Friday, January 16, 2009

A Little Background Info

I am building the car to run under ROSSA rules (Rules) for the "modified electric" class. This allows me to build the car with eventually moving up to the "open" class in mind but is based around a bit more affordability, which is important given the present economic condition.

Vehicles are classified as Electric Modified as long as the meet the following criteria
·Single electric motor any size
·Max cell capacity 15V 5000 mah
·Max length 1000mm
·Max width 300mm
·Commercial or custom chassis

Given all that I am designing the car as a lengthened streamliner with lexan upper and lower body shells to completely enclose it for maximum aerodynamic efficiency. Dimensions I know at this point are...

Overall Length: 32"
Overall Width: 8"
Wheelsbase: 18"
Chassis Length: 23"
Overall Height: 5.25" (may change if I can get the shock towers significantly lower)

The plan is for the chassis to be .125" carbon fiber (or Garolite if CF proves to be cost prohibitive) that will be have material removed to be even lighter. The lower tub of the body is also going to be a stressed member of the chassis (hopefully allowing me to remove more material from the chassis itself). The picture above have the basic layout, thing will have to change for mounting points and surprises later but as soon as I get all the mounting points laid out on it I will cut a prototype piece out of aluminum probably (because I have that available on hand already) before I do a final in CF.

At first I was not really concerned about weight as a speed car needs a bit of weight to stay on the ground (or lots of downforce which slows you down) but I think it would be better to build the car as light as possible (while keeping it rigid enough of course) and adding weight as needed in the form of stick on weights. This way I can position the weight where it will be most effective.

For electrics at the moment I am going to use a Futaba 3pm (modded for extra range) for control and most likely with a gyro for extra control. I am planning on using the Mamba Max 7700 on 4s lipo, which you are not supposed to per Castle but will work for a couple of runs and then let it cool. It is not as exotic setup as I would like to run but I think it will be a good affordable setup that will go fast enough for this first year of competing to get a good idea if the overall design will work (and there are a few guys getting some incredible speeds out of the MM 7700 on 4s anyway).

Gearing is still in the air as it will require a fair amount of testing but for a starting point though I will most likely begin in the 30/68 and go up from there as there have been others getting good results with that. There is a fellow known on various rc speed forums as Vassmar that has been running 35/68 (48 pitch) on his stock length, commercially available bodied TC4 with the 7700 motor and 4s and is claiming runs over 120mph. If I need to go bigger on the pinion I guess I will have to go custom as I believe 35 is about as big as you can commercially get.

Tires I am planning on running BSR velo sedan tires (which reminds me I need to call BSR about getting some of those ordered).

Anyway I will add more info as it comes along but right now I am still just planning, measuring, and trying to get parts together.


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