Getting Servos To Move More Than 180degrees

Hi everyone - I'm a complete Arduino newbie - I need to get 180 degree movement out of some servos in order to get them to move knobs on a guitar amplifier they are attached to. Ive got an arduino Uno and have managed to get a single servo to move via potentiometer input. I need to get 6 running together from different inputs. As I understand conventional servos only give 180 rotation, I have read that servos used in model-boat making especially can give up to 360 degrees - how would this work within the code - can the myservo object support this?

you might add a small gearbox so the 180 degrees become 360 or more on the smaller wheel.

I second that.

You may not even need a gearbox. A tight rubber band might suffice - audio pots seldom go past 270 degrees, in my experience.

The HS-785 Sail Winch Servo is probably the servo you are thinking about. You can make make little over drives for servos if not a lot of torque is needed. Servo City has external gears for servos that might be of use.

Not all servos give 180 degree travel, some as little as 90-120 degrees. It varies from model to model. Give it a 1000 usec command and then a 2000 usec command and that will tell you the minimum total travel your servo was designed to have. Most servo will have some 'overtravel' below 1000 usec and above 2000 usec, but how much you can only determine from the datasheet of the servo (if it gives that specifications) or by testing, see link below. Needing more travel then a specific servo can do can only be accomplised by external gearing or finding a different servo. Be cautious about '360' degree servos. Some make it to mean a true 360 and only 360 total travel, others mean a continous travel bidirectional variable speed motor that can no longer be commanded to a specific travel point and stop on it's own. Lots of misinformation and confusion for servos out in the wild.

http://arduino.cc/en/Reference/ServoWriteMicroseconds

Lefty

thanks for the help so far everyone, some of it a bit over my head as ive never done any work in this area whatsoever - i think im going to have a go with the winch servo - with an external power supply as i want to control a handful of them independently - i don't need continuous rotation but it needs to be bi-directional. if i just use the regular servo/pot example within the IDE , and change the range somehow - do you think this would work?

AWOL: I second that.

You may not even need a gearbox. A tight rubber band might suffice - audio pots seldom go past 270 degrees, in my experience.

ive decided to purchase two SuperTec S125 Sail Winch servos, i wont need more than 270 degrees as im trying to motorize guitar amplifier knobs with the servos, which don't need to go over that. im just not sure what code to use - im a bit of a noob really, will the regular myservo function controlled by a potentiometer be able to provide this for me?

Don't forget Nigel Tufnel's knobs go to 297 degrees.

Some Servos are modified for continuous rotation...

http://www.hvwtech.com/products_list.asp?CatID=294&SubCatID=297

Check the servos at HVW and check the descriptions. I have seen this elsewhere...

I think the new "tankbot" from Sparkfun has the modified servos.

Some Servos are modified for continuous rotation

...at which point, they become ex-servos.