UW Formula Electric Experience

The UW FSAE team designs a new electric racecar every year to compete in the Michigan and Hybrid FSAE competitions. I've had an amazing time interning on the team, and then continuing to work on the design team during study terms. 

 My main three highlights on the UW FE  team are:

• rapid repackaging and manufacturing of a high voltage electronics box

•  the complete design of the racecar's wire harness (wire harness lead)

• leading the manufacturing and IP testing of all LV electrical enclosures

This team has truly expanded my knowledge base of engineering design principles (DFM & DFA), manufacturing processes, electrical knowledge of automobile pcb boards, and HV battery systems. But more importantly, it's a team that feels like family and is always fun to be around in my free time (even if it cooks me for exams).

The UW FSAE racecar has two HV electronics boxes, one called the ebox, the other being the rear lid. The rear lid had to be repackaged, with redesigns of electrical enclosures, mounts, and busbars due to a competition rules violation. 

Old design consisted of the segment maintenance disconnect (Battery plus) connecting to the High Voltage Disconnect (MSD), and then to the TS fuse, and then to the IR/Contactor (Positive Isolation Relay). 

The fuse had to be put before the HVD in the schematic. Then, a second rules violation was unfortunately found a week afterwards, which required that the wire length of the fusing connection between the PCU (precharge unit) and the positive IR had to be less than 15cm. However, the PCU was too far away in the old design. 

This redesign had specific constraints:

• The rear lid sheet metal enclosure was already waterjet and bent, and the lead times + pricing of remanufacturing a new rear lid was not ideal, and thus considered a last resort. 

• To be specific, one week for the whole repackaging in cad and completion of engineering drawings, and another week for manufacturing. This is to meet the extended timelines of the HV enclosure IP tests.

• Rule requirements for both competitions we attend must be met. Specifically creep distances between conductors such as the copper busbars, as well as insulation requirements. During the rules validation, the tractive team and I realized that we missed the PCU wire length rule which required more cadding and planning. 

• A very important consideration is design for assembly. The rear lid is very tight when it is attached to the main accumulator container. Components that may fit in CAD may be impossible to assemble. In addition, the main accumulator container warped during welding, which changed some dimensions. 

I first drew many ideas on my tablet, and quickly cadded some out to see if things fit. I decided on idea 1 because it offered the largest clearance and spacing between conductors. Also, the connection from the fuse to the segments in the main accumulator container can only occur in a small cutout area.  

• The fuse and IR mounts were redesigned. These are electrical enclosures that are printed in PETG V0 due to UL94-V0 flammability requirements specified by the rules. Mounting was slightly difficult for the IR due to a cutoff line where no mounting holes can be under (would interfere with the main accumulator container).

• The IR mount has a upper lid and lower enclosure that allow for easy assembly, cutout areas for wires to come in and out of the IR, and specific regions for the copper busbars to come out as well. 

• I calculated busbar cross-sectional area to ensure that it is rated above 80A (max continuous current) with a safety factor greater than 2 at a temperature rise of 30 degrees celsius. Busbar connections  are clearance slots for tolerancing. 

• Creep distances were validated with the Solidworks measure tool, but either way, nomex barriers will be installed in open spaces and in between busbars. The HV wires and metal bolts for mounting will be heatshrinked for insulation. 

• Enclosures were printed and tested in cheaper PETG for fit of the actual component, and in the rear lid. 

• Old mounting holes are to be welded.

Then, the second rules violation was found during a re-validation of all rules. The wire length from the PCU to the nearest battery connection which is the positive IR has to be less than 15cm, but as seen in the picture above, it is far from it. 

If it is greater than 15cm, then the wire has to be a fused connection, and the distance from the fuse to the IR still has to be less than 15cm. 

I cadded out many ideas to test fit and assembly, but found a pretty creative solution below. 

I decided on reusing the old mounting holes for the IR. I designed a snug fuse holder that uses heat set inserts for the holes. Recall that the rear lid has already been manufactured so the old holes are still there unless the design doesn't require them - so welding them shut. 

Then, I created the manufacturing drawings for the busbars to be waterjet. 

The complete design process and making of engineer drawings took 1 week, and an extra night of grinding out the second rules violation. 

Overall, there aren't really any statistics that can be slapped on to this complex rapid repackaging task. In the end, something that was vital to the team had to be done quickly, and it was clutched. 

• Mock assembly with 3d printed busbars and PETG mounts/enclosures to validate DFA.

• Actual enclosures 3d printed in PETG-V0 for UL94-V0 non-flammability rating.

• Bent busbars using die set, brake press, and arbor press.

• Wired and crimped connections between electrical components.

On the racecar, there are 6 low voltage electrical enclosures:

• rear electrical enclosure: houses PCB boards that connect to rear electrical components via the wire harness.

• front electrical enclosure: houses PCB boards that connect to electrical components at the front of the car via the wire harness.

• RTML: the ready to move light enclosure which is an aluminum enclosure that houses lights that light up when the car passes the shutdown circuit.

• TSSI: the tractive system status indicator lights are in this enclosure. The red one lights up if the tractive system encounters a fault. 

• dash enclosure: contains the driver dash.

• LV battery: enclosure and mounting for a LiPo battery.

The rear enclosure was too big to print in one piece, so I printed it in two halves with PETG and glued them together using a waterproof adhesive. 

• Test lids were lasercut in MDF  (similar to plywood) to check for fit and potential 3d print shrinkage, before waterjetting the aluminum lids. 

• EPDM  rubber gaskets lasercut.

• For the front enclosure, our sponsor resin-printed it for us, however the front was bowing in due to warping. I fixed it by bolting in a test lid on the enclosure after spraying the print area with a hot air gun for a good while. Worked like a charm. 

• TSSI enclosure printed in ASA due to its heat-resistant properties relative to other materials.

• The RTML enclosure was originally milled by another amazing member. I had to remill the cable gland part to fully tighten the gland as it would interfere with the fillet. Also, I fixed the NPT thread for the cable gland as it was slanted. 

• The TSMP enclosure contains high voltage and low voltage connectors. I redesigned the TSMP enclosure due to interference with other car components, and a rules violation. 

• Created a test plan document for IPX5 testing enclosures, simulating the actual rain test during competition. This included how long water would be sprayed, at what length away from the part, and the duration. 

• Indicator dots lined possible ingress points. 3/5 enclosures passed the first time, whereas some, such as the RTML failed (red indicator dots signalling water). 

• Failed enclosures were improved and eventually passed IP testing. 

• Designed 4130 (due to good welding properties) steel headrest plate in Solidworks. The headrest plate is the plate (with a cushion) the driver rests his head on. Bonus points are given to cool designs during competition. I personally find my design straight fire. 

• Mass reduction cuts and sheet metal thickness optimization while ensuring design meets rules compliance load cases in Ansys FEA (900N frontal load, 300N side load)

I was tasked with machining a suspension damper collar that would be tunable. The damper collar's hole is a M24 x 2.0 thread that mates to the topeye. The 4 smaller 1/8'' holes on the collar allows a tool to configure preload on the damper spring. 

I first created 3 engineering drawings in Solidworks, each one signally a step, then made a step-by-step on machining the part. 

• Machined 4130 steel spacers and aluminum welding jig to ensure concentricity between the spacer and clevis hole. Then milled the actual hole size for press fitting a flange bearing after welding. 

• Bent 4130 sheet metal covers using a v-block and clamp.

• Taught new FE members lathing, milling, and threading with chassis inserts. 

• P.S. Check my projects page for all my machining experience.