bbarn

You are spot on with the 100 vs 200 HP, it is amazing to watch the requirements as speed increases. To go 150 MPH in a normal car, you can do it with as little as 200 HP. To go 200 in the same car you need almost 600 HP. There is a VERY steep logarithmic curve in getting from 100 - 400 mph. Aero plays a giant role, but it will only get you so far. As for turning, we run a straight 5 mile long course, no turns during the run. You line the car up at the start line, you have 1 mile to push the vehicle up to speed using a push truck, then up to five miles to get to your max speed. At the end of a run, after you have slowed sufficiently, you make a left turn while coasting to the return lane and wait for your support vehicle to come pick you up. We will not have to worry about differential speeds due to cornering. I was thinking of using two hall effect sensors and just varying the tooth count accordingly as you had stated, seems to be the easiest/best way to go. Where I really need help at is I have never done any PIC design or programming. I have only a fundamental understanding of how it works, that's not going to cut it. I would really like some basic guidance on what is needed to get started and a little nudge in the right direction on a structured approach to accomplishing the goal. High level goals: Collect input from multiple sources (2). Aggregate the input by subtracting non-powered input from powered input sensors. Output difference in sensor input to a gauge, bar graph or series of LED lights. Specific questions: Which PIC is best suited for accomplishing the goals? Which software(s) can you recommend for coding the logic? What equipment is needed to transfer programming logic onto the PIC? Will I need to design other items into the circut prior to or after the PIC? (Basically, do I need to breadboard a PIC and the sensors with resistors, capacitors or other elec equipment or can I just directly connect two sensors and an LED bar graph to the PIC? If you can't tell by my question, I have no idea how to design the circut...) Is there an electrical circuts for dummies book or some reference material that you can recommend? I'm not afraid to do some research and reading, however, I'm not looking to earn a doctorate in electrical engineering either. If I am going to be spending 6 weeks reading how to do it, I'd just as leave pay someone to do it for me. However, where is the challenge and fun of having someone do it for me? Thanks for you postings, I appreciate the help.

There are many cars that run more HP than this. Fast Freddie runs a 60% nitro-methane Hemi that puts out about 3,500hp. The current fastest wheel driven car runs a T-55 turbine engine that puts out about 4,500hp. You need a big hammer to get through the air at 400+, the density of the compressed air at the nose of the vehicle requires brute force to move what can't be cut. Even the most aero effective designs run into this issue at a given speed. The car will be four wheel drive, it has dual rear axles, making it six wheel drive is just not feasible, the distance between the front axle and transmission output is about 20 feet. Making a drive shaft that long and given the restrictions of space is just not feasible. Engine RPM, transmission and rear-end gear ratios have already been calculated, the mechanical "speed limit" is 428 mph. As for tires, you can't just go to tirerack.com and pick up a set of tires. Tires used at this speed are only manufactured by two people, Mickey Thompson and Goodyear. They are only good for running at Bonneville, they wouldn't last 2 minutes on a paved road. The reason they are so sensitive to wear is that the tread has to be super thin because of the centrifugal forces involved. A regular car tire would simply disintegrate at speeds much over 200 mph. The MT tires are speed rated to 590 mph, the Goodyear tires are only rated to around 350. The trick on the salt is to control the traction and get as much HP onto the salt as you can. Being that the engine is so far behind the driver, you cannot do this by ear, hence the need for a slip indicator. Here are some specific questions regarding the slip indicator design: The front and rear tires are different diameters, I wish they were the same but they are not. I either need to calculate the number of teeth difference on the front and rear indicator wheels or would it be easier to define a calibration routine between the two WSS? (I was planning on using a hall effect sensor) I was thinking of using a bar-graph LCD to indicate slip. No bars=no slip, more bars=more slip. I need to receive the two WSS sensor inputs, subtract the rear from the front, the difference is to be displayed. (or a factor applied to the difference then displayed, depends on what scale we want per bar). Is the logic for this project better/easier to run from a PC or should we be looking into a PIC setup? Thanks for the input!

The engine in the car puts out a little over 2,000 HP at full boost, the tires on the car are only 6 inches wide, and salt is not the stickiest of surfaces. The car will be 4 wheel drive, it will have two drive axles at the rear, but that will still not be enough to prevent slip at full boost. Traction control is something we have discussed, but do not have time to engineer/build into the car. Let me also say that when I say "building a car", I mean from scratch. There is no donor car, there is nothing from Ford, GM or Chrysler as a whole in the assembly or sub-assemblies. This car will literally show up at the shop in the form of some 2" roll bar and some 2x3" steel tubing in 10' lengths. To fit everything in the car vehicle that needs to be there, it will be almost 30 feet long. Making a drive shaft to power the front wheels is A) not practical B) takes horsepower to run. There is a lot of loss in engine performance when running it through multiple differentials. With the time that it takes to build the vehicle, we do not have time to engineer, develop, test and prove traction controls. The engine is EFI and computer controlled, but there is only 1 week of running to get it right. Having the complication of getting all of the systems to work together correctly is just too much risk. Even if we did a traction control setup, we would still need to have wheel speed sensors at each of the axles to know when we are loosing traction. The other issue with traction control is the legality of it within the classes we are running the vehicle. Having a simple indicator in the cockpit to notify the pilot that it is slipping will be sufficient. When the driver gets an indication of slip and how much, he can use the "go-fast" pedal to stop it. btw, here is the current car we are running (for reference), it is a lakester, we will be building a streamliner. The dimensions of the vehicle are about the same, but the streamliner will have a much more aerodynamic body and a bit more HP. www.spiritofstlouisracing.com

Greetings! I have never built an electronics project like this, however, I do understand the basics of what needs to be done. We are building a car that will run on the Bonneville Salt Flats in 2010. What I am looking for is to build a device to show the difference in wheel speed between the front wheels and the drive wheels. The reasons for this is to give the pilot information on how much traction he is getting at the rear wheels. Since the engine and drive wheels are located 15 feet behind the driver, you cannot do this by ear (especially at 400+mph). The second reason is that the tires used at these speeds cost $800 each, there will be 4 drive wheels, that's $3200 worth of tires. Because of the speed, the tire treads are very, VERY thin, any spinning will destroy the tires in short order. It's not just a money thing, at 400+ getting a flat tire could be fatal. My current thought is to place wheel speed sensors at one front wheel and one drive wheel. That data will be collected and one value subtracted from the other. That difference will be presented to the pilot. I am not opposed to an LCD display or a series of lights that will indicate 5, 10,15, 20 and over 25mph difference. I am a computer programmer by trade and we are planning to integrate a PC into the car for data logging and tuning. I will have a complete CPU available managing the input and output. If we can use the PC to create an application to do this, it should not be an issue. If it is easier/better to build a chip-set to do this, we can go that route as well. I am open to any and all ideas, I have a rough idea of what needs to be done, just no knowledge of parts or processes to complete it. Thanks, Brandon.