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Servo speed

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beakie

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Can anyone tell me precisely how servo speed differ between servos?

A part of the specs for each servo describe a different speed, but what is this... max/min/avg?

I am trying to code something that uses servos... eventually this will be used with a number of different types of servos. I intend to do some code to calibrate the servo speeds within the code, but I need to understand more before I can think about coding it.

Any info on servo speeds would be appreciated!

Nice one
 
It is the typical speed for a given voltage.

If your application is speed dependent, you should consider controlling the speed under program control. That is, between position 0 and position 1, increment/decrement the pulse width in small steps.

John
 
Thanks....

It is the typical speed for a given voltage.

If your application is speed dependent, you should consider controlling the speed under program control. That is, between position 0 and position 1, increment/decrement the pulse width in small steps.

John

This is my intention. To control it using code.

I am just trying to comprehend how this technique changes between servos.

How complicated with the callibration be? Is it just a case of using a scaler on any values I use that define the speed.

...or will I find the difference between fast on servo A and servo B will be different between slow on servo A and servo B.

Any info would be appreciated. I don't have any servos within reach for the next couple of months, so I am forced to understand this from googling/forum.
 
Forget what I just said. I get ya.

pulse width A makes it 28 degrees.
pules width B makes it 55 degrees.

If I want to make it take a second... increment the pulse width between the 2 values over a second.

Right?
 
That's (post #4) right.

You will find differences in the smallest increment to which a servo will respond. Many years ago, there was a study that showed definite differences in that "accuracy" between the popular manufacturers at the time (Futaba, Hitech, Airtronics, and JR). Unfortunately, that specification is rarely, if ever, listed. Coreless and/or digital servos may be better in responding to smaller increments. I don't think I would depend on the specification speed for tight control. When modelers gang multiple servos for large models, they try to match them.

What you want to do is so vague at this point that it is hard to give specific advice. Unless there are specific and different needs for the different servos (such as max speed, torque, shaft wobble, handling shock loads, etc.), I would get a bunch of identical, general purpose servos. You can get modern servos for about $25 each that are quite good. Even the $10 class of servos work fine. You can also go up to $200 servos, which is probably overkill.

John
 
That's (post #4) right.

You will find differences in the smallest increment to which a servo will respond. Many years ago, there was a study that showed definite differences in that "accuracy" between the popular manufacturers at the time (Futaba, Hitech, Airtronics, and JR). Unfortunately, that specification is rarely, if ever, listed. Coreless and/or digital servos may be better in responding to smaller increments. I don't think I would depend on the specification speed for tight control. When modelers gang multiple servos for large models, they try to match them.

What you want to do is so vague at this point that it is hard to give specific advice. Unless there are specific and different needs for the different servos (such as max speed, torque, shaft wobble, handling shock loads, etc.), I would get a bunch of identical, general purpose servos. You can get modern servos for about $25 each that are quite good. Even the $10 class of servos work fine. You can also go up to $200 servos, which is probably overkill.

John

Thanks for this.

I actually have a few HS-5645MG's... but the are on the opposite side of the world... I won't get them until the new year. I prefer to design things considering the bigger picture than my one, current need. It's a habit learnt from working as a programmer. Sometimes its better to consider these things up front rather than have to hack prewritten code later. I find this is where most of the frustrating bugs are born :)
 
That is a good servo. I typically use metal geared servos in applications where there is jarring, as in the rudder/tailwheel or power planes and flaps of sailplanes. As mentioned on the ServoCity site (**broken link removed**), they do wear more and develop more slop.

ServoCity gives the dead band as 8 µS and lists a 450 µS change for 45 ° rotation. That should allow steps of <1°. Hitech sells a programmer. You may be able to adjust your speed adequately with that.

John
 
Operating Speed (4.8V): 0.23sec/60° at no load
Operating Speed (6.0V): 0.18sec/60° at no load

I actually have a few HS-5645MG's... but the are on the opposite side of the world. .. I won't get them until the new year.

I can get HS-5645 in 24 hours.
 
Operating Speed (4.8V): 0.23sec/60° at no load
Operating Speed (6.0V): 0.18sec/60° at no load



I can get HS-5645 in 24 hours.

I didn't mean I had ordered them. I mean, they are at home... but I'm not :)
 
I was just checking some new options for a plane I am completing. Hitech coreless seem to run about 4 µS dead band, and some digitals (e.g., HS6635) have a 2 µS dead band. After dinner, I will add dead band to my tables. This is the first project I have bought servos for in years -- time to throw out some boxes of 1990's vintage. They don't get better with age.

John
 
Last edited:
I was just checking some new options for a plane I am completing. Hitech coreless seem to run about 4 µS dead band, and some digitals (e.g., HS6635) have a 2 µS dead band. After dinner, I will add dead band to my tables. This is the first project I have bought servos for in years -- time to throw out some boxes of 1990's vintage. They don't get better with age.

John


You could make some young kid happy... stick em on ebay
 
I don't believe in selling kids junk. I just give them to needy beggars. :D I have given away several complete trainers and such to kids and their dads. Unfortunately, the dads don't realize that airplanes don't have a re-boot button. You have to actually repair them. Our club has several very generous members who will do the repairs for others.

Actually, many of my old, new stock servos were bought for some 1/4 scale and larger sailplane projects. Being short of tow pilots for those aircraft (up to 16 ft. wingspread), I decided to learn myself. I have spent the last 2 years doing that. Problem is, you can't tow and fly your own sailplane. ;) So, I just fly 2-m and 3-m, winch-launch sailplanes, a few electric sailplanes, and scale power.

John
 
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