weChook Racing: Electric 3Galoo Build Log – Lessons Learnt

In case you haven’t worked out from the lack of us being at races so far this year, 3galoo has not been progressing smoothly.

We’ve had numerous problems with the wheels and driveshafts at the rear of the car, and I thought it’d be a good idea to record what we’ve learnt so that other teams out there don’t repeat the same mistakes.

Without further ado:

Bearing Fits

We had the hubs and bearing spacers for the wheels machined by a local engineering shop. Having checked my drawings with one of the technical specialists at work, I had good confidence that the drawings were correct, and most importantly, correctly toleranced.

Sadly, the parts we received back were not up to scratch. The recesses within the hubs for the bearings were too small for us to fit the bearing, although not by an amount that we could measure with a set of calipers. It wasn’t until I sent the parts to my friendly technical specialist that we realised that they were less than 1/10th of a mm too small – this was enough to completely prevent us from fitting the bearing.

Foolishly, we wrecked one hub by trying to turn out the extra hundredths of a mm with our bench lathe which really was not up to the job – we went from not being able to fit the bearing, to it falling immediately back out.

This all put a massive damper on progress, and enthusiasm – as the first thing that we’ve not done ourselves, for it to go this poorly was a bit of an eye opener. We know for next time – make sure our tolerancing is documented properly, make sure the person doing the machining understands and agrees what is required of them, and if possible, get the bearings to them that you want to fit!

Shaft diameters

Our next problem was with the shaft that we bought to use as the rear axles. To our calipers, the shaft we bought was a constant 18mm diameter the whole way along, so we couldn’t understand why it would only fit part of the way through the holes that we needed it to, and why it slopped around at other points.

Again, a measurement with a higher resolution tool showed us that the shaft was definitely not a constant diameter along its entire length. We were advised to instead purchase Cold rolled bright mild steel, which has a much more consistent outer diameter, and has really reduced the amount of wobbliness at the back of the car.

From this we learnt how much difference an imperceptible change in diameter can make, and therefore the importance of using the right materials.

Tolerance Stack up

The design we came up with introduced a lot more ‘critical tolerances’ than it needed to, meaning that many dimensions on many parts needed to be machined perfectly for the design as a whole to work.

The redesign at the rear end used a shaft that we knew would fit well into the I/D of the bearing with no further work, reducing the number of ‘critical characteristics’ by two.

This approach of designing to minimise the ‘critical characteristics’ of any given part makes the entire system more robust, and easier to manufacture, which is a big win!

Hopefully this has been of some use to someone who’s looking at building their own car!

weChook Racing: 3galoo Design: Wheels

The first thing we decided upon for Electric 3galoo was a change to smaller diameter wheels – 16 inch rims down to 14 inch. The main reason we hadn’t done this previously were concerns over the cost and availability of tyres that fit this size rim, but after discussions with Matt from Renishaw (https://twitter.com/Hunter_Concepts) we decided to take the plunge.

The main advantages of smaller wheels are aerodynamic. The steering envelope is reduced, meaning the total width of the car can be reduced (or the same width can be maintained with less cambering of the front wheels), and the top surface of the car can be lower, reducing the total frontal area.

Plot showing estimated aerodynamic vs rolling drag for 2galoo

Plot showing estimated aerodynamic vs rolling drag for 2galoo

The con of smaller wheels is higher rolling resistance. Rough calculations say that at F24+ speeds, aerodynamic drag exceeds rolling drag by at least a factor of 4, so it shouldn’t be too hard to get a win in the trade off.

As well as reducing the diameter of the wheel, we wanted to make them narrower. The widest point on Electric 2galoo is at the centre of the rear wheel, at 560mm. As well as being well over the minimum track width of 500mm, having the widest point on the car so close to the back is aerodynamically very disadvantageous – we found it impossible to make a smooth curve for the bodywork that came back to point, as seen on Reprobation and Jet.

In order to reduce this width we needed to forego spokes, replacing them with solid carbon disks. We’d also have to replace the standard bike hubs we’d used on our previous cars with something a bit more bespoke.

Our original design (made before we’d actually got our hands on the rims we planned to use) is shown in exploded view below. We planned to fit some foam cored carbon sandwich panels inside the rim, with a hub bonded and bolted around them. We would have had the same wheel design at the front and back of the car – the front wheels would have been bolted through in a similar fashion to 2galoo, whilst the rear wheels would be attached to a brake disc holder to enable driving/braking torque to be transferred to them.

Initial flat wheel design

Initial flat wheel design

Once the rims arrived, we noticed a few problems with this design – the inside of the rim was angled, which would make it very difficult to get a good bonding surface between it and the carbon discs. The outer surface of the rim however was vertical,  making it a perfect bonding surface. This led to our second design iteration – instead of bolting the hub around the carbon discs, the discs would be attached around the hub.

Second flat wheel design iteration

Second flat wheel design iteration

This reduced the complexity of the hub, reduced the number of parts we’d have to turn, and increased the bonding surface area on the rim, hopefully resulting in a stronger final product (in fact, my calculations say that each bond should be able to support 865kg – slightly more than we’re planning for 3galoo to weigh). This still allowed us to keep the front and rear wheels identical – a big benefit when it comes to keeping spares.

If anyone would like a closer look, the drawings for the first hub is here: Hub and the second is here: NewHub

Next up, the chassis!

Aerodynamic bicycle wheel coverings

It has been some time since I have stayed up til 1am working away to get a project done. It seems once you leave University and start working for a big company times like this are rare and I find myself missing the feeling of satisfaction when, at the end of a long session of chooking, you get to go to sleep.

Fortunately this void has recently been filled by Driven…..from my projects page, ‘since starting my graduate scheme for Jaguar Land Rover I have joined the ‘Driven’ engineering project. A team of graduates who design and build a new car every year for an electric vehicle race hosted by Greenpower.’

So far the Driven project has helped me meet many talented people all with the common goal of making an electric vehicle. This has also presented some unique challenges as the team is far bigger than those I have worked with in the past, with the idea behind this being that we function as a microcosm of the overarching company. In addition to building a car every year the team hopes to (and hopefully succeeds in) inspiring the younger engineers at the race events. I plan to use this blog to document some more of my work for the car in the hope that some principles can be applied by other teams to their cars.

Covering the wheels of our cars we can reduce the loses we have due to aerodynamic drag and hopefully this will increase our top speed and efficiency. Although I am no aerodynamics expert I am aware that a spinning wheel made of spokes presents a drag factor when those spokes are moving through the air. My housemate Shawn would be able to describe the effects of this in far more detail than I can but essentially forcing more air to move in and around the car is BAD.

As well as the spokes going through the air creating turbulence we also want to make the side of our car as flat as possible so that the air is passed down the side, rejoining neatly at the back. Since both our Driven cars have open front wheels covering these can further improve (reduce) the drag coefficient of the body. As an added bonus covered wheels can look pretty cool.

This is a quick and easy way to cover wheels we have been experimenting with. It is cheap and can be done easily at home (this was done in my kitchen). So far I haven’t done any quantitative testing on these wheels vs uncovered but as far as I know the aero benefit should outweigh the slight weight penalty.

Tools used:

  • Stanley Knife
  • Hole Saw + Drill
  • String
  • Pencil
  • Electrical Tape
  • Cutting board
  • 1 screw / nail
  • 1x beautiful assistant, thanks Ben!

We started our build with a big sheet of thermoform plastic, around 1 – 2mm thick should be perfect. Ours is thermoform but only because it is what we could get our hands on, any plastic should work here. We did try some basic thermoforming but found that the plastic would just sag on to the spokes and create a very wavy surface.


Start by drilling a hole where the centre of the wheel will go. We then insert a screw in to this to act as a centre reference. A piece of string and a pencil can then be used as a giant compass to draw a circle of approximately right size to suit your wheel. Cut big to start with, it’s always easier to make the circle smaller than bigger if you go wrong! Once you have your circle drawn you should be able to use a stanley knife to cut around the line. Be careful here.

I apologise for the poor picture quality, it was late and my kitchen isn’t the most photogenic place anyway (though much improved by a photogenic assistant!).


Next up select a hole saw that is a bit bigger than a convenient flange on your hub. Use the hole we drilled earlier as a guide and the hole saw create a bigger hole.

Now the ‘overlap’. Our wheels (like all bike wheels) are slightly convex in that the hub sits out wider than the rim. This means that a flat piece of plastic won’t simply fit on top. To overcome this we must create a very slight cone to fit the wheel. This ‘overlap’ method is far from perfect as it does create a slight bump on the wheel which makes for a not perfectly flat surface, however, it is easy to achieve at home.

Start by cutting from the inside of the cover to the outside. Then place on your wheel. It should be noted that as the outside of the cover is pulled down to the rim a natural overlap can occur at the new cutline, simple. At this point you may have found that you have to adjust the size of your cover. Ideally you want to have around half of the rim showing and half of it covered as this will make life easier in the next step.


Next we run a line of electrical tape all the way around the outer edge of the rim. Covering the new cover and then folding some over the edge of the rim and in to where the tyre sits. Electrical tape actually seems pretty good at going around the circumference of the circle and with practice I can always do it in one long pass. A piece of tape neatly covers that overlap line and then we finish the wheels with some black hot glue just to hold the centre to the hub. It can be worth doing both sides of your wheels, just remember you still have to have access to the valve holes! I just cut a small window on the inside covering to allow access to this.

eCumbent – Welding Begins

This post is a little late in coming and the eCumbent trike is now a lot further along in development, as usual I find myself forever playing catchup.

The first step was to harvest some donor bikes for parts and build the rear forks. Every time I use my chop saw on steel I realise just how useful it is, this thing cuts through so easily and saves me from hacksaw hell. The forks were jigged up and some axle holding tabs fabricated to hold the wheel in place. These have been made from much thicker (5mm) steel plate: heavy but they should hold down the torque provided by the rear hub motor that I plan to add.


Once the fork came together I started building the spine of the frame. The pictures below show a crude setup using toolboxes of convenient heights to get the frame geometry correct to the plans. It took several attempts to get the spine of the frame true. After using a myriad of distinctly average measurement techniques I eventually settled on a set of tack welds I was happy with and managed to weld the spine together.

I also received the components to build my front wheels, 20″ with 20mm axles. I haven’t laced wheels in a while and the small rims with 3cross lacing proved a challenge but as always it all pulled true in the end. Lacing wheels is a very therapeutic part of building a bike and I would recommend it to anyone who has some level of patience.


More progress to come.