3D Printed Robot Actuator

A high speed and high torque robotic actuator using low-cost brushless motors, custom controller, 3D printed parts and bearings.

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I wanted to make a quadruped or biped with enough power to jump off the ground. Typical servo solutions were not good enough.

Design sections
Mechanical - Cycloidal gearbox with rolling elements, bearings and dual input and output shafts
Motor - Low-cost high torque Brushless outrunner using Multistar Elite Motors
Sensors - Dual absolute magnetic encoders for motor position and joint position
Electronics - Custom PCB including Mosfets with Mosfet driver DRV with Cypress PSOC4 SOC, sensor inputs and communications. Plus Magnetic Encoder PCBs
Software - Field Oriented Control (FOC) for position control. Mosfet Driver, Encoder and CAN communications.

The purpose of the Actuator is to create a design than I can easily make with a 3D printer using cheap and powerful Brushless motors from China. I have three prototype sizes of Cycloidal gearboxes 44mm, 60mm and 78mm diameter. The size of the motor, number of poles and their shafts are also adjustable.

Repaired Pack and go file for SEA leg

x-zip-compressed - 28.52 MB - 04/24/2019 at 16:48


PSOC4 Project files Hardware and software (code) files More CAN comms and move instructions

x-zip-compressed - 1.76 MB - 10/23/2018 at 16:28


Full Tail CAD Files Inventor Pack and Go

x-zip-compressed - 21.73 MB - 10/21/2018 at 17:40



Full Tail Step Files

stp - 3.93 MB - 10/21/2018 at 16:28



Full Leg (with SAE) Step files

stp - 5.83 MB - 10/21/2018 at 16:23


View all 16 files

  • 1 × CY8C4247AZI_L485 PSOC 4 SOC uC with FPGA and CAN
  • 1 × DRV83055PHPR MOSFET Driver with SPI and 3x Current Amps
  • 2 × AS5147-HTSM 14-Bit Magnetic Absolute Encoder Sensor
  • 6 × SIR638ADP-T1 N-MOSFET 40V Ron 1mOhms (100A*)
  • 1 × MCP2557FD-H/SN CAN Transceiver

View all 11 components

View all 34 project logs

  • 1
    Actuator Assembly

    1x Brushless motor with extended shaft (6mm Silver Steel)

    1x Custom Brushless Controller Board

    2x AS5147 Absolute Position Boards

    2x 6mm x 2.5mm Diametric Neodymium Magnet

    12x 3D printed parts

    16x 5x8x2.5 bearings

    2x 6809 Bearings

    5x 12x18x4

    1x 6x10x3

    8x 3mm dia x 30mm Silver Steel shaft

    26 (or 13) 3/32" x 28mm Silver Steel shaft

    26 (or 13) 1/8" x 16mm Brass tube (thin wall)

    24x M3 bolts

    10x M2 Bolts

    3x PZT screws

    1x M6 thin wall washer

    1x 2mm dia x 11mm Silver Steel shaft

  • 2
    Sources of information


    • CCDIY 3D filiment
    • Plaig Bearings
    • MiniTech
    • Digikey/Mouser
    • Apollo Bearings

    Favorite Makers

    • Makers Muse
    • AVE
    • Clickspring
    • Tom Stanton
    • Ivan Miranda
    • James Bruton
    • Gear Down For What?
    • MRB Engineering
    • Thomas Sanladerer
    • ODrive Robotics
    • Benjamin's Robotics
    • Laura Kampf
    • Tested

View all instructions

Enjoy this project?



outkasst wrote 12/19/2022 at 20:29 point

Hi Paul, I sent a note to the application. i need to have some targeted iimprovement on this design for prosthetic elbow design. i am a father a child who needs one, i need to work or get some work done on this specific design idea.. thank you 

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Tor wrote 08/06/2021 at 17:56 point

Hey, thanks for making such a great project public and taking the time to document it so well. All the best!

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tyler wrote 08/13/2020 at 20:25 point

what did you use to design the gear profile? everything i find is using java or fusion360, both of which im not sure how to use (and i dont own fusion360)..

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mrninhvn wrote 10/07/2019 at 13:06 point


How much does your quad robot weigh?

Thank you!

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Paul Gould wrote 10/07/2019 at 13:22 point

I estimated between 14-15kg with head/tail and batteries. Which seamed a bit "fat", so I'm making a simpler one with no SAE (springs) and a simple head and tail. It will be about 9-10kg.

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max wrote 07/21/2019 at 04:59 point

Hi, your project is very, very nice. I'm considering to try it out. I was wondering, how large is your backlash? Why do you feel the need for two encoders? How will you use both in your control loop?

Also, I don't find the code for your mkr zero port (have you abandoned that front?)

Thanks a lot

  Are you sure? yes | no

Paul Gould wrote 07/21/2019 at 06:09 point

I have 6 of these actuators and each one has a different backlash. Most have about 0.3mm @ 200mm. One has 0mm and one has 1mm @ 200mm. The main reason for the two absolute magnetic encoders is so I know where the motor is at power up and I know where the joint is at power up. There is no referencing or calibration required after each power up. This has to be done only once and the offsets stored in FLASH/EEPROM. I have two separate control loops. One for FOC of the motor-position and one PID loop for joint control. The output of the joint control just tells the motor the direction and speed/power.

  Are you sure? yes | no

Paul Gould wrote 07/21/2019 at 12:25 point

I'm still working on the Arduino Zero/SAMD21 port. I'm slowly putting the individual feature code on git. It as taken a back seat while I work on the CAD and electronics.

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max wrote 07/22/2019 at 18:52 point

Thanks for the very complete answers.  I really hope to find time to try out you design and eventually collaborate. Do you think it could scale well to smaller scale motors/gears?

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Ryanwallace18 wrote 06/10/2019 at 03:14 point

What modes and input signal types does the motor controller support? Step/Dir, position, torque etc.

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Paul Gould wrote 06/10/2019 at 04:27 point

At the moment it supports simple CAN packets (goto position) and UART commands (goto set position and move x degrees). I will add others types and more features as I need them.

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Daren Schwenke wrote 05/10/2019 at 23:03 point

Greetings again @Paul Gould   I have private messaged you.

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praveen wrote 05/10/2019 at 05:57 point

sir may i know what is the reduction ratio of this cycloidic gear box

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xvart wrote 05/10/2019 at 05:23 point

So how long do the plastic (I guess cycloidal part) inner gears last under load???

Also what is the wear rate on the pins and would it be better to use pins with bearings.

  Are you sure? yes | no

Paul Gould wrote 05/10/2019 at 12:17 point

I'm not sure. I've only really be testing at about 10Nm max, as this is all I need. The wear seems good so far. It is 3D printed ABS, don't expect too much. If you use bearings for the outer pins the diameter would be large, which means the reduction ratio is less and the pressure angle lower (torque produced in the wrong direction).

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Alexander Zipper wrote 04/24/2019 at 13:33 point

Hey Paul! Amazing project, I can´t stop reading all the instructions and logs...

I wanted to download all the files but unfortunately i am not able to download  the file

Is it offline?


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Paul Gould wrote 04/24/2019 at 16:50 point

Thanks, I have just uploaded it again, please try it now

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Alexander Zipper wrote 04/26/2019 at 15:33 point

Thanks its working now :)

Do you think 25% infill and 1.2mm wall thickness is enough for those parts?

  Are you sure? yes | no

Paul Gould wrote 04/26/2019 at 16:54 point

Hi Alexander. I would suggest printing a single actuator first before you get to the leg. The SEA leg is complex. I've put it on hold while I develop a simpler quad ( See the tail project). I was trying to literally run before I learnt how to walk. With that said, if you can print the leg and learn more about it then maybe you can teach me somethings. It is open source after all.I use ABS 75-85% infill, 2-3 perimeters 0.4mm nozzle, 0.2mm layer height. Printed on a perforated board with a 3 layer raft, to stop warping. Also what controller are you planning on using?

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Alexander Zipper wrote 04/26/2019 at 17:56 point

Alright I already have started to print some parts in PLA with 25% infill, 4 perimeters and also 0.2mm layer height but I guess I should increase the infill.
I just wanted to build that leg and understand how it works :D I prefer to hold something in my hand...even if PLA is not very useful to print gears.

I was really mesmerized by that video testing the leg... It looks like it is by far the most promising leg for a robot dog.

Right now I really have no idea what controller to use. Some days ago I explored the OpenDog project by James Bruton (some people mentioned it before in the comments) and he is using the ODrive for his brushless motors.
I think this is okay for his project but it is way too expensive for a hobby project in my opinion...
What do you think about using an Arduino Mega like he did?

Today I was looking for the 5008 Multistar Elite Motor but it looks like they are not in stock anymore... while printing all the parts I wanted to solve the question about the controller...maybe there is a suitable open source solution?

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Paul Gould wrote 04/27/2019 at 01:57 point

I'm now using Gartt ML5010 300KV from They are good price and already have a small mounting plate. Controller information to come shortly.

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Paul Gould wrote 05/10/2019 at 12:18 point

How is the design going?

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Alexander Zipper wrote 05/12/2019 at 11:19 point

Hey Paul! 

Thanks for asking :)
I am really busy right now with our baby so my printer is not running right now ;)

Some parts are printed and I ordered the Gartt ML5010 motors since I couldn´t find any other motors with similar technical specs.

I can´t wait to test the leg!

Have you tested your brushless motor controller yet? The PCB looks fantastic!

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Rob Menting wrote 03/23/2019 at 14:28 point

Hi Paul, do you use the current for force/impedance control or do you use some extra sensing?

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Paul Gould wrote 04/25/2019 at 15:21 point

No, nothing yet.

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perry wrote 12/23/2018 at 02:34 point

Hi, Can you tell me where you got the extended axle shafts? and motor mounts?


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Paul Gould wrote 12/26/2018 at 14:05 point

motor shafts are silver steel rob from then cut to length and file a flat spot for the grub screw. The motor mount is the one that comes with the motor, it has just been attacked with a hacksaw. I have just got some of these which will not need the mount to be modified.

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perry wrote 01/02/2019 at 16:22 point

Thanks a lot Paul. Appreciate the links. My shafts have grooves in them for the circlips. I was wondering if you found shafts that had the groove in them already. I guess I could use collars or something on straight shafts.

  Are you sure? yes | no

Paul Gould wrote 01/03/2019 at 00:03 point

Hi Perry, I have not found any off-the-shelf shafts that would suit what I need. You could make a groove with a saw or go to your local maker space and find someone with a lathe to make one for you.

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perry wrote 01/03/2019 at 16:42 point

Thanks again Paul. I have a lathe so I think I will have a go at it.

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Jarek Ceborski wrote 12/16/2018 at 21:13 point

Hi Paul, I'd like to say that your contribution is remarkable - thank you! I've picked your actuator, among all others I've ever found, to test in my mobile robotic arm :) Fingers crossed for the Arduino version you work on!

  Are you sure? yes | no

Paul Gould wrote 12/26/2018 at 15:02 point

I have just finished an anti-backlash version of this gearbox which I will upload in a few days time. I am still working on the Arduino version. I'm having trouble getting the SPI with DMAs working on the mkrzero. Maybe now I'm on holidays I will have some time to work it out. What sort of torque and speed are you aiming for on your joints?

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Jarek Ceborski wrote 12/26/2018 at 19:54 point

Anti-backlash version, that's great Paul! I don't have experience with DMA, but I had some issues with mkrzero in the past - with interfacing IMU mpu-9250. Ported the code to both Nodemcu v3 and STM32 (blue pill) and worked without any issues. Maybe that will help you too. For the robot a 300kg/cm (30Nm) torque would be ideal, but for proof-of-concept 10Nm in sufficient. For speed 20-30RPM is enough.

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Paul Gould wrote 01/03/2019 at 00:06 point

Hi Jarek, I have finally got the SPI with DMAs working. Next is the ADC with DMA and RS485. I will then make a board. What voltage and current would your motors work at?

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Jarek Ceborski wrote 01/04/2019 at 08:23 point

Clapping and fingers crosses! I have exactly the same motors as you.

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Jin Han wrote 10/29/2018 at 19:57 point

Hi, just a quick question on the PCB design (specifically for the encoder).  The schematic says "NF" which I know that not-fitted, but does this mean that you don't use any resistors at all? or what are the values for the resistor? I'm trying to make them in bulks and have PCB companies to assembly the board for me as well.

Also are the sizes for capacitors and resistors?



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Paul Gould wrote 12/26/2018 at 14:17 point

"NF" is "not fit" or no resistors. There are for optional extras. R1 (0 Ohms) is for 3V3 operation. R2 (0 Ohms) is needed if this is the last one in the SPI chain. R3 & R4 (1K) maybe needed for noise issues. All of the components are 0603 except R2 which is 0805

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Dan Royer wrote 10/27/2018 at 17:31 point

Hi!  Saw your latest Youtube (subscribed) and I'm interested in using a version of your actuator design in the next Sixi robot.  Our worst case at the base has a 20Nm holding torque.  Can you advise us how to proceed, please?  We'd love to collaborate.

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Dan Royer wrote 10/27/2018 at 17:35 point

Also we're interested in making a version that mimicks ulna rotation between wrist and elbow - so the input and output mounting brackets are coaxial to the rotation.  Have you spent any time on that, and if so what are your thoughts?

  Are you sure? yes | no

Paul Gould wrote 10/28/2018 at 04:00 point

The actuator is very rigid because it has both top and bottom housings and output shafts. I'm not sure how to make it rigid for ulna joints, I'll think about it. What angle of rotation do you need?

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Paul Gould wrote 10/28/2018 at 03:57 point

Hi Dan. Yes, we can collaborate. My suggested starting point is with the CAD. I'm using Autodesk Inventor. I think that you are using Fusion360. What format would you like the CAD in? Can you use the "pack and go" files that I have already uploaded?

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Dan Royer wrote 10/28/2018 at 18:47 point

fusion would be great. We probably have to make a gearbox at the shoulder that is stronger than your current model. What do you think of


I’d love to have a parametric way to make the gearbox I need, then follow your wiring recipe. In your experience, will this generator work for among the printable profiles?   Is your package already parametric? Sorry I’m not up to speed yet.

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Paul Gould wrote 10/29/2018 at 03:00 point

You should be about to use the ipt files from the "pack and go" as per the instructions

I haven't used Fusion 360 but the script from the reddit should be useful.

I have created a parametric in inventor. I doesn't port well.

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Paul Gould wrote 10/28/2018 at 04:07 point

What motor/controller did you have in mind?

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Dan Royer wrote 10/28/2018 at 20:07 point

I’ve used a Rumba board until now (6steppers). Since you use dc im looking at odrive x3

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agenthimzz wrote 10/19/2018 at 18:10 point

Hi, Himanshu here from Youtube.. 

So, I have been thinking of this 4 legged robot and have observed that it is much better if the robot has a low Unsprung Mass. 

In Automobiles:

Unsprung mass is: wheels and Suspension.

Sprung Mass is: Body, Engine, Transmission, Chassis.... (and all other things)

It is said Unsprung mass should be very less so that when the car moves and goes over bad roads the Sprung Mass stays at almost level and Unsprung mass only moves and passengers feel very less vibrations

Hence instead of attaching the lower leg directly to the motor.. a Pulley would be connected. this pulley belt will be going above the motor, present above the Hip joint motor. and belt will be having tension using a spring return system like in 3D printer Extruder.

This definitely increases complexity and difficulty in designing and simulating but.. MIT Cheetah 3 is based on this design improvement. 

and the current Hub motor design is followed by ETH Zurich.

I don't know what Spot Mini does but they do it better, so if you find their method then do that.

  Are you sure? yes | no

Paul Gould wrote 10/20/2018 at 00:28 point

Hi agenthimzz, I would like to have as little unspring mass as possible. It was a trade-off between total weight/complexity and unspring mass. The actuators were designed to be integrated into the joint and were made as compact as possible. I found that if I used 3D printed parts as "Fixed-Fixed Beam Moment" instead of the normal "Fixed-Free Beam Moment" they were much better. There were also designed to be linked together in various combinations to form robot arms or humanoid robots. 

This design also meant that I could test my parallel linked series elastic actuator set-up. 

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AVR wrote 10/19/2018 at 17:04 point

Been following this project for a while, its huge for open source robotics!

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Paul Gould wrote 10/20/2018 at 13:50 point

Thanks AVR. I'm hoping that making the actuator work with Arduino will make it useful for more makers. I think that a combination of this and the "gear down for what" gearbox will make for a perfect system.

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jamma wrote 09/21/2018 at 14:36 point

Beyond the challenge of it, why did you create a custom controller vs the oDrive? Do you see any issues with oDrive and your actuator design for mere mortals like me who would go that route?

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Paul Gould wrote 09/21/2018 at 15:21 point

I large part of it was to see if I could make it my own way. Mainly using Voltage FOC with a saddle lookup table on a CPU with no floating point. ( ~10 lines of FOC C code). I wanted full control over the actuator with room to grow as I learn more. The PSOC4 is my favorite uC/SOC, plus it has a little FPGA and easy CAN comms. I can connect any type of encoder up to it for motor and joint control. I didn't like the calibration set-up of oDrive (you have to reference every power-up). Using Voltage FOC motor control and dual magnetic encoders, I can tell where the motor and the joint is at any time. I am currently adding Series Elastic to the actuator. The FETs I use are very low R-on. The board also fit's my space requirement and I can make them with a simple soldering iron.
oDrive are a great idea (I've never used one) and they will add more features over time. There is a large community following and they are currently working on absolute encoders, CAN comms, a smaller single axis board and more control schemes. The oDrive CPU is very powerful and has room to do some much more. YOu can modify the code to suit your needs.
The PSOC4 is not an easy CPU/SOC system to learn. Half the work is done in the CPU and half in the FPGA section. Debugging errors can be a pain.
I started looking at porting the design over to a SAM D21 (Arduino Zero) but I didn't like the SPI. I will work more on this in the future as having an Arduino brushless actuator controller will make the project more accessible to more makers.
I hope this helps.

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Donovan M. wrote 09/07/2018 at 12:44 point

Great work! I like the compactness of the gearbox system.

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lion mclionhead wrote 07/08/2018 at 07:09 point

Didn't have much luck with this concept.  Direct drive is a bit too power hungry.  Modern brushless servos can do pretty incredible things for a lot less money.

  Are you sure? yes | no

Paul Gould wrote 07/08/2018 at 09:09 point

Hi lion, this design is not for everyone. It's not direct drive, the cycloidal gearbox is 25:1 reduction. The cost is about $150 (the time is huge). The aim is 20Nm (200kg-cm), with speed of 0.05sec/60deg (testing required). The backlash is extremely low and it also backdriveable. I created this because I couldn't find a servo that suited me, if you know some good servos please let me know.

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