Good day, good people...
I'm curious to know why one would use a continuous rotation servo rather than a stepper... or even rather than a plain old DC motor. (Especially since it seems to be quite a pita to open them up and modify them....)
Do tell....
At a guess, I'd say a combination of price and ease of use. A ready-hacked servo is pretty cheap, and can be driven by the servo library.
That makes sense, since steppers are a bit pricey.
How does direction work?
Normally if a servo was at say 90, and I sent it to 180, there's only one way to go. From 180 if I sent it to 90 it would reverse. But if it's continuous, what does it do? If it's at 180 and I send it to 90, does it go back to 90 or go thru 3/4 of a rotation thru 0 to 90?
If you accept the lack of fine control, they can be a useful proposition for quite a few applications.
A motor, gearbox and electronics in a single package with very simple wiring and drive requirements.
I have four on a CD-bot driving omni-wheels, with very simple but sturdy mounting, and still room spare for sonars.
Especially since it seems to be quite a pita to open them up and modify them....)
Ten, fifteen minutes tops.
The most difficult bit is getting rid of the physical endstop.
I used to use a razor-saw, but getting rid of the sawdust is difficult, and it tends to stick to the grease on the other gears, creating the potential for a jam.
Now, I just use wirecutters.
Normally if a servo was at say 90, and I sent it to 180, there's only one way to go. From 180 if I sent it to 90 it would reverse. But if it's continuous, what does it do? If it's at 180 and I send it to 90, does it go back to 90 or go thru 3/4 of a rotation thru 0 to 90?
Normally, you would mod the pot so that it is in the centre (0 degrees) position, or replace it with two resistors of equal value, which gives the same effect.
The electronics are very simple and just try to minimise the error between the demand position of the servo and the measured position.
Obviously, the measured position never changes in a modded servo, so a positive error will always cause the servo to move in one direction, and negative error in the opposite direction.
I'm curious to know why one would use a continuous rotation servo rather than a stepper... or even rather than a plain old DC motor. (Especially since it seems to be quite a pita to open them up and modify them....)
Actually some of the servos can be modified for contionious rotation in a couple of minutes. Not necessairly perfect for all jobs, a modified servo is probably the least expensive variable speed, bidirectional gear motor setup available.
Cheaper and lower power than a stepper, but you have no control over position, just over speed (within limits...) 0 degrees runs full forward, 90 degrees stops and 180 degrees runs full reverse.
Works nice for simple rolling robots. 2 drive wheels, If both are rotating the same direction at same speed it moves. If the speeds are different or the directions are different it turns.
If you used a multiturn pot you could get as many as 10 turns from 0 to 180 inputs.
Is a nice openloop solution.
Thanks for the replies