Electric motor Idle Up

There is a suggestion that keeping the motor spinning , at minimum revs, when the throttle stick is fully down speeds up throttle response and lessens stress on the motor. A TX control would need to be be assigned to enable idle up on take off and disable it after landing.

Before I dive into my TX programming manual has anyone done this and have anything good or bad to say about it?

Hi Alan
The startup mode of a sensorless brushless motor, (the type we use for E flying), is different to the normal high rev running mode. It is not as efficient because the phase switching points at low revs can only be guessed at by the electronics. What I do not know is what speed a motor starts to run in normal mode. If your tickover RPM is below this threshold, then the motor and ECU could be stressed and it would be better to stop the motor completely.

I think the idea is to get the motor to 'tickover' at just above its start up phase but still running at very low rpm. I've only played with a small motor so far and one click of throttle trim gets the motor from 0 rpm through it's start up phase to smooth but low rpm. From there on the throttle does seem crisper than when starting from 0 but I'm not sure what benefit this will have with a bigger motor in flight.

Hi Alan,

I do it with a throttle curve, and just lift the low end until the motor starts to run and add a faction more. I also drop the top of the curve until I can hear the max RPM start to decrease, and then up it again until I don't here the RPM increasing any more. This is after setting up the ESC, on some you can tell it where the end points are by moving your throttle stick.

I have one switch which overrides the throttle channel with a -100 value.

On the Atlas I felt the throttle response was better with a curve as seen in the attachment, but on the Mythos (different ESC) when I tried a similar curve it didn't feel right at all so I went back to the straight line.

At start-up, a brushless controller sends a pulse to the motor and the motor will either spin clockwise or anticlockwise. The controller senses the back emf and determines if the motor is spinning the correct way. It will then send another pulse to keep it spinning the same way or the opposite pulse as necessary. In flight, a windmilling prop can confuse this sequence and the controller/motor combination squeals and shuts down. This is more evident with some controllers and the cheaper ones seems to suffer more. Keeping the motor ticking over at low rpm avoids this problem.

Also, a motor at tickover will keep air moving over the control surfaces at low speed. This gives better control on landing.

I have a higher tickover speed in normal flight compared to landing mode. The higher tickover speed pushes more air past the rudder during stall turns. I have watched other electric model pilots attempting to do a stall turn with the motor off and it is not a stall turn!

Thanks for that Chris, Ill have a look at assigning an offset throttle curve.

Apart from assigning different curves, did you find that having the motor spinning at '0' throttle made any noticeable difference.

Thanks Mike, you've just given me three reasons why I will be definitely doing this. I just need to find the best way to implement it.

AlanF wrote: Thanks for that Chris, Ill have a look at assigning an offset throttle curve.

Apart from assigning different curves, did you find that having the motor spinning at '0' throttle made any noticeable difference.

Without the idle you probably have a dead area at the bottom of your throttle travel, so all your fine throttle control is now compressed into say 3/4 of the stick's movement. I should say that fine throttle management is perhaps one of those nebulous subjects, a bit like the use of the rudder, both are used on the ground, and the next and only time you use them is in a stall turn. I guess that's why they combined both controls on the one stick :evil:

I've always had the motor spinning at '0' throttle, it was one of those things that both Mike and Jon said to do, and I was young & naive and, well you've got to take advice from someone so I cannot really say how I find it compared to not setting it up that way.

The big difference was putting in the curve for the Atlas throttle (YEP esc), it was something JRI suggested playing with and that did shift the power sweet spot and made the throttle somehow more proportional to the stick movement... sorry, not finding it easy to explain. However I tried a similar curve on the Mythos with a Jeti ESC and it just didn't feel right at all, so I don't know if Jeti have a preprogrammed curve already built in... I'll try and explain:

This is from memory and I cannot remember the article I read it in, but a basic ESC will provide a liner RPM output, but a linear RPM output will not give you a linear thrust output... I'm in danger of giving incorrect info, so I'll have a look tonight to see if I can find the article I'm trying to remember.