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Sep 15, 2020, 06:22 PM
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Thread OP


Hi there I have not posted in Electric Airplanes section before and maybe there is a more appropriate place for my question and if there is please let me know. Forgive not using the correct terminology if I'm wrong in this but I think what I'm looking for is information on what is known as sequencing? The ability to have a Electric motor move to and stop within or on a particular phase. In particular used with retracting propeller mechanism used on a Sailplane. I would like to be able to have my two bladed propellers align with either the trailing or leading edge of a wing upon going to zero throttle for a smoother landing with say a flying wing or other belly lander type aircraft in preventing a blade from snagging grass or otherwise striking the ground. How easy is this with a programmable transmitter such as one that runs open tx?
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Sep 15, 2020, 06:27 PM
Slow Flight
i had just asked the same question in the lemon forum....the answer was ....not possible.
i hope you have better luck.!

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Sep 15, 2020, 10:26 PM
Registered User
Wintr's Avatar
You could try a folding prop.
Sep 16, 2020, 02:07 AM
An itch?. Scratch build.
eflightray's Avatar
As Wintr said, try a folding prop.

Most if not all ESCS have a 'brake' option to slow the prop enough to ensure it folds and not continue to windmill.

Folding props can be used in a 'pusher' position as well as the more usual tractor tor position.

Sep 16, 2020, 07:32 AM
AndyKunz's Avatar
In a Spektrum transmitter with a sequencer, you could put the throttle cut, retract, extract, throttle enable on a sequencer driven by a single toggle switch. It's actually pretty simple. We have a thread in Radios regarding Spektrum sequencers, and a PDF to go along with it that is a magazine article reprint.

The problem with aligning the prop for retraction into the top of the fuselage is more of a mechanical issue, but also very solvable (mechanically).

Sep 16, 2020, 07:51 AM
A man with too many toys
I agree a mechanical solution might be the easiest.

Might be able to make such a device using a servo. Maybe some sort of curved cone device that extends and retracts. You will need some transmitter logic to prevent activation when the motor is running (easy with OpenTx).

Last edited by RC Man; Sep 16, 2020 at 07:59 AM.
Sep 16, 2020, 07:58 AM
Registered User
scirocco's Avatar
Some very high end ESCs are able to adjust the motor angular position after rotation stops in order to align at a minimum drag position. While the only example I can find at present is a full size sailplane application, I thought I had seen an F5J application.

However the cost would be exorbitant, so the best bet for a belly lander is to simply use a folding prop. In a pusher it can fold all the way, but even in a tractor installation with a fat fuselage, even a small amount of folding helps a lot. I used it in a little Bearcat - very effective in preventing prop breakage and motor mount damage.
Sep 16, 2020, 08:09 AM
Registered User
Is there a specific purpose to wanting it to line up that way?

If it's to prevent broken propellers on landing and you're not using a folding prop, I have been belly landing planes for years and rarely break a prop with it freewheeling at touchdown.

A folding prop on a sailplane is by far the best solution as you just set the ESC brake to active and it will stop the prop allowing it to fold for better aerodynamics and also less broken props at touchdown.
If on landing approach you notice the prop is in the wrong position you can just give it a small amount of throttle to move the prop, it may take a couple tries but you should be able to move it so the prop blades are sitting on the sides instead of the bottom.

I've never heard of a sequencer that will cause the motor to stop at a predetermined position. I think you would have to be using a sensored brushless motor as the system would otherwise not know where the prop was in it's rotation.
I doubt there is a way to do what I think you're describing.

I would just use a folding prop system and turn on the ESC brake function. That's how I have my electric gliders set up and I haven't had any issues so far.
Last edited by CR5; Sep 16, 2020 at 08:17 AM.
Sep 16, 2020, 08:55 AM
Slow Flight
This video indicated that just activating breack function is sufficient to save the prop.
ESC Brake - what it is, why to use it, how to activate it (10 min 45 sec)

ESC brake setting (6 min 32 sec)
Last edited by herreraa; Sep 16, 2020 at 09:02 AM.
Sep 16, 2020, 10:31 AM
Blue Sky Mining
batballs's Avatar
A folding prop is the most practical fix for +8” props. But there prop positioning is possible.

I just posted this video in response to the same question in the Lemon thread then found this thread while hoping to find more info on the yge esc being used.
(YGE 120HVT-NP controller with propeller positioning.)
Diana 2 Full Scale Propeller-positioning (0 min 13 sec)

Propeller positioning appears to be an option on some yge controllers. Maybe a firmware option?
Like many things it looks like this particular application is being driven by aesthetics on a scale glider.

PS. Broken props are unavoidable flying smaller pylon models unless you’re willing to pay +$60 for a 6” folding GM prop!!
Last edited by batballs; Sep 16, 2020 at 10:37 AM.
Sep 16, 2020, 06:03 PM
Registered User
Thread OP
Huh I thought it may be a pretty simple matter. Im seeing that the brake function on esc may achieve the desired propeller orientation a percentage of the time. It seems Spectrum has such a matter dealt with. If Spectrum can do this seems to me this could be written as firmware for OpenTx though not by me thats for sure.
Sep 16, 2020, 06:15 PM
homo ludens modellisticus
Ron van Sommeren's Avatar
→ T-Prop & FES Ex

T-Prop POWERED BY TORCMAN (0 min 48 sec)

FES Ex by TORCMAN (0 min 23 sec)
Sep 16, 2020, 09:47 PM
Blue Sky Mining
batballs's Avatar
Originally Posted by Brianmh13
Huh I thought it may be a pretty simple matter. Im seeing that the brake function on esc may achieve the desired propeller orientation a percentage of the time. It seems Spectrum has such a matter dealt with. If Spectrum can do this seems to me this could be written as firmware for OpenTx though not by me thats for sure.
I think Spektrum (and other high end Tx's) can control the sequence of stopping the prop, disabling the throttle, then retracting it into a hidden position and closing a hatch (and visa versa) but I don't think the TX can control where the prop stops. Unless its a feature in their new telemetry ESCs?

I'm sure AndyKunz will correct me if I'm wrong.

PS. I love that Torcman pop out spinner and prop.
Sep 16, 2020, 11:48 PM
AndyKunz's Avatar
Correct. That's why I suggested a mechanical stop for aligning the prop to fold it down into the fuselage. I've seen that done, so I know it works.

Sep 17, 2020, 12:16 PM
B for Bruce
BMatthews's Avatar
For simply stopping the prop sort of horizontally so it doesn't drag a tip and cause the prop to stress or break the brake function can work just fine. You simple need to have a look at the model when it gets down where you can see the prop and pulse in a little low throttle then cut off to the brake mode a time or three until it stops within a few degrees of level.

I've flown a couple of models with no landing gear from way back when and found that with the bigger prop needed by the old gear drive can motors and later with the brushless that the props did get stress marks in the plastic at the hub if allowed to drag a tip heavily. So early on I started jogging the prop with short pulses of low throttle until the prop stopped at something like within 30 of horizontal. That's more than good enough to avoid even lighter accumulative stress damage to the props we use.

If you wanted something more than that you'd need to get more creative. The motors we use are not set up to "know" where they are in their rotation. So a first step would be adding a rotational angle sensor setup to the motor. And that would need to run to some sort of "brain" (arduino or similar) that worked with the ESC to pulse the motor around to the desired setting.

Or you'd need to use some other sort of device. Perhaps a pin stop off a servo and you let the model go into cutoff freewheeling and once it's slowed down and is only freewheeling from the airflow and not the run down energy a pin stops the prop. I'd expect this to not be a pin that sticks out into the prop but instead one that indexes into a metal back plate on the rear of the motor. And you would NEED to remember or use programming through something like OpenTx to ensure the pin is withdrawn before power is applied to the motor again.

Something along that line would work well with folding props where you want then to fold against the side of the fuselage. And to lower the shock to the components the stop pin could be cushioned with grommets or some other elastomer mounting method so when the pin engages the stop plate/arm that there's a few degrees of spring in the action. At that point the prop blades would fold just from the air flow.

For a retracting motor pylon that lays back into the fuselage you can also use wire whiskers that work near the hub and push the prop into alignment. I think that's what Andy was referring to. I've not seen it done but a couple of early designs were said to use this method. It would obviously need a lot of special tweaking of the wire shapes.

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