Mike's Robot Dog

Boston Dynamics' robot dog, Spot Mini is unavailable at any price. A Chinese copy is $30,000. Cut 99% of the cost and build one at home.

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Using a 3d printer, off the shelf servo motors, an Arduino and three ultracapacitors; I have started something along the same line--but the cost is more like $300.
Hopefully, this dog can be a companion within the home (maybe help with aging in place), a tool for gardening and a scout for hazardous locations.
Don't get too excited--my dog doesn't walk or stand yet, but it can lift its own weight and I have overcome a couple of challenges.

Spot Mini is an amazing (perhaps scary) robot dog built by Boston Dynamics--not for sale.

If you want to purchase something similar, a company in China produces a research platform for around $30,000. Another legged platform, Anymal, can follow you into an elevator.

Using a 3d printer, off the shelf servo motors, an Arduino and a couple of ultracapacitors; I have started something along the same line--but the cost is more like $300. 

Don't get too excited--my dog doesn't walk or stand yet, but it can lift its own weight and I have overcome a couple of challenges.

If you want to use the 3d print files (and some of the design files) go to Some of my .stl files do not have a corresponding design file because the .stl files are 1) the combination of two or more .stl files in Tinkercad or 2) they are mirror images of .stl files, mirrored in Tinkercad. The leg pieces can take 10-12 hours each to print as they are sizable.

I use twelve high torque (277 metal gear servo motors at a cost of about $18. each. These have no end stops and they draw a fair amount of current to move, but they respond consistently to commands.

Under heavy load, each servo motor draws 3.5 to 4.5 amps. To move from a sitting to upright position, eight motors need to provide significant torque--meaning 30 to 40 amps are required for a second or so. I use three 350 farad ultracapacitors (in series) across my motor power supply and they take care of the momentary load of the servo motors.

Here's where I am on March 16.

My first "shoulder connection" put all the "up/down" and "rotate" stress on the servo motor.

This looked like a bad idea, so I created a bearing block and heavy shaft to absorb the "up/down" load and let the servo motor's gearing handle the rotation only.

The bearings are snowmobile bearings available on Amazon.

I designed the servo motor mounts such that there is a sort of "back bearing" opposite the shaft so that it is easier to attach moving limbs.

The first foot was a wheel--but that rolled all over the place, so I created a movable flat pad for better traction.

I mounted a digital voltmeter up on the body--just to keep track of what was available for the servo motors.

So, there's a long way to go, but this walkable platform (when it works) will be useful for robotics on smooth or rough terrain.

On February 27, the first attempt at standing was made. A couple of the joints couldn't take full speed movement--we learn by trying!

Now, with the feet not rolling or bending, it is possible to get the front and back to lift together.


Sit test

ino - 1.60 kB - 03/16/2018 at 19:11



This rotates an arm to the 90 degree position to test a servo motor's torque.

ino - 289.00 bytes - 03/13/2018 at 19:00


ino - 1.55 kB - 03/12/2018 at 20:43



Stand up and sit down test

ino - 1.61 kB - 02/28/2018 at 00:22


  • Torque Damage and Sitting

    Mike Rigsby2 days ago 0 comments

    The right rear leg quit--I figured a motor was cooked, but the problem turned out to be a stripped out plastic servo horn (note the bits of black plastic on the table).

    I pulled the leg off to remove the old plastic horn.

    The new aluminum horn fits the servo motor, but it's a bit dicey attaching the new horn to the 3d printed leg joint. It kind of works, but I'll have to redesign the joint and rework all the legs.

    Changing two of these servo horns allowed enough control that I could attempt a sitting position.

  • Testing Servo Motor Torque

    Mike Rigsby5 days ago 0 comments

    The servo motors I am currently using claim to have a torque rating of 20 kg-cm (277.6 oz-in). Rather than just accepting an advertised claim, I thought it would be a good idea to know if the motor could really produce such torque.

    My test rig involves a 1" x 2" pine board attached to a servo motor. At a distance of 21" from the servo shaft, I have taped 8.3 ounces of lead weight.  Twenty-one inches multiplied by 8.3 ounces yields 174.3 ounce-inches of torque. The 8 ounce wood arm (assuming even distribution and that the center is 11 inches from the arm) contributes 88 ounce inches to the torque required. Adding 174.3 to 88 yields 262.3 ounce inches of torque. I didn't play with weights to find the absolute max, but I have no reason to question the 277.6 oz-in advertised.

    Under load, it looks like this:

    As an interesting side note, the current required to hold the arm horizontally (at 7 volts) is about .4 amps. If the current limit on the power supply is less than 2.5 amps, the servo motor won't rotate the arm.

  • Repair Broken Joint and Stop Slipping

    Mike Rigsby6 days ago 0 comments

    I printed a stronger joint piece and replaced the broken and damaged joints.

    This photo shows the replacement of the "back bearing" for the servo motor.

    This is the installation of the servo horn.

    This is the attachment of the servo piece to the leg.

    The servo attachment piece has to be fastened to the servo motor using the servo screw.

    Next, I made a wider wheel, one that will not turn, to be in the foot position. Part of my trouble with standing involved the foot "moving around" instead of the body lifting.

    For test purposes, I clamped the body to the "hanging support" so that the body could not be lifted.

    Next, I "asked" the leg to push as hard as possible. The result was 1.24 kilograms.  At least under some circumstances, four legs working together should be able to lift about 5 kilograms.  The body is about 1.5 kilograms, so there should be enough push to get off the ground.

    I probably need some feedback and better software, but things are progressing.

  • First Stand

    Mike Rigsby02/28/2018 at 00:19 0 comments

    On February 27, the first attempt at standing was made. A couple of the joints couldn't take full speed movement--we learn by trying!

    To attempt the first standing test, I needed to determine the servo angles for each motor. Below is the schematic for the system.

    With the mechanism suspended, I determined the servo angles for each servo.

    The numbers I retrieved are:

    I applied those in an Arduino sketch (found in  files on this project).

    Two joints couldn't take the stress (I went full speed on the servos, kind of a worst case situation).

    I'll have to redesign and install joints--then full torque ahead!

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Duke Circuit Co.,Ltd wrote 2 days ago point

Looks cool,wish you can have a good market.

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malvasio.christophe wrote 02/28/2018 at 07:41 point

is this printed in full ?

missing legs rotation

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Graham Toal wrote 02/26/2018 at 20:00 point

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jorge wrote 02/24/2018 at 14:29 point

Hello, congratulations

Can you tell me which condenser you use (link)?
Thank you!

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lion mclionhead wrote 02/23/2018 at 17:12 point

Boston makes a micro version out of servos.  Because of the limited torque & speed of servos, it's very slow & moves more like a toy.  The Ghost Robotics Minotaur has come the closest to replicating Boston, for a lot less money.

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ActualDragon wrote 02/23/2018 at 17:21 point

+1, the ghost is super cool

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John wrote 02/22/2018 at 00:06 point

As the shoulders  carry the loaded weight, I would consider using 2 bearings (with some distance between them) per the improved shoulder joint. It would take the weight torque off of the single bearing ... which would be coupled to the motor. Also, to reduce the weight of the legs, you might want to use cabling to connect the driver motors located on the "body", down to the joint. It is a little more complex, but reducing the inertia of the legs might help the motors "upstream". Usage would be similar to a bicycle's brake / shifting shielded cables. That would also allow you to gear the motors, IF you have enough motor speed to trade for reducing the power loads.

When I saw the Boston Dynamics "dogs", I wanted to build some, too! Glad to see someone doing it! I like your design! IIUC, they use Neural Networks to learn to walk, etc. What are you using (or going to use)?

A possible optional material to use MIGHT be PVC pipe, rather than 3D printing the "bones". The schedule 40 stuff is pretty tough. You'd still have to print the joints.

Just for fun, there is a linux voice interface called "Mycroft", just in case you ever want to call your dog, or give it vocal commands. I think it runs on a raspberry PI.

As a final thought Home Depot has 2 sizes of bearing, in drawers in the hardware section (where they keep nuts, bolts and washers). I know that that is not helpful if there is no such store where you live.

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Mike Rigsby wrote 02/22/2018 at 00:48 point


Thanks for your well thought out comments! I am using two bearings per leg--but no distance between them. That gives me 24 mm of bearing surface (which is better than the nothing I started with). 

Cabling the downstream joints would reduce the leg inertia--I'll have to see how much of a problem that is before I make changes there.

I'm not going to pretend that I have all the answers and "learning to walk" is a challenge to be addressed. If the legs have enough torque and speed to stand up with load and potentially walk, then I'll address the programming and feedback tasks. I can get double the torque if needed, but the motors cost $70. each instead of $18.

I didn't know that Home Depot had any bearings--I'll take a look next time I'm there.

I am interested in voice recognition and visual (camera) recognition, but I have to know how much weight I can carry before I go there.

Really, if I can get a self-contained (battery on board) platform up and walking, then it will be something that a lot of people can enhance with their skills.

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John wrote 02/22/2018 at 02:12 point

I just recently stumbled across the HD bearings, myself!

Again, great project!

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ActualDragon wrote 02/22/2018 at 02:50 point

two words: magnetic. bearings.

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Stephen wrote 02/14/2018 at 01:19 point

This looks really promising! Congrats for getting it to stand on its own! Can't wait to see it walk.

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