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Recommednations for 180+ degree servo — Parallax Forums

Recommednations for 180+ degree servo

RobotWorkshopRobotWorkshop Posts: 2,307
edited 2012-02-04 18:24 in General Discussion
I'm looking for some standard size servos that can travel at least 180 degrees (a bit more would be better). Does anyone know of some off the shelf servos like that? There is one that I'm using on a robot and I could really use a replacement that has larger limits on its travel.

Robert

Comments

  • PublisonPublison Posts: 12,366
    edited 2011-10-17 12:59
    RobotWorkshop wrote: »
    I'm looking for some standard size servos that can travel at least 180 degrees (a bit more would be better). Does anyone know of some off the shelf servos like that? There is one that I'm using on a robot and I could really use a replacement that has larger limits on its travel.

    Robert

    Robert,

    I would look at ServoCity. They sell a lot of servos that they sell with modifications. One in particular:

    http://www.servocity.com/html/hsr-5498sg_servo.html

    can be ordered in 90 degree or 180 degree.

    You would have to go through all the servos to see what rotations they offer on each one.
    I have not found a table on their website to show what they offer across the board.

    Hope that helps.

    Jim
  • ercoerco Posts: 20,259
    edited 2011-10-17 13:05
    Robert: I know you know all about this, but you can modify a servo to go 180 degrees or more by:

    1) Modifying the internal mechanical stops, and
    2) Driving with pulsewidths less than 1 ms and greater than 2 ms. Alternatively, adding two fixed resistors in series with the existing internal pot to change the resistance range will increase travel for any given input signal.
  • RobotWorkshopRobotWorkshop Posts: 2,307
    edited 2011-10-17 13:07
    Hello Jim,

    I am looking for a servo in a standard servo case similar to the one that Parallax sells. That way I can easily swap it out with the servo I have in place now. I'll look around on their website to see if I can find any other ones that can do 180 degree rotation in a standard case.

    Robert
  • RobotWorkshopRobotWorkshop Posts: 2,307
    edited 2011-10-17 13:12
    erco wrote: »
    Robert: I know you know all about this, but you can modify a servo to go 180 degrees or more by:

    1) Modifying the internal mechanical stops, and
    2) Driving with pulsewidths less than 1 ms and greater than 2 ms. Alternatively, adding two fixed resistors in series with the existing internal pot to change the resistance range will increase travel for any given input signal.

    Since I am controlling it with a Propeller chip sending out other pulse widths won't be a problem. I don't mind modifying a servo but I'd rather not take out the stops completely. I just thought by now there would be an off the shelf servo with the larger rotation. If you can find some for $1 each like the other servos you seem to find that would be fine with me!

    This is for one of the custom robots that I built with a servo mounted ping on the head. If I can easily get it to pan a full 180 degrees it would be much easier for wall following, etc. I've seen some mechanical adapters to increase rotation but would prefer to find a quick bolt in replacement for an existing servo.

    Robert
  • PublisonPublison Posts: 12,366
    edited 2011-10-17 13:19
    RobotWorkshop wrote: »
    Hello Jim,

    I am looking for a servo in a standard servo case similar to the one that Parallax sells. That way I can easily swap it out with the servo I have in place now. I'll look around on their website to see if I can find any other ones that can do 180 degree rotation in a standard case.

    Robert

    What erco said, and

    they don't seem to offer many of the Futaba's in custom rotations. They have Hitec's in the standard size, but they have a different spline, so the horn would have to be changed.

    Jim
  • ercoerco Posts: 20,259
    edited 2011-10-17 13:32
    RobotWorkshop wrote: »
    I don't mind modifying a servo but I'd rather not take out the stops completely.

    Many servos have internal stops you can whittle back some on each end. Some on the gear, some on the case. As long as the feedback pot was reasonably centered and still had some travel on each side, they work fine. I have completely removed the stops on a Futaba and CAREFULLY gotten about 250 degrees of rotation, but one false move and you can damage the pot.
  • RobotWorkshopRobotWorkshop Posts: 2,307
    edited 2011-10-17 13:46
    erco wrote: »
    Many servos have internal stops you can whittle back some on each end. Some on the gear, some on the case. As long as the feedback pot was reasonably centered and still had some travel on each side, they work fine. I have completely removed the stops on a Futaba and CAREFULLY gotten about 250 degrees of rotation, but one false move and you can damage the pot.

    That's why I prefer to have some sort of stops in there. I've only modified them for continuous rotation. I suppose it's time that I experimented on one to see if I can get more out of it.

    Going to an airtronics, hitec, or no name brand is ok if the stops will let it travel 180 degrees. I can just use the servo horn that comes with it.

    Robert
  • FranklinFranklin Posts: 4,747
    edited 2011-10-17 14:09
    This http://www.parallax.com/tabid/768/ProductID/101/Default.aspx says it will do 180 degrees.
  • RobotWorkshopRobotWorkshop Posts: 2,307
    edited 2011-10-17 14:12
    Here are a few links I found about altering the servos:

    http://mypage.yhti.net/~dmcdnld/s148retract.htm

    http://www.aeropix.ch/support/180DegreeServoModification_HS85.pdf

    Looks like I have another project this evening....
  • GordonMcCombGordonMcComb Posts: 3,366
    edited 2011-10-17 14:39
    Most of servo manufacturers have sail winch servos that will do 1 to 3 turns, using the standard 1000 usec span. Prices vary, as do sizes and quality.

    Options include the GWS S125, Hitec HS-785, and whatever equivalent Futaba and Airtronics sells. The GWS is going to be the least expensive. I think it goes for about 20 bucks.

    -- Gordon
  • RobotWorkshopRobotWorkshop Posts: 2,307
    edited 2011-10-26 06:37
    I appreciate all the comments and suggestions in this thread. I've never tried any of the sail winch servos and will have to remember those since I think they may be useful for other projects.

    At any rate I was able to get things working just the way I wanted with a slightly modified regular servo.

    As mentioned the standard servo that Parallax sells is rated for 180 rotation. The issue is that I needed it to pan a full 180 degrees so the pin module could face exactly 90 degrees on either side for wall following. The stock servo just didn't provide quite enough travel. I didn't want to completely remove the internal stops but I didn't want to tell the servo to drive up against them and fight with the stops either.

    So, I pulled the servo apart and with a flat straight exacto blade trimmed part of each stop back (without completely removing them) and also trimmed down the stop on the output shaft to allow for more travel before it hits the stops. Now I can easily have the servo move a full 180 degrees without hitting the stops. It took longer to pull out and re-install the servo in the robot than making the modification itself.

    Robert
  • ercoerco Posts: 20,259
    edited 2012-02-04 18:24
    Just picked up a pair of Hitec HS-311 servos from a local hobby shop for $10 each ($8 at Servo City). Entry level servo: no bearings, plastic gears. But no detectable play and silky smooth rotation lock to lock, well over 180 degrees. I'll estimate 190+ degrees. Perfect shoulder servos for my poor man's micro robot arm.

    http://www.servocity.com/html/hs-311_standard.html
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