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Topic: Servo Motor Shaking Problem (Read 6 times) previous topic - next topic

Terraviper-5

Hi!

I have been trying to make hammers that strike on bells at every quarter of an hour. I got one TowerPro SG90 9G and it worked quite nicely, except for occasional sounds that motor was emitting, but they weren't too loud so I didn't mind. Then I got the second motor of same type, but it cannot be still. It is shaking and emitting loud sounds regularly. Not only that, when it is moving it is also shaking, making it impossible to strike nicely at the bell.
At first I thought that it was weight of the hammer causing it, but why doesn't the second motor have the same problem? And when its supposed to be still, I put it at 90 degree angle so that weight of the hammer is minimal and its still shaking. Not to mention that the hammer is made of few plastic lego cubes and one nut, nothing too heavy. Here is a video:

http://www.youtube.com/watch?v=-7OTvQyJdSg

Could anyone please help me on this? Is the motor defective maybe? Thanks!

AWOL

How care you powering all of this?
"Pete, it's a fool looks for logic in the chambers of the human heart." Ulysses Everett McGill.
Do not send technical questions via personal messaging - they will be ignored.

Terraviper-5

With old 200W computer power supply.

AWOL

"Pete, it's a fool looks for logic in the chambers of the human heart." Ulysses Everett McGill.
Do not send technical questions via personal messaging - they will be ignored.


AWOL

I'm not a fan of fritzing.
Is the load sufficient for the supply?
How is the Arduino powered?
"Pete, it's a fool looks for logic in the chambers of the human heart." Ulysses Everett McGill.
Do not send technical questions via personal messaging - they will be ignored.

Terraviper-5

Sorry, I'm just a beginner and not used to making schematics yet.

Arduino is powered via USB since I am using a Java app to send the control signals.
What do you mean by "is the load sufficient for the supply?" I though I only have to watch that servos are not too powerful for the supply?

Far-seeker

#7
Aug 24, 2012, 09:35 pm Last Edit: Aug 24, 2012, 09:37 pm by Far-seeker Reason: 1

What do you mean by "is the load sufficient for the supply?" I though I only have to watch that servos are not too powerful for the supply?


An unregulated, or poorly regulated supply, can have a significantly higher than nominal voltage output if it's insufficiently loaded.  Here's an explanation of why.  Now most computer PSUs are built to do a decent job of DC regulation, but some cheaply constructed brands or old ones with degraded parts don't regulate the outputs well.

Terraviper-5

Hmm, never heard of that, interesting to know. Servos are rated for 3.0-7.2 Volts, and I am supplying 5V. Could this "effect" be the cause of my problem? I still don't understand though why the 1st motor, when it was powered alone on this same supply, was emitting sounds only occasionally, and those weren't loud. There was not trace of shaking. While this second one is totally useless.

I read on some forum that those servos were drawing 0.6 A current, so together those two would draw 1.2 A. But I assume they don't draw much when they are idle yes?

AWOL

Check the grounds to both servos.
"Pete, it's a fool looks for logic in the chambers of the human heart." Ulysses Everett McGill.
Do not send technical questions via personal messaging - they will be ignored.

Far-seeker


Hmm, never heard of that, interesting to know. Servos are rated for 3.0-7.2 Volts, and I am supplying 5V. Could this "effect" be the cause of my problem?


You'd need to measure the voltage with a multimeter the at a point between the supply and the servos to be sure.  However, unless you have a defective or cheaply made PSU the actual supple voltage will probably be under 7.2 Volts.  As discussed below, the servos are going to be drawing some current even when the arms aren't moving.


I read on some forum that those servos were drawing 0.6 A current, so together those two would draw 1.2 A. But I assume they don't draw much when they are idle yes?


You have to remember just because a servo isn't moving it's not truly idle.  The control logic is constantly updating the position and even a light weight arm will take a small but appeciable amount of force to keep balanced horizonatally (unless you spent an irrational amount of time and effort ensuring it was constructed to be near-perfectly balanced).  Although you are right that it probably isn't going to be around 1.2 A, but the total current might be as high as 0.3 A to 0.4 A.

One other thing that occured to me, it could be the control board on your second servo isn't functioning properly.  Have you tried disconnecting the first servo and just using the second one by itself?

Terraviper-5

#11
Aug 24, 2012, 11:07 pm Last Edit: Aug 24, 2012, 11:15 pm by Terraviper-5 Reason: 1

Check the grounds to both servos.


I have checked the cables and they seem to be ok, although I am using a lot of different cables since I didnt have enough at home, put together to make 1 meter of a cable to be able to have my bells on the nearest wardrobe. Some of them are cheap shit, and I am using molex at the end to be able to use bridge cables for protoboard to be able to connect to servos as they have some special connector. It is possible that there is some crappy link in between. Will have to go and buy new quality cables.

I have measured the voltage and it was a little below 5, so that shouldnt be the cause of problems.



Hmm, never heard of that, interesting to know. Servos are rated for 3.0-7.2 Volts, and I am supplying 5V. Could this "effect" be the cause of my problem?


You'd need to measure the voltage with a multimeter the at a point between the supply and the servos to be sure.  However, unless you have a defective or cheaply made PSU the actual supple voltage will probably be under 7.2 Volts.  As discussed below, the servos are going to be drawing some current even when the arms aren't moving.


I read on some forum that those servos were drawing 0.6 A current, so together those two would draw 1.2 A. But I assume they don't draw much when they are idle yes?


You have to remember just because a servo isn't moving it's not truly idle.  The control logic is constantly updating the position and even a light weight arm will take a small but appeciable amount of force to keep balanced horizonatally (unless you spent an irrational amount of time and effort ensuring it was constructed to be near-perfectly balanced).  Although you are right that it probably isn't going to be around 1.2 A, but the total current might be as high as 0.3 A to 0.4 A.


Yes, but its 200W power supply, I would have though that that's enough for 2 mini servos.
I guess that its possible that those arms are too much load for those two mini servos. I wasnt sure about it because 1st servo didnt shake.



One other thing that occured to me, it could be the control board on your second servo isn't functioning properly.  Have you tried disconnecting the first servo and just using the second one by itself?


I will try that next.

Far-seeker

#12
Aug 24, 2012, 11:34 pm Last Edit: Aug 25, 2012, 12:00 am by Far-seeker Reason: 1

Yes, but its 200W power supply, I would have though that that's enough for 2 mini servos.
I guess that its possible that those arms are too much load for those two mini servos. I wasnt sure about it because 1st servo didnt shake.


Oh I didn't mean the servos were trying to draw too much current!  Instead, it was the possibility you were drawing too little with a poorly regulated supply and therefore getting a higher supply voltage than what the servos were rated for that I was wondering about.  However, as previously stated if they really are rated for upto 7.2 VDC that that's unlikely to be what's going on.  Still it wouldn't hurt to check voltage under load, especially if the second servo performs well by itself.

Edit: Ugh, "regulated supply" not "rated supply"

Terraviper-5

#13
Aug 24, 2012, 11:57 pm Last Edit: Aug 25, 2012, 12:04 am by Terraviper-5 Reason: 1
Ok, checked the second servo standalone:
http://www.youtube.com/watch?v=phKtGQzJfLY
Even without the hammer it is still emitting buzzing sounds!


Still it wouldn't hurt to check voltage under load, especially if the second servo performs well by itself.

I did, it was under 5 volts (about 4.2 volts). Varying a little (+- 0.2), but no way over 5. Servo goes from 3.3 to 7.2.

Far-seeker

#14
Aug 25, 2012, 12:09 am Last Edit: Aug 27, 2012, 05:40 pm by Far-seeker Reason: 1

Even without the hammer it is still emitting buzzing sounds!


Unless I'm missing something it seems like the servo is moving properly on command.  The sound is a little unexpected, but you previously mentioned some buzzing with your other servo.  So the problem is unlikely to be a defective controller board on one of your servos.



Still it wouldn't hurt to check voltage under load, especially if the second servo performs well by itself.

I did, it was under 5 volts (about 4.2 volts). Varying a little (+- 0.3), but no way over 5. Servo goes from 3.3 to 7.2.


The supplied voltage well within the operational ratings.  Next you might want to want to put your multimeter in series and measure current (if it has more than one setting for current measurement make sure you use the one with the highest limit), both while being held vertical as well as while moving.  After that, you can hook them both up and take similar measurement for the total current.

Edit: Forgot a quote tag...

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