Sunday, March 23, 2008

Chris's 150 mph attempt - Litespeed

Chris talking about his project:
Hey guys,

First of all, my name's Chris. I posted about this speed car project on the old forum, but as it's gone, I thought I'd re-post it here. I'm hoping to break the 150mph barrier - not an easy task - so here is the "story so far" as it were on my car.
It'd get a pillow and some slippers if I were you, because you might just fall asleep lol...

My car is going to be called "LiteSpeed"...reason being, that the major emphasis is going to be put on it
being a super-lightweight machine to get the best possible power/weight ratio. She's going to be based on the Tamiya F103GT chassis *design*, albeit using only a few Tamiya parts. The F103GT is a very lightweight, RWD direct-drive 190mm chassis; think a scaled-up 1/12th scale pan car, but with touring car proportions and you're very close! This design is ideal. It's got plenty of space for an outrageous power setup, a super-efficient drivetrain design, and many other advantages which make it perfect for an insane speed car!

After doing a fair of research and brain-aching thought, I realised that it'd be much cheaper and easier to build the car from scratch using upgrade and custom parts instead of buying the stock kit. I'd only be using a small number of parts from Tamiya there wasn't a whole lot of point in shelling out for the standard shebang. Instead (and after more research!) I discovered that 3racing make carbon-fibre chassis kit for the F103GT which looked perfect for the task of serving as the base of the vehicle. Not only does it use decent grade materials, but the price was ridiculous; under £50 for the whole kit; not at all bad. 28) The main plus-point of this kit was the weight savings of 30% over the stock FRP parts, with greater rigidity to boot. I'll be stripping the anodizing off the aluminium bits though, as blue just doesn't do it for me.

Unfortunately, a finger-twitch caused me to tragically order the kit, as well as some other bits of eBay. Such a shame, but I'll have to live with the mistake. Sigh.
Anyhoo...before you nod off to sleep, here are some images of the chassis as it sits now:

What's that transparent thing sticking out of the back? That's a polycarbonate diffuser. I won't go into super-dull details, but combined with a polycarbonate underbody that I'm going to make, it will help keep the chassis glued to the ground once she gets past 80mph. It works by causing an area of low-pressure under the rear of the car when it's at speed, pulling the chassis down without excess drag...just like on an F1 car. The underbody will keep the air flowing smoothly under the car, preventing it from getting up inside the chassis and causing aerodynamic mayhem. That probably makes less than no sense at all... but all will become clear!
Along with these parts, the bodyshell will play a crucial role in keeping the car fast, and not airborne. At these kinds of speeds a normal touring car shell just isn't up to the job, and neither are many others. Even the oval shells are useless, as many are assymetrical. I spent hours and hours, scouring the web for the right solution with a lot of guidance from aero-guro, Glypo and eventually found this gem:

It's called the "McAllister Dodge Charger HS". After some email chit-chat with the owner and a whole lot of aero-analysis with Mr Glypo, it should be perfect for the job. Turns out it's designed as a velodrome racing shell, and those cars reach it should be a great starting point at least.

Power System
Of course, the car won't go anywhere without a power system...and I put a lot of thought into this one (that means absolutely nothing of course, but it *should* be up to the job!). LiteSpeed will be packing a relatively massive Neu 1515 1.5D 2700kv motor with a pair of NeuEnergy 3S 4100 30/60C LiPo packs wired in series to create 6S. I opted to go for a lower-voltage, high-amperage setup as this would be lighter than a more common HV setup. Geared at a ratio of 2:1, it would theoretically high 197mph unloaded. Power output should peak at almost 4,500W, and it turns out that the car will have a power/weight ratio of 2,200bhp per metric ton. In comparison, a Bugatti Veyron has 536bhp/ton.

Motor Pod.
Because the Neu 1515 is so large - in both diameter and length - the stock motor mod plates just aren't up to the job. They aren't big enough, strong enough, have enough gearing options...and a 1515 just plain won't fit. The only reason why I have some stock plates bolted on in the above pictures is so that the diffuser can be attached for show). So...I broke out the CAD, and spent quite a few hours thinking hard and wearing my mousemat out. These parts were the result:

The first image is the motor mount plate, and the second is obviously the plate for the other side of the pod. Becuase the Neu is so long, I've had to drastically change the design of the non-mount plate so that the motor can will pass through/over it, regardless of the motor's position due to gear ratio. I've also gotten rid of the plastic bearing inserts that the stock parts use to alter ride-height on the rear axle, in favour of a fixed bearing holder (less slop). It was difficult to make room for long motor slots so that the gearing is widely adjustable without extending the car's wheelbase or it needing a modified T-plate, but I got there eventually! After which I went around trimming off every last gram of weight. Strength isn't a huge issue here, as the plates only havw to hold the large motor in a solid mesh...they won't be subject to abuse. I'll have them machined from 7075 aluminium to ensure good strength and minimum flex, though I'm not decided on where to get this done yet.

The last thing to talk about now is the Controlling Electronics really.
Key to the stability of the car will be a Futaba GY401 heading-hold gyro. This thing will help keep the car tracking straight and true under serious acceleration, greatly reducing the risk of spinning out. In turn, this will be hooked up to a fast, good quality servo. Something that's around 0.8 sec transit speed would be ideal, but I'm undecided on that yet. Speedo will probably be a Mamba Monster Max, with its huge amp rating, and the whole thing will be reigned in by my Nomadio React radio.

If anyone's been bored enough to read all that through, then thankyou! lol. Progress will be (and has been) slow due to having to spent money on other projects, but I'm really hoping to have her done by the September event.

Thanks for looking.

Litespeed looks good. I cant wait to see the results.

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