LiteSpeed: My speed record attempt car...

[Dagger Thrasher]

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:






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:




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.

[MetalMan]

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.

[What's_nitro?]

Can we have a video???

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.

[What's_nitro?]

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

[xcntrk]

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

[lutach]

Originally Posted by xcntrk

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

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

[Dagger Thrasher]

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...

Originally Posted by Dagger Thrasher

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...

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

[othello]

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?

[Takedown]

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.

[MTBikerTim]

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.

[jnev]

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?

[Dagger Thrasher]

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.

[othello]

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.

[brushlessboy16]

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

what radio r u going to use?