impaladave

Im building a retract system for a giant scale plane, and I need to convert a servo to run continuous in the up and down direction until a micro-switch is made. If anybody has a schematic or can link me to a website that tells how to do this please let me know..

p.s. futaba servo's

Dave Schmidt

dirtybird

My Feedback: (5)

Open your servo to expose the potentiometer and measure its resistance with an ohmeter. Lets say you find it is 5K. Obtain two small resistors 1/2 its value- 2.5k in this case. Solder the two resistors together in series. Solder the other ends of the resistors to the outside connectors of the potentiometer. Remove the center connector of the potentiometer from the potentiometer and attach it to the junction of the two resistors. You will have to remove the mechanical stops in the servo case.
Run the + line to the servo thru the limit switch to stop it from turning.

FHHuber

Umm... sort of... kind of...

but it just seems wrong somehow[&:] (and not cover the connections to the microswitch...)

If the microswitch turns off the power to the servo (is put in the red wire for the servo) you get the system into one position and... it won't move again.

See the thread about converting a S-148 to be a 180 deg servo.

Don't try modifying a S-3003 or S-3004... it isn't worth the hassle and it usually doesn't work when you finish.

The "intuitive" ways to do it... tend to not work.

**************

Well... the site that used to list the way to do it... and the link is dead. [&:]
http://www.uoguelph.ca/~antoon/gadgets/gadgets.htm

Might e-mail him and ask. He's done it.

Kmot

My Feedback: (24)

Why convert a servo and go through all that? If you want it to run continuously just buy a small Mabuchi motor and your done.

carlbecker

My Feedback: (3)

Dave,
I found the article from Model Aviation Mag. I am waiting for some more documentation to arrive so I can mail it together. Hope you can hang on. Tried to call you today.

Carl

dirtybird

My Feedback: (5)

He didn't ask for it to be returned from an extreme position. If all he needs is a 180 degree servo you can buy those.

mr.rc-cam

If you really need to do the limit switch thing, then it can be accomplished with two diodes and two limit switches and a little hacking at the servo's motor leads. I can draw up something if need be, but there are probably some better solutions available from the hobby robotics suppliers. For example, have you looked at www.robotzone.com?

pache11

My Feedback: (6)

This is pretty easy to do. Cut the leads from the the servo pc board to the servo motor and install the diodes and normally closed micro switches as in the included picture. Sorry about the crude drawing did it at lunch.

pache11

My Feedback: (6)

Updated pic

ZAGNUT

My Feedback: (1)

looks real good pache! never thought about doing it that way...always messed around with switches and resistors wired in place of the pot[:@][:'(]


dave

dirtybird

My Feedback: (5)

You still need the resistors in place of the pot along with the limit switches and diodes

ZAGNUT

My Feedback: (1)

i knew that what i liked is that there is no need to play around with ATV or anything to get the servo to stop when it hits the switch. any "dumb" channel would work just fine with this system.


dave

impaladave

If your gonna be removing the pot anyway, why not just put the switches there insted of messing around with cutting the motor leads? And I want to use a servo to drive my retracts insted of a motor because they are in a nice small package and are already geared down and deliver good torque

pache11

My Feedback: (6)

It is easier to interface to the servo motor then to interface to the servo pot. The pot connection are more complicated and can cause unexpected problems when radio tx settings are changed. Remove the pot and replace with 2 resistors. Cut the servo motor wires and wire as per circuit diagram. This is a proven circuit and works very well. I use it for hard limit stops when setting up home robot controlles using servos and will work well in a retract application

impaladave

What type of diode do I use. Sounds pretty easy... Thanks for the input guys

carlbecker

My Feedback: (3)

I bought servos from servocity modified for continious 360 for $5 each added to the cost of the servo. I could not find added resistors so I just added the diodes and switches. It worked well. Servos have advantages of lower speed and torque. Plus mounting is easy and wiring for the receiver is already to go. On a proportional channel you can set the speed by a wide margin. Gears for the servo output are available from servocity also. It would be possible to gear down more for lower speed and greater torque and have better scale like retraction of the gear. Still it is a fare amount of work.

Dave with the low power and voltage I think any diode from Radio Shack or mouser would do. They are cheap. I should have checked for extra diodes before I sent the package.

Carl

dirtybird

My Feedback: (5)

I would think youi should get diodes rated for at least 2 amps. Just in case you stall the servo.

pache11

My Feedback: (6)

Any of the 1n4000 series, 1n4001 - In4005 will work fine.

ismell

i did something exactly like this, except i replaced the servo motor with a bigger, higher powered one, and i was wondering what kinda mod i could do to use a separate power supply to power that motor.
I was thinking of using 2 MOSFETS a NPN and PNP so i could have it go forward and reverse but i don't know exactly how to wire this.
any suggestions would help
im using an old futuba servo and it outputs around 4.5v.
i want to use a 12v battery to power this motor.
thanks

mick15

Hi Dave

What you are try ing to acheive is very simple, I did it for the retracts on my scratch built DH 110 twin turbine. Use a standard retract servo (136G) take the "pot" out, its not a pot actually its a switch.

Connect the wires to two micro switches, centre wire and one outer to one switch, centre wire and the other outer to the other switch.

When you operate the retract switch the servo will run until the micro switch is closed, at this point wsitch the othe rway and the servo will run till the other switch is closed, simple.

I drove my undercarriage through a pair of geared tooth belts at a ratio of 1:3.5 this gives a retract time of 4.5 seconds and enough power to pull a house down!!

M

mick15

Forgot to mention some part of the undercarriage is used to operate the switches, this way the u/c is controlling the servo, not the servo controlling the u/c.

M