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Questions With A Hd 1501Mg Servo

I have one of these HD 1501MG servos. I'm having problems with it fluttering towards the end of travel. I would guess it's the pot inside with a bad spot or some grease on the wiper. I took the servo apart but it a sealed unit. Also I'm only getting about 60 degrees of travel. Has anyone seen any of this behavior using this servo? I thought it may just be this unit but I found a couple reviews with people having the same problems. I also found a video by our own josh demonstrating this servo and he had the same issue. Maybe it just effects a few servos and not all? Any ideas?

This would be a perfect servo for me as I need a standard size servo no bigger then this one and it needs to be analog with as much torque as I can find. The torqueier standard size analog servos seem to be going away in loo of digital. I'm using a Hitec HS-545MG now and it's just barely doing the job. It's OK with springs added but I really don't want to use them. ;)

Here's Josh's Vid. You can see the flutter at about 2:50 point.

#1  
Do you have another servo to test? Fluttering usually means a bad pot... I google them and found limited stats for this servo... One web site stated that it's pulse range is 500us to 2100us ... Which makes me wonder why it isn't all the way to 2500us? Or is 2100 us a typo or just normal for 180 deg servos...? I assume the pot has be extracted and relocated on the output shaft?
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#2  
@Dave.

I don't know if this will help you Dave. Nobody is giving much away in the specs department about these servos, but i managed to find a little info and put a few links up for you that you may find helpful. The first one says that it has a +/- 60 degree turn. The second is the insides of the servo in question, and the third is a reviews section where people were asking about increasing it's travel, no answers but it looks like it has a limited movement less than 180. Have a look and see what you can make of it.:)

1501 servo range and click "Specification".


Stripping a 1501 servo



Turnigy 1501 servo discussion
#3  
Thanks guys for the input.

@Richard, I should have mentioned that the pot I have is still installed in the servo and not relocated. I'm not sure about the setup that Josh is showing in his video above but ServoCity's gear boxes come with or without an external pot. I was guessing that the one he shows did not have the servos internal pot removed. Maybe I'll get lucky and he will chime in here. However I do think the problem with the flutter is the pot. I don't have another servo of this kind to test. However other types of servos do work just fine in this location.

@Steve, Following your kindly provided links (Thanks by the way) I found a datasheet link to the Power HD company for this servo (not the Spec tab).

Power HD HD-1501MG Datasheet

It shows this servo's operating range at 180 degrees ± 10.

BTW, your last link is to a different servo I think. Thanks anyway. ;)
#4  
@Dave... I think the pot has to be relocate to the final output shaft (because of the gear change ). The servo still turns 180 but the large wheel only turns a fraction of that... Putting the pot on the large wheel will give you the 180 drgrees as normal...

If you're only getting about 60 degs then you must have a 3 to 1 gear ratio on the large external gear....
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#5  
No problem Dave. Yeah I wasn't sure about the servo in the last link, but added it anyway as it had the same model number. I just had a look at the data sheet. I'm just curious why the specification info stated the servo is +/-60 degree, and as you said the data sheet says 180? Still, 60 degree, 180 degree, I wouldn't expect or like a servo to shudder like that when it reached maximum travel. *confused*
#6  
@Steve.... the reference in the specifications you posted to 60deg is for speed... 0.14 seconds to reach 60degs at 4.8V.... It doesn't mentioned whether or not it is a 180deg servo but we should assume it is otherwise it would have been mentioned in the specs...

***Edit*** Dave's PDF confirms it is a 180deg servo.... The pot has to be relocated to the large output shaft if you want to get 180 deg of rotation with the new gearing...
#7  
@Richard, I'm not useing the gear box like Josh shows, just the stright servo, no gearbox. Sorry for any confusion.

I just wanted to show that video to illustrate that I'm having the same issue. Also the link I posted leads to a data sheet saying that it travels 180. In reality it will only physically only turn 90 degrees but when commanded by ARC to move from 1 to 180 it will only move about 60 % of what it's capable of moving. Just like what Josh stats in his video above. Yes I have the servo control configured from 1 to 180. ;)
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#8  
@Richard.

Okay, gotcha. To me it looked like it was saying it could travel 60 degrees in one direction or the other from centre position. But a picture I found looks like it should rotate 180 full travel. Blame it on lack of coffee.;)

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#9  
@Steve... Ok... your first link didn't have the reference to rotation, just speed so I assumed... sorry about that... So the servo has limited travel to 60deg from centre instead of a normal 90?

@Dave, ok thanks no worries.... The PDF you posted says it is a 180 deg servo, however so maybe a faulty pot?...
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#10  
@Richard.

Hey no worries. The link I posted for some reason reverts back to the "description" page, so I added the "click specification" bit. As Dave has the PDF stating the servo he has is 180, you could very well be right about the pot then.

@Dave.

Sorry about any confusion.:)
#11  
Yes, the servo will only rotate to 60 not 90. However with power off I can turn it to 90 with my fingers.
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#12  
@Dave.

Well if you can turn it by hand to 90, my guess is that yourself and Richard are correct then, and it could be a faulty pot. So there's no way you can open the rest of servo up then? I know you said it's a sealed unit, but I'm just asking on the principle that "it had to be put together in the first place" theory.
#13  
I haven't had any issue with these servos and they do almost 180 deg. not 60.
If you modify the servo then you need to use the right pot to get the full movement.
A servo tester or RC receiver never moves a servo the full 180 deg at least the ones I have used wont give you full movement.
Test it with your EZ-B to see the limit it will move. If it stutters at one end of travel the pot could have a bad spot.
So far all of my 1501MG servos have tested good.
Anyone test how strong these are with 7.4 v?
They have passed every test I have given them and if you release your servos, they hold their position without overheating the V3 or the V4.
#14  
Well, I'd like to bring this to a close and tell you how it all ended up;

I ended up buying two more of these Power HD 1501MG and I'm glad I did. The first one I posted about here did have a bad pot. After replacement of the pot the servo didn't have the shutter anymore but the pot I used couldn't be re-installed into the servo where I needed it. Relocating it on the joint is not an option. So I decided to get two more of these because I really liked the torque they put out, they fit where I need them and they are smooth.

The position hold feature when the servo is released may or may not be a good thing for me. I haven't worked that through yet but it doesn't seem to heat up when sitting and released. I also haven't placed an amp meter on it to see what the draw is when as it sits idle. The spec sheet says it draws 5ma when stopped and idle. Another worry I have with this feature is longevity. Will the servo sitting and released but holding position shorten it's life span? I wont know this till time wears on.

My last concern with the 1501MG is quality. As I said above I bought two more of these. The cost was $16 USD on Amazon or $20 from Pololu. I ought from Amazon. Not a lot for such a strong and smooth servo. However the first one had the bad pot (Reviews have stated that others have had this same problem). Then the second 1501MG I installed froze up after just a few swings back and forth with hardly any load on it. When I took it apart I got the motor to work again but only in one direction. Then the board flamed out after a few seconds of running. However, now I have the third 1501MG installed and it seems to be holding up with no problems. Not sure why I had to go through two servos before I found a good one. I did buy from Amazon and suspect they were returns that were reshipped to me. This has happened to me several times when buying from amazon. Perhaps if I buy directly from Pololu I would get newer and vetted Power HD 1501's with no problems.

Anyway, I'm going to stick with this servo for the time being as it does exactly what I want. At 6 V: 0.14 sec/60°, 240 oz-in (17 kg-cm), 60 g it's a monster.

@Mcsdaver, The spec sheet says it is only rated to to 6 vdc. I guess you could run it at 7.4 v but given my concerns of quality I'd be afraid to push it up to that voltage. The extra voltage may not hurt it but the extra torque may put too much stress on the circuit board. However you never know till you try and go too far. ;) Here's a link to this spec sheet:

Power HD HD-1501MG Datasheet

If your looking for a way to to drop the voltage from 7.4 down to 6 or lower I found a great little Bec 10A 6S Switching Regulator by Castle Creations. It's super small (only about 1 inch x 1/2 inch), programmable output voltage (With an extra unit you have to buy), runs cool and will handle up to 10 amps draw. Here's the specs:

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*1.2" (30mm) x .6" (15mm) x .4" (10mm) , Weight: .4oz (11g)
*Input voltage: 5V to 25.2V (2S to 6S LiPo)
*Current output: 12 volts input = 7 amps continuous, 10 amp peak
*Current output: 24 volts input = 5 amps* continuous, 7 amp peak
*Selectable Output: 4.8 - 9.0V via the Castle Link (sold separately), Default voltage is 5.1V


www.amazon.com/gp/product/B000MXAR12/ref=oh_aui_detailpage_o05_s00?ie=UTF8&psc=1

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