How do I convert a servo to continuous rotation ?

[Trevor HollowayParticipant @trevorholloway99134]

[Trevor HollowayParticipant @trevorholloway99134]

I want to be able to switch a servo to continously rotate from the fifth channel of my transmitter, simple On / Off control is all I need direction of rotation does not matter.

I know I will need to disable the position sensor and remove the stops somehow but how would the on / off signal side react ?

[Malcolm FraryParticipant @malcolmfrary95515]

If you just want it to rotate permanently, remove the electronic board and just connect the motor to a battery.

If you leave the board in, it will act as an ESC with the position sensor mechanically disconnected from the output gear. It will be a poor ESC, because the off band will be very narrow. It might be possible if using it with a switched channel to reliably set "off" using the pot as a tuning control. Another alternative is to use a switcher to replace the servo electronics to just switch the motor on and off, or use the electronics to operate a relay, and have the relay contact work the motor.

[Runar MadshusParticipant @runarmadshus11679]

If you have messed with microcontrollers before, it is pretty easy to set up a system like that and at the same time avoid the narrow off band that Malcolm mentions.

I think I have a code snippet for that in my computer folders somewhere, actually. Tell me if you're interested and I might be able to hack something together and send it to you.

[Dave MilbournParticipant @davemilbourn48782]

I suspect you will have problems using a fifth channel in as much as the signal to the servo will simply be "full throw" in each direction, there being no neutral point with a two-way switch. Translated into English this means that the servo will rotate at full speed in one direction as soon as the radio is turned on, and the only thing that moving the Ch5 switch will achieve is making it run at full speed in the opposite direction. You might get away with inserting a diode in series with the motor to restrict it to running in one direction, but you would need to experiment with this. I'd start with a 1N4001 which will handle 1A maximum.
Malcolm's suggestion of removing the electronics from the servo altogether and using a simple R/C switch to turn the motor on and off is the one I'd go along with.
Dave M

[Malcolm FraryParticipant @malcolmfrary95515]

Another thought – examine the PCB to see where the tracks are feeding the motor. Cut one, connect a diode across it (something like a 1N4001 for the current). That way, the motor will only turn one way, any signal that tries to reverse it will do nothing. Cheaper than buying chips and easier than learning to program them. The servo case might need a bit of a mod (i.e. a hole in the right place) to fit the diode, they are a bit lumpy by today's electronic standards.

[Runar MadshusParticipant @runarmadshus11679]

You're solution is probably the simplest and the best one in this case Malcolm. But on the other hand, a little eight legged uC isn't much more expensive than a 555 these days and as a model hobbyist you can do a lot of cool stuff with them.

It never hurts to learn something new either.

[Malcolm FraryParticipant @malcolmfrary95515]

This is true, but the servo electronics are already paid for, therefore free, and a 1 amp diode does not cost a great deal, and needs very little programming skill. – http://www.maplin.co.uk/p/1n4001s-1a-silicon-rectifier-ql73q- cost 49P.

Learning a new skill is good, but I would balk at learning programming in order to effectively throw a switch when the parts are pretty much to hand at low cost. One of the problems with little 8 leggers is the cost of the programming board, impossible to justify for a single job, especially a simple one, but an investment if you see yourself getting into that aspect.

That, and the fact that somebody will probably do it for you before you finish the job. I got bitten by that back in the early days of TTL when I was designing a test circuit which had to look for varying conditions on 3 wires. After several weeks of head scratching and a lot of parts, the next edition of the RS catalog had an addition – the rather magical 4 way "X-OR" gate. Durn, drat and double drat.

That was about the same time that PE magazine was doing a desk calculator build series. In the mag with the concluding article, the Sinclair Scientific was announced. 1/50th the cost, did more, and fitted in a shirt pocket. Progress.

[Dave MilbournParticipant @davemilbourn48782]

It never hurts to learn something new either.

Runar
You have to allow for the abilities of your target audience, mate. I know of folk who still can't grasp the difference between positive and negative battery terminals ("does it really matter?&quot, and the lengths to which others will go to avoid learning how to solder is quite amazing! Show some very able modellers a length of wire and they panic.

PIC programming requires some ability in maths and would be beyond about 95% of average boat modellers.

Dave M

[Trevor HollowayParticipant @trevorholloway99134]

Well, last night I connected a standard Hitec servo to the 5th channel, with the switch in one position "O" the servo moved to one position and switching to "I" it slowly moved 90degrees, returning the switch moved it slowly back again.

Removing the end stop and disabling the potentiometer (drilling out the gear that sits on top of the potentiometer shaft) has it turning when "On" and slows to a stop when "Off".

Rotation speed looks about right for a radar, however I really want a very slow rotation of abot 4rpm so a little playing with the potentiometer may be in order.

So success there, a simple easy way to use the electronic switch and geared motor in one unit.

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