if my limited (and probably long forgotten) understanding of aero effects is correct, open wheels generate a fair bit of turbulence hence le mans prototypes, salt flats racers etc. running closed wheel designs. We can discuss more next week - don't forget this time!!
The cars must have 4 wheels, arranged symmetrically about the centre line - but if three wheels were allowed I'd definitely have a morgan style three wheeler.
The open wheels are there to reduce frontal area, and overall weight. there will be no brakes at the front and the wheels will have full discs to reduce their drag. the brakes are mounted at the rear and as close inboard as they can be to allow them to be fared into the main tub. I don't really know if this would be better or worse aerodynamically than a similarly proportioned fully enclosed car, but am hoping the weight benefits will pay off. I like the outboard wheels as well because I can make the axles wide for stability - not that open wheels don't have their own problems. I have to be aware that they are other peoples children! so cant be too "Colin Chapman" about the car, which is why the previous efforts have been distinctly W.O. Bently!
Something I am wondering about looking into is perhaps mounting thin styrofoam pontoons on the sides in line with the wheels, sort of like Golden Rod.
So, less than a week to go and Eco-3 is still a pile of parts in the corner of my classroom. The rear sub-frame/roll bar has taken longer to get back from the welder than expected, but it is of course a spare time job. I've been doing a bit of fabbing for the front end.
One of the lads fish-mouthed the stub axles, Dennis and I set up the mill with a 20mm end cutter, then a student did the machining.
Which then got turned down to size and the bore taking out to 12mm (for an M14 thread), so that they would fit in the jig which holds them at the correct angle for welding to the king pin tubes.
These were tacked and then popped out for the rest of the welding. The jig is four layers of 4mm thick MDF cut on the laser cutter.
A tool which also came in handy jigging up the rest of the front axle. The rear axle acts as a backbone, with the stub axles located parallel with MDF cut outs slotted over the ends, and bolted through the wheel bolt holes. The front axle tube sits in half height saddle pieces to keep it parallel to the rear axle. The U brackets are bolted through the kingpin tubes to keep them in the correct position.
Again, these were tacked in place and then stripped down to weld up properly. No close up pics, it's not pretty.
The stub axles have since had flanges welded onto to act as a rear stop for the 20mm through hubs that are the basis for our wheels. All but one of the wheels have been built up from scratch by our students, I did the first one so I could teach them - that one was the first time I'd built one! It's a very satisfying job I which we'd built our own wheels from the start, it would have saved us £££!
Dennis knocked up a truer for us to build the wheels.
Next up will be the tub - but that will have to wait 'till Wednesday. The subframe should be assembled by then with the motor mounted and rear axle in position.
Subframe arrived with Dennis over the weekend, so he got that fitted up with the electrickery, and drive train.
The mounting boss for the freewheel needed welding to the axle so it was all stripped down for that. While the axle was getting dismantled I got on with cutting out the body tub parts.
Here's one side bing fitted, epoxy adhesive and lots of screws...
Once both sides were on the base was cut to shape,
Then stitched together with cable ties, ready for a fillet of epoxy adhesive/filler to be applied,
The rear tapers in to where the brake light is mounted,
One of the lads also got on with machining the disk brake mounting boss',
They will be drilled and fitted to the axle with roll pins.
I'm heading back in in the morning to fit the front axle and steering. Then all the kids are back in again on friday for finishing off and practice for race day. It'll be tight for getting it up and running!
We got a bit more done this morning. Not as much as I'd hoped, but I slowed us down a bit first thing by knocking the argoshield bottle over and smashing the gauge on the regulator. A fair bit of gas escaped, but fortunately the bottle was fairly full. Once one of the guys had been out to get a new regulator we were back in action again.
The front axle was clamped in position with the load spreading mounting plates and tacked in place, before removal for welding fully.
I also attached the steering arms to the kingpin tubes, another mdf template cut on the laser cutter got them positioned correctly.
Finally the car was able to stand on it's own four wheels for the first time.
There's a great article on the team in today's (07/06/12) Portsmouth Evening News too.
I'm not sure how we could loose any weight from the wheels - it's generally accepted that fewer than 36 spokes wont be up to the job. They do get disks though to reduce the drag.
As a cyclist, I can't see how they wouldn't be. Look at slopestyle riders and megavalnche stuff, many of them ride with 32 spokes. The main point I was trying to make was that lighter wheels are easier to get moving. Making the right choice with tyres too, possibly even going with latex tubes. Sent from my A500 using ProBoards
It didn't stay dry It tipped down at 3pm so a quarter of the race was done in appalling conditions. This unfortunately caused one of our cars to expire in the last hour. The new car was much better, and rolled home the highest placed car from a hampshire school, Yay! We finished in 16th place covering 86.4 miles (Eco-3) and 31st covering 69.6 (Eco-2). Eco-3 should have done enough to qualify for the national final, but we might do another heat to see if we can get Eco-2 to qualify as well - If we haven't fried the speed controller.
Seth, did you spot the flying eyeball with the spellings too. There is a little castor, about 5degrees I think. The students don't seem to think that it has caused trouble to drive.
We are racing again next weekend, in the Western regional heat at Castle Combe. The team are trying to get last year's car Eco-2 qualified for the final, and improve the qualifying position of Eco-3 (its currently qualified in 29th place, but we can do better!)
We've made some improvements to the car, lighter more aerodynamic wheel coverings, and better motor cooling for increased efficiency.
I don't know what budget you're on mark but also being a cyclist you can loose ALOT! of weight from those wheels and maybe even gain strength. The tyres are great, nice and light, some of the lightest but your loosing it all on the rims hubs and spokes. As someone else mentioned, latex inner tubes or even some super lightweight rubber ones are a cheap weight loss. Just a little advice sorry if I'm preaching.
Otherwise this project is totally awesome and knowledge wise totally beyond me.
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everyone keeps going on about losing a "lot" of weight from those wheels (err... 100g maybe?) I'd be more worried about the steel steering wheel setup, that looks like it could easily weigh nearly 2kg by itself