So the goal for today was to finish the Z-axis. I almost succeeded.

The first step was to turn a hollow axel that I could use to change direction of the Z-axis ball screw nut. These nuts contain a large number of tiny metal balls that are tightly fit between the ball screw nut and the ball screw itself. If you unscrew the nut, all of the balls fall out, and I doubt putting them back is is even doable without proper tools or whatever they use to assemble these in the factory.

Todays task was to complete the driveshafts, ensuring they are completely stiff as well as adapt the axeljoints to fit on the motors. This turned out to be more interesting than planned.

The first step was to test the bearings I made last time and ensure the were properly shimmed and were completely gap free. One of the shafts needed one additional 0.1mm shim. Now they are all three rock solid. The flex in the construction is smaller than the flex in the 10mm thick steel plate that they are attached to.

Z-axelns homing switch

Det ser ut som att det är så här den skall sitta, men då når inte pinnen till den innan kulleden går i taket.

Z-motorns hål

Vad är bästa sättat att göra hålet i aluminiumchassit stort nog för motorn att gå ner? Helst skulle jag använda en liten handhållen sticksåg med metallblad. Finns det en bättre metod?

Y-axelns montering i chassit?

Jag kommer behöva montera isär och ihop både X och Y-axlarnas lagerhus för axlarna pekar ut ur fel ända inser jag nu. För åt minstonne Y-axeln så behöver jag dessutom montera isär den helt och hållet en gång till för att alls kunna gå in den.

Seems to be my new main project for the forseeable future. Building a CNC machine is not done in a day, even if all of the parts mostly exist… Also, I have done my first 3d-print but I will need to colect it tomorrow as it did not quite complete before I had to go home.

So today I started with the rebuild proper. A run-though by Eric Cederberg about which parts belonged where, and I got working.

So the Terco was not going to do any more work until it got some love and some spare parts. The spare parts are still on their way, but the love was availible here and now.

The insides of the Terco are jam packed with cables and electronics. Three power converters, a complete computer, three drivers, and an inverter to drive the spindle. Not every single cable connecting all these parts together had been done in cleanest of ways. I even found one original cable from the 70s. The rubber was fascinatingly different from what we use today, and was cracking completely.

So today, the plan was to start mass-producing frame parts. I need a total of 4 side frames and two front/back frames. The plan was to make half of these just to see that it all fits together.

Unfortunately, this is what the CNC machine looks like now. One of the motors has given up and needs to be replaced. New motors are ordered and the machine will be rebuilt, but it will be about 2 weeks.

So today I knew that I needed to finish one of the motor mounts, complete with bearings and opto-switch and make sure that the entire electro-mechanical setup actually works. And yes, it really does!

[vimeo 374277351 w=640 h=564]

So yeah, the video just looks like a motor starting and stopping, and admittedly, that is what it is. But the rotary encoder on the motor is actually used to rotate the motor exactly 0.8 revolutions via a P-regulator. And now, the opto-switch is also conected so the arduino is detecting every time a full revolution is completed.

So armed with a new design, It was back to the makerspace. Results were mixed to say the least.

In order to not once more find that I had designed something that could actually not be built, I decided to mill a prototype out of plywood. I had a hunch that is might not work, and boy was I right!

Promising start…

Everything worked out really well until the final finishing passes when then forces from the milling simply lifted the pieces out from their frames and shredded them to splinters.

So my original design has some serious flaws. Going back to the drawing board, I decided to start completely from scratch.

I had two problems. The first was that all of the screws were not as accessible as I needed them to be. The second was that the fram required me to drill holes into the short ends of the front and back walls. This would have required a manual step and I could never get good enough tolerances on that.

So to build a robot, you need to design a robot. Since RHex was designed by universities (Using military money, of course), you can actually find documentation.. Not great documentation, but still: https://kodlab.seas.upenn.edu/uploads/Main/xrhextechreport.pdf

So the original weighs in at something like 10kg and cost like a small car. I decided to aim for a 2.5kg machine. So what sort of motor would I need? Top-of-the line brushless DC motors are out of my budget range, but six of these solid little ones would give me a pretty good kick. This would give me about 10kg (98N) of max upward force. For a 2.5kg robot that leads to a vertical acceleration of about 3g when all legs are pushing at the same time.