3D Printing and Assembling my Robot

 Finally I have enough parts printed to start to assemble my final robot.

Some parts require supporting during the 3D printing process. I have an IDEX printer (Independent Dual EXtruder). This means it has 2 independent tool heads/hot-ends. They can each print a different material. So here I have printed my main part in PLA+, but used PETG for the support material. These different plastics do not stick together very strongly, so I can completely eliminate the vertical separation normally required to make supports removable. Above you can see the indented rectangles and the arch (this part was printed the other way up to how it is shown in the photo. The PLA+ is totally supported in these areas, and the PETG just snaps cleanly off (you can see the small PETG supporting parts behind on the desk).

Around 3 weeks to the competition and I have so much to do! I am away for a week around Easter too, so I have to turn this pile of parts into a working robot this week.

It isn't all advanced digital design and manufacturing. I cut these 'washers' out of plastic milk cartons as the polythene these are made of is really low friction. I put one of these between every pivot joint in the grabber so that the rougher surfaces of the 3D prints move smoothly over each other.

CAD Model Completed

After several late nights working on my CAD model I think I have everything done.

Learning from past mistakes, I included a sketch of the maximum allowed robot size. I also used this to label which motor sockets on the Motor2040 board each of my wheels is connected to, so that I reassemble it correctly when I disassemble my test chassis and rebuild it with the 3D printed parts from this new design. I reused the Pi 5 case design, but reprinted it in better quality in ABS. I added mounting space for a USB-C battery pack which after testing I was happy to confirm is capable of powering the Raspberry Pi 5 with no issue. The twin cell Li-Ion battery pack between the wheels powers the motors (via a 6V UBEC) so they get a constant voltage supply whatever the level of charge of the battery. Using separate batteries also ensures the motors don't cause brown outs for the Pi power supply when the going gets tough.

The whole CAD design is highly modular. This enables each part to be printed separately, reducing the time lost if a print fails or a part needs modifying and reprinting. It also allowed me to get parts printing while I was still working on the rest of the model, saving valuable time.

I really need to get working on my own robot!

Just one month to go until competition day, and I have not started building my own robot yet! Panic has started to set in and I have done some initial work on the CAD for a small chassis to hold the motors and a battery. Based on the design of my small tracked robot, but needing 4 motors instead of 2. I have a design which uses commercial camcorder batteries still commonly used for LED video panel lights. So they are easy to swap out and drop onto a charger.

I spent more time than I probably should on designing a model of the mechanum wheels. But now I have them to add to my common robotics parts CAD model library. I will share them on GrabCAD when I have time to think about things after the competition, so that other members of the robotics community can use them in their own CAD models. I'll do the same with the battery model. I have learned it really pays to model every component and put in all the machine screws and hex nuts in the CAD assemblies. This allows interference detection to be calculated and avoids costly mistakes which require re-printing parts when you discover a servo collides with a nut of some such problem when you try to assemble your design for real.

Working on Attachments with my Young Persons Team

Since my holiday coding, all my Pi Wars time has again been spent mentoring my young person's team. Together we designed a barrel grabber to go on the front of their robot, and started 3D printing the parts for their proper robot. By the time we get to competition day, I will have built 4 robots in total! 2 test platforms and 2 actual competition robots. I am teaching my young persons CAD using SOLIDWORKS. We based the grabber off designs we saw when searching for robot claws on eBay and other direct from China tech selling websites. This is what we came up with.

But I have a cunning plan. Having 3D printed all the parts to fit onto their robot chassis, I am going to design the front of my own robot to have exactly the same mounting points. So I can print a second grabber, camera mount and sensor mounting block and put them onto my own robot. Hopefully this will not over balance my much smaller robot. I plan to put my battery on the back to act as a counter balance for the grabber.