I Want to Build a Go Fast RC !
 

I have ben hanging out with a crowd on Firday nights behind the local Lowes and everyone races straight line for max speed. I made a few runs with my modded SLash 4x4 and hit 64mph befor lift off, Tried again w/o the body and hit 69mph. Anyway, Now I'm kinda hooked and want to purposely build something for this and bust the compition. They're almost all Nitro guys:whistle:

Heres what I'm thinking about
http://www.horizonhobby.com/Products...rodID=LOSA0809

ANy other good candidates for this prodject about the same price ??

I have a NEU 1521 1Y and plan to run it on 6s, A RCM mount of course and possibly a home made battery tray.

Curious what you guys whom have had experience with doing something like this have to say or reccomend ?

Heres what I've come up w/via BrainG's calc
Differential Ratio: 3.3076923076923075
Transmission Ratio: 1
Other Ratio: 1
Spur Tooth Count: 47
Pinion Tooth Count: 26
Total Voltage: 22.2
Motor KV: 1577
Tire Diameter (inches): 4.5
Tire Ballooning (inches): 0.10
Motor Current Draw: 0
Motor Coil Resistance: 0.008
Spur/Pinion Ratio: 1.81 : 1
Total Ratio: 5.97929 : 1
Tire Circumference (inches): 14.77 inches (375.04 mm)
Rollout: 2.47:1
Total Motor Speed: 35009.4 RPM
Vehicle Speed: 81.87 mph (131.51 km/h)
Effective KV Value: 1577
KT constant: 0.86 oz-in/A
Motor Torque: Amperage not specified...
Final Torque: Amperage not specified...
Final Power: Amperage not specified...

How about an Ofna DM1. I'm not sure what they go for $$ wise, but there are some pretty good builds here on the forums.

-JB

A 1/10 scale would be a cheaper build and fast also. I run a tc4 for speed runs and like it seems pretty tough.:yes:

ofna dm-1 spec is 330 on towers http://www3.towerhobbies.com/cgi-bin...?&I=LXVVS8&P=0 just buy the ofna buggy motor mount from rc-monster to make it electric

LX-1E would be cheap and easy.

knowing the nature of my projects, i'd prob drop that motor, batt, and all onto a slab of wood directly to a 3.3 deff and good tires haha. then make a weird body to keep it on the ground

Go with your gut, looks like you got it figured out, plus you really got my attention.
P.S. Your still going to need some weight up front:lol:

You'll get an 8ight buggy well over 100mph on 6S using a 2650 with 43/25

I'd love to see a L8ight tweaked up for speed runs though. Can't imagine why you'd consider a 1521 though? unless you want to be running continuously...I'd use a 1515 1.5 - good for a couple of 6S passes before you let it cool down

Get some of these;

http://www.grpgandini.it/index.php?p...chk=1&Itemid=6

Vertical stabilisers & no wing at the back, big splitter at the front. Good to go

Your really going to need weight upfront I have the neu 1521 1y original and its ballistic on 6s it is hard to control the steering in the straight full throttle, I guess check your punch control and ripp it and have everyone stand out of the way LOL I do it with my XT8 and its insane:intello:

+1

i've seen some really fast buggies. my lx-1e should be here on tuesday and i bought a 18-20t novak pinion combo to do some speed runs on 6s with the castle 2200kv motor i bought for it. should be good for at least 80mph. any faster and i will need belted tires.

i've seen another lx-1e in person and the quality is very good for the price. the quality is better than my CEN matrix, but not quite as good as my crt-x2. it isn't too nimble on the track, but it should be just fine for speed runs. if you want crazy speed, limit the shock travel to lower it, use a 2200 or 2650 motor with 6s and a 26t pinion, and get belted tires. that setup should be good for at least 90mph. the center diff will make it easier to keep the front down as well.

Ultra LX-1E

I'd consider adding downforce before weight...no need to blunt the acceleration

Talk to snellemin and sonnyhoutx as they both are go fast guys.

The input and suggestions are much appreciated gentlemen.

I'd rather stick with 1/8 scale over 1/10 scale, I like the bigger RC's and definitely want a full body rather than a 1/8 scale buggy format.

The DM1 is a hellava good foundation but one of the faster guys at the spot has a real nice DM1 running a 2650 on 4s and it's wicked fast and sounds like a jet ! After 2-3 quick runs he thermals, I think thats kinda dumb. I want to be able to rip pass after pass and/or just screw around and not worry about heat issues. Hell, 80mph is pretty good start, I may not need anymore ?

I'm thinking the 1521 due to abundance of efficent power, but I also have several other motors in my treasure drawer to choose from. So I have some options.
Castle 2200kv
Castle 2650kv
Castle 1800kv
Neu 1512 2550kv
Tekno 2000kv

The draw back of where they race at is it's only about 500 hundred feet of clean smooth concrete, on each end it's cobblely uneven rough asphault so she's gotta get up to speed and back down again quickly.

mechanical brakes sound like a must

Excellent advice !
Not sure I know what a BIG SPLITTER for the front is ?


Yeah, I actually have ben contenplating this. I've ben bouncing back and forth looking at Mikes and Tekno chassis and the option of installing Servo brakes myself.
I'd much rather mod something myself to keep expense down considering this is something I'd only drive once in a while. I already have everything I need to build this except a roller and a motor mount.
Need to find pictures of someone's stock chassis with servo brakes to see if theres even enough room to do this ?
One of my buddys bought a rip off of Mikes Slipperental a few months ago and he hasn't ben able to tune it to his likeing(imagine that?) He's willing to donate it to this build, like to see if this peice of shiz will work. It would be nice to have a slipper for the concrete and 6s ?

http://i703.photobucket.com/albums/w...ySplitter1.jpg

Once you get up over 50mph, you need to control the air around the vehicle as you push through it. A splitter helps you trap some air at the front which creates a high pressure zone - see pic. In simple terms this creates frontal downforce which will eliminate the need for weight forward...an additional benefit is that is adds to the vehicle cord length, which lower the drag coefficient. This is good of course

If you have a look at phildogg's avatar, you'll see the vertical stabilisers and lack of rear downforce, you don't need much rear downforce (if any) because the faster you go, assuming the frontal elements are correct, the more downforce the vehicle as a whole will generate (this is a simplistic summary, thousands of variables influence the aero dynamic). Phil's run his creation well over 100mph...

You'll need to keep the body under control also, use velcro along the sides of the body. If the sides start flapping you'll blow over and/or rip the body off. You can use body mounts also but keep them as short as possible so they don't create drag. An added benefit of velcroing the sides is that you'll usually need to fill the space between body & chassis, this improves low pressure flow under the vehicle...an example by Nic case, he uses polycarb bent to shape

http://i257.photobucket.com/albums/h...y/IndyISR7.jpg

Personally, I'd use the 2650 on 6S...more than enough for 100mph

Interesting !
Thanks PBO for the explanation and pictures, very discriptive.
Doing something with the sides like that is a welcomed idea also !

I'm thinking about the DM1 a more seriuosly but hate to have the same thing as the other guy in fear of being accused of being a copy cat. It's just much cheaper than the Losi and can double for track duty. IDK yet ?

I will def install the 1521 first, if the need for more speed is needed I can easy install another motor to satisfy.

Nice explanation PBO! :)

@Bondonutz: I would go for the DM1, even if begin accused for a copy cat. Just install a different set-up which will run much faster and cooler and you're the man :mdr:

Just found this at NitroHouse

http://www.nitrohouse.com/catalog/pr...ducts_id=21777

I'm really likeing the DM1 but parts will be all internet, If I go w./the Losi I can get everything I need in town.
I work at a LHS and can get stuff at cost via Horizon Hobby, but Horizon doesn't have the DM1pro ? So it's either the higher qaulity Losi or go w/the Ofna E-Dirt oval which will be mega cheap and parts will be readilly availible via HH. So at least my dicision is narrowed down to 2 choices, I think ?

Bondo, here's a few things to keep in mind from what I've been through with speed runs.

1. ESC will thermal after back to back full throttle, high speed passes. More often than not, this will happen when geared for speeds more than 60mph. The higher you go from there, the quicker you will thermal or even damage a motor after consecutive passes.

2. Get high quality batteries like Hyperion, Neu, Thunder Power, etc.. The gains you get from the better packs are very noticeable and they can take the stresses of speed runs well.

3. Do not fully lock front/rear diffs if you're using a car with suspension or a lot of chassis flex. You will lose control of the car very quickly.

4. Front splitter that PBO mentioned is something similar to what NASCAR uses in the front of the car which creates down force up front. This is definitely a must-have. (Oops... didn't make it to page 2 before I posted)

5. Do not use a fully covered bottom chassis plate. You must allow air from below the chassis vent upwards into the body cavity and then be quickly vented out the back. To that end, clear obstructions as much as possible to help airflow in the body cavity. Cutting vents in the back window, cutting out the panel where the tail lights would be, etc., will help.

6. Vehicle weight is not the enemy when it comes to speed runs. It will help keep the car on the ground.

7. Unless you run on a prepped track, grooved rubber tires with belts or capped rubber tires are a good option, especially on concrete. Rubber also works better in hot weather after the track and tires have warmed up a bit.

....

I'll add more as I recall more pointers.

SunnyTX,
Great points, especially #5 !
Any more info you remember will be appreciated.

Big Thanks boss !

A good TX. You'll want excellent range & the ability to adjust your dual rate as well as your end points

Video...no need to expand on this point! :lol:

The TX is covered, video will come along in a couple weeks.
Thanks Guys !

... 8. Speaking of TX, numb (negative expo, restrict EPA, etc.) the steering so that it's real mellow. Also, think of getting a gyro if you can.

I think most of the important items have been touched on so far in the various posts. Now it's a matter of trial and error. Just get the thing running and try different gear combos and change aerodynamics as needed. Good luck man!

8.1; if you install a gyro, start with the gain set low & increase, if you don't they have a tendancy to "hunt" or overcorrect & this can cause a crash...again this is where video is important

^ Yes, that's very important :yes:

On the topic of aerodynamics and down force, do you want the front of the car to have less clearance than the rear? To me that would create low pressure under the car and suck it to the ground, but you probably want a full lexan under body to make it work.

I don't believe so. If you change the angle of attack dynamically it would change the dynamics & handling characteristics of the car too rapidly. If you combine dynamic changes with running surface changes (temp, friction, camber etc) & atmospheric changes & lets not forget driver input, then I'd be surprised if you could replicate similar conditions enough to give you a reference point for tuning. That's not to say it wouldn't work though...

I'm involved in this project which in a roundabout way uses a similar concept of preset dynamic tuning. Summed up simply, there are too many variables in play to allow a "sweet spot" to be anticipated or predicted. Obviously this is an experimental concept to say the least but it's still governed by F=MA & it's hard to trick #2 with a slight of hand

I say that because there are racing wings for the rear of the car, but underneath the bumper, that points down towards the front of the car, creates a low pressure and thus downforce on the car.

I would at least put a full lexan under body as to create a consistent air flow over the car, top and bottom. IMO.

I'm not sure what you're explaining?

As for the enclosed underside, it has been done & Nic Case makes the best example with one of his streamliners

http://i257.photobucket.com/albums/h...h_DSC03517.jpg

If you look at the large image you can see channels that train the underbody airflow out of the vehicle which does create low pressure

Sunny mentioned leaving openings for airflow to enter the inside of the vehicle - this also works and both Nic & Sunny are using the venturi effect. If you don't create a venturi (somewhere for the air to escape) you are typically creating an aerofoil (the top of the body resembles the top of a wing, the flat, solid bottom - the bottom of the wing) which in itself creates lift because the airflow over the top is at a lower pressure than the airflow under the body...then you suffer blow overs at a certain speed depending on length/width/weight/speed

So it can be done but without the veturi effect the airflow underneath compresses to become higher pressure than the airflow over the top...you can of course change the airflow over the top by changing the body shape to create lower pressure than underneath but it's much harder than creating venturi's

I hope that makes sense? I've glossed over a few things

ZeroPointBug is talking about a rear diffuser as with on F1 cars

Rear diffusers in an RC car are only mildly effective IMHO.

The way that Nic has his car set up in the photo that PBO posted, and the way we set up our RC drag car bodies, makes the whole body act the same way as a diffuser, but at higher effectiveness, and the down force is distributed over much of the length of the car rather than just behind the rear wheels (which will cause the front end to pick up).

Diffusers in the traditional sense may have negligible effect on our little cars but some slightly unorthodox diffuser designs will create a significant difference. You're basically trying to make a relatively flat front end and streamlined rear. A teardrop shape or airfoil of sorts but for ground effect. That combined with some vertical stabs and you're set. This is all very unnecessary to only hit 100mph but to go beyond this point they may be needed or atleast aid in maximizing speed with the power available.

PBO, that's exactly what I'm talking about in the picture, nice streamlined, with channels to hold the low pressure and reduce eddy's. The openings are also something I had in mind, was looking for the term Venturi's, which makes alot of sense.

^^^ Very key. Holding the sides of the body steady and not flapping around plays a big part here as well. Actually, something to keep the sides from being sucked in is all that's needed sometimes.

Here's the back of my RC funny car showing an "aid" to evacuate air out the back of the car:

http://i256.photobucket.com/albums/h...40085Small.jpg

And same from my True 10.5/Pro Stock

http://i256.photobucket.com/albums/h...40057Small.jpg

Mind you, the funny car goes 90+mph and weighs at 48oz (3lbs) and hasn't been airborne at those speeds. That gives you an idea how effective low pressure under the body is. Also note that the angle of the wickerbill is not that extreme: just enough to be effective and not create a lot of resistance.

That is in essence a diffuser...just a very large & efficient one, sucking the car down harder, the faster you go

I don't consider it a diffuser in the strictest sense simply because the area of influence of the low pressure created is much larger here, but that's just me :rules:

But the important thing is that this all helps keep the car stuck to the ground :yes:

Hahaha...fair enough. Giant venturi is probably more acurate

As far as aerodynamics, what do you guys think of the dirt oval body Ofna has?

Or any suggestions for the most aerodynamic body? My LHS guy did 112mph at ISC with a Ferrari body. I would get one but I want to be different than his.