Odd ball question: Does an ESC in governor mode use brake to govern as well?

[Teodorico Terry]

Hello all,

I have been under the impression that an ESC when running in governor model will add power to bring the prop up to the target RPM if lagging behind and it will allow it to windmill if the RPM exceeds the target value. Is this correct or does the ESC use the brake (if enabled) to lower the RPM if over speeding? This question is in particular for a Castle but I would also be curious to know if the Jeti behaves in the same way.

Thanks,

Teo

[Matt Brown]

Can’t say positively but I’m guessing no. Governors became popular because of RC helicopters. They have a one way bearing/clutch that allows free forward rotation primarily for autorotation purposes. Since there’s no gain to braking the motor in that situation I doubt they would have developed braking control in their governor software. They do use braking in rc cars of course but not in a governor situation.

Matt

[Ken Culbertson]

Can’t say positively but I’m guessing no. Governors became popular because of RC helicopters. They have a one way bearing/clutch that allows free forward rotation primarily for autorotation purposes. Since there’s no gain to braking the motor in that situation I doubt they would have developed braking control in their governor software. They do use braking in rc cars of course but not in a governor situation.

Matt

I am sure someone with actual knowledge will clear this up, but I tend to agree with Matt.  Most breaking that I experience seems to come from the timer, not the ESC.  I have never had to change settings on my ESC's once set.  The break settings only seem to only control the "how much", not the "when" on the Castle and Jeti I have used.

Ken

[Teodorico Terry]

Thank your for the replies, that is generally what I was thinking; the ESC simply adds power to maintain RPM and lets it freewheel if over the RPM target. A friend of mine was lucky enough to buy Sergii's model at the W.C. and I was surprised to see that he had programmed two different RPM levels in the ESC (Jeti). The model uses the Burger active timer but if the timer simply changes the throttle signal based on G load I do not see how the motor would slow down in a downline if the ESC is in governor mode (which it is). I know that you can set more than one RPM level and tie it to the different throttle signals which is the timer would provide.  I am guessing that the low RPM is for level flight or downlines and the high RPM is for the uplines.  I will probably have to do some more reading. The point is, I do not think that the active timer can actually slow down the model on the downlines but my friend seems to think it can.

Thank you,

Teo

[Jim Hoffman]

This is a question for Castle tech support. They have been helpful to me when I’ve reached out to them.

[CircuitFlyer]

During the powered portion of the flight the motor does not freewheel nor is there any reason to use braking, at least for control line anyway.

Freewheel or windmill - the voltage signal output of the ESC is 0 and the motor windings are essentially an open circuit. The prop only has to over come the weak cogging effect of the motor an can turn easily.

Braking - again the voltage signal output of the ESC is 0 but this time the 3 motor leads are essentially shorted together. Due to the current flows internally in the motor windings it makes it difficult to rotate. The faster you try to turn it the more resistance is generated.

A brushless DC motor is a synchronous motor. The rotating permanent magnets run lockstep together with the ESC produced “rotating” electromagnetic fields. There is no slip between them. The ESC can control the acceleration and deceleration of the motor. It would require a fair amount of torque to cause the rotor to slip and freewheel as you say. We don’t get anywhere close to those kinds of loads on the prop in control line.

I can’t speak for  Castle or Jetti but I don’t suspect there is a need to add braking to govern the RPM for control  line use. Multirotors or quad racers may need that level of performance. For them the stability of the aircraft relies on near instantaneous response to the output of the inertial measurement unit and throttle.

[Ken Culbertson]

I think we are using the term 'Brake' differently.   An Active timer produces "boost", an increase in RPM and "brake" a decrease in RPM.  At no point does the RPM go to -0-.  The Jeti Spin series actually has a parameter for minimum RPM. 

Ken

[Teodorico Terry]

I fly R/C pattern as well and we generally program some brake into the ESC to help slow down the model in the downlines.  Obviously the brake kicks in when the throttle is fully pulled back. We generally do not use 100% brake but rather a smaller amount, about 50% depending on your taste.  What this does is to slow down a wind milling prop by adding more resistance to turning than just the cogging of the motor. The benefit is an increases drag; a useful feature when the nose is pointed straight at the ground.

In C/L what I was wondering about was if the ESC in governor would provide any "braking action" to hold the prop RPM when it naturally wants to overspeed; for example in the down leg of a wingover. I suspect that it does not, it simply reduces the power and the prop will simply have to over come the cogging action of the motor. My friend seems to think that it does when using an active timer but I suspect that what he was seeing was the difference between boosted power on the way up versus un-boosted on the way down.

Thank you guys for the input,

Teo

[Matt Brown]

Just my opinion, but even in the wingover, I don’t believe the plane accelerates enough on the down leg to windmill the prop beyond the governed rpm. I’m sure if you have some Castle Creations flight logs saved, you won’t see any point during flight that the ESC output is zero which it would have to be in a case where the prop was windmilling beyond the governed rpm. I’m going to see if I can find some of my SV11 flight logs and have a look.

Matt

Update! I looked at one days (5 full patterns) practice logs on my SV11. At no time did the current ever fall below 20 amps. This was on a Castle Creations Phoenix Edge 75 amp ESC with the Fiorotti active timer. Since current never dropped to zero, I’m guessing the prop never windmilled.

[CircuitFlyer]

Your friend is correct.  The ESC has full control of the motor RPM.  If the active timer asks for more RPM in a climb, the ESC will increase the motor RPM.  If the active timer requests a decrease in RPM on the down leg of the wingover the ESC will oblige and the motor RPM will decrease.  So, does the ESC provide a sort of "braking action" to hold the prop RPM even in a dive?  Yes it does, that its job.

[Ken Culbertson]

I fly R/C pattern as well and we generally program some brake into the ESC to help slow down the model in the downlines.  Obviously the brake kicks in when the throttle is fully pulled back. We generally do not use 100% brake but rather a smaller amount, about 50% depending on your taste.  What this does is to slow down a wind milling prop by adding more resistance to turning than just the cogging of the motor. The benefit is an increases drag; a useful feature when the nose is pointed straight at the ground.

In C/L what I was wondering about was if the ESC in governor would provide any "braking action" to hold the prop RPM when it naturally wants to overspeed; for example in the down leg of a wingover. I suspect that it does not, it simply reduces the power and the prop will simply have to over come the cogging action of the motor. My friend seems to think that it does when using an active timer but I suspect that what he was seeing was the difference between boosted power on the way up versus un-boosted on the way down.

Thank you guys for the input,

Teo

Terry, if you were referring to my comment it leads to a question I would like answered.  I use the Fiorotti timer which has a min setting.  I can feel the difference when I change that setting.  If what you suggest is true, then I would not feel the change.  Slowing the plane down on the down legs in wind is easily accomplished by lowering the minimum RPM it is allowed to "brake" to.  However, like so many other trim factors a lot more goes into what you feel and/or think you feel at the handle so you may be correct.

Ken

[Matt Brown]

Your friend is correct.  The ESC has full control of the motor RPM.  If the active timer asks for more RPM in a climb, the ESC will increase the motor RPM.  If the active timer requests a decrease in RPM on the down leg of the wingover the ESC will oblige and the motor RPM will decrease.  So, does the ESC provide a sort of "braking action" to hold the prop RPM even in a dive?  Yes it does, that its job.

There’s a big difference between active braking action and just reducing power. My ESC flight logs only show lowered current but no active braking.

Matt