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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.

Leg.zip

Repaired Pack and go file for SEA leg

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

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WS3.cywrk.Archive02.zip

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

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tail.zip

Full Tail CAD Files Inventor Pack and Go

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

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6807_tail.stp

Full Tail Step Files

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

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6908_LEG.stp

Full Leg (with SAE) Step files

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

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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

  • Arduino Brushless FOC Controller - Development

    Paul Gould10/20/2018 at 08:08 4 comments

    The Cypress PSOC4 Controllers are not very common in the maker community. As I would like more makers to be able to use/modify/improve this Actuator, I am designing an Arduino version. It will be based around the MKR Zero with the SAM D21.

    Earlier I got the Centered Aligned PWM working for controlling the MOSFETs for driving the Brushless motor. Next was the SPI for reading the Magnetic Absolute encoders for the motor and joint positions. The SPI on the SAMD21 only has a single buffer which is not time efficient for this application. It does have a DMA on the SPI which is much more complex but the most efficient for operation. The problem is that it is not a standard feature for the Arduino system. 

    I started with the following information.

    https://forum.arduino.cc/index.php?topic=344029.0

    Now the Adafruit Zero DMA library makes it too easy

    https://github.com/adafruit/Adafruit_ZeroDMA

    and can now be installed by the standard Arduino IDE --> Sketch --> Include Library --> Manage Libraries

    It also support Interrupts "dma_callback" to tell when the transfer has completed.

  • Robot Control software (for initial testing)

    Paul Gould10/13/2018 at 16:09 4 comments

    Visual Studio and C# in .Net was used to write a simple test program. An X,Y foot position is generated, converted to hip and knee angles using Inverse Kinematics and sent to the serial to CAN converter (spare PSOC actuator controller). These packets are addressed to the two robot actuators to move to the required position. A second mode just returns Joint positions.

  • Series Elastic Actuator - CAD

    Paul Gould10/13/2018 at 16:02 4 comments

    I have modified the base robot actuator to make it into a full robot leg for a quadruped. It has a parallel linkage with springs and 2 robot Actuators. This means that the spring direction changes from rotation to almost vertically linear when the leg is in the standard walking positions. Different strength springs can be swapped for testing, with the aim to store energy at the end of a jump cycle and use it for the next jump. It will also be used for efficient walking/running.

    Everything rotates around the same joint, for the centre joint, described from top to bottom of the drawing.

    • 6mm shaft running most of the way though
    • Motor bell and flux ring
    • Stator housing with 2 motor bearings
    • Top outer housing
    • Top Thigh plate with 6809 bearing
    • Top Series elastic output plate (also actuator output shaft) with 6809 bearing
    • Eccentric Cam with 2 lobes with 2 bearings each and 2 cycloidal gear
    • Bottom Series elastic output plate (also actuator output shaft) with 6809 bearing
    • Bottom Thigh plate with 6809 bearing
    • Bottom shaft mount with bearing
    • Motor angle Magnet holder
    • Motor magnet (diametric)
    • Bottom outer housing
    • Motor position PCB
    • Silicon steel flux cancellation plate (0.5mm thick)
    • Joint position PCB
    • Joint bearing holder (old protects the PCB)
    • Joint magnet (diametric)
    • Joint angle plate with bearing

  • Quadruped Jump Jig

    Paul Gould10/13/2018 at 15:42 0 comments

    Components

    • 2x Linear rails
    • 4x Linear Bearings
    • wood and screws
    • 11.1V 1500mAh Lipo Battery
    • Analogue Current Meter 20A
    • Digital Current / Voltage Meter
    • Robot Leg

    Assembly

    The rectangular extrusion is the same size as the quad's "backbone" and the robot's hip joins with the following design.

    The robots hip has three mounting points to the rectangular extrusion.

  • PSOC4 - CAN and FLASH

    Paul Gould10/13/2018 at 15:23 0 comments

    The PSOC4 and the IDE Creator helps you to write code for the Arm processor, the CAN peripheral and the FPGA logic. When you use it for standard operations, then you rarely need to go deep into the component datasheets to make the design work as required. The examples are quite useful.

    But, if you want to design something that is not normal, then it is hard to find the information required.

    CAN Problem 

    Each Actuator needs to have it's own individual address or CAN IDs. In my robot there will be at least 12 actuator controllers that will be CAN slaves, with one controller configured as a CAN master.  This requires setting the CAN Receiver Mailbox ID via software. It is normally done in the .cysch CAN configuration page.

    There is a easy for setting the Transmit message ID.

    CAN_SET_TX_ID_STANDARD_MSG(0,(TX_ID));

    There was no such sub-routine for the setting the RX message ID. So after a lot of reverse engineering and some trial and error, the following code is used. Set different IDs for each actuator. 

    CY_SET_REG32((reg32 *) (CYREG_CAN0_CAN_RX0_ACR), (0x0200000u*ID));

    This only works for Message Mailbox 0 and is good for my current needs. A second mailbox maybe required in the future that will be a broadcast message so all the receiver message Mailbox IDs will be the same. This could be used for an Emergency stop message. Send one message and all the actuators stop.

    Additional CAN information

    If the RTR in the Configure 'CAN' is enabled, the CAN transmitter will re-transmit the current packet until the received sends an Acknowledge packet back. 

    FLASH Problem

    As each Actuator needs to have it's own individual ID, this value and some others needed to be stored in flash memory. But when the PSOC4 software is updated it erases ALL of the standard FLASH. It also does not have EEPROM. It has an emulated EEPROM but again this is erased after updating the program. The PSOC4 I'm using has user FLASH but there is no information on how to use it. 

    The set-up code is

    #include <CyFlash.h>
    
    #define CY_TEST_USER_FLASH_ROW       (CY_SFLASH_NUMBER_USERROWS - 1u)
    #define CY_TEST_USER_FLASH_ADDR      (CYREG_SFLASH_MACRO_0_FREE_SFLASH0 + CY_TEST_USER_FLASH_ROW * CY_SFLASH_SIZEOF_USERROW) //255
    uint8 Flash_User_Array[CY_SFLASH_SIZEOF_USERROW];

    To Read from FLASH, I set up a RAM array the same size as a FLASH row.

        uint16 i;
        for (i = 0u; i < CY_SFLASH_SIZEOF_USERROW; i++)
        {
            /* Define source value */
            Flash_User_Array[i] = (*((uint8 *) (CY_TEST_USER_FLASH_ADDR + i)));
        }

     To Write to FLASH, I set up a RAM array the same size as a FLASH row.

        cystatus returnValue = CYRET_SUCCESS;
        returnValue = CySysSFlashWriteUserRow(CY_TEST_USER_FLASH_ROW, Flash_User_Array);

  • Arduino Brushless FOC Controller

    Paul Gould06/18/2018 at 14:04 2 comments

    In an effort to make the controller accessible to more makers I've strated designing an Arduino based system. It uses the SAM D21 G 32-bit micro-controller as used on the MKRZERO board. This chip has an advanced Timer Counter Controller which can generate three centre aligned PWM signals. After sorting out the correct pin mapping it is up and running.

    The code is based on information provided in the Arduino forum by MartinL.

    https://forum.arduino.cc/index.php?topic=346731.0 

    Now with deadband

    I will create a github shortly

    Next up dual SPI. One for the absolute magnetic encoder sensors and the other for the FET gate Driver IC.

    PID and FOC should be easily ported across.

    Voltage and current measurement may be difficult because the Arduino doesn't support free running sequential ADCs very well.

    The SAM D21 does not have CAN commucations so it will need RS485 and USB.

  • Biped Design

    Paul Gould06/09/2018 at 15:22 1 comment

    6x Actuators

    Do all the joints need the same size actuators?

    Are different reduction ratios required? Higher torque less speed.

  • Mini Quadruped Design (CAD)

    Paul Gould06/08/2018 at 16:16 0 comments

    12x Mini Actuators

    Needs a head, tail, electronics and batteries. 

    Two leg has been 3D printed. Some assembly required. See end of YouTube video. It's the little one on the left.

    I have made some 2 axis legs for testing. They have enough torque but the speed is huge, even under load. Jumping is not impossible. 

  • Robot Quadruped Tail

    Paul Gould06/08/2018 at 15:41 0 comments

    Tail Design

    3x Mini Actuators (5 Joints)

    Joint 1 is tail "wag"

    Joint 2 has figure 8 pulley to Joint 3 and the angle is opposite

    Joint 3 is actuated up/down

    Joint 4 is actuated up/down

    Joint 5 has a figure 8 pulley to Joint 4 and the angle is opposite

    Distance between Joints is 100mm

    Motors are Multistar Elite 3508

    The tail is used for the quadruped's balance.

    Was thinking about putting an end effector, camera or gripper

  • Robot Arm Design

    Paul Gould06/08/2018 at 14:38 0 comments

    Robot Arm

    3x Large Actuators

    2x Small Actuators

    1x Gripper ???

    Based on previous testing, it should be able to lift 0.5kg at the end effector.

View all 18 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

    Suppliers

    • 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

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Discussions

Alan Timm wrote 06/28/2018 at 18:05 point

Hey Paul, I've been really studying your actuator model, and I have a few suggestions that I'm incorporating into my build.  The rest of my parts should be arriving next week.  Here's a link to my work in progress model:  https://a360.co/2yxWgQO

 - If you separate the eccentric lobes you can pin them separately during assembly. I'm pretty sure that having a single pin driving both lobes is going to be the weakest point at load.  I'm also looking at 2mm v 3mm retaining pins.

 - I've reduced the drive rollers from 8 to 6, and included 6 through hole bolts.  The locknuts need to be trapped into the motor bracket earlier in the assembly.  This should make the actuator much stronger.  I'm on the fence between having 6 drive rollers and 6 bolts, or going 4 and 4.

I hacked together a parametric cycloidal gear box generator into Fusion 360, changing ratios is almost automatic by adjusting the parameters.  I've been going back and forth between a 26:1 and 32:1 gear reduction for the Gartt 5010.  Out of curiousity, what design software are you using?

https://i.imgur.com/29jmPCP.jpg

https://i.imgur.com/juXSZ5D.jpg

On the electronics side, I have even more catching up to do.  How are things going on your next controller?  Depending on how invested you are in your SAM D21 design, the stm32f103c8 may be another option.  It's what's used in the "STM32 blue pill" board.  They're cheap, fairly well supported, and include CAN as well as a bunch of other features.  

  Are you sure? yes | no

Paul Gould wrote 07/02/2018 at 15:42 point

Hi Alan, Adding the bolts is a good improvement. Just be careful you still have enough material at that diameter so that it doesn't weaken the gear. I tried to replace the 3mm rods with M3 bolts with a long shank. I had some problems getting the alignment correct. (It also took along time to take the unit apart). 

I have just created a parametric cycloidal gear in Autodesk Inventor (All my CAD is done in this program, I have it on my laptop for my day job). 

Have a look at the testing of the motors here http://build-its-inprogress.blogspot.com/2016/01/motor-characterization-for-small.html

This is main reason I choose the Multistar Elite 5010/5008. I am looking at Foxtech and Arris for their 5010 motors but I just searched the Gartt 5010 on ebay and they are 1/2 the price. mmmm

I got the SAM D21 up to the point where I don't like the CPU. The SPI only has a single buffer TX and RX and requires the DMA to use it properly/efficiently. I wanted to create an easy solution (Arduino) for brushless actuator control. I'm not sure if I can hide the DMA in an Arduino library. I have thought about using the STM32F3 family but the PSOC4 is just so good. The problem is that is too complex for most makers.

I have some STM32Fx development boards so I will see what i can up and running. The stm32f103c8 will still require the use on DMAs for the SPI unless I change the structure of the code/interrupts.

  Are you sure? yes | no

MattB wrote 06/26/2018 at 04:00 point

Hi! In your video you showed it pulling 10 Nm @ 12 V with a peek of 5 amps. This is with the Multistar elite 5008 & a 26:1 gear ratio, right?

I love the results, but am a bit confused. The 5008 is 330 Kv, which would be a Kt roughly 0.029 (Nm/A). 

0.029 * 5 = 0.14 Nm * 26 = 3.75 Nm

Which is way under 10 Nm. Is there something I'm missing?

  Are you sure? yes | no

Paul Gould wrote 06/26/2018 at 10:49 point

Hi MattB, Your maths is right. I have never done the Kt calc befre. Where did I go wrong? 

The arm is ~330mm between the centre of the 3kg weight and the pivot point. The battery is 3 cell Lipo ~12V. The cheap current sensor from Hobby King max value shows ~5Amps. I would guess that the filtering / averaging / update rate of the current sensor is not showing the actual peak. Is it the measurement Amps RMS?

I wonder what the efficiency of the cycloidal gearbox is. I would be surprised if it was over 80%. 

Hobbyking claim that the KV is 330. I should be able to check this. Does the KV change as the speed approaches 0RPM/stall?

Does the Saddled Sine wave output of the controller give a different reading than a normal sine wave. Could this effect the Kv and Kt values?

As the arm moves from Vertically down to horizontal the torque required will increase. Maybe it is better to use a large pulley with a weight as this torque will be constant. 

I will set-up the test again with better equipment and post the results. It would be nice if the theory matches the actual.

  Are you sure? yes | no

Alan Timm wrote 06/20/2018 at 15:51 point

Hey Paul, this is an outstanding project, and congratulations on your win! 

For the parts that require you to center them, it would be a snap to design and print a centering spacer to use during assembly. 

I've been eyeballing the failure modes, and I think the first part to fail at load will be the eccentric bearing lobes. That's based on the stresses between the top and bottom lobe and a single eccentric bearing pin, which I assume is going through the center of the top lobe. Maybe sticking a second pin through the center of the lower lobe would help mitigate that?

And, did I see that you can backdrive the actuator? I wouldn't have expected that.
I have to admit that I've watched this video about 12 times already to understand how you've accomplished this. I'm looking forward to building a couple of these to see how they work. 

Aliexpress would be a great source for most of the parts like the bearings, bulk 2mm x 28mm steel dowel pins, and 3mm (2.6mm internal) brass tubing.  the 2mm pins are a bit smaller (15%) than the 3/32".  Do you think those will work?  Otherwise there are other sources for true 3/32" x 1 1/8" steel dowel pins.

Can you share a bit about the modified axle/shaft?  Did you fabricate it?  Or is that something that can be found and ordered online?

  Are you sure? yes | no

Paul Gould wrote 06/23/2018 at 15:38 point

Hi Alan, I tried to put a second pin in the eccentric top lode but the "order of assembly" did not allow it to happen (unless I press fit the motor on the main shaft after assembly, this was not going to happen). I get silver steel rods from minitech and the brass tubes from the local hobby shop. I always buy local if I can get the right part (no matter what the cost) and only order overseas if I have too. i prefer to make parts from scratch if I can. Hacksawing a rod and filing the ends are easy to do.

The main 6mm shaft is a silver steel rod from https://www.minitech.com.au/. i just file a flat spot for the motor's bell grub screw and drill a 2mm hole for the pin at the right distance for the second lobe. I don't have many tools. (Cheapest 3D, cheapest drill press, cheapest vice and files and that's it). I can use my vice as an arbor press. I pressed out the motor's original shaft and pressed in longer 6mm silver steel shaft

  Are you sure? yes | no

neilmbajaj wrote 06/19/2018 at 23:16 point

Can the actuators be backdriven? I suppose if you want it to stand passively, you would not want that, bu it seems like putting the bearing in, on at least the interior pins, could greatly reduce internal friction. 

Since your external pins touch two of the cycloid rings at once, would bearings not help there? Your cad odel appears to have bushings over the exterior pins, but i feel like they might have the same issue.

Backdriveable actuators are especially nice when you want to do force control, or try to map motor current to torque, which might be useful when trying to make this robot walk or jump.

  Are you sure? yes | no

Paul Gould wrote 06/20/2018 at 01:00 point

The Actuator is backdriveable. It is only a 26:1 ratio. I think that having it backdriveable with regenerative capabilities is a must for overall efficiency. I had a prototype with bearings on the outside pins but the reduction ratio was lower because of the bearing spacing around the circumference. Also that is a lot of additional bearings, which increases cost and weight. Series Elastic actuator is also much better for efficiency (the big quad design has this). I am also trying to work out how to store potential energy from the elastic actuator (spring). Store the energy on a foot fall and release when going to jump/step.

  Are you sure? yes | no

Dan Royer wrote 06/19/2018 at 19:42 point

I saw a project recently that used an atmospheric pressure sensor (very small) wrapped in a rubber material.  When the rubber touched a flat surface the pressure on the sensor was registered.  Made for a really quick contact sensor for feet.  Might be useful for your quad walker.

  Are you sure? yes | no

Paul Gould wrote 06/20/2018 at 01:04 point

That is a nice idea but it will only tell you after you have hit the ground. It would be nice to know just before then so that you can turn off the motors so the joints are a bit "softer".

  Are you sure? yes | no

Dan Royer wrote 06/20/2018 at 01:09 point

how about... if the motor senses resistance and the foot is not touching then we know it's not ground interference.  not sure what the logic branch from there would look like, tho it's an interesting edge case...

  Are you sure? yes | no

K.C. Lee wrote 06/20/2018 at 08:36 point

The sensor deforms make contact before the leg reaches all the way down and transfers its full weight.  It is like the pads and hairs on the bottom of a cat's feet can provide feedback for the cat to walk quietly.  Or your keyboard keys making contact before it reaches full stroke.
Pressure can travel, so the sensor doesn't need to be where actual impact happens; 

  Are you sure? yes | no

albertson.chris wrote 06/19/2018 at 18:10 point

Maybe just to re-state one point.  I had the idea that a motor controller should live INSIDE a length of the 25x25 tube.

I had a robot fire a year of so ago.  I has dumb and THOUGH the cable has protected from overcorrect but the design was faulty and I vaporized a #8 cable (3mm diameter copper conductor)  I

I saw that 25x25 tube and though "use it as conduit", "use it as housing for electronics", "use it as a heat sink",  "EMI shielding if you ground it." "I wonder of batteries will fit inside?"   

I thing the most valuable space in the robot might is the inside of the 25mm square tubes

Robots like these and to fall and take bubbles down stairs or worse the limbs get into self-collisions and rip wires from each other.  At least until the motional planner is fully debugged.

I know first hand that LiPo battery fires can't be put out, you just have to wait.

  Are you sure? yes | no

albertson.chris wrote 06/19/2018 at 03:25 point

I think a good way to design a motor driver is to look at what controls the driver.   I think anyone building a walking robot is going to be using ROS/MoveIt or ROS/TOWR so you'd want to run ROS Serial and a joint controller node on the driver.  It would save a ton of work to build the controller on a CPU platform that can run ROS Serial.    Not looking upward at the higher level controller might mean you later have to introduce a layer between.  A chain of controller adapter PCBs is ugly.   

STM makes the STSPIN32F0 with builtin MOSFET drivers the chip is designed for robotics and BLDC motors.  

The higher level controller likely a "Joint Trajectory Action Controller" attempt to place joints in space at a given time and velocity within the limits of the hardware.  This is the controller this driver will need to interface with.  best to make it seamless.  

All that said.  I'm pretty sure I'll be using a stepper motor at fist.  Steppers are easy to control.

  Are you sure? yes | no

de∫hipu wrote 06/19/2018 at 07:23 point

> I think anyone building a walking robot is going to be using ROS/MoveIt or ROS/TOWR so you'd want to run ROS Serial and a joint controller node on the driver. 

If you look at the walking robot projects (https://hackaday.io/list/29475-walkers), you will notice that very few of them use ROS in any way.

  Are you sure? yes | no

albertson.chris wrote 06/19/2018 at 17:35 point

But they also lack any interesting behavior other than walking.     What's the point of that?   I would think the reason you use legs rather then wheels is because wheels can't work for you application.    But so many of these robot have no application.

As a minimum, I'd want antonymous navigation and route planning that gets from point A to point B without attempting to walk through solid objects, replannrng aroubd obstacles.

We see this a lot with hobby robots, nice mechanics with no software

  Are you sure? yes | no

de∫hipu wrote 06/19/2018 at 18:37 point

Some of them have pretty interesting behaviors. Also, lack of application is not an exclusive feature of ROS-less robots.

For "antonymous" navigation you need sensors that cost two orders of magnitude more than the whole budgets of those projects. But they usually do obstacle avoidance, so they don't walk into things.

No software is often better than crappy and bloated software. At least you get to learn how it actually is done.

  Are you sure? yes | no

Paul Gould wrote 06/19/2018 at 12:36 point

Albertson.chris - can you tell me about the joint controller have you have made? 

The PSOC4 controller can be configured to support the following communication protocols PWM,  I2C, SPI, UART, RS485, USB, CAN, Step/Dir and LIN. I like CAN the best, as the packet handling is supported in hardware and it has a higher immunity to noisy environments. The CPU is running at 90% idle, so i'm sure adding some sort of Trajectory planning should be possible. 

The current big quad I'm designing requires interaction between the joints as the two actuators are joined as one parallel linked series elastic actuators. Two controllers, two gearboxes and one series elastic actuator. This will most likely require a centralized controller.

The CPU in the STSPIN32F0 is not a "high end" controller. 4KB of RAM is not much for a Robot controller.

  Are you sure? yes | no

albertson.chris wrote 06/19/2018 at 17:59 point

I think a robot controller for a robot that has as many degrees of freedom is a quadruped is going to be hierarchical.    Every group of 6 MOSFETS controls one motor has one CPU.   The cPU only has to run a position and velocity feedback loop and monitor temperature.  I would bolt the mosfets to the 25x25 mm tube as a heat sink.  These controllers could live inside the structurel tubes and all connect to a bus and DC power.     4K is easy enough to run a couple loops and control one motor if not get a bigger uP.   

The next layer of control like does coordinated movement.   It receives as input a series of vectors.  The vector has a target position and velocity for every joint and also a time tag for when those positions are to be realized.   It then sends commends to all the motor controllers to update their set points such that every point gets to it's target at the same time.

The next level above os motion planning.  It's output is the vector of joint targets

Above that is the SLAM and navigation.  The robot needs to know where it is and how to get to where it needs to be and hw to rout arub fixed and moving obstacles.  This means a LIDAR, Vision, IMU, Kalman filters and so on.   This is where ROS is best used.  One person could never write a modern SLAM and sensor integration suite in one lifetime.

The level above is what decides the where it needs to be part which is likely based on a high-level command give by the owner of the robot who just said "go downstairs and fetch me a beer"

Using the "fetch me a beer" scenario is a great place holder.  It the design can do that is is general enough.  I don't need a beer fetcher but I do want a personal assistant for a blind person.  A machine that cn read signs and not bump into walls and communicate by voice.

  Are you sure? yes | no

albertson.chris wrote 06/18/2018 at 16:09 point

I've been looking for motors.  Hoby King has the one in the you tube video.  But then checked industrial brushless motors and found a line of them a StepperOnline.com   One of them has a Kv of 111.  That means 3X more torque per  amp.  Same price but physically larger in the axial direction by a lot, but on the other hand I doubt it needs cooling.  Likely more weight.  

Maybe suitable for an indutrial robot arm that with base fixed to platform

  Are you sure? yes | no

albertson.chris wrote 06/18/2018 at 05:18 point

I just read the comment about casting.  It is not hard. You can print a mold, pour in the resin then, here is the key:  the mold comes apart in two or three sections.  The mold parts have flanges that bolt together.  and have registration indents for precision alignment.  Coat the inside with some kind of mold release and car past wax.    

I will have access to CNC mill just as soon as I finish my CNC conversion project.  Milling from mild steel is not as hard as it seems

Comercial cscloidic drive this size use grease only the larger ones need a oil bath.  I'd stay with white lithium grease

Now to find suitable motor

  Are you sure? yes | no

albertson.chris wrote 06/18/2018 at 03:40 point

I have been looking for an actuator for the exact same reasons you were.  My goal was an affordable quadruped that could jump off the ground.  Yours is great and (I say this in a positive way) there is room for modification which means it could be even better.   

I think the electronics can be very much simplified. and I don't know how your position/velocity feedback works yet or anything about the magnetic encoders.  

About cooling, yes, the motors likely can run hotter than you are letting them get and remember that heat flows in proportion th the difference in temperature.   So hot is not bad.  My first try would be putting a fan in the shaft then making the mount out of aluminum and a thermistor some place to measure temperature.   I'm going to have to build one of these and study it.    Thanks for all the hard work

I need to buy a brushless motor -- Sorry I've not read everything yet, do you a source  for the motors? Or a model number i can google.   

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Paul Gould wrote 06/18/2018 at 10:40 point

Any ideas and improvements are always welcome. For the electronics you can get a uC with inbuilt FET driver but then I loose the ability of the PSOC FPGA section (which is very useful). The advantage of the magnetic encoder is you can get full torque at 0RPM at angle angle using FOC. The motors are from Hobbyking Multistar Elite 5008/5010 or from Arris Hobby 5008/5010/5020 or from Foxtech 5010 or T-motor 5008/5012

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JoshuaBRussell wrote 06/17/2018 at 20:23 point

Really cool project! I'm interested in motor control myself. What resources did you use when helping design the motor control electronics? Specifically related to the PWM, DRV chip, etc.

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Paul Gould wrote 06/18/2018 at 13:53 point

ODrive and VESC are a good starting point. For the FET Drivers, I like the smarter chips of TI's DRV8xxx family. They offer various control and fault detection options. Gate control can be tricky and these chips handle them easily. The main reason for my custom controller was to have full motor torque at 0RPM. 

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Deinactivation wrote 06/17/2018 at 18:43 point

This is extremely interesting, but how does it compare to the commercial actuators on price? You said those ones are ~$500, but what I can find looks like this one has to be pushing at least $200. A full BOM with sources and costs would be awesome.

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Paul Gould wrote 06/18/2018 at 11:04 point

I was comparing the actuator to the DYNAMIXEL PRO line of robot servos. They start about $500. I will update the BOM over the next few weeks.

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Dan Royer wrote 06/17/2018 at 14:22 point

Nice work! I’m very interested in your project. I’ve tried to make cycloids in the past. My sixi robot arm needs a min holding torque of 20Nm at the base. What kind of play are you getting? (How’s the repeatable accuracy?)

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Paul Gould wrote 06/18/2018 at 11:13 point

The backlash is quite small but that is all relative. It is good for a quad, not sure about a robot arm. It depends on the tolerances of the 3D printed Cycloidal gear. The joint position sensor is 14bits but getting the magnetic sensor and diametric magnet concentric will effect the accuracy. I have seen people have a calibration table for the magnetic sensor, so maybe the usable accuracy is only 12bits.

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Josh Starnes wrote 06/13/2018 at 13:58 point

It reminds me of transformers and other robots that have rotating discs in the joints, and you made it real, waaaah !!

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Josh Starnes wrote 06/13/2018 at 13:57 point

Khudos, I really hope you were one of the individuals in the top 20 who got the $1000 prize, this concept is really cool and I love it!! It could be used in any joint in robotics.

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Paul Gould wrote 06/13/2018 at 16:48 point

Thanks Josh. I was one of the 20 finalists. I think that the electronic part of the actuator is not the easiest for makers to implement into their designs right now so I might improve it a bit. The PSOC4 is not an easy chip to learn. Maybe something Arduino compatible.

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Josh Starnes wrote 06/13/2018 at 16:52 point

I hope the prize encourages you to keep developing it, I normally use high torque servos on my robots but I would like something better and purpose built like this, if there is any way I can help .... even testing some setups I’m happy to be involved

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Dan DWRobotics wrote 06/08/2018 at 18:02 point

Can only second my previous comments. The level of work and detail on this project is incredible. I am very excited to see the outcome!

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Alberto wrote 06/06/2018 at 12:07 point

Incredible project! Super neat mechanical design.

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Paul Gould wrote 06/05/2018 at 11:54 point

@Dan DWRobotics  I do have a little bit of backlash, but it is hardly noticeable. The teeth of ABS cycloidal gear acts like a mini spring, so the back increases a bit with increase load. As you said the software can compensate for this. Backlash was the main reason I started to look into my own actuator design. I made a little biped with RC servos and my own servo amplifiers. The servo backlash was terrible.

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Oskar Weigl wrote 06/04/2018 at 06:14 point

This looks super awesome! There's a group of roboticists that would love to hang out with you on the ODrive Discord: https://discord.gg/J9bG3dH

Swing by if you have some time to chat!

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Paul Gould wrote 06/04/2018 at 09:37 point

Thanks Oskar. I just joined your ODrive Discord, but remember I'm on Australia time.

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Dan DWRobotics wrote 06/03/2018 at 20:30 point

This looks amazing. I always considered cycloidal gears to be just too tricky to make into actuators for joints, but seems like you have done a great job. Also seems like they are very strong and quick joints. Look forward to seeing future progressions. The quadroped construction you have looks really interesting.

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Paul Gould wrote 06/04/2018 at 05:11 point

Thanks Dan. I was surprised it worked so well. The first 10 prototypes were tricky but now they are made quite quickly. Cutting the silver steel rods and the brass tube still takes time. ABS is not the right material to make the cycloidal gears with. I sure other filaments would have better mechanical properties. I am using ABS because I can't get other materials to print well on my cheap 3D printer.

I've been watching your project for a while, as cost is a huge factor in how I design robots. Things start to add up when you have 20ish joints. Do you have a problem with backlash? All of the tooth gearboxes I 3D printed were very bad. 

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Dan DWRobotics wrote 06/04/2018 at 22:25 point

I have a couple of methods for dealing with backlash, but unfortunately there is still a bit. The cost savings across an entire platform justify me programming strategically to mitigate those effects. But I can't pretend that backlash is not an issue. I can imagine you have zero back lash on those gears? 

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Josh Starnes wrote 06/13/2018 at 17:22 point

have you considered casting the parts out of urethane or nylon? both have lubricating qualities and are much stronger than the pla or abs. I wonder if a outer casing and lube grease might make the mechanism more quite

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drew wrote 06/13/2018 at 19:45 point

You might want to think about using Dowel Pins for the drive pins instead of silver steel. They're available in lots of diameters and lengths. 

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Paul Gould wrote 06/15/2018 at 14:50 point

Josh, I would like to try casting but it doesn't seem to easy. I was thinking to 3D printed Nylon. I haven't added any grease to the gears yet. The final actuator will be fully sealed (outer housing to be added later).

Drew, I didn't know about Dowel pin, thanks for the tip.

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