Need a simple on/off control.

[grumpE]

Hey folks,

I am looking for a simple on/off switch or control that can be triggered on a retract channel. Here is what I am doing.

I have a simple home made smoke pump set up that is controlled by a servo closing or opening a circuit by closing or letting a small switch open. It works well but is not very elegant. I am installing the set up it in a new plane and now is a great time to fix it up.

It actually smokes as well as my Sullivan Skywriter and only cost me $30 to slap together. Now I want to tinker some more with it.

I was thinking of using a simple brushed GWS ESC but am curious as to what will happen if I put it on channel 5 and have it set for 100% on and 100% off. I do not have much knowledge around electric set ups and ESC so any advice would be appreciated.

My second idea was does anyone offer a switch that can be plugged into a servo slot. Or does anyone know hoe to build one? Again, a simple switch to open or close the circuit to turn a pump on or shut it off.

Specifics:
I will have this on a 4.8v pack
The pump motor is a windshield washer pump (cheap electric pump)
The Tx is a DX7 and I would like to use ch 5 for On/Off
I regulate oil flow with a pinch valve so I do not need to have pump speed control

Thanks guys,

Eric

[Malc C]

Google "RC switch" or search this forum... its been covered here 100's of times, with schematics, PIC code if you want to go down that route, and links to commercial switches - all of which plug in to a spare channel (such as ch5 normally used for gear) and thus activate from the TX

[Bearded Flyer]

Eric - Try this http://www.uoguelph.ca/~antoon/gadgets/rc-sw.htm or the parent dorectory for more circuits.

Richard

[grumpE]

Thanks guys!

Eric

[Brandano]

I tought I had posted here, but actually replied to the wrong thread.. sorry.
I was wondering, is a servo motor controlled in PWM or is it always on/off? Because in the latter case to make a simple rc switch with an adjustable trigger point would only take an old servo, a diode, and optionally small relay ripping off the mechanics and the motor. The pot controls the switch over point, and the diode ensures the power only goes through the circuit for signal higher (or lower) than the switch point. the relay is only for an application that requires more power than the circuit can handle.

[Bearded Flyer]

Brandano - Do you mean like this http://www.rcgroups.com/forums/showthread.php?t=122136 ?

Richard

[Malc C]

Most RC switches work by reading the PPM pulse from the receiver, and generally if its less than 1.5ms in width then it sets state one (ie on) and if its above then its in the other state. Because a switched output will either be 1ms in one position and 2ms in the other then it is either above or below this centre threshold

If you plugged the switch into a proportional channel, then as you move the stick you will see the point (should be mid stick) at which the switch changes its state.

A normal servo requires PPM (Its pulse proportion modulated, similar to PWM but with slight differences), and operates within the 1ms - 2ms pulse width to provide its full standard defelction. Sending pulses less than 1ms and greater than 2ms can provide a wider travel, providid the servo has no physical stops to restrict the rotation of the output spindle

[Brandano]

Richard, yep, that's pretty much what I was thinking about. An old, slow servo or one with a stripped gear (ask an heli pilot, he'll have one handy :)) will do fine, lose the motor and the gear and casing, add a diode and you are set. However, I fear that the motor on a servo doesn't receive a steady voltage but rather a pulsed signal with a variable duty cycle, so that its speed is slower as it approaches the target. Maybe modern servos have more sophisticated circuitry that power the motor full on until they are near the mark?

[CrashingDutchman]

Have a look at these:

http://www.dimensionengineering.com/PicoSwitch.htm
http://www.dimensionengineering.com/BattleSwitch.htm