Week 13: Wildcard Week

Project Plan

I needed this week to be helpful towards my final project otherwise I would have a hard time justifying to myself spending a bunch of time on it. I figured that it would be a good opportunity to try and make the members between the actuators. I had considered 3D printing then and that could be the back up plan but I was concerned that to achieve the rigidiy I was looking for it would become bulky but more importantly, unnecesarily heavy.

After the presentations in class, I was debating between choosing composites, metal lasercutting and welding, and the waterjet. They all had potential to create the strong, light limbs that I was looking for. I spoke to Alfonso about composites and he advised that while they are super cool and would be a great fit for the project, they are very sensitive and mistakes cost lots of time. As there is still lots more to be done on my final project, I decided composites wouldn't be the best use of my time. After I thought about it a little longer, the laser cutter was the best option because I would be able to weld the components together and wouldn't need any additional components. If I waterjet them, I would need to attach them somehow anyway so the laser would just leave me better off.

The Assignment

My self assigned assingment for the week is to learn to use the xtools metal laser cutter and some form of welding. To do so, I will design and make the members that will connect the actuators in my final project.

Execution

I met with Dan after class on Wednesday and we agreed that I would come in Thursday from 7-9 where he would show me how to use the tools and we could talk through my plan. I knew he was short on time and again, I didn't want this week to take up a ton of time so I went home and began designing. I hadn't gotten too much detail from Dan regarding what material we had access too or what the kerf and tolerances of the machine were and so I determined I would make a fully parametric design so I could work around the material options that he had available.

I thought back to the joint styles I used in lasercutting week and I thought that I could design a highly symmetric desing and have two pieces interlocking and then two base plates that would sandwich and lock the interlocking pieces together. For the interlocking pieces, this was the initial idea that I had pictured in my head, its a super rough sketch but it helped formulate the idea.

With that in mind, I jumped into Fusion 360 and began modeling and added parameters as I went. I was able to achieve something pretty similar to what I sketched out.

I designed them so that they would interlock like this:

I then designed a base plate that would interlock with the tabs at the bottom of the cross members.

These combine together into the complete arm structure that I'll use in my project.

With that all prepped, I was ready to go and meet with Dan in the CBA shop. He showed me the tool, an Xtools metal laser cutter with a removeable laser for welding.

It was actually super simple to use, the UI was pretty straight forward. It takes a picture of your stock and sizes it to your screen.

You're then able to drag and drop your compoments as seen above. I then had to select the material, I measured mine to be .0455" and Dan suggested to overestimate a little so I chose my material to be 2 mm steel. I then used the capactive touch sensing to focus the laser and then used the suggested dial setting from the software to fine tune it. The cutting itself went off almost without a hitch. The only issue that I ran into was that sometimes the parts wouldn't completely fall through and rotate up and the head would crash into it, sensing a crash the machine would stop. I solved this my just pausing the process and pulling the parts out before it had the chance to crash. These were all the parts that I ended up cutting.

Here is a timelapse of the cutting process.
With them all cut, I was able to do an initial assembly of the components.

With all the pieces cut, Dan then showed me how to use the TIG welder. I figured that I'd be better off trying to learn tig because I'm going to lost access to the laser welder at the end of the class anyway. This was the setup/equipment that we were using.

My first attempt didn't go swimmingly, I found myself melting through the material or having a hard time getting the puddle to bridge between the two plates, the plasma had a tendency to just jump between the sheets. It was pretty rough but it was a great start nonetheless.

I decided that I didn't need to weld along the seem of the cross members, for one, it looks pretty ugly and these are going to be completely exposed on the final project. Two, they were more than strong enough with them just welded to the base plate. Thats what I did for the rest of the members.

Thoughts and Reflection

I was super happy with how this week turned out! I spent a good amount of time debating between the different machining systems and I'm really that I edned up choosing the laser cutter, I think it worked out great. I wasn't really sure how I was going to make the members between the actuators. I was nervous about having to 3D printing them as they could very easily get pretty bulky and unnecesarily heavy. Using TIG was not nearly as hard as I thought it would be and I'm looking forward to continue working on it in the future.