Pololu Robotics & Electronics
My account Comments or questions? About Pololu Contact Ordering information Distributors

Pololu Forum

Suitable metal horn for DSM44 with 20T 3.5mm and FT1117M 25T 6mm servo gear



I’m using Power HD High-Speed Digital Micro Servo DSM44, which is 3.5 mm diameter 20T teeth gear.

I’m trying to find metal horn for this motor, to add metal pin with screw on this arm, to get this kind of hardware in result, as shown with my 3D models for particular purchased servos:

This example shows only the desired specific principle of attachment of pin with arm (in this case with own hardware models) of particular motors, Instead thread attachment, which seems only possible way with default plastic hardware included with DSM44, but not suitable in my particular case.

Most horns I’ve found on internet is 15, 23, 24, 25 teeth, then diameter also should be wider. I can’t figure out, how to choose adjustable or compatible aluminum arm for particular motor, from 15-30 mm length, and able to be fixed on 3.5 diameter gear with 20T. It seems impossible to find metal hardware especially for DSM44

I found number of different hardware, but I’m not sure, which one would be appropriate for DSM44, some of them 3mm diameter, but 25T, it is also not clear if 3mm diameter hole will match 3mm gear, even if it is adjustable:

  1. SWB 1.5″ Half Servo Arm 3mm (Futaba)
  2. 25mm CNC Double Lock Servo Arm, 3mm Holes with M3 CNC Clevis - Futaba by Intairco IAC-620F-C
  3. Heavy Duty 25T Aluminum Servo Arm (Futaba)
  4. JIUWU 5PCS 25T M3 Metal RC Servo Arm Horn for Futaba Savox Xcore HL HSP HD
  5. 2PCS CNC Aluminum Servo Horn Arm 4mm/4.76mm EMAX Servo Shaft Oppresive Clamp Horn Arm ZENOAH Carburetor Throttle Rocker Arm
  6. 15mm Single Hole 25T Teeth Tooth Steering Half Servo Arm Horn For 1/8 1/10 RC Car Boat FUTABA/SANWA/TACTIC/ACOMS/TAMIYA/AITEC
  7. K-power JB2006 CNC 20T servo arm
  8. ALIGN D6EF Metal Servo Horn For Align Mini/Standard Servo
  9. Rc Model 24t Metal Servo Arm Horn For Remote Control Cars CJG
  10. X8 Metal Middle Horn Set
  11. DS6125 Metal Horns
  12. RCmall 6pcs CNC Servo Horn Arm Aluminum 25T For Futaba Standard Servos 25T Blue Xcore

Also I’m using FEETECH Mini Servo FT1117M which is 25T 6 mm. It seems easier to find hardware for this motor, and I hope this horns should be appropriate, because it is most popular 25T, but anyway, I’m not sure if there is a same diameter of gear hole:

  1. Apex RC Products 25T Futaba Red Aluminum Dual Clamping Servo Horn
  2. Axial AX30836 Aluminum Servo Horn 25T

Need your help to figure out, how properly choose suitable adjustable or compatible aluminum horns for this two types of servo from lists given above or maybe any other, to not order the wrong hardware for the number of particular servo motors used in my project.

Otherwise, the only way I see is to order 3D printing for desired arm. Most cheap would be cost $7 for one unit SLS (Plastic) Nylon PA12 100-120 and $18 with Binder Jetting (Metal) Steel/Bronze 420SS/BR, for example with Sculpteo online 3D printing service.

I don’t have electronic digital vernier caliper, so that’s how I managed to measure sizes with usual tool:

Teeth width: 0.6 mm
Teeth peak diameter: 3 mm
Teeth base diameter: 3.5 mm
Teeth number: 20

Here is my model sizes for solid print, in this case plastic also may be useful, because problem is that it is not possible to attach such tiny shift to DSM44 arm with 1 mm hole, so it’s possible not to use metal, but in both cases, I’m not sure about combine gear with 3D printed arm teeth, considering the behavior of such materials and very small size, if they will connect to each other with given sizes, will not get stuck or stagger:

Teeth width: 0.4 mm
Teeth peak diameter: 3.1 mm
Teeth base diameter: 3.6 mm
Teeth number: 20

I can’t find scheme for this particular hardware, to not make a mistake:

Any guide, advice or example would be very helpful

DSM44 servo failure


Those servos do not have much torque. Is there a reason the normal plastic servo horns would not be suitable for your particular application?

We have not tried those particular servo and servo horn combinations together, so unfortunately, we cannot offer advice on which one fits best. We also do not have a specific recommendation for metal horns you might be able to use with those servos, but you can find specifications for the for the servo spline on the FEETECH mini servo FT1117M on its datasheet which can be found under the “Resources” tab on the product page.

If you do find a good solution, we would be interested in hearing what you went with and how it worked out.




Thank you for feedback

Yes, I’ve used both, as physical devices and this datasheet to create models of servo motors (shown above) to include it into my mechanic assembly design, in its natural scale, form and view, since I have not found 3D models for particular devices on the internet. Sure FT1117M with horn gear spline 25T (5.8mm) should be easier to find, but main problem with DSM44.

Motor accelerates mass about 50-200g maximum, 1.2 kg more than enough for my mechanics, I’m happy about speed and power, works exactly as needed. Drawback in my particular case is a hardware, because my mechanics requires 7mm shaft on arm. Problem with exist arm, it is impossible use 1mm hole for separate attachment, it is suitable only for thread.

So, I’ve designed desired horn for DSM44, and already ordered single test unit by online 3D printing service. But I’m worry about two things with this solution, If my quite random calculation (given above) will combine printed teeth with motor gear, and behavior of material in terms of expansion or reduction during melting-solidification, and material itself:

As you can see, solidity check shows fragile color on the peak of teeth with (left view) image. Well, original teeth also have some microscopic damages on peaks, if you remove horn several times and put it back again, in spite of that, keeps horn on the gear well. I did not ordered metal part, because solid good quality plastic must be enough for my project, and mistake with metal part may be expensive, so first of all I need to check Nylon. Let’s hope, that a group of twenty teeth will pass and hold each other well, in addition with a help of screw on top. We’ll see



I can’t say for sure, if it is solution for any case with similar requirements, but it works well for my mechanism - gluing of original hardware with 3D printed arm, example show here DSM44 servo failure


I’m glad you figured out something that worked for you. Thanks for letting us know what solution you figured out.