RICE ELECTRIC VEHICLe

The previous wheel mount, however, had visible damage and deformation, indicating that we should probably redesign. To make an improved version, I went and taught myself Solidworks, a powerful 3D modelling tool.

I modelled a wheel mount design that was similar to the previous one, but with key differences:

(1) Instead of the wheel shaft sitting offset and exterior to the aluminum box tube, I moved it to the tube interior, in hopes of symmetry reducing weird reaction moments.

(2) I moved the bearings to the tube interior to protect against potential external damage, and added a brake mount as well.

It’s pretty rudimentary, but I’m still proud of freshman me for getting that far. For some reason, Rice doesn’t even require a 3D modelling course for their Mechanical Engineering degree, so in that sense I was way ahead of my class!

I went to Joe the machinist, and we worked together to mill the parts out of 6061 aluminum.

Since I hate creating waste, my new design actually used materials from the old one! I was able to salvage all 4 bearings, as well as the rectangular aluminum tubes, saving some money and keeping stuff out of landfills!

After we machined everything, I pressed bearings into their pockets, and pressed both end caps and box tube together.

Threw some CAD drawings together, then got these inner caps cut and threaded on the school lathes.

The six holes are for us to bolt into the wheels, and the threading visible on the bottom left piece is for the bolt to tighten and clamp the outer end cap on, as mentioned.

After that, we cut some threads the shaft, then used a segment of threaded rod to tighten the inner end cap onto it.

We used tension pins were used to prevent them from ever separating.

Finally, everything was plugged back inside the suspension! Things are coming together!

First, we had to determine what went wrong on the previous team’s design, to better create our own.

(Basically an after-the-fact DFMEA session 😅)

They had attempted to use a double reduction gear setup, opting to mount the intermediate gears and layshaft on some badly-welded thin steel brackets, bolted to the rectangular tube of the wheel mount. Yes, this meant that the entire powertrain sat exposed, outside in the wheel well, as opposed to safely inside the car fuselage.

However, that wasn’t even the main problem. Someone had drastically underestimated the reaction moments these brackets would need to withstand, and decided to make them out of thin 1/32” steel. These were doomed from the beginning to fail under the slightest bit of torque, and indeed we found them completely mangled out of shape.

It was a very poor design.

Armed with knowledge of what not to do, we started again from square one with some serious flowchart decision-making.

Taking into consideration the steepest incline in the Shell Eco-Marathon race circuit, and approximating the expected weight of the car, we used basic physics to determine how much torque we would need to put down.

Our target figure was 21.695 N-m of wheel torque. However, our brushed motors were only rated to produce 4.05 N-m.

We considered purchasing new units with higher specs, but decided to save $$$ and engineer our way around the problem instead — Namely determining a gearing option that could multiply our motor torque to the required wheel torque.

In the continued spirit of reusing parts where possible, Marco and I started disassembling the old drivetrain.

We were able to salvage the intermediate gear and adapter, the 1/2” layshaft they were mounted to, and some bearings that conveniently fit as well.

This was important because it matched the pitch of the motor sprocket, which we couldn’t replace!

Taking into account our required gear ratio of 21.695/4.05 = 5.36, the parts we were able to salvage, and what was commercially available, I came up with a design with a ratio of 5.6, beating our target value.

I could have gone higher, but increasing torque would mean sacrificing RPM and top speed, which I didn’t want to do.

I drew out some schematics: Like the previous teams, we would use a double reduction setup (reduces the rotation speed using two different pairs of gears). However, our powertrain would be housed entirely within the car fuselage, and include a much stronger mounting bracket for the intermediate gear and layshaft.

After creating some nice documentation for inventory purposes, we went out and actually ordered the parts we would need.

Once our sprockets came in, we lathed our wheel shafts to fit them, then milled out keyways and keys .

Keyways are small channels cut into rotary shafts, that when locked into a complementary cutout in a gear, by small bit of metal called a key, allow them to rotate together and transmit torque properly.

Basically, we built a wooden replica using measurements of our car interior, to visualize and test powertrain designs in.

We used a sheet of 1/2” wood to simulate our CF chassis wall, and bolted on our wheel, motor, and gear mounts.

The next step was to transplant our functioning powertrain into the car, like a surgery!

Due to the trunk bottom being curved, it was very difficult to ‘place’ the intermediate brackets and position the drivetrain correctly in general. I came up with a genius (!!), multi-step plan to do it:

(1) First, I stuck a large patch of Velcro on the trunk floor, and the opposite Velcro underneath the wooden bracket.

(2) Before I placed the bracket on the trunk floor, I stuck in a sheet of paper to prevent the Velcro from grabbing as I shifted the bracket around, looking for an optimal position (chains tight and parallel, no clearance issues, etc.).

(3) When everything had been positioned correctly, I pulled out the paper, leaving the velcro to stick everything! This kept the parts from sliding all over the trunk as I did the last step…

(4) Which was to finally drill through both bracket and CF body together, and bolt everything properly.

It worked super well and I was happy the idea came to me quickly, as opposed to us being stuck for days or weeks on this.

With the ELECs’ help, we tested the drivetrain as installed in the vehicle for the first time.

The first video is us testing a single motor (the rubber-looking thing was surgical tubing we used to tension the chain), and the second video was a full test, with both motors powered and running! It sounded magical 🥰🥰

By this point we were machining pros, so we machined out both new rear blocks in a day!

In addition to shortening and widening the wheel mount block, this design included a few more improvements.

While we had used tension pins to fasten the previous mounts together, this time we used shoulder screws for easier disassembly! We also included tapered Timken bearings to resist axial forces into and out of the mount, something the radial bearings in previous designs weren’t able to do.

Mocked up with a wheel shaft and wheel.

This shorter suspension block allowed us to bolt in our new brake calipers and have things actually fit!

After fully assembling and re-installing in the car, I manually spun the wheel to confirm brake disc/caliper clearance. There was some wobble, probably from shipping damage to the discs, but everything still worked well!

So we loaded it into a crate, strapped it in snug, and had it forklifted into a truck bound for Sonoma, California — where our competition would be!

Shipping costs were actually a significant part of our budget. It’s not cheap to truck something ridiculous like this cross-country and back.

(1) Tent city! To avoid paying for a hotel, we brought along and camped in the REV team tent!

(2) The squad power walking around bright and early the next morning!

(3) Good to see our girl REVolution made the shipping journey in one piece!

The next few days were a delirious mess of final tuning, troubleshooting, and looking for misplaced tools. Before we would be allowed to race, we had to pass safety and technical inspections, so of course at the last minute we realized there was still a huge laundry list of tasks to do.

The inspectors came around, and we passed safety and tech inspections with flying colors, earning the small blue and red stickers below our 712 race livery!

Some tests performed included not losing traction while braked on an incline, vehicle roof being able to withstand a certain amount of weight placed on top without bowing or collapsing, and the presence of an E-stop (electronic kill switch).

After inspections, we had a brief window for photo ops before heading to the race paddock 📸

We ordered multiple yards of steel tube, thoroughly mystifying our college mailpeople, and set about cutting everything to length with a Johnson saw.

Once we had all the chassis members cut and labelled, I personally started welding the main structure, to make sure everything started level and square. After that, members took turns to each get some experience.

More welding happened, and gradually the stack of metal tube began to transform into an actual frame!

Here I am posing in a work-in-progress chassis!

With a brand-new frame came the possibility to redesign and simplify some systems!

As we were abandoning the overly-complicated knuckles and wing/fin design of REVolution, I designed an ultra-simple steering system.

The axle is welded to a C-shaped steering knuckle, which rotates about the chassis via mounted bushings and a retaining bolt.

We machined some bushing mounts out of steel stock, and welded on some square tube sections to create a flat chassis mounting surface.

Not the prettiest, but they’ll do.

I band sawed steel plate to size and welded them in a 90° jig to create the aforementioned C-shaped steering knuckles.

(1) We welded this entire assembly to the chassis, and you can see how the steering knuckle is meant to turn.

(2) As before, the same rack and pinion unit would push/pull the knuckles left and right to turn the front wheels…

(3) And is attached to the knuckle using a series of tie rods and ball joints. The rack and pinion unit bolts into a 3D-printed mount, which itself bolts into an aluminum floor pan.

At this point, I felt confident leaving REV in the hands of our new members. I felt that I had done enough for the team, and that it was time to move on (Senior Capstone + REGALIA).

However, I didn’t want to be like my predecessors and have my disappearance gut the team, knowledge- and skill-wise, so I nurtured new members, taught them what I knew, and waited until they could stand on their own before I said my goodbyes.

REV Class of 2023+, I entrust the team’s future to you.

I owe a lot to my experiences with Rice Electric Vehicle.

Maybe it was the lack of leadership or structure in the beginning, or maybe car culture naturally attracts more relaxed people - I dunno! But I will say that our culture of fluidity and expressive personality made REV the best engineering team I’ve ever worked on. Members were genuine friends who could trash talk, harass, and poke at each other all in good fun.

In addition to that, I got to really cut my teeth and get hands-on in real engineering work early in my undergrad career. I developed so many skills, learned so many tricks, and gained so much technical experience that it’s not even funny. It’s entirely because of REV that I know how to use Solidworks, CNC mill, lathe, weld, use composites, and problem solve in general.

I will miss the team and the times we shared dearly.

Thank you for reading. (Especially if you made it here to the end. You’re a real one!)