WEEK 4: Tack Welding Rotor End Cap Together, Warping issues, Removing the Fuel Tank from the MR2, Battery Module Design Perfected, Temperature Sensor Coding Circuitry, Flywheel Coupling Lathe Turning

After prepping the surfaces of the rotor end cap to weld to the coupling, I then pressed the coupling in flat and hopefully flush with the end plate surface, and clamped it into the vice in the welding bay.
I then got to tacking it together with the TIG welder, and afterwards noticed a major warp in the plate.
You could press down on the sides and it would be springy like a diaphragm, that's how bad it was. This really worried me as an electric motor has to be absolutely perfect for it to run well, and welding wasn't seeming to do it.

I am seeing this motor as more of a prototype at present for testing and seeing how well it performs with the 3 x SmartDrive Washing Machine motor stators.

I found that the warp could be forced flat if enough pressure was exerted on the plate flat.

Therefore I decided to try have someone stand on the actual weld piece with the aligning top end plywood to see if it would flatten out.

I then tacked it with the TIG welder and I am reasonable happy with how it is looking so far, I know it won't be perfect as welds always cause imperfections, but it will be good to see how it turns out.

After having several issues with the router bit sizing, as there is a 3mm metric and 1/8th (3.175mm equivalent flat end mill), I had to redo my cut file with hole sizing set at 18.5mm for each cell to fit into. I bought a 1200mm sqaure 9mm thick untreated plywood sheet from Bunnings Whakatane for just under 30 dollars for making the battery modules out of.

 I had spent an entire lesson trying to get a cut file sorted for a row of 11 modules which I quickly figured out wasn't working and to make it worse, Inventor, the CAD software I was using decided to crash while I was saving it. Nevertheless, I managed to get the design to the point I was happy to begin routing all 54 of these. What fun!

The previous weekend, I worked on getting the last main unnecessary part in the MR2 which was the fuel tank! I spent a good 3 or 4 hours in the wet detaching all the coolant and AC lines, the fuel filler pipe and a bunch of straps to finally be able to drop the fuel tank out from underneath.

This has left a large rectangular space in the middle of the car which could be used for something later on. At present I would like to integrate all the batteries at the front of the car to help with weight distribution of the MR2 (which is known for snap over-steering due to the weight on the rear wheels, being a mid engine car).

 I am also beginning to get underway with all the temperature monitoring circuitry for the battery modules through coding with the Arduino micro-controller. I am looking at using 5 of these Arduinos to account for all the inputs from each sensor and sending information to the cars head unit area via LCD displays.

Lastly, I worked on turning the flywheel coupling down and doing my best to get it straight in our lathe with a live center. I then proceeded to bore out the inner with a 24mm large drill piece, which one end of the SmartDrive shaft will be tightly fitted into, with a retaining M6 bolt to secure it together.

WEEK 3: Rotor End Cap CNC, Rotor Key Coupling, Battery Module Prototyping and Testing/Sorting all Cells

This week, I managed to get the rotor end cap routed out, which using the 2mm carbide end mill to do the tracks at 0.05mm cutting depth, took many hours to complete. I then used the 6mm carbide endmill to cut out the remainder of the steel to achieve a nice round looking plate design.

 After cleaning these parts up a bit, I moved on to getting the key coupling ready for welding into the inner bore of the rotor end cap.

I slowly turned down the coupling until it fit very snug into the rotor end plate, I then prepped the surfaces for welding when I get the chance. I am hoping that they will not warp when welding.

I also kept on working to perfect the battery module design for the best assembly I can make. I have decided on using 9mm ply to make 54 of these holders below.
In this prototyping I have also decreased the size as much as possible so as the modules stay strong and compact, and have added 2 slots down the sides to house the large copper shunts. I also have added 5 temperature sensor holes so it can be moved around to get a better idea of the cells temperatures in the battery modules.

Using my DIY battery spot welder, I began trialing out the resistor leg fuses and I am really happy with how they are looking so far. Each end is spot welded to the battery and middle part will be soldered to the copper shunt wire (6mm2 house wire doubled over).

I also began the long and tedious process of sorting each individual cell by their strength tests. I am classing all the higher quality cells as those that can deliver at least 14A short circuit and have not discharged below 4 - 4.1V over the year or so that I have stored these batteries as I collected and tested them.

I am happy with the cells I am left with and found about 20 to 30 bad cells in my lot of 650. This will decrease the number of cells but with safety in mind, it is the wisest idea to leave some out. Also because I am designing the battery packs to be largely expandable by twice the current size they will be.

WEEK 2: Rolling Rotor Housing (too small) and Test Fitting, Lathe Crankshaft Coupling, Rotor End Cap Design for CNC

This week, I finished rolling out my rotor housing with the metal roller at school. I am fairly happy with how it has turned out, but by design, there are 2 sort of flat ends.
I then went to fit 14 of the magnets in, only to find out the rotor was somehow too small. This really frustrated me as I had spent so long on perfecting the design and even left a 4mm oversize in case it ended up too small, but it still at least a 5mm gap.

I have to choose to stick with it now as the rotor cut took me a very long time in the holidays and it would not be worth cutting it out again. I had to think hard about why it ended up too small, and I managed to come up with a theory of how the steel rolls physically.

I had calculated my measurements from the (inner diameter of the rotor * pi), to calculate the length of steel I needed to roll. I thought this would be the same for when I roll the 3mm flat steel, but I have now realised that when you roll the steel, the inner compresses and the outside stretches slightly. This means the actual calculated diameter should have been approximately halfway in the 3mm steel, so effectively 1.5mm + 1.5mm larger diameter than I had calculated. This would make the rotor over 9mm smaller than needed, which would make sense in how my rotor housing turned out.

But I will have to make do with the current state and maybe weld a filler in between the gap to complete the rotor housing.

I also worked on lathing/turning my crankshaft coupling down to fit into the rotor end cap which I am preparing to cut out next week.

I decided on taking all the old teeth off to create a cylindrical coupling of 50mm OD to slot into the rotor end cap and be welded in.

Term 3 WEEK 1: Rotor Housing Cut, Started Rolling, 3mm SmartDrive Flange Mounts cut out

This week on Monday, I finished the rotor cut out on the CNC router after routing the rebate in the steel. I had to make another cut file to go a little bit deeper (0.3 lower) to get the steel out afterwards.

I then cleaned up the strip with getting rid of the burring and excess lubricant, it is looking quite good so far.

After the issues of the metal roller not bending exactly right, I decided to try and level the roller and try to align the rollers as much as possible so it would bend my piece uniformly. This is especially crucial for balance and precision of the rotor housing.

Once I was happy with the bender, I had one of my stakeholders Mr Smith help me with starting to roll it out. We also used a metal square and spirit level balance to get the steel feeding in right before beginning to roll it.

I ran out of time to finish it this week but will continue next week.

I also continued on working on the flange design and getting all the thin 3mm flanges cut out.

I tweaked my design after the first 2 or 3 plywood and steel tests to get a flange mount I was happy with. I then set up the router as usual and after leveling by planing with the 22mm router piece, I then began my cut with the 6mm carbide tip with settings I found to work well: 11 - 15% speed, 0.1mm cuts, 6000RPM, and a dab of lubricant around cut path.

After a few hours of more CNC routing, I managed to get all three flange plates cut out and after cleaning them up a little, they fit really nicely into the SmartDrive stators, with the 4 M16 threaded rods going through.