Topic: A simple DIY servo exerciser for soaktesting servos

Maplin JW59P

http://www.maplin.co.uk/2.54mm-0.1in.-pin-strip-1500

thas tha baby

Have already ordered some more y leads, dammit! 

Ok, got mine done.
Had some spare white LEDs from a car dashboard project that never happened and so used one of them. Switch came from Maplin as did the enclosure. Inside is an AA Instants pack and some wiring, the soak tester and some Y leads. The wiring/switch is set up so that the unit can only be charged with the switch in the off position.





I'm chuffed to bits with it!   

It is a great little unit, I use it all the time, from just setting the centre of a servo to checking second hand servo's I buy on ebay !

It is a great little unit, I use it all the time, from just setting the centre of a servo to checking second hand servo's I buy on ebay !

I feel the same about the Turnigy servo tester I got for £8 from hobbyking, but I appreciate there is pleasure to be had from building it yourself.

I feel the same about the Turnigy servo tester I got for £8 from hobbyking, but I appreciate there is pleasure to be had from building it yourself.

Absolutely. It's interesting and I've got a great sense of achievement from making it even though it's so simple in electronics terms.

I feel the same about the Turnigy servo tester I got for £8 from hobbyking, but I appreciate there is pleasure to be had from building it yourself.

I have both and they do different things. Phil's is great for checking that centering is the same coming from both directions at speed, and also for nice slow movements to check gears and smoothness etc.

I use mine mainly for bedding in the pots on new servos. You can often see a noticable difference before and after.

http://mobile.maplin.co.uk/module.aspx?moduleno=528801

Is this the maplin servo exerciser you   Are talking about?

Can you get the servo centred on start up with this?

 Or press a button to go to centre? Or does it start at centre?

Jimbo, no its a really simple DIY project, details in the first post of the thread. Theres a video to watch.

Just a minor update, chips supplied now output the servo pulses on all available output pins simultaneously, that is pins 2,3,5,6 & 7.  This means you can pick the most convenient pin and the same chip suits the bug version in the video or a veroboard multiple-servo exerciser:

The 'bug' version is the easiest to make, just follow the video exactly.

For a multi-servo one, simply use Y leads on the bug version, or make one on verboard as follows.
See attached for vero layout, just cut the 4 copper tracks under the pic, connect pin 8 to neg with a blob of solder, and then neg, pos and signal appear conveniently in the right order for the servo connector pins. The capacitor value isnt critical, its just for decoupling.
Note that pin 4 cant be used. In the pic thats hardwired as an input only. The servo pulses appear on pins 2,3,5,6 & 7 so you can use any (or all) of these. Each pin will easily drive 20 paralleled servos. Remember to insulate the underside of the vero to prevent shorts - sticky foam rubber is ideal.
Cheers
Phil

Phil do you have any kits left please,keep meaning to send some dosh off to you for a couple more to make up?
John

I'll keep doing them while ever people are interested John   
PM your address & I'll get a couple sent tomorrow
Cheers
Phil

What is soak testing?  Should we all be doing it?

CM

Hi Clive,
It gives the servo a workout for an hour, then stops. What prompted this was a chap on GC who had cyano'd his wing servos in, and then they'd failed, leaving him an awkward digging-out job. So the idea is that whenever you get a new type or brand of servo that you've never used before, you soak test it before fitting into a model. Old or crashed servos also get a good soak test before being put back in service.
Two reasons are that it gives confidence that all is well, and on a new servo, it beds-in the gearbox and pot.
So anyway, I made this thing for the GC guy, and he suggested that since its so simple, maybe others might be interested too. I wrote it up as a really easy project and its turned out to be very popular (well, hundred+).  If you're still curious have a look at the video in the article, linked in the first post of this thread.
Cheers
Phil

I'll keep doing them while ever people are interested John   
PM your address & I'll get a couple sent tomorrow
Cheers
Phil

Sorry for late reply Phil,will post dosh off to you tom when we are in town and put my address in also,although I think you still have it from the others you sent.
cheers
John

I reckon I'd better get myself one of these too... 

Funds sent by paypal. 

All sent.
John H, I had a few spare minutes so I made one of yours up, trust this is ok!
Cheers
Phil

As long as you know what you are doing and it works 
Cheers Phil
John
PS memo to self.DO NOT USE 5 CELL BATTERY WHEN TESTING SERVOS 

As long as you know what you are doing...

Ah. 

and it works

 

PS memo to self. DO NOT USE 5 CELL BATTERY WHEN TESTING SERVOS

The PICs max rating is 6.5v - maybe a couple of diodes in series?
Cheers me dears
Phil

Phil he must be a spektrum user   

Rec'd this morning Phil,did'nt post letter till wed and got them today with one made up,sterling service young man,thank you very much 
I analysed the Spectrum and decided I would like to keep my Taba and Mpx thank you very much
John

Mine arrived today - thanks Phil! 

I'll build/assemble it over the weekend sometime.

Rec'd this morning Phil,did'nt post letter till wed and got them today with one made up,sterling service young man,thank you very much 
I analysed the Spectrum and decided I would like to keep my Taba and Mpx thank you very much
John

Did you use a spectrum analyser? 

Think that was my"Tongue in cheek" reply to the impression I was a Spectrum user Mole
John

I've just added another test to the exerciser, after the 4 left-right cycles and the slow sweep, it now does this:
Full left, then full right, full left, etc slowly, then gradually getting faster... the idea is that obviously when its doing the left-right cycle slowly, the throw is equal either side of neutral. As the left & right flips get faster, there comes a point where the servo cant keep up and is still driving right when it gets the left signal, then it doesnt get fully left before the signal switches to right, and so on.  The signal generated by the exerciser is perfectly symmetrical, spending identical times on left and right, so the servo should oscillate faster and faster, moving less and less, around its centre position.  What can happen in practise is that the servo might wander off centre as the twitching gets too fast for it to follow, which indicates a servo with assymetric transit speed - ie faster one way then the other.  This isnt necessarily a bad thing but posh servos do seem to fare better than cheapies in this respect. Any subsequent chips ordered will have this additional sequence.   
Cheers
Phil

Phil,
Thank you for the video and inspiration.
When 2 channel radios first became affordable I put a missing pulse detector in a servo lead to toggle a relay for an electric motor in a glider giving an extra channel.
With the arrival of the Picaxe 08 micro it could now toggle between servo positions or speed controller powers but the arrival of cheap 2.4GHz rendered it obsolete.

A friend recently returned one asking "what can you do with this then?" He went home with a "New lamp for old." in the shape of a servo exerciser.  A switch provides 1.5ms to centre servos during installation. 128 bytes out of 128 available so no room for your recent enhancements.
Ora'best.
Dave

Thanks Dave.  I did a similar thing for a members scale truck in our model car club donks ago, he had only 2ch radio so I had the pic measure the time pulses were missing, and either played a 'General Lee' airhorn tune (switch tx off for 1/2 sec) or did the 'Nightrider' strobe lights (very quick switch off & back on) whilst simultaneaously doing direction indicator LEDs that flashed according to the steering channel.  Similar principle to your throttle control I expect.
Been using pics since they first arrived, having started in the mid 70s on the intel 4004...  always used either machine code or assembler. Not a big fan of picaxe, stamps, picC, etc to be honest, too restrictive especially on intricate or real time stuff where you're cycle counting and much to do in very few cycles.  HLLs are so wasteful, the truck thing was under 200 bytes including the music table. The exerciser is a trivial little project, has loads of cheap-&-cheerful inline code as the original was an urgent requirement, but still it only uses 14% of the flash - bags of room for ideas!
Cheers
Phil

Just done a 10-servo exerciser on veroboard for Chris W.
Been busy over Christmas but will post tomorrow Chris.
Cheers
Phil