Society of Robots - Robot Forum
Electronics => Electronics => Topic started by: 79Trapper65 on April 01, 2010, 07:34:42 PM
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Here is the question, I am designing fowler flaps for a scale model airplane I am building. These are a special type of flap actuation which moves out and then down, as on a commerical airliner. I wanted to acturate the flaps via a screw drive from a servo, which I modified for continuous movement. This works perfectly except I need some way to limit the travel in and out of the screw. I was wanting to use micro switches to change the feed back resistor from its present 2.2K to values which would cause the servo to stop at specific positions. The pot that was in my servo was a 5k pot. The problem is I am not sure this is going to work and would like someone to give me some input. Has anyone had this problem before. The solution must be repeatable and be fairly simple.
Best Regards
Dan
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You may be able to adapt a multi-turn pot connected to the screw by a pair of pulleys and a belt or gears or even on the end of the screw. I've used 10, 15 and 20 turn pots. Small board mount ones are readily available.
How many turns would the screw need to turn to extend the flaps?
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Walt
Thanks for your reply, I am not sure yet about the number of turns, to some extent it will depend on the pitch of the threaded rod I end up using. I was mostly wanting to know if the servo was say moving out and the flap reached the max of 40deg. and a micro switch operated to put the full scale resistance of the pot (5k) would the servo think that it has reached the proper setting and stop or keep turning as long as the drive signal told it to. The control on my transmitter could be either a proportional signal or a full on/full off signal. I dont quite understand the operation of the internal control of the servo.
Your help is greatly appreciated.
Dan
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Hi,
I was mostly wanting to know if the servo was say moving out and the flap reached the max of 40deg. and a micro switch operated to put the full scale resistance of the pot (5k) would the servo think that it has reached the proper setting and stop or keep turning as long as the drive signal told it to.
The resistance that you should loop in should be the resting value of course and that's the 1.5ms center position of an unmodified servo and hence the midpoint of the potentiometer.
If you take two resistors of between 2k and 10k (both the same value) and mount them like the potentiometer, with the point where they meet coupled to the point where the wiper of the potentiometer normally goes to the servo will stop, so just loop this point in or out of the circuit.
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Not sure if you solved this yet or not . . .
Digital servos can be reprogrammed to limit the angle.
Some remote controls also let you trim and limit the servo angles as well.
just two more options . . .