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Old Feb 14, 2013, 06:47 AM
Enjoy Life B4U Die!
Buzz_Man's Avatar
United States, GA, Powder Springs
Joined Dec 1999
4,250 Posts
Quote:
Originally Posted by Bugman Jeff View Post
I've decided I want to go fast, very fast. I also want to do it cheaply. Normally fast and cheap don't go together. Anyone can build a fast car, and anyone can build a cheap car. The challenge(and fun) for me is to see if I can put the two together. My goal, as seem to be the most common for speed run cars, is 100 MPH.
My opinions . . . based on some facts:
-------------------------------------------------
Long wheelbase = better tracking for high speed
Tracking --> precision setup for tracking straight
Steering --> at 100 mph, a tiny input can provide incredible results - get the car so full turn with the transmitter equals very little left-right steering with the wheels
Drivetrain --> 4WD --> I stand corrected - thank you
Very low turn brushed motor = cheap & fast
Gearing = will substantially determine overall top speed potential
Battery = use a small size battery with a very high discharge rate
Bearings = will help with speed, lowering rolling resistance
Aerodynamics = don't let the machine get air and lift up - seriously at 100mph it could be dangerous
Testing, testing, testing --> don't try to break the speed of sound on the first shot. Set small, realistic goals and make improvements and learn as you go

Sounds like an incredibly fun project - best of luck.
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Last edited by Buzz_Man; Feb 15, 2013 at 06:23 AM.
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Old Feb 14, 2013, 12:00 PM
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wparsons's Avatar
Canada, ON, Whitby
Joined Aug 2008
8,901 Posts
Hitting 100mph is much easier with 4wd than 2wd. 2wd doesn't have the traction for the power required and needs a LONG space to get up to speed without spinning out.
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Old Feb 14, 2013, 12:16 PM
Did you check the FAQ already?
SoloProFan's Avatar
The Netherlands
Joined Jul 2010
12,924 Posts
+1 on the 4WD vs 2WD, you need all the traction you can get, and there are cars with a light running 4WD drivetrain.

Also make sure the suspension is set for soft, but not bouncy. So mild bumps in the road don't rock the car.
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Old Feb 16, 2013, 06:23 PM
I'm a Registered User
Evansville, WI
Joined Dec 2006
3,689 Posts
I finally got my buck finished. It might need some more tweaking once I get a body fit to the chassis, but for now it's ready to go. I'm fairly certain I'm going to get webs off the back of the car, but that's not a problem because the rear section is going to need some more work anyway once the body is pulled and fitted. Now to clean up the dusty mess that is my basement...
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Old Feb 16, 2013, 08:40 PM
I'm a Registered User
Evansville, WI
Joined Dec 2006
3,689 Posts
Now the fun part I've got a little vacuum former that I use. My buck just barely fits on it. Seriously, I've got only less than 1/4" on either end, I didn't think to measure before hand. I really didn't think it was going to work.

For the first test bodies, I'm using .035" HIPS(high impact polystyrene). I usually use PETG, and I'd forgotten just how nice HIPS is to work with. It heats up nice, and forms VERY well. My former is about the size of a suitcase. It unfolds so that the heater is on one side, the vacuum table is on the other. The plastic is clamped in a hinged frame between the two. You heat the plastic up, then flip it over onto the vacuum side and turn the suction on.

It took three tries, but the third pull turned out very well, better than I expected really given it's size and depth. It's not perfect but it's more than adequate for test fitting to the chassis
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Last edited by Bugman Jeff; Feb 16, 2013 at 08:51 PM.
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Old Feb 17, 2013, 04:10 PM
I'm a Registered User
Evansville, WI
Joined Dec 2006
3,689 Posts
Did some more work on the body, getting it trimmed and fitted, figuring out what will work best. It's not left/right symmetrical, so it took some careful trimming to get it sitting right. Once I got the body fitting like I want it to, I spent some time with some card stock trying out different wing/diffuser ideas. Here's where she sits now.
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Old Feb 23, 2013, 05:17 PM
I'm a Registered User
Evansville, WI
Joined Dec 2006
3,689 Posts
Lots of words and few pictures today. I spent the day making some bodies. I'm not using polycarbonate because, quite frankly, vacuum forming Lexan is like trying to vacuum form glass. It's expensive, hard to work with, and needs a whole lot of heat to form. Instead, I'm using .050" PETG. Even if you've never heard the name, you're familiar with PETG.

You all know those heat sealed plastic packages that are so tough that even with scissors they're hard to open? Those are PETG. It's nearly as tough as Lexan, but 1/2 the price, and it forms at 100F lower temp. It also doesn't "seal" against the surface like Lexan does so you get a better form with less work, Lexan will seal against the surface and you'll get air bubbles that don't bleed out. PETG doesn't form as easily as styrene, but it's not to far off. It also doesn't require special paint like Lexan does, regular paint will crack, but won't flake off as the body flexes.

This is a very tall form, the back is very square, and the mold just barely fits in the former. It took me 6 tries to get a body pulled cleanly enough to use. As I suspected I would, I got major webs off the back corners. PETG starts to get soft around 200F and forms best around 290F. To help with the webbing, and to prevent the soft plastic from freezing too quickly when it hit the cold mold, I put the mold in the oven and slowly heated it up to 200F(heat it too fast, and the plaster might crack). After the initial forming, I followed up with me heat gun to resoften and suck down any areas that weren't fully formed. You can just see the hint of a web left on the back corner, but it's not a problem because the bottom 3/4" gets trimmed off anyway.
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Old Feb 23, 2013, 11:26 PM
I'm a Registered User
Evansville, WI
Joined Dec 2006
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I got my body trimmed so that it's level with the bottom of the chassis. With the body trimmed, I started on my under plate. It's also made from .050" PETG, and it's also serving as the base for the front splitter. You'll notice that it stops about 2/3 the way down the chassis. I decided to make the rear diffuser a separate piece. It's going to take a bit of work to make and I've already got plans for another, more aerodynamic body that will have a different side profile and I don't want to have to remake the diffuser. This way, I'll just have to change the front section
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Old Feb 24, 2013, 11:41 PM
Did you check the FAQ already?
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The Netherlands
Joined Jul 2010
12,924 Posts
Looking pretty nice so far. I'm pressing my thumbs you won't crash it the first speed run, and damage this sleek looking body.
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Old Feb 25, 2013, 12:43 AM
I'm a Registered User
Evansville, WI
Joined Dec 2006
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It's ok, I know the guy that makes them
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Old Feb 27, 2013, 12:58 PM
I'm a Registered User
Evansville, WI
Joined Dec 2006
3,689 Posts
If you remember my first baseline run video, you'll remember that I crashed into my radar test stand. Since I definitely don't want that happening again, I made up a new test stand. This one hangs the radar gun out on a boom with enough clearance that I can drive right under it There's not much to it, it's a quick and dirty stand made from some scrap wood I had laying around. The boom pivots, so it's easy to store too. The counterweight keeps it from tipping over.
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Last edited by Bugman Jeff; Feb 28, 2013 at 12:24 PM.
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Old Feb 28, 2013, 10:51 PM
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United States, CA, Oak View
Joined Jul 2012
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very good job impressive i try to get into onroad rc cars and i was looking at getting the same car
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Old Mar 01, 2013, 01:26 PM
I'm a Registered User
Evansville, WI
Joined Dec 2006
3,689 Posts
Here's how my belly pan is coming along. I've got the front section trimmed just about right. I'm not happy with how the diffuser is shaping up, so I'll probably start over.
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Old Mar 01, 2013, 05:54 PM
I'm a Registered User
Evansville, WI
Joined Dec 2006
3,689 Posts
I spent some time mocking up my front splitter. I have a feeling that the scoop is much bigger than it needs to be, but I really don't want my car going airborne. Too much downforce just adds extra drag however and will push the belly pan into the road. I'll make a couple different sizes so I can get just the right amount.
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Old Mar 03, 2013, 11:18 PM
I'm a Registered User
Evansville, WI
Joined Dec 2006
3,689 Posts
I didn't get much done this weekend. I did get most of the diffuser made. I wasn't happy with the first one, it didn't fit well, and it was pretty wavy. I'm much happier with the new one. This one fits like it should. I got the fins made and fitted too, they just need to be glued on. They're made from .040" PETG. Once they're glued, I can trim them to the final size/shape.
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