These tires are very very soft and they are the correct outside diameter (3.25") and width (1.5") for the X2. Since these tires weren't working, I had to go a different route. The 1/8 scale tires are approximately the correct outside diameter (about 75-80mm) but they are much harder foam. The only problem is they are very wide (3"). What I did was to make my own aluminum rims and remove the foam from a 1/8 scale rim. This way I could use the same method of mounting (1/10th scale clamping hub). This is what I started with:
I removed the foam from the 1/8 scale wheel and glued it onto the aluminum rim. Here's what the new wheel looks like (left) compared to the old one(right). The new wheel is much much stronger and should hold up to the extreme forces.
I also modified the front suspension. I moved the tie rods from up above the upper arms to very low to maintain correct front end geometry:
Data from the last street run. Link to the FDR file from my run on 10-11-07. You can view this after downloading and installing the Eagle tree software.I have also updated my spreadsheet. I added the ability to choose a motor based on what Kv and Kt requirements are calculated. I also added a section where you can calculate the amount of downforce created by a wing added to the car. And based on the traction created by this wing, you can see at what speed your total traction will intersect with your traction needed to accelerate at your desired rate.
Here is the link to download the spreadsheet for use on your own calculations.
Graph showing traction available vs traction needed. The point where the two lines intersect is the speed at which enough downforce will be created to give you the traction to accelerate without spinning the wheels.I am still working on the wing and how to attach it to my car. Once the wing is completed and attached, I want to get out to the Houston Dragway as soon as I can to do some more high speed testing.
5 comments:
aside from the tires easily get rip, it won't run as fast as nic case's, as long as it uses the direct drive motor to wheels principle.
I don't know how you came up with that. If you can show me how its not going to work, let me know. Otherwise, I'm just wasting my time!
I was wondering something about the wing... as your speed goes up, a fixed wing is going to gradually generate an increased amount of downforce and drag. Is that desirable? I wonder if somehow a wing could be devised that would feather off at higher speeds to reduce downforce (but not eliminate it) as speed increases to keep a more constant downforce. It probably overcomplicates things, but it is just a thought. I was also wondering about ways to generate a vacuum underneath as F1 racers do to draw a car down. You are the aerospace guy, though. I am just a hobbyist.
-T-
I was thinking about the comments of anonymous and trying to decide if they have any merit. The only thing I can think of is unsprung mass. The motor itself is unsprung mass, isn't it? That is, the motor not part of the load supported by the suspension of the vehicle, is it? As you hit bumps, this could mean more impact on your tires and the car as a whole. The suspension cannot compensate for the unsprung mass of the motor. Most 1:1 high-performance cars go for the least unsprung mass possible. I don't know if this is what anonymous is getting at, but this does cross my mind. My understanding is that you want as much of that car's weight as possible to be supported by the suspension so that the suspension can do its job. I may be misunderstanding your design, however.
-T-
Terry, both your comments are things I have been working on for a while. I am working on designing a wing that does exactly what you describe. A wing to provide maximum down force at low speeds, then decreases as speeds increase. I will post information on my initial wing design soon.
The diffuser/ground effect force that you mentioned is very desirable. It is much more efficient at making down force than wings themselves. I have been studying ways to create this same effect in my X2. I have a picture on my other site showing a great car design with a diffuser:
http://bp2.blogger.com/_3N0hwXEVK9I/RxlB_otdjxI/AAAAAAAAAyo/HNSnkP55tpk/s1600-h/am-d01.jpg
I have thought about the mass of the motor in the suspension system. It isn't good practice to have so much weight in the suspension. But my theory is that the surfaces that the car will run on will be fairly smooth and not much suspension travel will be seen. I saw this first hand when I tested at the Houston Drag way. The surface was glass smooth with only a few expansion joints every 100 feet or so.
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