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goddlediddles
(@goddlediddles)
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Joined: 2 months ago
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2020-10-23 7:57 am  

Hi all. I bought an Arduino starter kit from Elegoo on Amazon. My main purpose was to learn how to use a servo motor to turn the shaft of a high voltage variable capacitor through 180º. I have now got the SG 90 sweeping, using the sketch in the tutorial. The problem is that it will not sweep the full 180º, more like 165º. The SG 90 is not a genuine Tower, so could this be the problem or is it a feature of all small servo motors? If so, I will have to abandon servos and maybe try to use a stepper. I need a full 180º movement to get my variable capacitor adjustment right. Any help on this would be greatly appreciated. 

Always make up your own cables.


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Pugwash
(@pugwash)
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2020-10-23 3:26 pm  

I bought some SG90s on eBay and none of them has a full 180° sweep.

If that is any comfort.

You may have more luck with more expensive servos!


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goddlediddles
(@goddlediddles)
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2020-10-23 3:50 pm  
Posted by: @pugwash

I bought some SG90s on eBay and none of them has a full 180° sweep.

If that is any comfort.

You may have more luck with more expensive servos!

Thanks, Pugwash. You say more expensive servos might do the job. I don't mind spending more money on the project. It's got to be done. Which ones would you suggest? I'm 8 hours now searching all manufacturers, but none of them will confirm that a full 180º is possible straight out of the box.

Always make up your own cables.


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Pugwash
(@pugwash)
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2020-10-23 4:01 pm  

@goddlediddles

 

You would probably agree that if Elegoo is putting these things in entry-level, all-encompassing beginners kit, then they are probably not the highest quality servos available on the market.

Unfortunately, I have only used these for simple demos, therefore I am unable to point you to any high-quality servos but some of the forum members, especially those building robots would have a far better insight than I do.

Best of luck, perhaps one of them can give you a pointer or two!


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Cap Electronics
(@cap-electronics)
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2020-10-23 7:32 pm  

@goddlediddles yep I think your problem is the servos are not very high quality you see cheap servos usually don't work as well as they are advertised so using better servos might be better.

I recommend the high tech servos ( https://www.hitecservos.com/) I think they might be quite a bit better than cheap ones from elegoo.


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goddlediddles
(@goddlediddles)
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2020-10-24 2:01 pm  
Posted by: @cap-electronics

@goddlediddles yep I think your problem is the servos are not very high quality you see cheap servos usually don't work as well as they are advertised so using better servos might be better.

I recommend the high tech servos ( https://www.hitecservos.com/) I think they might be quite a bit better than cheap ones from elegoo.

Thanks Cap Electronics. I will get onto it right away.

Always make up your own cables.


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Spyder
(@spyder)
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Posts: 849
2020-10-26 11:14 pm  

@goddlediddles

I'm looking at the code for a thingy that I'm working on right now, and, unfortunately, I'm using a mix of different types of servos on the same robot arm, which is slightly confusing, anyway, I've been playing around with a combination of different pulse rates as well as changing the angles, which is also confusing, and I've found that varying the pulse rates can give you a different amount of swing

Have you tried that ?

Also, have you manually swung the thing back and forth to see if it actually can physically move that far in the first place ?

Just a thought


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goddlediddles
(@goddlediddles)
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Posts: 9
2020-10-27 7:04 am  

@spyder

Thanks for those suggestions, Spyder. I've tried fiddling with the PWM, but any change from the norm drives the servo crazy. I also tried turning it manually and it was very stiff, so I left it for fear of damage.

I've decided to follow Cap Electronics' advice, and look at the better quality ones from hitecservos.com. The problem there is that none of their specification sheets give the maximum travel. I emailed them yesterday and am waiting for a reply. I don't mind spending the extra dosh on a better quality one with metal gears and more torque.

Always make up your own cables.


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goddlediddles
(@goddlediddles)
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2020-10-28 8:49 am  

I started off learning Arduino in order to accomplish one simple task, and that was to move a variable air-spaced capacitor through 180º exactly. I bought an $80 top-of-the-range learner kit from Elegoo on Amazon, thinking that I would have no trouble in making a prototype servo-controlled mechanism to do the job.

I watched all of Bill's YouTube servo videos and implemented the required code and wiring set-up. Everything worked as planned, except to my horror, the cheap Elegoo servo would not go the full 180º - more like 165º.

It took me quite some time to learn, with the help of contributors on this forum, that the servo motor itself was the problem, and that it was common with cheap servos. I have trawled the internet for a full 3 days looking for a suitable servo motor, and eventually landed on the Hi-Tec Servos website. It gives just the barest of details about each and every one of hundreds of servo motors - never a mention of maximum travel capabilities.

I believe that I need to re-programme a digital servo to achieve 180º rotation. The problem is that I do not know where to even start looking for this information. Hi Tec Servos have not answered my email, when I outlined my requirements and asked them to suggest a suitable servo to do the job. There is an article on the web which mentions the refusal of Hi Tec Servos to give any meaningful detail at all about their products - LINK

I'm 3 weeks now trying to achieve a simple task, which must have been done by many on this forum. Building my antenna is a complex physical task requiring a lot of time and skill, but it seems that I have become bogged down at what seems to me to be a simple task done regularly by members of this forum. Godammit, I'm 73, and I don't want to spent my last years learning how to turn a simple shaft through half a circle. Robotics and model RC control is not my thing, but I need to learn something about it to complete my project.

Maybe if I post my request for information in a different topic on this forum, I might get in touch with someone who has done this, but which topic? In the meantime here is a photo of the simple air-spaced capacitor that needs to turn through half a circle. CAPACITOR LINK

 

This post was modified 1 month ago by goddlediddles

Always make up your own cables.


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frogandtoad
(@frogandtoad)
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Posts: 540
2020-10-28 10:41 am  

@goddlediddles

Posted by: @goddlediddles

I'm 3 weeks now trying to achieve a simple task, which must have been done by many on this forum. Building my antenna is a complex physical task requiring a lot of time and skill, but it seems that I have become bogged down at what seems to me to be a simple task done regularly by members of this forum. Godammit, I'm 73, and I don't want to spent my last years learning how to turn a simple shaft through half a circle.

There is always another way to skin a cat.

If you are unable to find a servo that can rotate 180 degrees (I thought they all did, or at least were supposed to), I have read some posts in the past where people pull them apart and remove the pin that stops them from rotating further, essentially they hack them to turn a full 360 degrees.

If that's not something you're willing to do, have you thought about introducing a couple of gears?  Such that in a 2:1 ratio, your servo would then only need to rotate though 90 degrees to get your 180 degrees on the main shaft?

Cheers.


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goddlediddles
(@goddlediddles)
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2020-10-28 10:57 am  

@frogandtoad

Thanks, frogandtoad. I'll try removing the end stops. I've nothing to lose with the Elegoo penny servo. Going too far beyond 180 will increase the step width though (I think). I need as much precision as possible. Anyway, I'll give it a go.

Always make up your own cables.


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frogandtoad
(@frogandtoad)
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2020-10-28 2:05 pm  
Posted by: @goddlediddles

@frogandtoad

Thanks, frogandtoad. I'll try removing the end stops. I've nothing to lose with the Elegoo penny servo. Going too far beyond 180 will increase the step width though (I think). I need as much precision as possible. Anyway, I'll give it a go.

No problem... just throwing up some ideas... the mechanical approach could even use small timing belt and gears, or even a small gear and rack with a linear actuator.

Good luck.


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goddlediddles
(@goddlediddles)
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2020-10-29 6:21 pm  

I've given up on the idea. I've just bought a 3.5 RPM reversible DC motor on eBay. No more servos, no more code, no more Arduino. A great feeling of relief has descended. Thanks to all who did their best to help.

Always make up your own cables.


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frogandtoad
(@frogandtoad)
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2020-10-30 5:16 pm  

@goddlediddles

Posted by: @goddlediddles

I've given up on the idea. I've just bought a 3.5 RPM reversible DC motor on eBay. No more servos, no more code, no more Arduino. A great feeling of relief has descended. Thanks to all who did their best to help.

Fair enough, but wouldn't a stepper motor have been a better choice in terms of positional accuracy?


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goddlediddles
(@goddlediddles)
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2020-10-30 5:51 pm  

@frogandtoad

 

Maybe, I don't know enough about the subject. I can't spend any more time learning it all. I've got to get on with my RF project - too old. Many thanks for all your efforts to help me.

Always make up your own cables.


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