Electric Flight in Australia

 

How can I retune an electric motor?

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You can retune a brushed motor, but you cannot retune a brushless. The tuning of brushless motors is achieved by the speed controller. The top of the range Schultze brushless controllers, the Hyperion brushless controllers and the Scorpion brushless controllers featured on this site, do have programmable timing, but most early controllers did not. It is best to use recommended speed controllers with brushless motors to achieve the best match between motor and controller. This is imperative if you want the best performance from your brushless motors. For example, the K2 series of Electronic Model brushless motors had very low timing (no longer available) and should have been used with the EM Flash controllers for maximum efficiency. Now that outrunner motors are becoming popular, most controllers feature programmable timing so that you can adjust your controller to suit the motor that you are using, but you cannot retime the motor.

Now, back to brushed motors. The popular can motors are supplied with the backplates crimped in place. The timing at this location is 'neutral' timing, meaning that they are in the best location for running in either direction. You can prise open the crimps and grind them off. You can then play with the timing. Once you have decided on the best location for your purposes, you can relocate the backplate with tiny screws by drilling holes through the metal can into the backplate. However, there is not much to be gained for all this trouble.

On the other hand, improved ferrite motors have more to offer and often have adjustable backplates. For example, the Leisure Gold motors that I have in stock do have adjustable backplates. These motors are supplied with maximum advanced timing (24 degrees or 7.5mm) which is the best position for forward running. For reverse running (in some gearboxes for example), you need to rotate the backplate to 7.5mm the other side of the neutral mark. I have some motors available already tuned for reverse rotation.

Maybe you want to tune your own motor. You do this by rotating the backplate and brush holders in relation to the rest of the motor. The same principles for retuning apply to all brushed motors. Retuning is necessary when you think that your motor is drawing more AMPS than it should, when you want to fit your motor to a gearbox that reverses rotation, or when you change armatures.

Remove the pins or loosen the screws that hold the rear of the motor to the front case. Mount your motor on the bench so that it is held by the front case only and that the rear is free to turn. Hook up about seven cells and your ammeter. Run the motor without any load holding the backplate in place by hand. Rotate the backplate in each direction until you find the point in which the motor draws the least AMPS – mark the position. Take care while doing this that you keep the backplate well seated on the motor. Any mis-alignment will load the motor and give a false reading.

Now fit a propeller to the motor, and use extra cells if necessary, to give a load of about 20 AMPS. Repeat the above exercise and adjust again for lowest AMP draw. The position will be the same as before, or not much removed from it. Drill new holes for the location pins or screws and fix the motor together again. A little heat-resistant LOCTITE or super glue may also be added to the pins or screws.

You can also experiment with the motor timing to achieve an increase in current draw and an increase in revs. You advance the timing to do this, but you should check both the current draw and the increase in revs. The amps will go up much faster than the revs, and you will reach a point where the amps will continue to increase but the revs will not (they may even decline). You need to choose the optimum point for your purposes.

The above information was originally provided courtesy of Jan David, past team manager of the German F5B team, and has been embellished with experience!