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03-05-2009, 05:42 PM
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#1 | ||||||||||||
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Senior Member
Join Date: Mar 2009
Location: Wellington, FL
Posts: 116
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Top speed 4-Tec project...
This is my first real attempt at a Top-Speed setup....I plan to get this car to triple digits one way or another....
 its an evolving project so be sure to check back periodically for updates!I began with a factory Traxxas 4-tec and added a few off the shelf mods to make the car a bit faster than the rest... ...after initial testing with a brushed setup(35mph) i quickly noticed i was opening Pandora's box and installing every part that came in it! Within a few days the new parts began finding their way onto the car and with each testing session the "little 4-tec that could" became more and more like "the little 4-tec that WOULD!" ...here's a basic rundown on the setup: CF chassis 7700kv BL motor (Mamba - added Mar-23-2009) Mamba Max ESC(addded Mar-25-2009) 3000mah 4s1p LiPo 43p/75s gearing Futaba GY401 Gyro Futaba 3PM FASST radio Castle Creations 10A BEC ....(Current Radar speed as of 4/05/09 - 111mph).... My plans are to build the car to a competitive level for the ISC (International Speed Challenge) and hopefully get a crack at a record!..I have choosen to do all testing with a GPS unit rather than a radar gun...my reasoning is that the GPS averages its speed instead of creating an instantaneous measurement...so this will be similar to the "trap speed" system used in the ISC..stay tuned to see how it goes....(The GPS was heavily damaged in a 100mph crash...so i will be using Radar from now on...) -Jack
tested once more with my regulator and new servo.....all is looking good....87.0mph gps
big thanks to Anthony ( my photographer friend) for nabbing these great rolling shots!... Last edited by BoostCrzy; 04-29-2009 at 08:35 AM. |
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03-06-2009, 01:22 PM
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#2 |
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Administrator
Join Date: Feb 2009
Posts: 166
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Seems to me if you added a little more expo to tame the steering you would get a straighter run = MORE SPEED!
Nice job though.... that thing is scooting! |
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03-06-2009, 02:08 PM
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#3 | |
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Senior Member
Join Date: Mar 2009
Location: Wellington, FL
Posts: 116
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Quote:
 ....its tracking straight as an arrow now....ill put a new video up as soon as possible...should be in the mid 80's next week...next round of mods on deck: I will be trying a 75 tooth spur and a 43 tooth pinion....should pick speed up to around 83-85mph GPS .... Last edited by BoostCrzy; 03-08-2009 at 01:11 AM. |
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03-07-2009, 05:58 PM
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#4 |
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Administrator
Join Date: Feb 2009
Posts: 166
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Sweet.. Bring it. nothing like squeezing every ounce of speed out of a car.
If you hear a thunderclap, the air explodes in a burst of ectoplasm and your car is gone... You went to fast. 
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03-07-2009, 06:00 PM
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#5 |
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Administrator
Join Date: Feb 2009
Posts: 166
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Also.. I know it would look kind of Jake, but have you thought about forming some front wheel covers out of poster board and tape or something just to help with that drag the wheel opening is causing?
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03-08-2009, 12:23 AM
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#6 |
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Senior Member
Join Date: Mar 2009
Location: Wellington, FL
Posts: 116
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.....well....from what i can gather about aerodynamics...the front wheel openings at speed actually create a vacuum(venturi effect) which in turn pulls the front of the car down, acting as a wing of sorts....high pressure builds on the top...low underneath....
....but im sure it would go a little faster with them closed for sure!!.... ...might have to try it on the next body...
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03-08-2009, 10:11 AM
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#7 | ||
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Senior Member
Join Date: Mar 2009
Location: Wellington, FL
Posts: 116
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....took the car out this morning and got a few good passes in ....posted a new best!... 80.5mph GPS!! ..
Last edited by BoostCrzy; 03-26-2009 at 12:10 AM. |
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03-08-2009, 02:51 PM
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#8 |
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Administrator
Join Date: Feb 2009
Posts: 166
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Man.. good run!
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03-08-2009, 04:28 PM
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#9 |
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Member
Join Date: Mar 2009
Posts: 39
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Man I have seen this car go and man what a turd.
Thing is running good can't wait to get mine going to give you some local competition.
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03-08-2009, 04:42 PM
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#10 | |
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Senior Member
Join Date: Mar 2009
Location: Wellington, FL
Posts: 116
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Quote:
.....BRING IT Squirrel!....  
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03-08-2009, 06:55 PM
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#11 |
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Administrator
Join Date: Feb 2009
Location: Corvallis, OR, USA
Posts: 43
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You are getting up there in speed, and have reached the point where cleaning things up aerodynamically should gain you a few mph.
I'd start with the body posts. Circular cross-sections are very draggy. Trim those as low as possible to the top of the body, and put some tape over the clip. The antenna causes the same problem. Try to make the body as clean as possible. Since these draggy items are fairly far forward on the car, it is likely they are contributing to yaw instability as well, which must be countered elsewhere, which causes further drag. I concur with Steve that the front wheel wells should be covered. I don't see the advantage to leaving them open. Yaw stability is apparently coming from two sources. First, we have the fins in the back. Second, we have the gyro. Understand that the gyro is not "free" from a drag standpoint because even though it doesn't stick out in the wind, it does create drag in the form of the front wheels which are oscillating to keep the car going straight. Turn the gyro gain down to the lowest level needed to keep the car straight, and consider trimming the fins as well. You also need to consider whether you are creating too much downforce. It would be worthwhile to shim the spoiler up and down to find out what gives you the top speed. Too much downforce, obviously, creates a lot of drag. Not enough downforce and the car won't stick enough to propel itself. You clearly know what you are doing and have probably already thought of these things, but I thought it might help to offer what I could. Jim |
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03-08-2009, 09:19 PM
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#12 | |
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Senior Member
Join Date: Mar 2009
Location: Wellington, FL
Posts: 116
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Quote:
....I will definitely try to cut down drag as much as possible....the gyro is at 25% gain right now....but i have a high speed servo on the way to maybe allow for a bit more gain without scrubbing too much speed....i am also going to be trimming the vertical stabilizers a bit more....as mentioned i may also seal the front wheel wells.....but im afraid of losing the theoretical vacuum being created by them......the rear wing is completely flat at this point with very little area rising in the corners where they meet the Vert. stabs... -Jack |
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03-08-2009, 10:51 PM
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#13 |
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Administrator
Join Date: Feb 2009
Posts: 166
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The top car is Nic Case's 160 MPH Custom Works 2WD dirt-oval and the 134 MPH Nitro TC3 on the bottom.
Give an eyeball the bodies, see if anything might help you. This is a really cool project. Please keep posting updates, I am really digging this! |
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03-08-2009, 11:27 PM
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#14 | |
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Senior Member
Join Date: Mar 2009
Location: Wellington, FL
Posts: 116
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Quote:
....looking at his body choices its plain to see that frontal area reduction is the main goal of this sport....i may be looking into some data acquisition equipment to measure some of the power consumption going on....this may translate the drag load a bit clearer for tuning..... -Jack |
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03-09-2009, 06:25 AM
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#15 |
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Junior Member
Join Date: Mar 2009
Posts: 2
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No matter what it is, if you want it to go fast, you have to make the aerodynamics as clean as possible. I have some suggestions for you.
The bottom of the car needs to be aerodynamically clean. Use polycarbonate sheeting to make a clean pan that actually connects to the body shell. This will have a two fold effect. It'll lower your drag by lowering the number of gaps under the chassis and stabilize/strengthen the body shell so it won't flex as much thus keeping it from deforming and changing the aerodynamic qualities of the shell. You might want to look into vacuum forming your own polycarbonate. There's several resources online such as www.instructables.com that can help with vacuum forming. Not as difficult as you'd imagine. Remove whatever weight you can! Every little bit counts. Carbon fiber, titanium, aluminum alloys... expensive but light and strong. Speed costs an arm and a leg, remember. Instead of using conventional body mounts use neodymium magnets. They're extremely strong! You can thus eliminate the body post drag yet still be able to easily access the inside of the RC for charging/work. These magnets can also be used to attach the under pan mentioned above to the edges of the body shell. Ceramic bearings with DRY lubricant for the lowest rolling friction/resistance possible. Wet lubes/grease not only attracts grit but causes drag. They do reduce wear with gear meshes and such but the lubricating material causes a bit of drag. Dry lubes reduce this parasitic drag. Balance ever rotating part you can! Typically the only thing you'd have to balance will be the wheels/tires. Vibration/Oscillation robs power, causes wear, and makes it harder to drive straight line. This has been my first post to this new site... I hope it's been a helpful one. Good luck on your quest for speed. Sincerely, Sarkazmo |
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