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servo range
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Rookie

Joined: Fri Oct 04, 2013 10:06 pm
Posts: 5
servo range
When giving the commands to run the servo from -127 to 127, we only get a range of motion of about 120 degrees. We would like to have a 180 degree sweep of the servo. What is the limiting factor and can we do anything about it?

Fri Oct 04, 2013 10:07 pm
Professor

Joined: Sat May 18, 2013 1:24 pm
Posts: 271
Location: Olympia, WA
Re: servo range
The specs for your servo should tell you its range of motion. I don't know about Vex, but in FTC, modifying servos to extend their range is illegal. Of course, if you don't care about that, there's ways to do it

_________________
FTC Team 6424, the 'Oly Cow - Chief programmer.
FRC Team 4450, Olympia Robotics Federation (ORF).

Fri Oct 04, 2013 11:01 pm
Rookie

Joined: Fri Oct 04, 2013 10:06 pm
Posts: 5
Re: servo range
The servo I have is a futaba S3003. The specs that I can find on the website, and on the box, do not include a range of motion, as far as I can tell.
Here they are:

S3003 Standard
S3003 Standard
FUTM0031
Volts Torque Speed
4.8V 44 oz-in (3.2 kg-cm) 0.23 sec/60°
6.0V 57 oz-in (4.1 kg-cm) 0.19 sec/60°

Dimensions Weight
1-9/16 x 13/16 x 1-7/16 in
(40 x 20 x 36 mm) 1.3 oz (37 g)
3P

Sat Oct 05, 2013 8:01 am
Professor

Joined: Sat May 18, 2013 1:24 pm
Posts: 271
Location: Olympia, WA
Re: servo range
According to this site: http://www.servocity.com/html/s3003_servo_standard.html
"Operating Angle: 45 Deg. one side pulse traveling 400usec"
So, the entire range is around 90 degrees or so. There might be models out there that can turn 180 degrees, but that could require some bit-banging. I'm an FTC programmer, so I dunno how you would do that on a Cortex. Basically, you have to modify the length of your PWM pulses longer/shorter than the standard 1520usec. Every 400usec off of that should be an extra 45 degrees of motion. You could also take apart the servo and look for any mechanical limits

_________________
FTC Team 6424, the 'Oly Cow - Chief programmer.
FRC Team 4450, Olympia Robotics Federation (ORF).

Sat Oct 05, 2013 10:55 am
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