Fabrication

I've now re-installed 30 of the 36 cells in the rear battery box. I added plates at each end of the box to make the walls flat, so it will provide better compression to the cells. This is working better than with no plates (there is a lip at the bottom where the floor of the box overlaps and is spot welded to the sides, but this lip is only 10mm high), but sadly it turns out Auckland is shut in January, and the cutting department is still on holiday. I improvised with 1mm steel (old computer cases turn out to be good for something) and a plasma cutter. Many thanks to Edward for lending me his plasma cutter, it's fantastic, no home is complete without one. I need to reinforce the outside of the battery box, as it bulges a little when you swash the cells in. I realised this only after I'd put three coats of paint on it :-(

Anthony (woody on the AEVA forum) is in Auckland this week and came to have a look at what I'm up to. He was a great help, passing clamps while cutting, sanding the terminals on all the cells and helping me install the cells. He also pointed out many obvious things that I missed (things like you should hammer cells on the edges and the conical plasma cutter torch is conical, but it still has a flat face which you can use to run down the side of a guide and get a straight line).

Sadly the second battery rack was to complex to finish in time for the LCA Open Day and KillaCycle tour so I'm going to have the same 36 cells and 118v or so open circuit that the car had last time it was working.

I've mostly finished the bracket which will hold the front mount (where front is closest to the front of the car if the motor was in a north south configuration, which means it's on the left on this car). The mount is the black round thing hanging below the pipe I welded in earlier, and I've spent the evening grinding the curves on the bracket between it and the pipe. The bracket needs a bit of tidying up I'll be ready to weld it onto the frame.

In unrelated news, the KillaCycle arrived in New Zealand safely, the Tumanako VC motor controller had it's first drive yesterday in the Greenstage electric Saker (first time that has moved under electric power too!) and I have about a week left to put this car together before I'm leaving for LCA2010 in Wellington.

I've mostly finished the rear battery rack. I need to fold up some feet to lift the rack up off the boot floor, decide how to support the front and rear sections (cantilever from the middle one? more feet?) and devise a way to hold the cells down.

For a while, the rack came with added vice grip.

I once said I should get a load leveller. Well, I finally gave in and got two. I think I did well with $50 Chinese units from Save Barn. After a little fabrication, they hang at right angles and I can adjust everything in comfort. I'm never installing another engine without one.

Part of the fabrication involved a strap with two holes, and the levellers came with a piece that just needed a little straightening. I'm not sure if this steel is particularly hard, or just poor, but it did not take kindly to being straightened.

I'm making progress fashioning the structure between the gearbox and the mount that will isolate it from the frame of the car. I'm using an aluminium and rubber mount from a small Nissan (the round silver and black thing between the tube on the left and the gearbox in the middle).

After many hours of fettling and weld practice, I've managed to weld the reinforcing bars into my front subframe. The motor will hang between these bars and they also provide strength at the front of the frame for cells or other equipment.

My 175A welder took a bit of tweeking to make good welds in 3mm steel. The biggest change that made the most difference was switching from 0.6mm to 0.8mm wire. I think this could also have been achieved by turning up the wire feed on the 0.6mm wire. MIG is a little counter-intuitive, if you weld isn't penetrating and the wire is building up in a large bead on top of the work, you'd think that you have to turn down the wire speed and weld slower so the heat has more time to penetrate. Actually you want to do the opposite, as the faster you push the wire into the work, the smaller the arc, the greater the current and the deeper the penetration. Of course wire speed isn't the only parameter which affects the current.

I'm welding reinforcing plates onto my subframe which has some overlapping plates. To bend 3mm steel to conform to the steps requires joggle bending. This metalworking technique should not be confused with joggling.

I used my press to make the bends, and before I put the blue square bar in, I got a little close and found that sheering is just as easy as bending.

Last week, Neil Fraser CERTZ came and had a look at my engine mounting arrangement. I want to rubber mount the motor while hard mounting some cells in front and the inverter on top. He recommended diagonal 38.1x2.5mm roll cage tube between the suspension towers and the front corners to provide a location for the motor mounts. A structure to hold the inverter and cells will be attached to these new members too. The cells will need to be mounted such that they can break away in a crash.

The tube is extremely strong, it comes in 5.5m lengths and has a bit of flex when it's that long, but boy, when you cut off an arm sized piece, there is no give to it at all. He also recommended 3mm steel plate to reinforce the subframe where the tube joins. As conic sections are somewhat new to me, I've made up a dummy tube -- the threaded rod lets me adjust the length while I get the end profiles correct. When it's time to make the real thing, getting things right first time will be more critical. The taped on cardboard shows the shape of the spreader plates.

We also discussed putting another layer of cells in the boot and this won't be a significant problem. The cell frame will be made with 50x25x3mm angle iron and hung off 3mm C sections welded to into the boot floor/wheel arch corner. I'll probably connect it to the firewall too. I was only able to get 50x50x3 angle iron, so I may well be ripping it down with the grinder.

The Mini has independent rear suspension comprising of a radius arm, shock & conical rubber spring. A shaft passes through the bearing at the front (left) end and is bolted to the rear subframe. The photo above is taken from the inboard side looking out, the wheel bolts to the other side of the drum brake. When the wheel moves up, the arm rotates around the shaft pushing the rod to the rear of the car, compressing the rubber spring. The bearing is in two parts, a needle roller bearing on the inboard side, and a bronze bush on the outboard side. In my case, the shaft at least is worn where both of these bearings run, leading to a small amount of play, so it's off to Lee at Minibitz for a new shaft and bearings.

I'm preparing the car for a motorkhana organised by the Mini Car Club of Auckland on the August 1, so I have to deal with a few loose things. I've also got to tie down the auxiliary battery, improve the throttle pedal mount, and improve the torque arm on the motor. The electric system ought to be a big advantage in motorkhana as it can go from forwards to reverse at the flip of a switch, and there's no faffing about with the clutch.

My EVision is my only instrument for use while driving and so far I'm not really looking for more.

Months ago, I took my instruments apart and removed the seemingly Victorian wrapped wire on bimetallic strip fuel and water temperature gauge from the middle of my dashboard. Phil came over and wielded his Dremel-like tool to make the EVision fit into the space left behind and I'm very pleased with the result. My EVision is my only instrument and so far I'm not really looking for more. It measures Volts, Amps, Watts, Amp-hours, State of Charge, Wh/km, km/h, km To Empty, Time To Full, Temperature, Balance (the difference in voltage between the two halves of the battery). I find the most useful display is state of charge on the bar graph, and Volts & Amps on the numeric displays. The Wh/km is averaged over what feels like 20 or 30 sections - long enough that it's hard to hold a steady state, and short enough that you can't repeat the same trip in opposite directions. I haven't fooled with the miles to empty feature yet.

My biggest complaint is there are too many options. You use a remote knob to scroll between no less than 20 different combinations, but there is no way to reduce this to a manageable number. I set up 5 and repeated them 4 times, and then after I connected the speed pulse, I added Wh/km. I foolishly only inserted this page once (the configuration software is very painful to use) so I often loose it and have to scroll. It also needs a trip average Wh/km display.

The EVision has a PWM output to drive a fuel gauge. Since I removed my fuel gauge, I plan to ask Victor if it can be reprogrammed to drive a tachometer, or build a voltage to frequency converter. Since I only plan on using one gear, motor revs are directly proportional to road speed, so I don't need the tach. State of charge displayed on the tach would free the bar graph on the EVision itself for something else. I think I'd put battery current on the bar graph and I don't know what I'd do with the spare numeric readout.

Update: See a more recent post where I made the EVision drive the tachometer movement directly.