RR1: Real Robot One - a DIY Desktop Robotic Arm

The first preview of RR1 rev. 2 in the following short video. This is just a sneak peek, not even a test yet. I have just checked if wiring works.

I would like to announce that I have decided to release the complete source CAD files for the RR1 robotic arm. Everything is here on my github: https://github.com/surynek/RR1/tree/main/rev.2/CAD.

These are sources that correspond approximately to revision 2. Although the files are a bit messy and not everything is named nicely, I believe that you will appreciate the CAD files when constructing your own RR1 copy. I believe that sources are better than having only the STLs, because sometimes you need to change the size of a part by +-0.1mm so that everything fits better, which is not possible without sources.

In the future, I will post the sources for RR1 revision 3, which I am currently working hard on.

A new video about a broken PETG planetary gearbox from the RR1 revision 1 robotic arm. It was the gearbox from main shoulder joint. A surgery and analysis of the gearbox is shown.

What I found shows an important hidden weakness of the old design and is an excellent lesson for the future designs.

I am happy to announce that all STL files for 3D-printed parts of rev.2 are published in my Github reposity: https://github.com/surynek/RR1. I have not yet published the source files in CAD, I will send them on request for a specific part (sometimes parts need to be adjusted by a few tenths of a millimeter for a specific 3D printer). The design of the RR1 robot represents lot of work for me, so I don't want to make the sources completely freely available (at least for now).

Together with my colleagues from the Faculty of Information Technology, ČVUT, we filmed a new documentary about the RR1 robotic arm in our well equipped faculty studio. Unlike my previous videos, this one is more professional, better lit and shot with better cameras. In addition, I show things in the video that I have not shown in other videos.

I finished assembling the gripper for the RR1 rev.2. Most notably each finger of this new gripper has two parts connected by a joint, so it is much more dexterous and can grip an object much better than the fixed gripper in RR1 rev. 1. I also improved friction, the inner surface of the gripper has many small inti-slip pads (rubber bands as in rev.1 are no longer necessary). I did a test and, for example, the gripper is perfect for holding a glass or a can. The tip of the gripper when closed can operate as tweezers.

As for the material, it is a combination of PETG, flexible filament and polycarbonate with carbon fiber. Plus some linear bearings many screws and bolts.

After running the RR1 rev.1 (the black one) at Maker Faire Prague 2023 for two days, we experienced a crash of the main shoulder gearbox. One of the axles holding the planet gear moved out and the planet went out of its position which resulted in an irrepairable collapse of the gearbox. So I made a new gearbox, now not from PETG but rather from polycarbonate blend with carbon fiber (Prusa PC blend).

Replacing broken gearbox of the main joint means decomposition of the robot into quite small parts interconnected via cables.

The new gearbox ready for assembly into the robot.

And finally everything assembled together again. The new gearbox improved rigidity of the robot which made RR1 rev.1 even better than before. After this incident I decided to replace the big gearboxes of the shoulder and the elbow joints in rev.2 (the orange one) originally made of PETG with new ones made of polycarbonate blend with carbon fiber (Prusa PC blend).

I have some good progress on the rev.2. The elbow link is finished and mounted on the rest of the arm. The following figures show what does it look like. The elbow link is shown separately, the rest of
the arm separately (in a folded position), and finally the elbow link and the rest fixed together.

The encoder nicely fits between the aluminum extrusions on the elbow. Parts of the wrist joint are again made of PC blend with carbon fiber (the black parts) - all the gears and rings in the gearbox. The reduction ratio for the wrist joint is approximately 1:10. Much less than in rev.1 which I believe can make the robot faster without compromising its strength. Another notable improvement from rev. 1 visible in the folded position is that the elbow link can rotate freely without touching the upper-arm link.

Now it is time for finishing the base turret and the wrist link with the gripper. Some important design changes will come on the wrist link as well.

There is some progress on rev.2: not big but steadily going ahead... I am just completing the gearbox for the wrist joint which is one of the smaller joints on the RR1 robot (the second smallest to be exact). The picture shows well lubricated planetary mechanism for the wrist joint without the disk that will cover everything and the outer ball bearing ring that will go aorund.

Most notably, I switched from PETG to polycarbonate with carbon fiber (Prusa PC-Blend Carbon) for some machanic parts of rev.2, namely for gearboxes on the elbow and the wrist which seems to give much better results. Gears made from PC are very tough and feel like even not plastic. If I compare big shoulder and the elbow joints on rev.2 where mechanic parts were made from PETG, this is big improvement. Ovearall backlash is reduced in the mechanism and visual look and feel is much more pleasing than PETG.

The progress with RR1 rev.2 is not as fast as I would like it to be, but at least I can show some new designs concerning the base turret. Currently the main link connecting the base joint (shoulder joint) and the upper joint (elbow joint) is mounted on the redesigned base turret as can be seen in the photo below.

The main new feature of the base turret is that the encoder is moved from the motor shaft directly next to the base joint. The torque is transmitted to the encoder via belt that goes all around inside the base turret. The belt is directed out of the base turret towards the encoder by two pulleys (see photo below).

I expect higher precision from this design and as I wrote before, also increased collaborative ability.