Keeping a prop horizontal..

[MatC]

Hi folks,
I have an XE2-400 flying wing, and considering a scratch-build for my next project. Both the XE2 and the next project will benefit from some way to keep the prop horizontal during landing (prop at the back).

Any ideas how to do this? [I'm no stranger to the electronics bench and microcontrollers]

First thought: brake the motor, measure position optically, and drive the motor like a servo, attempting to keep it in the correct position. But instinctively I just feel this won't work too well.

Second thought: brake the prop mechanically, and then rotate the brake till things like up. It will work, but awfully heavy and inelegant.

Anyone else have any other crazy or not-so-crazy schemes?

[MatC]

Third thought: brushless motor, energise one coil? I don't have any experience with brushless motors, so don't know if that will work or not.

[Chippie]

Third thought: brushless motor, energise one coil? I don't have any experience with brushless motors, so don't know if that will work or not.


Energising one coil will work if the motor is wound Delta.......2 coils are energised if its wound Star

[Acetronics]

Heuuuu,

Vectorial propulsion ??? ( like F22 Raptors ) might be fun in flight ... and just place axle vertically for landing !!! :rolleyes:

not so stupid ...ehhh :p

Alain

[vintage1]

Servo attached to the throttle that sticks a stick in the prop?

Or use the gear channel. :D :D
Sorta fits.

[MatC]

Alain: vector propulsion is reserved for (another) future project :)
vintage1: that might actually work... or some other dog-clutch activated by a servo. Would ideally come from the throttle channel, for the safety of the motor and speed controller :)

[vintage1]

If you uses a 'servo slower' then it wouldn't cut in till after the throttle had been closed a while..but you need something to move it away IMMEDIATELY the throttle opens. ;)

Another possible is a solenoid or relay in series with the battery pack..as soon as you draw current it pulls the thing open.

Some kind of crude electronics would also do. Monitor current and retract at the instant it rises, but extend after 3 secs of inactivity say..

[Brandano]

4 small neodymium magnets (2 on the prop and 2 on the wing trailing edge) and a servo to slide the wing magnets forward and back until they nearly but not quite touch.

[MatC]

vintage1: good ideas... worst case a PIC will take care of throttle issues.
Brandano: nice idea... reminds me of my old BigTrak (anyone else old enough to remember those?)... it had two magnets on the powered wheels that engaged during forward movement to keep the thing going fairly accurately forwards, but disengaged during turns while the motors went in opposite directions.
I'm not sure the magnets would actually stop the prop though, air keeps the prop spinning and while magnets will lock the prop, they might not slow it down enough to stop it (ie the prop accelerates towards the magnet, then decelerates again...)

[Brandano]

MatC, in that case you could just add a motor brake, easy to do on an electric brushed motor and several brushed controllers already have one in place to allow folding of the propeller on glider models. And in case of a brushless motor energizing one (or two) coils will do the trick. The magnets would only need to keep the prop there, having some guarantee it's able to restart is a bonus IMO. Btw, dunno what RPM are you running the thing at, but a folding prop is hard to break in a landing. Have you checked to see if there's any suitable one?

[MatC]

Brandano: good plan, I'll look for a folding prop too if they're as robust as you suggest :)

[PaulVi]

Playing the devils advocate here but why do you need to do this..

Been flying wings for 3 years and havenever broken a prop on landing.. as the plane comes into the ground the prop just pushes out of the way

[AndyKunz]

How about just a pin that extends into the prop arc (use a super-tiny servo) when the throttle is off+full down trim? Doesn't need to be strong - a soda straw will do.

Andy

[Majortomski]

I used a couple of popsicle sticks to make a skeg on the bottom of the plane to keep the prop out of the grass

[GlennS]

thought about this myself for a while as my flying wings have same problem. But in practice, never broken a prop on the wings on landing. Sometimes I give the throttle a flick if I see the prop is vertical when coming in to land and sometimes it ends up horizontal.
Glenn.

[Pete P]

When throttle kills, have a switch plop a rod out on 'top' of the shaft, so after braking it freewheels, letting air push it into the rod.

[olmod]

Another way may be to use a motor that the shaft at the other end of the motor, that can be used to mount a small disc wich has 2 holes opposite one another around the outer edges and use an ir block to sense postion when the motor is off to activate something,perhaps the disc itself could have 2 flats that a small solenoid could press against. just throwing it out there :)