screwjack actuator

[Frank Skilbeck]

Looking to activate a canopy opening and a commercial linear actuator is going to be a bit too long to fit in easily. One option would be to convert a servo to drive a threaded bar with end stop microswitches, similar to an electric retract. Anybody done this?

[Barrie King]

Yes I did it for a mate to operate wing swing on a small Tornado. You first need to remove the internal stops on the gearbox to allow it to rotate fully, then take the wires off the feedback pot.
I will have to check what I did next.

[Alan King]

did a similar thing with a servo too but instead of microswitches used a linear potentiometer to stop it.

process I used was to make up a screw to fit into servo output, I used a cheap metal gear servo, literally used a woodscrew and threaded end of it to screw into servo where belcrank arm retainer screw would normally go , locked it in place on the output arm.

I then removed the potentiometer and fitted the linear potentiometer , this was controlled by the screw travel.

nut to fit screw was made from phosphor bronze drilled and then self tapped with a screw of same pitch.

you could also possibly use a rc yacht winch servo which you can adapt to pull canopy up and down on a cable arrangement.

[Frank Skilbeck]

Alan thanks, we'd come to the same conclusion and have just received a hitec winch servo, this is 3.5 turns so with the standard pulley has around 10" of movement. We'll be able to put in a bit of slack and set it up so that by increasing the "throw" we can slide the canopy back off it's rails for removal. Well that's the theory.

[Steve Perry]

Have a look at one of those low cost Hobyking retract units that use screw jacks, pull out the jack and electronics from one and you have a plug in solution
Rapid RC stock Hobbyking stuff and may have one that you can eyeball at a show if there are any this year, try an email to Rapid asking them if there is one that has the travel that you require