that the propellers you obtain are designed specifically for electric motors. Electric propellers are manufactured from lighter thinner composites than glow propellers. This is because there are very low levels of vibration from electric motors whereas glow engines have reciprocating parts with considerable mass that generate relatively high levels of internal vibration that is transferred to the propeller.
When it comes to calculating the diameter and pitch of your propeller, the same basic theory is used for either electric or glow use.
DO NOT, under any circumstances, try to charge your lipo batteries with a normal charger designed to charge NiCds, NiMHs or Lead Acid batteries. Lithium polymer Batteries require a totally different approach to charging. You must use a dedicated charger, ideally, one that is capable of balance charging each individual cell. This ensures that each cell contains, as near as possible, equal amounts of charge.
Lipo battery chargers come in many different power ratings. For our purpose we don’t require anything more than the capability to charge a four cell lipo with a current rating of 4 amps or more. There are many such chargers on the market.
This is the last of electric motor accessories for our power train so let’s take a look at: