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Arduino project - Servo Exerciser - RCM&E Dec 2018

Electronics in the mag

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Chris Bott - Moderator24/11/2018 12:09:11
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In case anyone was wondering "what's the point" (It's a very good question), here's a video of what the servo exerciser electronics project in the Dec mag does.

I find it most useful for checking the centring of servos, or even control surfaces. For anyone extremely picky you can just detect a centring difference in the video, depending on which direction the servo is coming from.

Phil Green24/11/2018 12:59:17
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From 2010.  Skip to 7m44s, the first 7 minutes is the build smiley

 

Edited By Phil Green on 24/11/2018 13:10:55

Chris Bott - Moderator24/11/2018 13:03:40
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I thought you might recognise it Phil. You even get a mention in the article. laugh

Much as I tried to come up with something original, no sequence of events seemed better than than the one you had come up with.

Phil Green24/11/2018 13:15:27
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Hey no probs Chris smiley , they are very handy especially with cheap servos. Shortly after the video I added an end-to-end sweep with increasing speed, faster & faster until the servo cant keep up. The idea is that with alternate and equal left and right commands, even if the servo cant keep up, it should stay central. Some wander off neutral, indicating a speed imbalance between the two directions.

Cheers
Phil

Edited By Phil Green on 24/11/2018 13:16:19

Chris Bott - Moderator24/11/2018 13:17:40
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Blimey - as usual you're way ahead of me. Maybe folk can build one and try to incorporate your ideas themselves, or maybe with the help of this thread.

Phil Green26/11/2018 18:11:13
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Did you see my background servo driver for Arduino Chris,
makes anything like this a piece of cake smiley

**LINK**

Edited By Phil Green on 26/11/2018 18:12:02

Chris Bott - Moderator27/11/2018 10:24:34
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Hi Phil.
Sorry for slow reply, a bad back is suddenly taking most of my concentration.

No I hadn't seen that. I won't pretend to understand anything of how it works but it does look extremely useful to just cut, paste and use.
I assume we'd just make OFR1B = whatever we want the servo to do? (x2).

Edited By Chris Bott - Moderator on 27/11/2018 10:25:46

Alfred Vink29/01/2019 17:32:50
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Hi Chris,

Just read the article and was wondering why you decided to power the servos through the RAW pin.

Wouldn’t it make more sense to use Vcc? The Arduino can take up to 12V as input, I don’t think all servos would like that.

Looking forward to see what else we can do with the arduino.

Mike Blandford29/01/2019 23:48:51
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The regulator on an Arduino Pro Mini can supply up to a total of 150mA. A servo will very likely consume several times that amount when operating.

In addition, the regulator has a maximum power dissipation of 450mW at an ambient temperature of 25 degrees C. If you put 12V on the raw input, then, for a 5V Arduino, the regulator will have 7 volts across it. With about 64mA flowing, you will reach the 450mW dissipation limit.

Mike

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Phil Green30/01/2019 00:52:30
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Hi, yes they're clipped but with enough left to attach the power wires, see photos. However, I'd suggest Chris's Arduino variant for a new project, then you could amend it to suit your exact needs.

Cheers
Phil

exerciser_under.jpg

7.jpg

Alfred Vink30/01/2019 07:31:48
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Thanks for the clarification Mike, makes sense to me now.

SIMON CRAGG30/01/2019 07:43:07
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I was talking to Motion RC the other day about servo testing. They strongly recommended that all the servos on their models be cycled for at least six minutes, to establish if they get hot. I had one on my Freewing Hawk that was warm to the touch, which they replaced without question. I think this procedure is a "must" these days, when models come with servos of unknown quality etc. I certainly have adopted it as "standard" procedure. Potentially could save a model at the very least!.

Bob Cotsford30/01/2019 11:48:29
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I once had some brand new Bluebird BM621servos on test that got so warm that the leads melted!

Edited By Bob Cotsford on 30/01/2019 11:50:24

Chris Bott - Moderator30/01/2019 12:34:51
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Posted by Alfred Vink on 29/01/2019 17:32:50:

Hi Chris,

Just read the article and was wondering why you decided to power the servos through the RAW pin.

Wouldn’t it make more sense to use Vcc? The Arduino can take up to 12V as input, I don’t think all servos would like that.

Looking forward to see what else we can do with the arduino.

Alfred, Mike's answer explains why nice and clearly. Thanks Mike.

The servo is therefore powered directly by the battery while the voltage regulator on the Arduino drops the voltage to 3.3v for the processor .

One thing to note is that this means that the servo can have a supply voltage anywhere up to its limit, while the position pulses coming from the tester will always be only 3.3v. This can be an issue for some servos but is representative of exactly what happens with most receivers.

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Chris Bott - Moderator31/01/2019 14:03:16
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Supertigrefan there's nothing on line, unless you're a subscriber and can look at Decembers RCM&E.

If it's your first electronics project then you probably need the whole article but if you're determined enough then I'm sure we can help here.

The required items are:

  • Arduino Pro-Mini 3.3V 8Mhz £3.11 (bitsbox.co.uk M071)
  • USB – FTDI Program uploader £3.18 (bitsbox.co.uk M070)
  • USB cable – Mini USB.
  • 3 Servo sockets on leads. (Make your own or cut them off servo extensions/ Y leads)
  • The Adruino sketch – Downloadable using **LINK**
  • PC With Arduino IDE software – Free download **LINK**

In essence you'd need to follow these steps:-

  1. install the Arduino IDE software on a PC.
  2. Use the IDE software to open the sketch (program).
  3. Set the software up to suit the type of arduino you're programming and the right PC com port etc.
  4. Connect everything up, with the programmer set to 3.3v
  5. Upload the sketch from the PC to the Arduino board.

Here's some pictures to help illustrate.

Wiring diagram:-

exerciser.jpg

Finished project :-

completed servo exerciser.jpg

Uploading from PC to Arduino:-

programming the nano pro (2).jpg

A couple of different programmers:-

2 different ftdi boards.jpg

A couple of different Arduino Pro Minis

2 different arduino nano pros (1).jpg

Chris Bott - Moderator31/01/2019 14:18:22
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PS - This would work just as well on any type of Arduino. For example an Arduino nano Pro, which has a built in USB port. That would mean no separate programmer would be required.

Kevin Fairgrieve31/01/2019 14:47:27
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Any idea Chris, when the follow up telemetry article will be hitting the magazine?

Thanks.

Kev

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