Hydraulic Robot Arm 6-Axis by Blastronauticus

Last crawled date: 3 years ago

This is a 6-axis hydraulic "robot" arm. The axes are actuated with 10ml syringes which act as cylinders, and 1/8" inside diameter flexible tubing. I saw a few versions of these on social media, mostly made out of cardboard or kits with laser cut wood. I thought it would be cool to make my own with printed parts.
As you can see below, getting this thing to work was a process. I've added a counterweight (fill with sand) to help it hold position a little better, but it's not perfect. All 6 axes are functional, but it doesn't always hold position very well. Redesigning the controller to be self locking somehow would be ideal, but I just don't have time right now.
UPDATE 3/2/20 I've added STEP files for the arm and the controller, with an improved version of the base in it. I don't know when I'll get around to making more improvements, but feel free to take the step files and do a remix.
Update 11/4/2018 I fully assembled and tested the arm today. It does work but the weight of the gripper pulls the arm down if you let go of certain levers, depending on the position. I have a few ideas of how to fix this, including adding a counterweight to the arm, screwing the base and controller to a board (I also filled the base with pebbles for counterweight), and possibly re-designing the controller and adding valves to some of the axes for parking. All of this will take time to develop, and I'll keep it set to "work in progress" until I'm satisfied with it. Aside from the weight issue there weren't many other hang ups. Some of the holes were a bit tight and I just widened them out a bit with a drill bit. You can only access 4 of the 6 screws for the wrist, but 4 is plenty.
Update 10/26/18 I've ordered all the fasteners so I should have this thing built and tested sometime in early November. I'm going to give it a shot using 4mm wooden dowels instead of the M4 bolts, but I still had to buy all of the M3 stuff and the M4 threaded rod from the hardware list. I'm going to add printed retainers for the dowels and add an STL to print the large m4 washers for the pivot points on the arm linkages.
Update 10/8/18 I'm finished with the modeling and I'm starting to print parts. I've uploaded an STL of the entire assembly for reference to give you an idea of how it assembles. I have uploaded all the STL files, but I'm going to keep this as a "work in progress" until I have completely assembled and tested it. Files may change so print at your own risk. I've included a hardware list in an excel sheet as well. After I get it assembled I will consider doing different options for the gripper, including offset claws for grabbing larger objects.
Notes: (refer to PDF drawing for more details)

My syringes measure 16.5mm diameter with the outer section around 94mm long from end to end. The plunger sticks out 17.5mm from the end of the syringe when fully pressed in, and they have about a 55mm stroke length at 10ml. Yours may vary a bit. Hit me up in the comments if you need a custom part to finish the assembly.


You will need to adjust where each syringe is clamped at to get the optimum movement of the arm. The PDF drawing shows where to clamp them at.


Only use about 7-8ml of water in the wrist rotation syringe, otherwise it will crash the gear into the end of the rack. You should get at least a full 180 degrees of rotation.


The gripper syringe should only be filled about 3ml.


All the other syringes use 10ml of water. Might be able to add a bit extra to get a longer stroke on some of them.


Mostly all of the m4 bolts and the m3 bolts on the gripper links need to be a little loose so things can move. I recommend using nylon lock nuts in these locations. See the included hardware list spreadsheet for quantities.


The tabs for the frame pieces fit together tightly and permanently. You may need to clean up the edges a bit to get them to press together. I made an effort to idiot proof the tabs so you can't put the wrong ones in, but pay attention and make sure they are in the correct position before pressing them together.


Hardware for this will cost you a bit. I was able to find everything in the U.S. from Fastenal's website, for about $31.00 USD plus shipping. You might need to round up on the screw lengths depending on what you can find available. There's a hardware list excel sheet in the files for this thing. You could use 4mm wooden dowels for some of the fasteners to save money and glue on some sort of end caps. I would recommend using screws for the M3 fasteners though.


I've included instructions in the hardware list for using 4mm wooden dowel rods instead of most of the M4 hardware. This should help keep cost down a bit. You'll need to print 56 of the 4mm_retainer parts to do this.

For the rack and gear I would recommend printing them individually at slow speeds, and consider a smaller nozzle. I used a 0.2mm nozzle and 30mm/s for the outer wall speed, but 0.3mm or 0.4mm might be ok.