How to Make a Tiny Delta Robot

A "delta robot", a.k.a. a "parallel manipulator", is a robot that uses multiple arms to move one actuator. One might know them from pick-and-place machines as well as from the delta-type 3D printers.

The advantage of a delta parallel robot is that the heavy driving motors are usually at a base, decreasing the weight of the stuff which moves around, making this type of robots very fast. Some can pick and place 300 parts per minute! A property of the specific "parallel" version is that is uses paralellograms to keep the moving platform always in the same orientation.

I decided to make a small, even tiny, delta robot. Motivations driving me are having Fun in The Art of Tinkering, showing tech and creativity to my children, and making my wife shake her head. And just because I can (or think I can). There really is no use for this robot as far as I can tell.

When I say 'tiny',I mean that the moving parts will be tiny: the maximum reach is about 30 mm. The motors driving the arms and actuator will be relatively large :-)

Have fun reading and possibly making it - or an even smaller one!

And if you have a good idea about a commercial application, let's talk business ;-)

Step 1: Step 1: Making the Arms

Each arm of a delta / parallel robot usually consists of a single "upper arm" and a double "lower arm". The two parts of the lower arm form a paralellogram. Three of these sets attach the platform to the base. When the motors rotate any arm, the paralellograms move along, making sure that the platform keeps the same orientation. It is required that the joints are 'ball joints' so that they can move in all directions.

Let us make the arms.

The small ball joints cannot be sourced in tiny sizes, so lets make them. I created them using so called "bead connectors" from my wifes jewelry supply box. I used connectors made from cupper, such that soldering is easy. Solder two together as in the picture to make one link.

Use 2mm metal rod to make the upper arms. Start with a piece of about 60mm. Bend one end of about 10mm to 90 degrees. Grind the end of the long part so it looks like a flat-headed screw driver - this end is going into the servo. Drill a 1mm hole through the 10mm end (look at the picture for orientations) and push a ~10mm x 1mm metal rod through - fix with glue. Now glue a bead on each end of the 1mm rod.

In the next step, you can fold the bead connectors over the bead, et voilà (as they say in the Netherlands): a tiny ball joint!

Now make three arms, so you'll need to bend three metal rods, and out of 12 bead connectors you can make the 6 parts for the lower arms.

Step 2: Step 2: Make the Platform

The platform - the part that will move around - has three sets of ball joints.

First bend one piece at a 120 degrees angle. Solder a second piece on it such that you get a three-pointed star.

Drill holes in it for the thinner metal rods which will form the other ball joints. Make sure that the beads are at the same separation as the beads in the previous step! Accuracy is essential; being sloppy in this phase will have as a result that the displacement will be difficult to calculate :-)

On the 'bottom' side of the platform I mounted an M3 screw with which I later made the gripper.

Step 3: Step 3: Make the Base

The base can be a simple board of wood - MDF is easy to work with. A triangle (60 degrees corners) is nice to the eye. I made a triangular hole in it to be able to look from above, but this is not necessary.

Make three blocks of wood or plastic of about 15x15x15 mm - the height must be such that there is room to drill a hole at the height of the center of the servo when it is mounted on the base - the picture tells most.

Drill holes to neatly fit the 2mm messing upper arms (they should be able to rotate, with a little friction) and glue the blocks to the base plate. Position the blocks and arms as depicted in the figure: when the upper arm is flat, the centerpoint between the balls should be in the center of the robot.

Almost done!

Step 4: Step 4: Mounting the Arms and Platform

Now fix the bead connectors over the base-beads and the platform beads. You can now already move the platform by hand and see how the axes of the upper arms rotate. You can also rotate the upper arms by hand to see how the platform responds.

Position the three servos (I used 'mini servos') on the base. Press the 'screwdriver headas' of the upper arms in the opening of the business end of the servo's.

I used small glue-clamps with the long sides up to fix the servos: easy repositioning when setting up, and they provide the legs of the robot when you turn over the robot such that the actuator faces down. Move the servo's around until the platform moves good and each servo has the same effect on the platform.

Also look at the range of each servo / upper arm: you cannot go 'all the way'.

The mechanical delta / parallel part of the robot is done!

Step 5: Step 5: Controlling

You can now use your favorite micro controller to control the servo's. An arduino, a parallax propeller, anything that works best for you. I wrote a demo program in Spin for the propeller, for the sole reason that I had one available and my arduino's were 'busy' :-).

The video shows this demo: some slow movements of the individual servo's, and the quickest circular movement demonstrating the potential power of this type of robots (if you can find an application for one this size... :-))

Attached are the spin files containing the demo.

Step 6: Step 6: a Manipulator

A robotic arm which only moves around, like a husband near the fitting rooms, is useless. Lets attach a manipulator: a gripper, to pick up objects. I made a simple lightweight gripper by separating the controlling servo and the platform.

The gripper is made by folding a piece of thin plastic in a U-shape. Drill a hole in the center such that you can mount it on top of the screw that we attached to the platform. Fix it with two screws.

To use the servo remotely instead of on the platform, I use a wire in a tube like brakes on a bicycle. Take a thin tube (eg from electrical wiring) and push a stiff wire through it. Make two tiny holes in the gripper and push the wire through, and make a knot on the other side. If you now pull on the wire, the gripper will close.

Somewhere on the base plate mount another servo and fix the tube in the neighbourhood. Make it such that the servo can pull on the wire while the tube stays still.

Done!

Step 7: Step 7: Full Demo

Now witness the power of this fully armed and operational delta robot.

I have tasked my new minion with the important mission of picking up an M2 nut, swinging it around, and placing it back again on exactly the same spot. As mentioned before, I am open to business offers.

I hope you like the instructable and will be inspired to make an even tinier delta robot.

Anyone ideas on how to make smaller ball joints? Any ideas on a use? Perhaps with a different actuator? A needle, a drill, a pen?

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