Servo Torque and reliable servo motors

Anybody know where I can buy reliable servos?

I've tried cheap ones:

Long Runner Servos

...and expensive ones...

JX Servo

And they both give up the ghost within a few hours days weeks or months.

Sometimes the cheap pack contains servos which do not even work from day one.

Also, Torque. If it says ...

"Stall Torque (4.8V): 2.2kg.cm"

does that mean it can really lift a weight of (say) 2 kg at the end of a 1cm arm?

I'm lifting a pen which ways far less than 2kg!

Well, that's the claim, but you couldn't run it at that level but a few seconds, it would burn out. Advertisers will tell you the voltage, but never the current required, they will tell you the max torque, but never the current required to produce that torque or the amount of time it can hold that torque or the projected number of operations (estimated lifetime).
As for a more quality built, durable servo than the run-of-the-mill hobbyist types, you might search for some industrial "actuator" suppliers, but be prepared to spend ten times the price.
What are your project requirements?

"I'm lifting a pen which ways far less than 2kg!"

So how much $$$ you have to spend?

JCA34F:
As for a more quality built, durable servo than the run-of-the-mill hobbyist types, you might search for some industrial "actuator" suppliers, but be prepared to spend ten times the price.
What are your project requirements?

I thought the JX servo, with metal gears, and a much higher price, was higher quality, but it lasted about the same time as the best of the cheap ones. I don't mind spending 50x, but I'm not sure where to find them. I was hoping someone here had direct experience of a good supplier.

zoomkat:
"I'm lifting a pen which ways far less than 2kg!"

So how much $$$ you have to spend?

I'd spend €50 if the thing lasted.

The pen weights 35g, so 0.035kg and is at the end of a roughly 1cm arm, so clearly within spec.

The below robotics servos might be of interest. I think there are also some servos that might be a step above these.

https://learn.trossenrobotics.com/projects/159-trossen-robotics-dynamixel-guide.html

giovanniguerra:
Anybody know where I can buy reliable servos?

I’m going to try these, judging only by the price (not always a good guide) they should last longer…

…I’ll report back!

zoomkat:
The below robotics servos might be of interest. I think there are also some servos that might be a step above these.

https://learn.trossenrobotics.com/projects/159-trossen-robotics-dynamixel-guide.html

Many thanks for that link. I'll see how the helicopter servo goes and then maybe try the ones you suggested.

Hi,
How much do you move the pen?
How much do you tell the pen to move?

If you are moving the pen against mechanical stops, but tell it t move further than the stops, you will eventually cook the servo because the servo would be torquing against the mechanical stop.

Can you post a picture of the mechanism please?

Thanks.. Tom.... :slight_smile:

Hello Tom,

The pen only has a vertical movement, about 1cm.

There are no mechanical stops, so no pressure there.

The pen is guided by two thick wire loops, which hold it vertically very loosely.

The pen is pulled down by gravity, and weights 35grams.

See attached image…

The servo in the picture looks like one of the small "9G" servos, and just looks small/undersized compared to the size of the load. The gears in some of 9g servos strip very easily and are probably not going to do well with a 35g load as pictured.

If you attempt to drive a cheap servo past its endstop and hold there it will just cook itself. Some experimentation is needed to figure out the valid angular range for a cheap servo, they all differ as they
not precision devices in any sense of the word.

Its useful to monitor the supply current to the servo when experimenting to ensure its not stalled at high current.

zoomkat:
The servo in the picture looks like one of the small "9G" servos, and just looks small/undersized compared to the size of the load. The gears in some of 9g servos strip very easily and are probably not going to do well with a 35g load as pictured.

Does 9g mean 9 grams.cm ? Or the weight of the device itself?

Where in the specs of this do I find the actual torque the motor can supply?

I've tried a more expensive one with metal gears, with not much better results.

TIA!

MarkT:
If you attempt to drive a cheap servo past its endstop and hold there it will just cook itself. Some experimentation is needed to figure out the valid angular range for a cheap servo, they all differ as they
not precision devices in any sense of the word.

Its useful to monitor the supply current to the servo when experimenting to ensure its not stalled at high current.

The angular motion is only about 30° and nowhere near the end stops of the motor itself.

"Stalled at high current" does that mean it will work again once load and power removed? Because it doesn't. I imagine the gears are mashed.

I've just found this site...

https://www.servoshop.co.uk/

...if anyone is interested. They have a huge range.

"And they both give up the ghost within a few hours days weeks or months."

What is the actual failure mode, mechanical or electrical, etc.?

zoomkat:
“And they both give up the ghost within a few hours days weeks or months.”

What is the actual failure mode, mechanical or electrical, etc.?

Hmmm. Stupid question from me, how would I tell if it was electrical? The arm just gets stuck in one position.

giovanniguerra:
Hmmm. Stupid question from me, how would I tell if it was electrical? The arm just gets stuck in one position.

If you can turn the arm manually with it unpowered, only try for a small movement. Then the servo has probably failed electronically. It is not advisable to try to hard, as you can cause damage to gear teeth. Especially if the servo has PLASTIC gears.
If you can't turn it, then it has probably failed mechanically, the gears may have stripped or jammed in some way.
This is not unusual with cheap plastic gear servos.
If I have an elcheepo servo seize, I have taken them apart and release the jammed gearing, this will sometimes restore the servo to proper use. (You have nothing to loose.)
Tom.... :slight_smile:

TomGeorge:
If you can’t turn it, then it has probably failed mechanically, the gears may have stripped or jammed in some way.
This is not unusual with cheap plastic gear servos.
If I have an elcheepo servo seize, I have taken them apart and release the jammed gearing, this will sometimes restore the servo to proper use. (You have nothing to loose.)
Tom… :slight_smile:

Thanks for that suggestion, from what you say I think it has jammed mechanically, I’ll see if I can take it apart…

giovanniguerra:
Thanks for that suggestion, from what you say I think it has jammed mechanically, I'll see if I can take it apart...

It might be worth putting a drop of oil or vaseline on the gears.
Tom... :slight_smile: