Saturday, August 18, 2007

Matt Shumaker's Carbon Fiber Supercar

Matt says:

Well, I have been talking about this for a while and I felt it was time to show my car. For those who just want to know "How fast is it?" The simple answer is--------- I don't know. That is, I haven't had it wound out fully yet. I have seen 115mph on 6S while still accellerating big time. On 12S (different motor), the car went by at 100+ while wheel spinning an indicated 140 mph (4wd). Since then I have installed BSR cap tires. These tires hook very well. With the caps, the car has run 83mph at less than 30% throttle (in two seconds) and 100mph at 60% throttle. The weather stinks right now and the car has officially become faster than my street will allow. So, I am looking for a suitable runway to really wind it out.

Anyway, the car setup is as follows;

-Neu 1515/3D
-Thunder Power 2070 Extreme cells (12S)
-Castle Creations HV110 ESC
-Spectrum DX3 (love this radio)
-Futaba GY502 Gyro with digital steering servo
-TC4 drive components (basically stock other than a modified center driveshaft and 1 inch stretched wheelbase).
-BSR cap (radial) tires. AWESOME tires!
-Complete Eagle Tree data logging system with all accessories.
-Venom Speed Meter for wheel speed data (I have a radar gun too).
-CNC machined carbon fiber/plywood laminate chassis. This is an item I designed and made in my shop on my CNC with 7mm thick CF/ply laminate that is made to m y specs by my CF supplier for my helis products.
-CF body. I hand made the CF body by making a foam mold and laying the CF over the mold. The body by itself weighs 10.5 ounces. I need to thin it from the under side to shave a couple ounces.
-All up weight is 93 ounces.

The aerodynamics of this car are such that I have good downforce, but low drag. I did a HUGE amount of research and testing to come up with the final design. The front wheel wells are needed for front wheel steering clearance. I did quite a bit of testing to assure that the net drag of those wheel wells is zero. Also, the nose of the car went through numerous changes (hence the added body weight) to achieve the correct downforce/drag ralationship. I am not going to devulge the specifics of what I found as it is too lengthly to get into here.

The power system draws over 3800 watts continuous at full throttle. Also, the car accellerates at over 2.6 Gs (2.98 peak) and corners at roughly 2.5 Gs. (This is all data I have logged on my Eagle Tree).

Originally I speced the car for a Neu 1512. However, that motor built up with too much heat. So, I went to the 1515 you see with a finned can. That gave me a tad more power with a large improvement in heat dissipation. I also mounted two fans to the ESC and one to the motor.

When I got the car to the running point, I quickly found the motor heat issue and secondly, traction. Oh, also, the foam tires only last a few runs. So, I contacted John at BSR tires. He set me up with some touring car caps. These tires have good hook while allowing some wheel spin to protect the driveline from all the horsepower. They are also very long wearing. I am thrilled with the caps! Now, I just need to see if they will handle full speed.

I have about 30 to 40 hours in the body and about 30 to 40 more hours in the rest of the car (fabrication time only). Then I have about 5 hours in component programming and setup. Beyond that, I have about 100 hours in two previous TC4 setups to learn the drive system and what is needed for world class speed. So, this car has been hugely time consuming to develop.

At this point, the car has crazy horsepower (4.5hp), is super fast, handles (corners) very well, is reliable, runs relatively cool, and is very stable at high speed.

By far the most difficult part of the project was matching all components to work together, matching the drive system to the weight of the car and the CG, and getting the aerodynamincs matched to the chassis and capabilities of the car. When you are pushing the edge of the envelope, matching equipment and individual component setups is super critical!

Oh, I have so much power that gearing has proven to be only minimally important. I have gone up a few teeth and down a few teeth with very little affect. Basically I have it geared for 150 mph at full throttle under load. We shall see what it will actually do.

Anyway, I think that is it for now. I will give more information as questions are asked.


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