Week 14 - Moulding and Casting

This week started with printing the first parts for the sun tracker.

Here is the lower half of the main body after cleaning the support material and with nylon hex nuts inserted into the flange.

I also tested some joints / rod ends for arm and the fit to the carbon fibre tubes.

PCB Design

Because I have already decided on the motors, encoders and other peripherals, I could finish the PCB schematic.

Here is a screenshot of it:

Then I went ahead and designed the PCB.

First I wanted to use a double sided PCB, but I decided to try with a one-sided first. The large copper area for dissipating heat from the h-bridges.

This time, I'm going to use through-hole JST connectors with 2,54 mm pitch, as they will give a stronger and more reliable connection.

It also means, that the PCB faces outwards with the soldered components, but the connectors face inwards, which is very practical.

Then I asked my instructor to take a look and see if there are any obvious errors I made.

A name for the project

It is very common to name airplanes, trucks, ships and more with a reference to old norse culture / literature. For example there is a huge custom-built truck with eight wheels on 78'' tires. Of course it's name is Sleipnir.

Because my final project will chase the sun, I remembered in the famous Eddukvæði poesm, a wolf is mentioned that chases the sun. Here is the quote:

Grímnismál 39.

Sköll heitir ulfr,

er fylgir inu skírleita goði

til varna viðar,

en annarr Hati,

hann er Hróðvitnis sonr,

sá skal fyr heiða brúði himins.

There are many different and greatly varying translations. Here is one:

Grímnismál 39. - english translation

Skoll is the wolf

that to Ironwood

Follows the glittering god,

And the son of Hrothvitnir,

Hati, awaits

The burning bride of heaven.

It is therefore very appropriate to name the sun tracker Sköll.

If I ever will built a moon tracker - it's name will be "Hati".

PCB production

After my instructor had reviewed the drawing, I went ahead and milled the PCB in our Roland MDX-20.

And here is the result:

Then I soldered all components that were already available, while waiting for the connectors.

Just before I was going to solder the H-bridges, using paste on the bottom pads, I realized a major failure on my board. All pins of the H-bridges were connected together with the bottom pads! This is of course due to insufficient space in the design, but I didn't see it until now.

The fix was to use a small hand mill and seperate the pads from the main ground pad in the center. After having checked with the multimeter, that there was no conductance I could proceed soldering the H-bridges.