Hello all
I plan on buying HS-475HB and HSR-1422CR servos. I think both of them come with a geared shaft. As I understand it, It’s not a simple round shaft but a geared one, and the only way to connect anything to it is to use the horns. Therefore I need a horn. I browsed the product section and the only horns I found were the “Hitec Spline Metal Servo Horn” (Tapped and untapped - HMSH-02 and HMSH-01). Does anyone know:
are there other horns to choose from?
Is there a simple round shaft I can attach to the servo? and why do they manufacture the servo with the geared shaft in the first place?
Do the afforementioned horns fit these servos?
what is the distance between 2 opposite tapped holes in the horns?
Each servo comes with a hardware pack and a servo horn on the servo. You also have the option of replacing the stock servo horn with the metal SES type servo horns. You also get the metal servo horns for each servo if you purchase a six-pack of any type of servo. It’s a great deal! I purchased the metal servo horns for my servos, and it is very worth doing to use them with the SES.
Thx. If I buy a servo six pack, how many metal horns do I get? and are they tapped or untapped?
And one last thing, how do you connect the metal horns to the servo shaft?
You get one per servo and have the option of tapped or untapped. I suggest getting the tapped versions. I got untapped when I ordered the horns and really wish I had gotten tapped. You will be glad if you get tapped horns.
The metal servo horns mate perfectly to the servo spline, just like the stock horns do and they use the same screw. This is true for Hitec servos sold by Lynxmotion.
hobby servo output shafts are splined not geared. the hardware pack has several different horns all of which have mating female spline for the shaft. The horns are fastened to the shaft by a screw that goes through the horn into the end of the shaft.
different manufacturers servos, and even different class servos within a particular manufacturer, do not necessarily have the same spline arrangement. therefore it is important to make sure the horns you buy/use are intended for the servo you are using. the metal horns available from lynxmotion are intended for the hitec “standard” size servos (that their SES bracket series is designed around.)
I agree with linuxguy that tapped is preferable to untapped. an added benefit is you can use touch of non-permanent threadlock on the screws and get really solid connections to the servo that will not vibrate loose over time. The standard nylon horns with sheet-metal screws will eventually give some as you abuse them.
This is exactly what I have experienced using the non-tapped metal servo horns, and it is NO fault of the servo horn. I will definitely get the TAPPED versions of the SES servo horns the next time I order servos. I have to constantly re-tighten the servo horn screw for the pan servo of WALTER’s pan/tilt turret now.
How do you connect up to the un-tapped servo horns? I like (and bought) the 2-56 tapped ones, of course. Not that hard to thread the horns yourself! ;>)
I wish they’d used a 4-40 or whatever thread instead of the self-tapping thread in the end of the splined shaft. LocTite is a good tip.
Has anyone seen a broach to cut the 24-tooth spline that Hi-Tech uses? I need to run a small shaft, probably around 0.25", into a small miter gear. I might find a shaft adapter, but I’d prefer to machine the proper part myself.
The screws used to hold the horns onto the shaft may be different depending on the servo. I don’t remember the screws in my HS-5645 servos being self tapping, but an HS-422 which is all nylon might be. I don’t actually remember messing the the HS-422 though, just guessing.
The un-tapped horns I suspect work like a regular nylon horn and you use a pushrod connector that has a fastener on the bottom side. I suppose a self-tapping sheet metal screw might work but would have a hard time with the flexing I think. alternatively you just, uh, tap them.
I thought servocity had some splined shaft adapters now… if, you know, you can get them to ship some to you.
You have to use the four 2-56 size holes on the metal horns with the matching holes on the brackets or use the self tapping screws with the regular horns. The tutorials show which holes on the regular horns to use. It’s really hard to get the nuts on the screws unless you attached the horns to the bracket before mounting the horn to the servo. Believe me, I know all about this!
I have thought about creating a 3D model of the spline, but I want to do it from a proper 2D dimensioned drawing. With a proper 2D/3D model of the spline, you could do what you want.
The 422 is a self tapping screw. The 475 which has a carbonite (industrial plastic) also has a self tapping screw. Note these don’t have a sharp point like the self tapping screws in the #4 americal size. The 645 (metal gear) has a machine screw.
The untapped horns are good when you use 2-56 screws and nuts. Or they can be tapped for 4-40. They can to be because of a communication error between me and the manufacturer. When the untapped ones are gone we will not be ordering more.
OK, so the un-tapped holes in the metal servo horns are probably 0.089" (clearance for 2-56, tap size for 4-40), and can thus be tapped 4-40. Good to know. Yeah, I can imagine trying to get those little 2-56 nuts on!
It would be OK for a picture (3D model), but I would need VERY accurate dimensions of the tiny little spline. I might have to resort to a 3-wire measurement technique to determine the major and minor diameters of the spline. At this point, I haven’t determined if it’s a simple triangular-shaped spline tooth, or more rectangular. No rush, no immediate plans. If it looks reasonable, I can machine a cutter (broach?) from drill rod. With the proper temper, it would be able to cut quite a few splines in aluminum before getting dull.
OK, pushrods, like in the R/C model aircraft. I get the picture, but couldn’t envision using pushrods much in my robot (LM uses some bell-cranks, 'tho).
A sheet-metal self-tapping screw would be really tough to work with! But now that I know the hole size in the un-tapped parts, it makes sense.
I’ve seen these shaft adapters on servocity already, and they are o.k but i would have liked them to be with keyways instead of a threaded hole.
thanks anyway
Using some creativity you might be able to make your own shaft adapters. The below link has some pix of how I used a Radio Shack switch knob to connect a servo to a rotary switch shaft. The bottom pix show a quick way I attached a wooden dowel shaft to a servo for a test.
That’s one way to do it. I’m looking for a very compact solution, as I’m thinking of making a wrist design requiring using two R/C servos driving a wrist through a pair of bevel gears. The idea is to get the the bevel gear as close as possible to the body of the servo. I can machine a small flange to bolt up against the stock servo horn. Two servos and two bevel gears differentially drive a third bevel gear which carries the wrist. This gives both a rotate and a tilt to the wrist. Add a third servo or actuator to open/close the grip, and you’ve got a nice setup.
I don’t mind machining parts, but getting around the spline makes it harder to design/machine a compact wrist.
Another alternative might be to cut off the spline on the output shaft and remove enough of the shaft (or drill out the center of the shaft) to get down to the keyed hole where the keyed pot shaft resides. Then the pot could be lowered or part of the end removed such that an external keyed shaft could be inserted into the keyway.
