The Mini Monster, Cheap 6DOF 3D Printed Robot Arm

Update 10th April:

The mini monster has a sibling (almost, not quite finished). Printed in all black PLA. Designed primarily to look extremely badass:


I should just say, HELLO coolkidsrobots! Nice to meet you! I am glad I found this site and the rebels too. The older site was a bit of a ghost town, but enough said about that.

Over the last couple of weeks I have been designing and building my latest project. I've had this idea for a while and finally got some spare time to work on it.

    It's a budget 3D printed 6DOF robot arm. I re-used a lot of my own cog designs from previous builds but have added a couple of very nifty mechanisms to get position feedback out of the wrist and turntable. Unbelievably the turntable was one of the most difficult bits to design.

       It was completely designed on a free version of Sketchup I downloaded ages ago. It uses the standard arduino IDE at present. I still need to do some work on the code because they code is adapted from my previous 12 DOF Legs project that I had put up on that 'other website'. It's basically a smaller version of 'the monster' which I haven't finished yet.           
          It is entirely 3D printed and I am just using the little hobby geared motors that are very common amongst makers. Then using 10K potentiometers for the position feedback, mostly positioned on the axis of each joint. I am using an arduino mega2560 for the control. I am using some cheap L298 motor driver break out boards, as I bought a load from ebay a while back. At the moment it is just playing back positions I have taught it. However very soon I will be printing a little mini arm (with just encoders in) which will be used for teleoperation, so that I can control it remotely. Potentially this could be done through a phone app so I am going to do some reading on how to interface bluetooth to arduino devices, It can't be that difficult can it?

I am also hoping to add in a laser I have lying around, because, well, you would, wouldn't you?

The idea with this one is to make something that has much of the functionality of more advanced arms, but for the cost of a toy. I've long since wondered why OWI didn't ever add position feedback to their arm. It is pretty simple/cheap to do. Well as you can see this arm is not designed to be as accurate as some of the better ones, but I think I can make this for around £20-£30 so that more than makes up for the lack of accuracy. I will add some more details and photos as I make them.   
       I just bought a powerpack for it because I am using two 9 volt batteries and they drain after almost a minute or so. The power pack I bought is a variable voltage 5-15v, 4A powerpack, so it seems to work well with that. The first video it is using 9volt batteries, the second video using 6volt powerpack.

        I made lots of mistakes during the design process, the arm is supposed to be able to fold up almost flat when the elbow is fully contracted but I put the position sensors right in the way of the joint for some reason (doh!) so I will be revising that soon and also making the upper arm (femur)  a bit thinner as it doesn't need to be so wide.   I also need to make the grippers slightly bigger and give them rubber pads to grip onto objects. Well, let me know what you guys think. I am pondering whether to get all the files together and create some youtube videos on how to construct it. I am going to do some testing first and see just how accurate I can make it.

Let me know if you guys have any comments/suggestions!!!!

I've made some changes to the arm. I improved the elbow joint so that it can fold up flatter when in a resting position. I also improved the accuracy of the turntable so that it can do more accurate pick and place type stuff. The turntable can only move 300 degrees now but this was a small price to pay for better accuracy.

I have a cool idea now to add a row of red LEDS on the front of the gripper at the top and then have them slowly pulse from left to right like a cylon or knightrider. This will add a little personality to the arm and I can program animal like movements like tipping the head to one side like a dog would.




First demo of learnt moves, still needs work to the design.
First time picking up object, so proud of the mini monster, he/she is growing so fast!
Redesigned elbow joint allows the arm to contract flatter and makes the resting pose 50% cooler looking.


Submitted by danphobic on Sun, 2016-04-03 07:14

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  Ah yes, good questions! The reach of the gripper from the centre is 38cm. But if the arm is pointing straight up from the bottom of the base to the tip of the grippers its 52cm high. It's quite funny when I was messing around making videos I had one set movement where it lurched right towards my face and stopped just in front of my face. I may still shoot that video when I have a better designed arm to show off.  

 The max lift weight I have no idea of yet. I have been too busy designing and printing to do some proper tests on that yet. Rather annoyingly when I am 3D printing I can't work on the other stuff because my Mac does the 3D printing. I really need to sort that out! 

The max lift will also be affected by the programming. At the moment I don't have the maths right for it to make fluid strong movements. You can see in the video it appears to struggle and jerk around. That's not because of the strength but the way I programmed it to cut movements up into segments. Well I am going to put my neck on the line and predict around 500grams at 35cm. That's based on what I know about the design and the strength of the motors/gears. I am going to conduct some strength test soon though. I will base it on the videos that the trossen guys do for their hobby arms.


Submitted by Roxanna77 on Sun, 2016-04-03 09:31

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Let me also welcome you to CKR! Thanks for the post! 
Great job on the arm, looks like it is sturdy. Something I'll have to make at some point.

Good to have another 3D printer person here, I have 3, 1 Prusa i3, a Kossel mini and another Kossel based on the Kossel Pro (or XL) that I am just about finished building.

"Propeller Girl"
tinker, therefore I am.....

Submitted by danphobic on Mon, 2016-04-04 14:04

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Thanks Roxanna! Yes I love 3D printing. I only have one and it's not a well know one ( Velleman K8200) but it does the job. Looking forward to posting up my projects here and seeing everyone elses creations.

Submitted by mtriplett on Wed, 2016-08-03 13:56

Great work.  Very very impressive.  My 3D design and printing efforts to date are far simplier by comparison.  I'd like to get to the point where I can design cogs and the like for more articulated bots.  Well done.



P.S.  If I had your skills, I would try my hand at designing arms, where the shoulder joint (your base) is vertical and not horizontal.  The other one would be some king of articulated "johnny 5" like bending torso, another one where gears to increase the power would be very important.  The InMoov joints are very interesting.  Have you looked at those designs?

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Last updated: 
10 Apr 2016 - 17:18
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