I Want to Build a Go Fast RC !

[PBO]

Originally Posted by Bondonutz

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

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



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

[Bondonutz]

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

[Bondonutz]

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 ?

[SunnyHouTX]

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.

[Bondonutz]

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

Big Thanks boss !

[PBO]

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!

[Bondonutz]

Originally Posted by PBO

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!

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

[SunnyHouTX]

... 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!

[PBO]

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

[SunnyHouTX]

^ Yes, that's very important

[zeropointbug]

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.

[PBO]

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

[zeropointbug]

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.

[PBO]

Originally Posted by zeropointbug

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'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



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