$5 Continuous Rotation Servos
http://www.ebay.com/itm/Spring-RC-SM-S4306R-Continuous-Rotation-Robot-Servo-360-degree-for-Robot-DW-/172172067295
I bought two and left some for you. Temporarily. Man up and buy fast before I hoard the rest!
BTW, these include a large servo horn disk which can be a wheel all by itself. Cut a slice of bicycle innertube and stretch around it for a grippy tire. Works great.
I bought two and left some for you. Temporarily. Man up and buy fast before I hoard the rest!
BTW, these include a large servo horn disk which can be a wheel all by itself. Cut a slice of bicycle innertube and stretch around it for a grippy tire. Works great.
Comments
@erco - see my bargain pick-up today in the General Section - You will likey!
Remind me to check spline compatability later, Futaba vs HiTec. Can't recall offhand, but it includes several servo horns anyway.
A pair of servos I do not like are my GWS CR servos. Blech, they are incredibly mismatched and require out of spec pulse width to reach reasonable speeds. This is odd because I've modified a pair of regular GWS BB servos for CR, and they're champs. I over volt them to 7.2 volts and they're powerful and responsive. My favorite pair of CR servos.
-Phil
http://www.rcmodelreviews.com/mg995review.shtml
You and I pounced on Pololu's FS-90R because they are the only 9g CR servo available. Fortunately, there are plenty of choices in the world of standard-size servos.
-Phil
I purchased four "MG996R" servos which turned out to be junk. The servos didn't have ball bearings and the servo quickly became very hot with mild use.
I posted some photos of the guts of my ebay "MH996R" servos and the insides of a couple different vintages of HXT12K servos from HobbyKing.
IMO HobbyKing is a good source for inexpensive servos.
Hobby King HX12K Metal Geared Servo
Hobby King Vigor VS-11 Large Servo
Hobby King HXT900 Micro Servo
Metal Gear 180 Degree Servo
The HXT900 servos will rotate a little bit more than 180 degrees.
In case any of you haven't seen my 32 servo demo, here it is.
The above video shows 16 HXT12K (or HX12K) servos and 16 HXT900 servos.
My Halloween Hex uses 18 HXT12K servos and 4 HXT900 servos (to control the eyes).
I'm not sure I would want to use these HobbyKing servos to control an expensive airplane or helicopter but I think they work great in robots.
I purchase a lot of stuff from ebay but I don't purchase servos from ebay. I'd rather spend a bit more and get servos, which have a much better chance of working well, from HobbyKing.
I will add that I got my Spring servos from US seller nyplatform, who makes it known that these are from China. It's possible that these from China are clones. Time will tell, I ordered a pair.
If I get a chance I'll make a quickie video later.
I found Spring's servos have some dimensional issues, which may or may not affect you. First is that while they have Futaba splines, the molding isn't quite the same, so horns and wheels can be hard to get on and off. Second, the top of the casing is ever so slightly bigger than "standard" servos. This can make it a challenge to insert the servo into certain mounts. YMMV.
At least, these issues were ones I ran into back in 2012 when spec'ing-out servos for my Popular Mechanics article. Pololu has a big a big proponent of these, and they've remained in stock fairly readily over the years, unlike the GWS S-35 continuous servo, which in my experience was had hit-or-miss availability. I'm not even sure they make it any more.
Exactly!
Edit: Per Gordon, it's got the Futaba spline, so you can use these metal servo horns: http://www.ebay.com/itm/New-Disc-Type-Metal-Horns-for-25T-MG945-MG995-RC-Servos-Robot-Arm-Round-5-Pcs-/181580932492
Well I certainly hope they live up to my hype!
That's cuz they aren't analog. A lot of "analog" servos now use digital control electronics, so there's far less drift in the error circuit (and they are surprisingly cheaper to make). Give it 1500 us, it goes to center each time.
In a follow up, let us know about the dimensionality issues these servos have been known for -- spline and mounting.
In fact, I've been mulling over a simple line follower (OK edge follower) based on 2 such CR servos driven by the same pulse from a 555 timer. Purposely offset the servos to drive straight forward at speed X at some value when a photocell is centered on the edge of the line. When it drifts off, one servo will slow, the other will speed up to turn and resume following the line.
Prolly Tilden or some other BEAM person has beat me to it. Too simple, too obvious.
It's possible it has a wider dead band, especially around 1500 us. The tighter the dead band (typically about 6-10 us for lower-end servos), the more drift you'll see. But I tell you what. Try again this Sunday when it hits 100+ in LA. Let's see what the temperature does to its stability!
I liked the GWS S35 continuous rotation servo, when you could get them. They were constantly out-of-stock at their US warehouse. It did not have a pot, and pulling one apart, you could see it was 100% digital. There were a couple of bypass caps, I think a resistor or two for various chores, and that was about it.
Fellas: Can we agree to disagree?
Will advise between beers. Happy Fathers Day to all in advance!
I'm starting to think that cheapie analog servos are also voltage dependent for their null point. We've all nulled and re-nulled for unknown reasons, maybe just because the battery voltage sagged a bit. Maddening with alkaline batteries. I'll have to test someday.
I read martin's earlier post, and we possibly had different vintages. Didn't notice anything too unsavory. I stopped using/selling them a few years before they went discontinued, as they became harder and harder to order from GWS, and they didn't want to do direct shipments from Taiwan for the smaller orders I was making. I don't know what changes might have been made in the last years.
The S35 was fundamentally their standard servo, altered in factory so it didn't have the pot. The low-end models didn't have ball bearing upper/lower, but bronze bushing -- being modeled after the venerable Futaba S-148. As they used the same electronics for all their "analog" servos, it's hard to know why there might have been a difference.
Out-of-spec: isn't a CR servo, by definition, out of spec? In that configuration, it's basically just an open loop motor that happens to use a fairly limited pulse train to control it. I know GWS *tried* to provide a better acceleration ramp on either side of 1500 us -- on most servos, you get pretty poor speed control. Maybe this resulted in having to go beyond the normal 1000-2000 us, or even past that.
$15@MCM $17@Fry's, FYI
http://www.ebay.com/itm/NEW-OSEPP-Arduino-Compatible-Servo-360-Degree-/371553165271
http://osepp.com/wp-content/uploads/2012/09/LS-3006_datasheet.pdf
Specs seem pretty decent (I'm guessing there's more plastic than the Spring RC model, considering the reduced weight). One thing confuses me, though. In the PDF, what does 6.8 (Maximum Travel) refer to?
I'll have to pass on testing them though. Still haven't gotten around to playing with the 4 I did get. (The VSCode extension is sucking up much more time than I was planning on...)
6.8 sounds more like torque. These are considered 6kg/cm servos.
My gut feel is that these SpringRC 4306 servos have a more stable null point and are better long-term for robotics use, even if they cost $7.19 now.