Otto LC

Finally we do have good pictures. I added the first hand full to the gallery. Here are some more:

May be I need to do something with his facial expression. He looks so happy with his mouth open. But that's not how he is supposed to walk around.

With his mouth closed he looks a bit worried. I promise: We will take care of you!

A lot of details on a single picture:

The programming port with the USB port of the Arduino Nano, the custom engraving on the side, the button to switch between modes and the hinge for opening the head/body. The hinge "axle" is pressed on a tab which is part of the back wall. This allows having a hinge without needing additional parts. It also opens the full 180°.

Here the details of the new ankle. The C-ring needs to be glued on. It allows adjusting the angle of the foot so we don't loose travel due to the large steps the servo horns can only be adjusted in.

And once more from below:

The servos actuating the feet are just built into the legs. There are no screws nor glue needed for holding them in place. This picture shows the bottom plate of the leg holding the servo up and bracing against the mounting tab.

The Otto Bot had still been in the "Unstable" group all the time. Very soon next year a school class is going to build a whole set of Otto Bots. Also there is not much left to do. I did some last tweaks and set the default for leg length to 34mm instead of 37. This is barely enough to fit the servo in but makes the robot a bit more stable.

This makes it stable enough to move it into the "Misc" category.

As we are going to laser cut a bigger number (ok, only 15ish) of Otto Bots having to deal with separate pieces would be a pain in the ass. So I added a new "tab" feature that add little gaps in the circumference of the parts. Right now it is only supported for Edge classes and straight lines.

While proper Edges get the tabs automatically parts drawn "by hand" with .edge() and .corner() or .polyline() need to get their tabs also added by hand. I will add tabs to corners in the future but the situation there is a bit more complicated (and not as pressing).

First tests have shown that value of 0.2mm works well  with our laser cutter. The parts stay in the sheet but are easy to snap out.  Making the tabs bigger results in a surprisingly strong connection of the between the pieces and their surrounding.

In theory the tabs should be enlarged by "burn" on both ends. But "burn" is not only used to adjust for the width of the cut but also the determines the stiffness of the fit between parts. So I rather decouple burn and and tabs. This way the proper value for the tabs will just work no matter what burn value is used.

When we decided to do a Otto Bot workshop in early 2017 I drafted the chassis pretty quickly. Although the legs are a bit complicated - the body basically is just a hinged box I already had - it quickly looked like a robot. But only with the workshop approaching got the last details fixed - e.g. the holders for the PCB, the "teeth" holding the head shut, the hole for the main switch, the final size of the ankle screws.

In parallel a group of people was working on a new firmware for the robot and a GUI for moving and calibrating the robot and to create new movement pattern. They currently still lack proper documentation and I have not yet decided whether to make them part of this project here or if they should get their own place - either here on HackaDay or may be just on GitHub.

As a result of this effort the chassis grew an additional mode switch that allows switching between different programs.

We also did building instructions in German with a lot of pictures.

With this in place we did two workshops with 5 kids each.

Lessons learned:

• Kids do not that the strength put the part together if they are cut very stiff - adults often do neither unless one uses tools like a vice or a mallet.

• Pressing the ankles onto the servos is hard and prone to damaging the servo gearing.

• Pressing on the legs is a bit better as they can get pulled on by a screw.

• Building the robot takes kids 3 1/2 hours + the soldering of the electronics which we did in fore hand for our second workshop.
• The legs are pretty complicated with several possibilities to put things together the wrong way.

Improvements to the chassis since:

• New driven ankle now uses a servo horn
• Simplified main switch position
• Simplified the legs a bit