Anna Aflalo

Fab Academy 2015 | Wgtn

WEEK 16 | Mechanical & Machine Design

-- Link to the group project page! --
Who is Scribbly-Bro, what is he gonna do?

This week, we decided to make a drawbot together.

We brainstormed about the drawbot's functions and agreed on which material to use.
Afterwards, we divided the group into two teams: one focusing on the gondola, the other on the motor mounts.

I was in the second team. We started working on the pulley with Geoff.
The pulley
We decided to use Grasshopper in order to make parametric pulleys. Indeed, we knew that we would have to adjust the design a few times. It was nice to work on it with Geoff because of his mechanical design skills.
We had to iterate the design three times before having the ball chain fitting perfectly in the pulley. We had to improve the press fit tolerance though. The test with the final Gondola and the motors has shown its weakness.
To improve the pulley efficiency, we decided to sand the motor stick and make a D slot on the pulley. But the motors got too hot and we de-magnetised both of them. So we replaced the motors with new ones that we grinded using a wet sanding grinder.

Download the .stl file here
The pulley assembly
The second challenge was to make a bearing that would attached the Gondola to the ball chains. Luckily, Wendy had skate wheels hidden somewhere in the lab. We hammered the wheels and the 608ZZ elements (bearings) felt out. Ben had this great idea and suggested that we could reuse our pulley design. So we scaled down the pulley and added a clip to it (photo above). We printed it out and realised that the clip was too fragile and it broke when we tried to plug the bearing. So Geoff had this idea that we could pause the 3D printer, add the bearings and resume the print.
Test 1:
We just tried to guess the right time to pause the machine. The thing is we didn't want to pause it too early so we obviously did it too late. And the "clip" above the bearing was to thin.

Test 2:
Craig told us about the function "pause at" on the UP printers. So we told the machine to pause at 15mm (the perfect height for us). The result was not bad! But we thought that we could improve it by heating up the bearing before placing it on the print. That way the last piece printed won't lift up that much. But...

Test 3:
We used a heat gun onto the bearing and the result was not so different from the second test. We ended saying that the plastic can't stick on metal anyway. So the plastic will lift up whatever we try.

The pulley assemblies press-fitted into he Gondola.

Download the .stl file here.
Ben and I also focused on the drawbot weight distribution. Daniel had this great idea to use water bottles on each side of Scribbly-bro. We filled the bottles with the same volume of water. And Ben cut a rod of steel weighting the sum of the bottles weight.