180 degree travel with USB16?

Hi all,

I’m about to purchase the 16 channel USB servo controller and i read in the manual that because of the increased pulse width range possible with this controller, servos can be moved 180 degrees or more.

I’m trying to use 2 servos to rotate a pair of polarisers as part of a camera aperture. So my question is, can all servos be used to achieve 180+ degrees of rotation or only some brands/types?

If it is only some, can you suggest common servos that can do 180+? i’m hoping to get the little 9gram servos to minimize size.

thanks :slight_smile:

I’m personally fond of Hitec servos, which are usually advertised as having a 90 degree range (some stores will offer to modify them for 180 degree rotation, I’m not sure what exactily they do to them). Except for special-purpose servos that are specifically advertised as having less than a 90 degree range, I’ve found that Pololu servo controllers can move standard-size Hitec servos slightly more than 180 degrees. Actually, they can command the servos to move even farther, but you can hear the servo shuttering as it presses against the gear-stop which protects the internal potentiometer.

Offhand I can think specifically of the HS-311, HS-422, HS-475HB, HS-645MG, and the HSR-5955TG (which is actually sold as a 180 degree servo, but would be total overkill for your application). For smaller servos, I did once work on a robot that used some of the Micro-sized Hitec servos for a very small 180 degree pan/tilt platform, but I don’t remember the exact model. I would guess that any of them would work for you though. I’m also fond of the GWS NARO HP/BB micro servo, which Pololu sells, but I forget if it could reach a full 180 degrees (it came close to it at least).

Your project sounds very cool, but from your description I’m not sure why you need a servo to rotate 180 degrees, or even two of them for that matter. I’m imagining two sheets of polarized plastic over a lens, and if one is stationary the other only needs to rotate 90 degrees to go from transparent to opaque. Am I missing something?

In any event, if you only need to control two (really 8 or less) servos, and you’re comfortable with a small amount of wiring/soldering, you might consider getting a Pololu USB-to-serial adapter and a Pololu micro serial servo controller, which together cost about half the price of the USB 16 servo controller. The 16 servo controller is very cool though, and has the plug-and-play advantage.

Good luck!


Hehe yeah… it’s not really being used as a standard “shutter” type thing… and the camera isn’t really a camera per say… it’s more an array of ccd’s which i am using to evaluate the wavefront of incoming light. So the polarizers both need to move 180 degrees to be able to polarize the light at a very large variety of vectors :slight_smile:

I think i’m going to try a few of those cheap 9g ebay servos and see if they can do 180degrees and if that fails i’ll try some hitec ones.

Thanks for the reply :slight_smile:

I just noticed I have a GWS Pico+ F BB in my bag-o-servos in my office. I tried it out just now, and it gets slightly but definitely less than 180 degree travel (eyeballing it at 165). If full 180 is critical for you, I would stay away from the little GWS ones. If you do pick some up, I would be curious to know if the smallest Hitec servos still hit 180.