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[on:]

Hello,

I have a continuous rotation parallax servo. I'm trying to reproduce the functionality of a regular hobby servo. Basically I send à 1.6ms pulse for 1sec. and then try to return it to its original position by sending it a 1.4ms pulse for 1 sec. I observe a drift in the starting and ending position. It may be a completely normal situation, but I was not sure why exactly.

Thank you in advance

M.

[Reply #1 on:]

A standard servo, once modified to be a 'continuous rotation servo', is not longer able to perform as a standard servo. You cannot command it to go to a specific position and stop there like a standard unmodified servo. Once modified you really own a bi-directional geared motor driver capable of only variable speed rotation in either direction or to be commanded to stop turning.

 So if you want position control, get a standard servo, if you want to rotate something in either direction and at variable speeds then use your present 'modified' one.

 Many beginners buy 'continuous rotation servos' because they think they are getting a servo with some 'extra features' where in reality they are in fact not gaining a true servo at all, it's an ex-servo, the servo part is dead, not just pining for the fjords. 

Lefty

[Reply #2 on:]

Thx Lefty,

I did not think I was buying a servo with extra features. I find these servo Ideal when you need to control the speed! But I guess you are right that without feedback it is impossible to start and stop the motor at exactly the same rotation on both side. I guess that with the addition of a Encoder I could get a response closer to a real servo with the addition of the 360deg rotation.

M.

[Reply #3 on:]

Thx Lefty,

I did not think I was buying a servo with extra features. I find these servo Ideal when you need to control the speed! But I guess you are right that without feedback it is impossible to start and stop the motor at exactly the same rotation on both side. I guess that with the addition of a Encoder I could get a response closer to a real servo with the addition of the 360deg rotation.

M.

That is the situation. Keep in mind that there are true servos available that have 360 degree travel range/stops and even a few with 720 degree travel range/stops, often used in model sail boat winch operators. However those are not modified types for 'continuous' rotation service servos, which as I said before are no longer real servos.

Lefty

[Reply #4 on:]

That is the situation. Keep in mind that there are true servos available that have 360 degree travel range/stops and even a few with 720 degree travel range/stops, often used in model sail boat winch operators. However those are not modified types for 'continuous' rotation service servos, which as I said before are no longer real servos.

The below hitec servo seems to be an exception the the general rules.

http://www.robotshop.com/ca/hitec-hs785hb-servo-motor-2.html

[Reply #5 on:]

That is the situation. Keep in mind that there are true servos available that have 360 degree travel range/stops and even a few with 720 degree travel range/stops, often used in model sail boat winch operators. However those are not modified types for 'continuous' rotation service servos, which as I said before are no longer real servos.

The below hitec servo seems to be an exception the the general rules.

http://www.robotshop.com/ca/hitec-hs785hb-servo-motor-2.html

Yep, it's amazing what $52 CAD can deliver. 

The winch servo is not like other standard servos since it can provide both continuous rotation in either direction (variable speed), and position control over 3.5 turns. See image below for details:

Lefty