Tomorrow, We Race!

A lot has happened since the last post and finally tomorrow is the day we have building up to. The Race!

We have test driven the car now 5 times and only the last time did we decide to end testing, the other times the car decided it wanted to stop. So there have been many bugs to fix and finishing touches to apply over the last few weeks.

The drive train has been playing up with loose chains, chains falling off, bent sprockets and more. After a lot of tinkering and fine adjusting it is working fairly steadily now. The chain tension is not 100% how we'd like it, but we are confident it will last the hour.

The main fault has been with the... well errr, we're not entirelt sure, but it has cut the power to the motor more than once during testing. Is it an ESC temperature cut off? Or dodgey wiring? Or maybe its the fuse holder? We're not sure what it is so we adressed all our theories with some cooling systems - an air scoop and a whole bunch of heatsinks on the motor - a redo of the wiring and a new bigger better fuse. The cut off problem did not rear its head during the last testing session so we are hopeful our electrics will go the distance.

The Skin is Finished and an Air Scoop is Added.

 The lycra skin has now been finished and really completes the car. We put a lot more effort into the appearance of the car this year giving it a bit of a paint job and some finishing touches.

Steven Drives the Car for His First Time

The Car Corners Very Well Indeed

Guy Picks Up Some Speed Down the Straight

Tomorrow is Race Day, where we put our car to test against many others with the same goal of winning the eV Challenge! Tactics come into the race a lot but it should be a level playing ground this year with a new track. We'll get to the track early tomorrow morning, register and get the car scrutineered then check and double check the car over. By 11 we should be out on the grid ready to start the eV Challenge 2011.
How well we'll do, we're not sure, but from my point of view im just stoked we're going into the race tomorrow with a car we designed and built ourself. Now Lets Race!

Oscar

Drivetrain

Sit back and relax, coz this is a long one.

From the very start of this project, we knew this years drivetrain was going to be a beast to complete. After many, many designs and layouts we finally decided on a motor > gearbox > rear wheel arrangement, all chain driven. Sounds simple? Unfortunately, far from it.

Here are the specs for our setup.
Brushless Motor with inbuilt ESC - 400w, 24v, 2500rpm
Sturmey Archer Gearbox - 3 speed (1st - 33% reduction, 2nd - 1:1, 3rd - 33% increase)

The main difficulty was that the motor revs at a nominal speed of about 2500rpm and we want the rear wheel to max at around 450rpm (40km/h). This means a huge amount of down gearing is needed. So we needed a small motor sprocket to large gearbox-in sprocket then a small gearbox-out sprocket to large rear wheel sprocket. Unforutatley no one really makes the extreme parts we needed, like a 53T rear freewheel sprocket! We had to make one out of a regular bicycle freewheel and 2 large chainring sprockets. In the end (after a bit more bodging) we had a 9T motor sprocket, a 28T gearbox-in sprocket, a 21T gearbox-out sprocket, and a 53T rearwheel sprocket. This gave us roughly the ratios we were after.

The other difficulty was that we now had 2 chains to align, whilst keeping them taught and all inside the rear triangle of the bike frame. Chain alignment is very important in terms of efficiency. Not only can a badly aligned chain fall off, but it will also grind on the sprockets causing friction that will slow the chain down and make the motor do more work. It will also wear away the chain and sprockets faster. Its preferable to have the chains nice and tight so there are no losses to vibration and slipping.
A lot of patience was involved in this process of adjusting the positioning of the gearbox and motor into alignment and then making sure the chains were tight. It actually took 2 goes...

Guy Welding in the Gearbox Mount

Good Job

Rear Supports

We also added some support members to the rear of the chassis to strengthen it during cornering.

Bicycle Dropouts Were Used for the Gearbox Mount

Motor Mounted in Place with a 9T Sprocket

The Drivetrain Setup

For a bit of fun I decided to make a teaser vid of us testing out the drivetrain.

Now to fine tune the setup, fit cooling systems and finish the skin. With the race only 20 days away now things are coming together nicely.

Oscar