Need help with servo control for a jig.

[asennad]

I am building a jig in which I hope to utilize a standard servo. I need the servo to move forward and reverse at constant speed which can be adjusted. I unfortunately have little electronics experience. Would a servo tester work for this application? If not could someone point me to a circuit which I can build which would accomplish this? Thanks.

[orraman]

Greetings asennad,

A servo exerciser might be more on the lines of what you want.

More information on the operation of your jig and how you would wish to control it would be helpful.

Dave

[asennad]

I wish to control the servo with a stand alone unit as opposed to a computer or radio or such.

What I need the unit to do is simply have the servo go from one stop to the other at a constant speed which can be set by the operator.

Will a servo exerciser work? Can i buy these prebuilt? How much and where would I find one?

[orraman]

I have on the bench a simplistic circuit on a small board powered by 4 AA cells oscillating a Hitec HS-300 servo through about 140 degrees.
The cycle speed is determined by the potentiometer (volume control) position. The six sweep times vary from about twice per second to once per fifteen seconds.
Angle and speed could be altered to your needs. A board is not strictly necessary, leads could be soldered between the 10K potentiometer and the 8pin chip, or it's socket with a 0.1uF across the battery leads.

A search on this forum found this thread but it has more components.
If that would better suit your needs I could try to programme the pic chip for you but there is no possibility of making alterations.

http://www.rcgroups.com/forums/showthread.php?t=94261&highlight=servo+exerciser

Dave

[asennad]

I have on the bench a simplistic circuit on a small board powered by 4 AA cells oscillating a Hitec HS-300 servo through about 140 degrees.
The cycle speed is determined by the potentiometer (volume control) position. The six sweep times vary from about twice per second to once per fifteen seconds.
Angle and speed could be altered to your needs. A board is not strictly necessary, leads could be soldered between the 10K potentiometer and the 8pin chip, or it's socket with a 0.1uF across the battery leads.

A search on this forum found this thread but it has more components.
If that would better suit your needs I could try to programme the pic chip for you but there is no possibility of making alterations.

http://www.rcgroups.com/forums/showthread.php?t=94261&highlight=servo+exerciser

Dave

I saw that link and the servo contoller you linked to but I have no idea to program a chip. I wish I could and it's a skill I want to learn one day.

Does your circuit require one to program a chip? Because that's one thing I don't think I can do.

[alexcmag]

asennad,

If you really need it I strongly recommend you to learn how to program a chip.

With a small and cheap chip (PIC12F675 for example), this circuit is very simple, just one chip, one capacitor, one trim-pot to set the speed if necessary.

With discrete electronics (without programming a chip) it would need at least 3 complex circuit blocks:
1 triangle wave generator: http://www.ecircuitcenter.com/Circuits/op_tri_gen/op_tri_gen.htm
1 50Hz oscilator
1 timer, triggered by the 50Hz oscilator and based on triangle wave generator

To keep things simpler, you can use the triangle wave generator with a commercial servo-tester, but even the triangle wave generator is not as easy to adjust to the speed you want.

[orraman]

asennad,

A friend has written a small program in Proton Lite Basic for you that can be made to suit your needs, it is rather better than mine, so you now have some options.
Proton Lite has a limit of 50 lines of Basic and is a free download of the very powerful Proton. In common with most Pic systems the program must be loaded into the Pic by a small electronic programmer. UK electronics magazine EPE has an offer this month of £9.99 for Pickit 2 programmer and this is possibly the best available.

My simplistic program runs on a Pic with a pre loaded Basic interpreter and needs no programmer, loading the program into a Picaxe chip is done with three wires on a 9 pin serial socket. The Picaxe Programming Editor is a free download, Picaxe chips cost about 15 pence more than the standard Pic but the advantage to the beginner is enormous. Changes and alterations can be made in a few seconds while the original program is still running.

Either program could be sent to you by Private Message or by email and we would help with any problems but with the Picaxe a few words of assistance would see you OK.
Have a look at these sites and if you feel the need we could try to send the programmed chip to you.

http://www.picbasic.org/proton_lite.php

http://www.rev-ed.co.uk/picaxe/

Dave

[asennad]

orraman,

I found a copy of the EPE magazine and read the offer for the Pickit 2 programmer - unfortunately the offer is only valid in the UK. I am in Toronto Canada but the offer does sound pretty good so I think I may get one of my English relatives to pick that up for me. Still it's says the delivery may take 28 days.

I am going to send you a PM so we can talk further. And BTW thanks very much for your help! Much appreciated.

[orraman]

asennad, your welcome.

The Pickit 2 will reprogram any Pic 12Fxxx chip irrespective of the original program pin assignments, this is not true of several other programmers. Delivery of the offer has been about 7 days, normal price is about £36 inc. P&P, your local price is guaranteed to be better.

Gordon's Pic 12F675 program can now drive 2 servos independently, each with 50 sweep rates with pulse width increments of 1 micro second giving smooth movement from 1 second per single sweep up to 35 seconds. With these improvements he has still shoehorned it within the limits of the Free Proton Lite compiler.

Standard servo pulse width varies from 1ms to 2ms giving a servo arc of about 90* any greater arc will depend on the servo's internal end stops. Standard servos here are Futaba 148 and Hitec HS-300 and the program could be tailored for one of these to about 140*. Once you have a programmer this could increase to about 180* for your particular servo.

Dave