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Old 11-08-2010, 02:39 PM   #1
WayneG
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Default Servo as a switch

Anyone got some kind of a schematic on how to use a stripped servo as a switch?

Thanks
Wayne
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Old 11-08-2010, 05:33 PM   #2
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I'm sorry I don't have the schematic any more, but about 1975 I used the circuit board of a servo, replaced the feedback pot with 2 resistors, and put a diode in series with a relay coil, in place of the motor.

The 2 resistors were equal value, and totaled to the resistance of the feedback pot, this made the circuit board think the servo was in the center position. The coil resistance of the relay was a little more than the resistance of the motor.

When the signal was low the board would try to "move the servo" one way, but the diode would stop the relay from pulling down.

When the signal was high the board would reverse the power to the "servo" and the diode would pass the power and the relay would pull down.

I used this to control the motor on an electric glider, I recently rebuilt the power system to BL, but I didn't keep the home made switch.

You should be able, with some tinkering, to make this work. At that time I bought the parts at Radio Shack, but their parts area is pretty dismal now days.

Dave R, Proud PGR rider.
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You become a master at repair.
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Old 11-08-2010, 06:41 PM   #3
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How about this:
http://www.dimensionengineering.com/PicoSwitch.htm

~Tim
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Old 11-08-2010, 08:18 PM   #4
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Originally Posted by whitecrest View Post
GREAT link Dude, thanks!

...The Bum
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Old 11-09-2010, 04:24 AM   #5
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I've got to put that Sidewinder light on my truck as an alarm light.

Thanks for the link

Dave R, Proud PGR rider.
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Old 12-02-2013, 02:11 AM   #6
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Hey Wayne, A while back a young fellow had the information you want on Flite Test. He made a lost plane locator. It worked fine and he used just the board out of the servo.I'm green at this stuff and don't know how to link, but I,m sure if you want just go there and search "black box".
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Old 12-02-2013, 02:14 AM   #7
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Originally Posted by Saddlebum View Post
GREAT link Dude, thanks!

...The Bum

Yup
I made one of those a month or two ago. And, the parts cost came to about $20 or so. Plus the time it took to build it, and write the software for the PicChip microcontroller!

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Old 12-02-2013, 11:22 PM   #8
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I use these.
https://www.hobbyking.com/hobbyking/...ed_Switch.html

I use it to turn lights on when my gear goes down.

But there is also a multi switch.

https://www.hobbyking.com/hobbyking/...perated%20swit

Darn, I didn't realize how old this thread was. lol
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Old 12-10-2013, 01:52 AM   #9
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I have used a servo arm to press on a micro-switch button. Have also used a single servo with a pushrod having egg-shaped cams that pressed on two or more micro switch buttons to turn different things on or off sequentially. Useful on model boats.
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Old 12-10-2013, 12:00 PM   #10
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My County Class Destroyer had servos that pressed on Micro-switches ... in fact there was a company in UK that made a small add-on for servos that micro-switches were fitted to ... so the normal arm would click on whichever side you wanted ...





Now though with the solid-state Rx controlled switch as in Hobby King ... it's only high power stuff that really needs such switching.

Nigel

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Old 12-10-2013, 05:01 PM   #11
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Default Good Idea!

Originally Posted by whitecrest View Post
Yea but Wildflyer's idea is free if you have a stripped servo and some spare parts and some time and patience and soldering skills... Anyway thanks to all for these ideas cause they're both valuable info.
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Old 12-15-2013, 09:18 PM   #12
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I once needed a magneto kill switch for my 1/3 scale Space Walker. I took a standard size servo glued a micro switch that I got a Radio Shack to the top near the servo wheel. I then shaped the servo wheel into a cam. When the servo wheel came around it tripped the switch. It worked perfectly for many years.
Andy
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Old 12-15-2013, 09:34 PM   #13
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Originally Posted by abborgogna View Post
I once needed a magneto kill switch for my 1/3 scale Space Walker. I took a standard size servo glued a micro switch that I got a Radio Shack to the top near the servo wheel. I then shaped the servo wheel into a cam. When the servo wheel came around it tripped the switch. It worked perfectly for many years.
Andy
Years ago - cars and boats used circuit board material plates stuck to servo tops ... then a wiper arm fitted instead of servo arm ... the wiper then when servo gear turned 'wiped' the contacts on the board to provide stepped speed control.

Simple, reliable and cheap.

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Old 12-30-2013, 02:29 AM   #14
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Cheapest/simplest method is gutting a 9G servo, the ones we all know and love (And likely have a stripped one laying around, if you were wondering why, this is why you saved those broken $2.65 servos). All I do is pull the gears/motor, and solder new 22ga. wires from the control board where the original motor wires were and extend them through the hole at the top of the case (Where the output of the servo was).

You need to solder a diode (1N4001 is a good choice, and easy to find) inline with one of the wires. I use 1 red, and one black wire, and put the diode inline with the red wire with the striped/banded end of the diode on the exit end of the wire. And you can just adjust the existing potentiometer to it's middle position instead of eliminating it and adding 2 resistors. When done, reassemble the servo case, and use you hot glue gun to squirt glue in the hole around the wires, I push it up tight, and get a good amount inside, keeps things solid, and keeps you from wiggling the wires and breaking electrical connections inside. Servo reversing will change which direction your transmitter switch turns your new electronic switch "On".

What you do with that output is up to you, but you will have limitations on the load you can drive. You can use the 2 wires to run a relay and greatly increase your power handling options, but I use another diode when doing so (Banded end connected to the red wire, non-banded connected to the black wire), because a relay coil is an inductive load, and the voltage spike back when turned off, could cause damage without it.

I prefer to use FET's and Transistors to up the load capability, but that conversation can get a little too complicated to type out here and have it make any usable sense. It takes all of 10 minutes to convert one of these servos if you have all the stuff handy, and is still in a nice clean case when you are done!

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