So this week I haven't actually been able to do much with the shopping cart for multiple reasons which all kind of route to one reason being that I need to get my hands on the square steel tube stock. Last week when I left off I was trying to find a solution to the deformation of the shopping cart. My original design although the permanent deformation isn't quite visible there is one glaring flaw which is a little bit hard to see in the stress simulation.
In my original design you can see that the square steel tubing is bending up a bit when under load but what's more important is that you can see the points which are under the most stress. The holes where the 90 degree bars are bolted onto the shopping cart are under a lot of pressure, 574 megapascals. Why that number is important is because mild steel, the steel that I am using, has a yield strength of 250-350 megapascals meaning in this simulation the steel would probably start to seriously bend or even break at the mounting holes. Obviously something had to be done about this so I came up with a solution last week but that turned out to not work. But then I returned to another idea which was to extend the square steel tubing all the way from the axle to the front of the shopping cart and have contact points there as well.
The great thing about this design is that the max amount of pressure the steel goes under is no where close to 250 megapascals. This current design having the square steel tubing extend all the way up to the front reduces the pressure on the mounting holes of the bars by over half. Now the new problem arises which is where can I even get this steel. Because McMastercarr, the site I was getting my steel from initially only sells in increments of 1, 3, and 6 ft and the bars I need are 4 ft long each. Also McMaster is really expensive with its shipping costs. After some digging around at local metal shops I found one in Woburn which was able to supply me with the exact metal I needed so next week I will have my hands on the square steel tubing. After figuring that out I didn't really have much else to do with the cart for the rest of the week so I finished printing the second coupler for the stage which came out fine with no issues.
I'd considered the thought of starting a side project for times like these where I have downtime in between doing shopping cart things so I decided to revisit the zoetrope. The zoetrope has been done but it has room for improvements. Last year I finished the zoetrope in kind of a rush. I'd originally planned on adding potentiometers to control the motor speed and strobe light flash and having a power switch to turn it on but I left those out in the final design because I ran out of time and I wasn't interested in working on this for longer than a year. The holes for potentiometers and a switch are still in the original CAD model of the zoetrope so I decided that while I have nothing to do with the shopping cart I would brush up on my electronics knowledge and try to add some knobs to the zoetrope.
I first had to relearn the zoetrope electronics which didn't take long so I replicated the PCB on to a breadboard. I put potentiometers on the breadboard and I tried it but it didn't work. I tried switching out parts to see if they were just busted but still nothing. Then I checked to see if I was using the potentiometer right so I set up a very simple circuit way back from the analog read guide, but the potentiometer didn't work for whatever reason.
The next day Scott Campbell gave me a part for our science fair project which I had to make. I had to design the mounting plate for the EMP to mount onto the 3D printer. I had to start by actually finding a schematic of the EMP because Scott doesn't have it yet so I looked through the github that he sent me. After some digging I found a 1:1 scale drawing of the EMP so I got that printed out and grabbed a Pi Pico to see if it was to scale and it was only a smidge bit off. But then I was told that a gerber is actually a schematic file type which I had no idea about so I saw the real measurements of the EMP mounting holes which honestly were not far off from what I got. So hopefully next week I will have my hands on the square steel tubing and the axle can be mounted on to the shopping cart at last.
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