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Affordable, Programmable Robot Arm

Building an open source robot arm for makers and small businesses

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This project was created on 04/28/2014 and last updated 3 days 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
  • Uneven Bevel Gears

    3 days ago • 0 comments

    Here's a close up of the gearing in the wrist. Everything here works in theory, but needs to be proven in reality. I tried printing some of these gears.

    The cap on the bottom is a test fit for the rotation sensors.

    Turns out these gears don't mesh correctly. Add that to the big list of "thing I find out a little too late". A line along the edge of each gear should all meet at a common point.

    I tried to re-engineer the gears and got this:

    Although they all meet at a point...there are big gaps in the teeth. I'm doing it wrong.

    Can you help me get the right gears? I'm completely lost when I look at SDP/SI's gear page.

    The larger gear is 48mm pitch and an 8mm hole. The smaller is 16mm pitch and a 5mm hole.

  • Ouroboros, God of design

    6 days ago • 0 comments

    Solutions create problems create solutions create problems....

    Added the rotation sensors. The caps over both sensors do two jobs. The first is to keep grit out - I'm thinking ahead about the Ingress Protection rating. The second is to hold the sensor over the magnet so that the brain knows where the finger is located at all times.

    The cap needs to be secured to the green frame, and glue is not an option. Screw would only work if there is access to both sides. The large reduction gear was blocking access. I had to move the motors all the way behind the elbow in order to make everything work.

    Along the way I discovered that my notes for the original bevel gears had been lost so I couldn't just make another to match the old gears - I had to regenerate them from scratch. Best believe I made a backup copy before going nuts on the design and I made damn sure to keep the notes this time.

    With this I miiiiight be done with the arm from the wrist down to the elbow. At the elbow I've already mounted the rotation sensor and I still have to mount these motors. Should be two laser cut parts, no biggie. Once that's done the gearing between the shoulder and the anchor need to be worked on, but that should be the last piece (fingers crossed).

    Due to the lack of software I can't test this arm virtually and confirm that it carries the weight I want at the precision I want... but I think the math checks out and there's ways to get more torque without headaches.

    The electric pistons arrived today and I've already got the drivers. Rotation sensors claim to ship this coming Tuesday. I might use a 5/16" rod instead of the far more expensive 8mm rod the design calls for. Every other part I can either laser cut, print, or already own. This is happening, people.

    Make a comment! Hello, is this thing on?

  • attempted mounting solution

    7 days ago • 0 comments

    Trying to be more open about what I'm working on. Feels more productive and maybe maybe it will help down the road.grey is the magnet. green is the PCB. the hollow shaft is where the I bolt used to be. Now I'll put in an M8 rod with no bolt head. the small thru-hole is to pop the magnet out of the printed holder (if needed). The two gears on the bottom are printed as once piece, the magnet holder is one piece. I imagine screws will have to come from the magnet end, go all the way through the holder, and then into the bottom gears some way.

    I don't feel like I know what I'm doing with the angular contact bearings, but I can't imagine a way that will work with anything smaller.

View all 35 project logs

Build instructions
  • 1

    Instructions so far:

See all instructions


Andrew Becker wrote a year 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 a year 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 a year 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.

Are you sure? [yes] / [no]

mad.hephaestus wrote a year 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 a year 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 a year 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 a year 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 a year 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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