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A project log for Mjolnir

A hammer than only Thor can pick up!

Brandon HartBrandon Hart 07/13/2016 at 02:350 Comments

Ok, it has been a while since I posted any updates on this project. That's because I was waiting for a crucial component to be completed by a third party. I finally got it and...it was wrong. So I got another one made and I'm moving forward with the build again! The part I was waiting for was the main chassis. This is made of welded aluminum because it's lightweight and strong. See below for pics.

The major challenge with this chassis design is that there is virtually zero room for the screws to go into the insides of the 2 magnet brackets! It took me a while (and a lot of overly complex designs) before I figured out the simple solution. I can screw in one set of inside screws while the other side is empty, and then I simply filed down the threads on the second one to form perfect pins! To hold those pins in place I used a bit of packing foam I had lying around (you can see it the background). Now it holds perfectly!

With that hurdle overcome, the next step was to do a quick test of the breadboarded version. This version uses a breadboard and small jumper wires, plus it's only pulling current from a single LiPo battery to run the whole system. Yet it still performed admirably!

Below is a picture of this less-than-ideal setup holding up the weight of the 1/4" steel plate. I'm not sure how much it actually weighs, but it's heavy!

Then, just to see how it fits, I put a rough version of the 3D printed enclosure around it. Definitely going to need to make some tweaks, but not bad overall!

The next step is getting the final layout completed and replacing some of the parts with final versions. One thing that needed to be replaced was the relays. The ones I was using with the breadboard were standard mechanical relays. This won't work because the illusion of Thor being magical will be shattered when people hear it CLICK as it turns off the magnets. DC-DC Solid State Relays are surprisingly hard to find, but I found a board with a couple of them on it at Sainsmart.com. Here's an approximation of the final layout. It turns out that these 2 LiPo battery packs are a perfect fit between the top of the aluminum chassis and the inside of the 3D Printed enclosure. Sometimes things just work out beautifully (but most times they don't).

I have started drilling and tapping the holes in the Aluminum, but I must be doing something wrong because I've only got 5 holes drilled so far and I've broken 4 drill bits. Additionally, when I've attempted to tap one of them I have only succeeded in breaking 2 different M3 tap bits. Once I get this figured out I'll mount the main electronics and start wiring them up for a test since I'm using slightly different parts now. I'm also going to design a bracket to hold the LiPo battery packs and RFID reader in place, then 3D Print it along with the rest of the final enclosure.

That's all for now!

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