Project Caretaker. Part 5. Tracks

We already have the chassis, the perimeter is known, the internal profile is determined by the wheels, and the external profile by the design.

Just a reminder of what the design and designed wheels look like:

And here's how I designed the track:

There are several aspects that need attention:

The track needs to be printed as a circle to avoid any tensions and structural irregularities that could affect smooth movement.

The print parameters should be selected so that the structure is uniform around the entire perimeter - for the same reason.

Here's the wrong way to print:

This is the correct way:

Since we're printing a circular track, and our wheel has a smaller diameter - we need to ensure the track can bend freely to the required radius.

We need to add some "breaks". During the research to calculate the necessary break angle, I filled a couple of notebook pages, but the angle turned out to be so small that it could easily be increased several times:

I took an excessive angle - during printing, especially with TPU, anything can happen. Such a gap doesn't significantly affect the fixation on the rollers.

Initially, I set the main thickness at 3mm - but the printed product turned out to be too much even for me, the motors struggled to rotate such a track with jerks.

Besides, at this thickness, the tracks were too rigid - the middle rollers were not engaged.

Therefore, the thickness was radically reduced along with decreasing the height of the teeth - it came out to 1.2mm (exactly 3 perimeters when printing).

The plastic is bestfilament TPU soft. I had to print at a speed of 20 mm/s, otherwise even the direct extruder couldn't handle it. In terms of flexibility and strength, everything is more than okay, I couldn't tear the 1.75mm filament by hand, the track fits perfectly.

The only area where expectations weren't met was the grip. The surface feels somewhere between plastic and rubber, when moving without obstacles everything is fine, but it may slip when pushing against an obstacle - can't climb a wall anymore.

And the printing didn't always turn out perfect, once the plastic got jammed due to retractions. About 3 more times the part turned into a mess, or gaps appeared in the layers. One such track managed to complete printing overnight and I was even able to salvage it by filling the gaps with a 3D pen.

But aesthetically it didn't satisfy me and was reprinted.

The final result with the chassis can be seen in the video below. Here you can also clearly see how you can run into issues when ordering motors in different batches or from different suppliers. Both left and right were claimed to have a gear ratio of 1:200, but in fact, the speed differs considerably. And the motors came from different batches because one of the initially purchased 2 pieces decided to seize up and wouldn't start again. Therefore, I ordered 6 pieces with a 1:150 ratio right away to avoid any problems (1:200 is a bit too fast for this project, although it could be tried).