LiteSpeed: My speed record attempt car...
 

Hi guys,

For the past few months I've been planning on building, and have started building, a car to run for this year's World's Fastest RC Car Competition...and thought you lot might be interested in it as I haven't mentioned it here at RCM. This is the story and basic concept of the car, so I'd suggest getting a pillow and some hot chocolate in case you fall asleep lol. Sorry if some of the language is a bit patronising, but this is from another forum where guys aren't quite as clued-up on this sort of thing as you all are!

Chassis
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! :D

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 anyway...so 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.
Here are some images of the chassis as it sits now:

http://img.photobucket.com/albums/v6...r/HPIM1685.jpg
http://img.photobucket.com/albums/v6...r/HPIM1686.jpg
http://img.photobucket.com/albums/v6...r/HPIM1687.jpg
http://img.photobucket.com/albums/v6...r/HPIM1688.jpg

Aerodynamics
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:
https://www.ssl-stormerhobbies.com/c...c=ns&pn=MCA197

It's called the "McAllister Dodge Charger HS". After some email chit-chat with the owner and a whole lot of aero-analysis with a friend of mine who goes under the name of Glypo, it should be perfect for the job. Turns out it's designed as a velodrome racing shell, and those cars reach 90mph...so 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. I know, some of you might roast me for that...but in this case, it should be worth it. The car needs to be light, and as it'll only be run in burst of about 10 seconds or so, a high-current/lower voltage setup should be better. Novak proved this works last year in an Xray T2 with an HV-Maxx system on 5S by hitting 118mph, so with higher voltage, a bigger motor and a lighter car...there's no reason why LiteSpeed shouldn't be faster.

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:

http://img.photobucket.com/albums/v6...espeedpod1.jpg
http://img.photobucket.com/albums/v6...espeedpod2.jpg

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, and I'm waiting on a quote for them right now.

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 the React.

That's it so far. I totally understand if no-one reads through all of that lol. Anyhoo, progress will be slow but I'll keep this updated. Thanks for looking.:smile:

Nice idea! What gears will you be using? Also, what will be cutting out those parts? A regular CNC mill won't really be able to because of the sharp corners, but if you rounded them out to a radius of 1/16" (to accomodate a 1/8" end mill) then it would be fine.

Can we have a video??? :lol:

I think you're on the right track here. I own an F103GT and I've thought about how fast I could make it go... You seem to have thought of everything so that should translate to fewer problems down the road. Except for the ones you can't control- like grains of sand getting under the tires at 90+ mph. Definitely keep us updated.

MetalMan- It would probably be done by a Water Jet machine. Except for the bearing recesses which can be done with normal CNC.

Dude that emachineshop is great! It's got to cost bucks though... :gasp:

It's free :lol:. It is the easiest I have used and I'm loving it.

Thanks everyone. :)

MetalMan, I'll be using the smallest spur that Tamiya do for the F103GT, which is something like 90T and in 0.6 mod tooth size. I'll then have a custom-made 45T (or thereabouts) pinion to match. I'm not sure how I'll get the custom pinions made yet, but I'm hoping RW Racing will be able to hook me up there.
As for the machining...they'll be cut by a CNC 5-axis mill. At the moment I'm waiting for a quote on the parts from a company called Penta Precision, and I believe they're able to deal with the 0.5mm radius filleting that the parts have right now. If not, then I'll just have to enlarge the fillets to 1.5mm radius...but hopefully that won't be a problem.

eMachineShop is great though! It's free like Lutach said, and very easy to use. On the downside, it's kinda limited in respect to 3D parts, and will only export DXFs, but it's amazing for free. It has a few annoying bugs too...but it's good stuff. You can even directly order parts that you've designed to be made through eMachineShop themselves, though I wouldn't...their prices are astronomical...:surprised:

Looks like a sweet setup! Should be a real beast. I cant wait to see videos of you breaking Nic Case's world speed record. I dont even get how you can control it at that speed let alone be able to keep it on the ground because once the sir gets under neath the body it will fly like a kite at that speed, and if anything should happen Im gueesing by the way that chassis looks that not much would be left after a bad crash.

here is a pic of a 76/40 (spur/pinion) that some guy on Ultimate Traxxas.com had on a Rustler

Sounds like an awesome car. A 45t pinion sounds really heavy to me. Any way you could get a smaller spur cut and use a smaller pinion (and still fit the motor in). This could shave some rotating mass which is a killer.

This is going to be an awesome project. Definitely looking forward to the progress. Other than the chassis and motor mount, will the rest of the parts be stock or will you go for some custom carbon fiber parts to make it even lighter?

Interesting project ... everything sounds very well pondered, but asking 4.5Kw output from a Neu 1515 sounds to optimistic. Efficiency at high Amp levels might be less then 80% requiring your battery to feed up to 5.4KW (900Watt wasted in heat) meaning 270A@20V (assuming around 3.3V per cell). Don't know if the windings of the 1.5D will hold up to 270A even for short bursts.

Which ESC do you plan to use?

Wow...I wasn't expecting quite so much interest lol. Cheers for all the compliments!

Takedown: Whether I'll beat Nic's record is pretty doubtful, this being my first speed run car...but I'm gonna give it my best shot. Keeping the car in check at speed should be made much easier with use of the gyro, so that's one less thing to worry about. As for the aerodynamics...well, the mistake a lot of people make is to try and create as much downforce as they can to keep the car on the ground. This creates a lot of drag though, so it's much better to simply try to kill any lift that the car creates. The shell I'm going to use provides a bit of downforce (you need some), but should create very little low-pressure over the rear. A low-pressure area behind the rear windscreen of a car (like on a normal tourer body) can be the problem that causes a car to lift off. It's kinda hard to explain without images lol. Anyway, that shell combined with an undertray and the diffuser should make for a very low-drag car with enough downforce to put power down at speed.

Of course, that's all just words...who knows what's gonna happen at the event lol.

MTBikerTim: That's a really good point, but due to the design of the axle and the size of the 1515, the motor needs to be a minimum distance from the axle...so I'm having to go with a larger pinion/spur combo. I'll see if I can't get the pinions machined from aluminium and lightened to minimise mass, though. :)

Jnev: I'm going to try to shave every gram I can off of this car, so there will be some other option parts...but it doesn't look like any major custom parts will be needed apart from a lexan undertray. I'm looking at going with full titanium hardware, an aluminium or titanium main axle, shaving some aluminium off of the 3Racing parts I already have, etc...but it doesn't look like any big custom stuff will be needed (part of the reason why I chose this chassis - the parts count is so low! lol).

Othello: That's a really good point, and I spent a looooong time deciding on the power system. Neu state that the 1515 motors can endure 2700W output for 30 seconds (I'm assuming this is while staying over 85% efficiency?), and as each speed run will certainly be no longer than 15 seconds - more like 10 - it seems to me that it should be able to handle double that for a really short period. What really swung it for me is Novak's system. Their motor is smaller, and must've drawn a heck of a lot of amps to hit 118mph, and they had no problems with it. The 1515 is larger, running on higher voltage and is powering an even lighter chassis, so it seems to me that it shouldn't have any problems if I gear it right.
The cells will be under a fair bit of strain, but the same applies...if MaxAmps cells can supply the current to hit 118 with a HV-Max, the Neu 30C cells also shouldn't any any problems in a burst (he says...)

Linky to the Novak car:
http://www.teamnovak.com/events/07wo...car/index.html

I'm planning on using a Monster Max (providing it's out by then lol) without it's case to shave weight, which should be up to the task.

Anyone, please correct me though if I'm wrong with any of this...which I probably am, lol.

this project is gonna be one fas m-f'er

what radio r u going to use?

After looking at some eagletree graphs of two high speed setups i came to the conclusion that 4.5KW shouldn't be needed for your small and lightwheight car.

Here is why:
. A 13.9KG (30.4lbs) 1:5 onroad car with 10s lipo, lehner 2240 needed around 4.5KW input to reach 95mph (145km/h). The graph can be found here (site is in german)
. A Rustler VXL needed 1560 Watt for 82mph. The graph

I know you reach for higher speeds and the faster you go the energy needed does not augment in a linear way. But i think you won't need 4.5KW at all. Your batteries should be able to provide it. I wouldn't count on a MMM to be able to provide 4.5KW. A high AMP flight ESC with slower ramp up time might do the trick as brakes might not be as critical for a speed attempt. If brakes are needed i would look into a MGM 22418 which should be able to provide up to 4.5KW. As you already stated those high power levels only last for a short period and judging from the posted graphes it seems as if your highest Watt peak will be shortly before you reach top speed. Holding top speed won't require as much power as accelerating.

Looking forward to see your final built and good luck with your speed attempt.

The gyro will be interesting to see if you can get the stabilisation to work at high speeds and not end up in a positive feedback loop - that would get very messy very quickly.

Gyro will make you look like a real R/C driver. I used to race oval and one day I tried a gyro and it made my car handle like it was on rails. It works too good and that's why it's banned from R/C racing. If you can hide it real good than you will be seeing the podium often :lol:, but for High Speed runs I think it's a must.

Interesting - I've never heard of it until now but looking around lots of articles - G190 seems to run for $44 so might pick one up to play with...

I won't bring it to the monster bash... promise!

Yep, gyros are fantastic for use in speed run cars...though only a few people used them last year for some reason.:neutral: If everyone used one, I bet the number of crashes would have been a whole lot less. I'm looking at getting a Futaba GY401 unit. I need a gyro for my heli anyway, so I'll be killing two birds with one stone. It's a very decent unit, so should keep LiteSpeed in check. :) They're dynamite for racing with though, like you say! Just hide it well, lol:whistle:

Othello...I see what you mean, and thanks for finding those graphs. At the end of the day, I can never be sure exactly how much power will be needed to get this car up to 150, but it's gonna be quite a lot...so I guess it's better to have the betteries able to supply more power than is needed in the end. I've heard several different opinions on how much power is needed to get past 150 (some say 6hp, some 4, etc) but it all depends on vehicle weight and other stuff. I reckon the MMM will be alright, though. It's rated at 200A constant, so some bursts above that hopefully won't be a problem. :)

Brushlessboy, I'm probably going to use my Nomadio React as long as it has the range.:yes:

Anyhoo, since I'm still waiting on a quote and can't afford the other bits yet, I just bought some pipe unblocker to de-anodise the ali bits:diablo:. I'll put up some pics when that and hacking-up the battery stay bits are done.:smile:

You could try and make a pack(s) using A123 2300mAh cells and if that's not enough voltage, go with as many 1100mAh cells as you can. The cells in Bosch's 36 volts power tool packs seems to have a 60A fuse and I'm wondering if it can actually handle 60A discharge. I might have to try it out and see how well they do. Here you can see the other pictures: http://www.rc-monster.com/forum/show...8&postcount=30

Nice little pack :lol:. I have attached the graph of some little bursts. This also shows the best regen braking action as well :surprised: at around 12 seconds I hit the brakes.

Thanks for the suggestion Lutach, but I think I'll stick with good ol' fashioned LiPo with this car.This chassis really lends itself to a 6S LiPo setup (the packs should fit beautifully), and I don't think the A123 cells would fit well. Their performance isn't really good enough for this sort of application either, but I appreciate the input! :)

Got it. Keep the pictures coming.

H'okay, got a very minor bit of progress done while I wait for funds to amass. Nothing exciting, but I thought I'd post anyway lol. I went down Tesco's and bought a bottle of Domestos Pipe Unblocker, and de-ano'd all the aluminium 3racing bits. I then took a hacksaw, file and wet & dry paper to the two main aluminium top deck support parts, in order to get rid of the stock-style battery clip mounts. These added unnecessary weight, and unnecessary weight gets the chop in this car! B) Even if it's the slightest thing. I also discovered that the rear body mount plate does perfectly well with only the two inner aluminium standoffs, losing no real rigidity. I might cut some excess material off of the plate itself at some point, but I'll leave that for now.

http://img.photobucket.com/albums/v6...r/DSCF0102.jpg
http://img.photobucket.com/albums/v6...r/DSCF0103.jpg

Sorry about the naff images btw...I just rushed them lol. Thanks for the interest in this by the way...I really appreciate it!

I have a few suggestions for you.

#1 If you use a gyro, you will need a super fast gyro and steering servo (GY611 is best) or you will get steering wag at high speed (ask me how I know)!

#2 Two wheel drive is VERY difficult for a top speed car because of traction issues. I run 4wd with a 1515 and I get tire smoke at 50% throttle (3800 watt power system). It accellerates 0 to 80 in 2 seconds. I have tried 2wd and could not get it to hook no matter what I did. It was like driving on ice.

#3 A 1515 is good for a maximum of 4000 watts before the efficiency goes in the toilet. However, it is very difficult to harness more than about 3000 watts anyway.

#4 Light weight is almost a moot point when you need to add alot of battery power (and weight) to it anyway. I mean, do not make it heavy if you do not have to. But, puting time and money into the best drive system and lipos you can get is far better for a top speed car.

Please forgive my negativity. I do not mean to rag on your car. The design looks very good indeed. However, I have gone round and round with these very issues with ALOT of money wasted and I would hate to see you go through the same thing.

It is a beautiful design and I wish you well with it. But, I have seen this time and time again and have been down this road myself.

Matt

No prob man, I'm all for input...especially form experienced people like yourself (I've seen your car on RCZ...what a piece of kit!). I answer to your points though:

1. I'll most likely be using a GY401 gyro, with as fast a steering servo as I can get hold of. I'd love to use a 611, but that's just simply out of my budget. I know what you mean by steering wag though...strangely, you actually get a similar thing happen on helicopters if you have the gain set too high; the tail wags. Obviously the 401 isn't quite as quick as the 611, so if I do get any issues, then hopefully turning the gain down will help.

2. 2WD...yep, it could cause real problems lol. I'm planning on using similar BSR tyres to what you've used before, but in terms of acceleration....well. I'm just gonna have to set up a nice, very smooth throttle curve up on the React and accelerate as gently as I possibly can. The React has a lot of useful mixing capabilities too, so I might be able to set up the steering to reduce its travel as throttle input increases which could help with control. By the way, I hope you don't mind my asking...but which of the BSR tyres would you recommend?

3. That's a good point. At the end of the day, the 4500W figure is really the absolute maximum that the system could deliver. As you know, the motor will only suck as much current (and so output the watts) that are needed to get it to a particular speed. Making the car ligher should reduce this figure, so that shouldn't be a problem. :)

4. I totally understand what you mean here too. The LiPos, motor etc are of course going to add weight and I am putting in what I think is the best power system for this chassis, but I may as well make the chassis as light as possible. The lighter the car, the less work the power system has to do. I'm not going overboard on it being lightweight in terms of price (the carbon chassis kit was barely any more expensive than the stock items lol), but if there's weight to be saved without much cost, I'll do it.

Thanks for your input man...it's given me a lot to think about (especially traction wise!) :).

Cool. Sounds good.

It looks like you have thought it all through. The one big thing that I have to advise is, if a 611 or another gyro just as fast, is out of your budget, I would say do not even use one. I have run a 401 in cars. They max out in performance at about 60 mph. Above that, they actually cause more problems than they cure. Of course, maybe you could mix it out with your React above a certain throttle?

I run BSR radials. Yours will be different than mine because I run them on touring car wheels.

They are awesome. But, I have shredded one in the past with too much wheel spin.

With two wheel drive, you will need alot of downforce for traction. But, that downforce will ultimately slow the car down. So, look for a good ballance.

Nic Case has alot of experience with 2wd and 4wd cars. Maybe he will chime in here. I may email him a link or call him and let him know about this thread to see if he has any suggestions.

Have fun with the car. That is what it is all about anyway!

Matt

Hmmm, ok. Well, I've been doing a lot of research into gyros and since I need a new gyro for my heli anyway (which I can use after it's done in LiteSpeed), I'm thinking I may as well get one anyway. If it works out, then great, if not...no real loss. As opposed to the 401 though, I've been looking at the Logictech 2100T. Everyone all over the net seems to agree that it's actually slightly better than the 401 and at a lower price, so I may go for that unit. I'll be sure to experiment with trying to mix out the gain on the React. :)

As for the tyres, thanks for letting me know which you're using. I'll also be using them on touring wheels, and *hopefully* the bodyshell with diffuser/undertray will provide the right amount of downforce with too much. You wouldn't believe the amount of time I spent researching that aspect lol.

Again, thanks for your help on this and that's be really great if you did send Nick this link. Thanks man. :)

Any updates? :)

Not as of yet unfortunately. I'm having a nightmare sourcing a Dodge Charger HS bodyshell for this car, which is a problem; the only place that I can find that sell it are Stormer, and their shopping cart doesn't appear to work with my card. This'd all be so much easier if oval racing shells weren't assymetrical.:no: So, I'm just trying to find another suitable shell that I actually *can* get hold of lol.

I have been ordering various bits for the chassis though, a lot of which are 3racing. It almost seems wrong to be ordering this many cheap "hopup" parts, but the truth is that the car needs to be as rigid and light as possible. Strangely, some of the 3racing parts are actually a bit cheaper than the components they replace, though better quality. I'm also still waiting on quotes for the motor pod parts, and been mulling over some other aspects.

Hopefully there'll be some updates soon. Thanks for the interest!:smile:

Bad luck about the body. I am running a pancar body on my car atm, the orange on in the ava. But i think it's generating abit too much dowforce for really high speeds. So I actually ordered the Dogde Charger HS from Stormer earlier today hehe.

Looking forward to those updates :wink:

Hmm, the only body I found that would work well over 50mph was a 200 lola body. Can't remember who made it, maybe proline? Anyway it worked great, up to 80 or so. That was on a windless day, on a windy day it made so much down force that the rear shocks could not keep the chassis off the ground! Oh well, my quest for speed was ultra budget, a tamiya tt-01 with a bearing kit, and a 380c 6s motor on 3s lipo with a mm. Pretty low tech, but it easily did 75, and had more to go. I just need to find a larger area to test it.

Dagger, your idea looks great, I had a stock version of your chassis and just could not make it work, it was all over the place. I could have spent more time on it, but decided to get into converting nitros!

These might be good.

http://www.shopatron.com/product/par...7260.17959.0.0
http://www.shopatron.com/product/par...7260.17959.0.0
http://www.customworksrc.com/Product...002-1057795266
http://www.mcallisterracing.com/racing/page10.html (Some awesome bodies)
http://www.mcallisterracing.com/racing/page8.html

Remember at high speeds the drag is so much that the rigity of normal lexan shells will be insufficient and will need some reinforcing or a whole new shell made in carbon.

I have to say that you have got me thinking about making an top speed car now out of an old tc3 chassis i have sitting around doing nothing.

World recored 134.4 MPH set with a lightly modded TC3 chassis. :mdr:

Matt

Thanks for the links there Lutach! Unfortunately I've checked out most of those bodies already, and most of them aren't really aerodynamically suitable...either too much downforce or too much lift/drag. The Oval shells you've pointed to would be fantastic, but they're all slightly "skewed" for oval racing...so in a straight line could cause weird stuff to happen lol. Thanks for the effort though.:smile:

Vassmar, you copy cat...lol, just kidding man.:mdr:

LincPimp: Thanks man. Hopefully with the inclusion of an undertray and the rear diffuser, it should stay glued to the ground with a less aggressive-downforce shell.:smile:

Chilled: Don't worry, I've been considering that. I may use some carbon tubing to add support to some more critical area...but it depends on the shell of course. I have another shell in mind which might be up to the task.

Again, thanks for all the support guys! I have a bunch of parts on the way, so I'll post an update when they get all fitted up.:yes:

Check into the oval shells. Some of them are not skewed for oval racing. Nic used an oval shell in his 160mph Intimidator.

Yup, I have two of those "Bullet Wedge" bodies here new and untrimmed for sale.

Any takers? :mdr:

Matt

i was looking into building a f103gt into a speed car before, but went against it since 2wd on such a light car with so much power would be dang near impossible to drive... actually looked into making an aluminum chassis to make it heavy enough to give hard traction but never did anything about it. and i was looking at pictures on tamiyausa.com of the f103... and the gt seems to have a graphite or cf chassis?! or is it just a look thing? not all pieces are, but it looked like the top piece deffinetly was... what about an outrunner. literally a direct motor to wheel drive? that and a big nasty 5 or 6s lipo under a 1/8 lola body.with some seriously stiff springs.

All of the McAllister oval shells are skewed with exception to the velodrome shell; I emailed them to check. Annoying, but true. I wonder what shell Nic used (Mod Man, sorry, I'm not sure if you're being serious or joking there?...hard to tell through text lol). I do have another shell that I'm looking into though, which may do the job.

RevRacer, yep...it'll be tricky. But with the right tyres and gyro - even if dialed out at high speed - it should be controllable (Nic demonstrated that with his Intimidator which can't be much heavier...and without a gyro I believe). The stock F103GT uses a material called CSC...at least, something very similar. It's kind of half-way to carbon fibre, with it using fibre glass for every-other layer, instead of carbon for the whole sheet. It's cheaper, and almost as rigid as carbon...but also a fair bit heavier.
An outrunner isn't a bad idea, but it'd require a complete re-engineering of the rear end...and would also mean that I can't have a diff. The current setup should be still quite efficient, and much easier to make. Thanks for the idea though. :)