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6DOF Robot Arm

Building an open source robot arm for schools and DIYers

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This project was created on 04/28/2014 and last updated a month ago.

I want to put robots on the moon to build my base. An industrial arm starts at $10k and go up from there. I figure I can make some money to pay for the space ticket by building and selling the robots myself. I'd like to drive the cost down by making an arm that others can tinker with, improve on, and build community around. I'd like to see two arms assemble a third.

So far I've built a 3DOF arm that I brought to the 2014 San Mateo Maker Faire. I've taught it to write so it can sign pictures and print your message here. I've also built a 5DOF prototype (pictured).

I need all the help I can get. Please share with your friends!

Thanks for reading,

I don't know what to write here that isn't covered elsewhere.   Ask questions?

You can get the full part list or support me by buying a copy of the current design here:


Project logs
  • Gearbox failure?

    a month ago • 11 comments

    So I built the pillow block described in the last post. First I 3D printed one in about 2.5h and when I went to install the gearbox I snapped the block in half along the layers (what's commonly known as 'delaminating').

    Then I designed and laser cut a replacement in about 20 minutes. So there. Ask your local make if 3D printing is right for you.

    The new block was assembled and a 45cm bar was attached to the shaft. Now at 55:1 reduction on a 50 N·cm stepper motor should give me 2750 N·cm, or a holding torque of ~61.1Nm at 45cm. That's a LOT of torque for such a small motor.

    The new block assembled, the gearbox stalls even with my hand on the bar at the 10cm mark. This thing should be almost unstoppable.

    I don't have enough engineering experience to solve the mystery and I'm led to believe neither the machinist who made the parts nor the designer who drafted them can spot what's wrong. I've got some expensive ideas, but I'd really like to get a Mechanical Engineer to take a look and tell me what's going on.

    So... two steps forward, one step back. Next step is to find the Mechanical Engineer who can help.

  • Gearbox prototype made

    a month ago • 0 comments

    ...aaaand that's about all I can tell you for now. It's made, it's assembled, and it's running on my desk. There's no discernible backlash - as promised!

    at 55:1 reduction on my 200 step per turn motor at 1/16th microstepping we're looking at 176,000 steps per rotation, or 0.002 degrees per step. It ain't fast, and it don't need to be.

    The first prototype cost $1050 CAD. The next five I'm told will cost ~$200 each. Once I get that far and have a demo arm, there will probably be a kickstarter for the gearbox.

    The challenge now is testing this thing to see how much torque it can handle. I need to make a pillow block to hold both ends of the output shaft so that all the force on the motor is just rotating torque force, then attach a bar and start hanging weights off the end until it can't move any more. Repeat for different speeds.

    I'm planning a single joint with two rotations. Three joints is 6DOF. Length can be increased by adding space between the joints.

  • Machining!

    2 months ago • 1 comment

    Thanks, for the feature.

    Today I received the first quote from a machinist for the gearbox prototype. In order to get my power and precision I need a gearbox that doesn't exist. Jim Shook, a fellow Hackspace member, designed a box as per my specs four custom parts and a bunch of McMaster Carr pieces. Each of the four pieces averages $250 to make one!

    I guess I don't know what I expected. The same company made parts for my first robot. It was a crab that walked and the parts cost over $600.

    So I'm putting it out to you, Internet: where do you go for machining? I have igs/step files and PDFs of the tolerances and materials.

View all 24 project logs

Build instructions
  • 1

    Instructions so far:

See all instructions


Andrew Becker wrote 10 months ago point
Hi Dan, sorry for the long delay, I took my family on holiday and decided to leave the hobbies behind. I have already had a good look at your project and it looks great, I would be more than happy to share my work with you, I'm also very curious as to what control system you're using.

Are you sure? [yes] / [no]

Dan Royer wrote 10 months ago point
The software is home-grown. The electronics are a RUMBA controller - think an Arduino MEGA and a super sized RAMPS board put together.

Are you sure? [yes] / [no]

Andrew Becker wrote 10 months ago point
So you are doing all of the forward and inverse kinematics from first principles? I've managed to logic out the geometric relationships for my arm because the axis pairs intersect which simplifies the maths. I've then moved all of that into excel to visualise it and plan on using that to implement it in Linux CNC. It works out fairly simple because the alpha, beta and gamma angles fix the position of the 3rd link in space, thereafter it's a matter of working back through each joint position. Because of the geometry I chose there is only one solution to the set of equations and it's not necessary to use matrices to solve. How are you handling it?

I have a Reprap Ormerod and initially I had some trouble with the software. It turned out that the PSU supplied was not supplying a stable voltage to the controller and when the heated bed switched on it would freeze. I went for an industrial PSU with a much higher rated amperage and the problem disappeared. It did however put me off using an arduino based controller considering how easily my first Linux CNC set-up went.

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mad.hephaestus wrote 10 months ago 1 point
I had a random thought:
If you take that whole arm section and put it in a 2 axis gambol, centered around the elbow joint (with the elbow being the outside joint), you could get a true R-R-R spherical wrist, without twisting the belts. The entire section you have now would rotate around the center axis. With a circular track around the edge the track race could then form the elbow joint on the out side. You could actuate it with a third counterbalance motor and a gear interface to the outer track.

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Dan Royer wrote 10 months ago point
That's the first thought I had. I've skipped it for now to ... Work my way up? Also as the gimbal turns the wrist motors could collide with the shoulder assembly. I'm looking for a method closer to what existing arms do where the ulna rotation is between the elbow and wrist. I have some drawings and I'm saving them for later.

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Dan Royer wrote 10 months ago point
One of the things that drives my business most is customer feedback. You asked for it and I can do it, so I'll start posting here more. Given how busy I am it will probably be a copy/paste from my website, which may hurt my SEO.

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zakqwy wrote 10 months ago point
Thanks Dan. Great work so far, it's been fun to watch your progress as you develop the 4th and 5th axes.

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zakqwy wrote 10 months ago 1 point
What are your thoughts on putting more info on I'm less likely to click through for project logs or other updates, it's easier to read everything in one place (and comment on it here, too).

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