High speed G-maxx for ISC event, 100mph or bust

[_paralyzed_]

Originally Posted by Rivermaxx

I actually have about 1* toe in in the rear the fronts are neutral also but it is still hard to control. The road crown probably didnt help at all either. I notice under acceleration it started to pull to the left. Whats up with that? If I cruise about 20 mph it goes straight.

sounds like torque steer to me. only thing you could try is flipping diffs and reversing motor operation, but I suspect it may go to the right under acceleration then.

also sounds like you are traction limited, you have a pretty small contact patch with the road. Needs more downforce!

[PBO]

That's all good news

The drifting or slewing may be as simple a fix as vertical stabilisers off the 1/8 wing end plates

Toe in/out? assuming it's at the rear - I'd run a max of 1.5 deg, any more starts to scrub off speed

If you use a gyro they take a little getting used to, wind the gain right down so that it is only noticeable under brakes...you don't need it hunting under acceleration

[PBO]

The left pull may also be a further sign of wheel spin, once moving forward but without traction, a vehicle will follow the natural camber of the road...it may be this??

[PBO]

I've posted this elsewhere in reference to an excellent mini revo custom build, it may be of some benefit? Apologies for being lazy....

"I see there are 4 basic elements to an open wheel design...1st is the splitter, 2nd is the body, 3 is the rear wing & 4 is wheels



You can adjust everything except the wheels fairly easily & this is the splitter function...



but in your case I think something more exaggerated in terms of length & perhaps even reducing the high pressure area by smoothing the splitter to body area - which increases the downforce...& then if you need to, you can reduce this effect by reducing the size of the splitter. I hope that makes sense?"

In most cases, the splitter can be mounted directly to the chassis via a simple CF or alum plate using the existing diff screws

I also think a 1/8 rear wing might be too aggressive & reducing the near vertical elements will work well to decrease drag but maintain sufficient downforce. Combined with the enlarged vertical end plates, it should work perfectly with some fine tuning

[Rivermaxx]

Whats funny it pulled toward the crown not away so it might be torque steer. I thought a gyro would help correct this problem. Now i have to find a gyro thats will work and reasonably priced. As my budjet is through the roof.

[Rivermaxx]

Here my wing:

I need to get rid of some of or all the down force kick up in the back. I was thinking of just removing kickup near the side of the stabilizers (see pic) or just remove the center leaving the rear side kick ups to help support the side stabilizers.

I could also remove the whole thing all the way across as I think I need the stabilizers more than the rear downforce as too much will cause the front to lift and I dont want that. even with the rear removed the front part of the wing still has a small kick up also(see first pic). What do you guys think?

[JThiessen]

Pull the wing off completely for a run and see how it acts. That will give you "data" at both ends of the spectrum, and you may be able to make a more precise "guess" at where you need to be.

I agree that you probably saw torque steer. Might want to change diff fluid.

Another thing you might try once you get to the fine tuning stage is some sort of mud guard on the A arms. You could possibly shape it so its not just a flat surface. May or may not make a difference.

Great diagram PBO - that's exactly what I was trying to explain in one of my earlier posts. I personally think its all about that front wing or spoiler with the body shape, height, extended arms and wheels that a MT has.

[PBO]

Originally Posted by Rivermaxx

Here my wing:

I need to get rid of some of or all the down force kick up in the back. I was thinking of just removing kickup near the side of the stabilizers (see pic) or just remove the center leaving the rear side kick ups to help support the side stabilizers.

I could also remove the whole thing all the way across as I think I need the stabilizers more than the rear downforce as too much will cause the front to lift and I dont want that. even with the rear removed the front part of the wing still has a small kick up also(see first pic). What do you guys think?

I agree you need the vertical stabilizers more than anything. I would also remove the "kickup" but I would dremel it down bit by bit across the entire length. I would expect you'll remove up to 1/4" of height by the time you're finished tuning

I would add some bigger end plates though...each 5 mph increase over 70mph changes the way your vehicle will behave & the vertical end plates will have a positive effect on each issue you have described the closer you get to 100

I'm not sure a gyro will be able to correct torque steer (if this is the issue) because it may end up "hunting" (over correcting itself), this is bad at any time but under acceleration it can obstruct additional throttle input. You'll need to spend some time getting it setup correctly - I tried to tune both a Dbox & Ace gyro on my Rustler & I got to a point where it was doing almost nothing under acceleration but would keep things tidy under brakes (this enabled me to run stock sliders to > 85mph because I could slow down slowly, without snapping the yokes off first dab of the brakes)

[Rivermaxx]

Never ran it with a wing at all . The diff has thick fluid and is pretty tight but I was told the front could be spooled or locked with diff grease. You think it would help with torque steer. Working on figuring a front splitter now , I will let you know what I come up with.

[JERRY2KONE]

Good test data so far River. My 2cents. Unfortunately I believe the only way you are going to reach your (speed)goal is from a lot more testing and trying different effects. Running a 1/8 scale vehicle at those speeds takes a lot of tweeking to get all of the variables just right. The ones I have seen up to now that do very well were running with a body that covers the entire vehicle, including the wheels, which prevents or elliminates alot of the turbulance and push that you will see. Take a good look at todays "Funny Cars" and see what you can use from that technology. You might try fabricating your own wedge type body out of thin lexan sheeting. This type of body will give you more control and also give you more protection for your equipment in the event of a roll over at high speeds.

Your steer pull issue does sound more like natural torque steer from your drivetrain. This is something that is almost impossible to over come completely. A strong servo setup and the Gyro may help though. It is good to see what you what are going through in order to learn what (to do & Not to do) when my project gets to that point. Good effort River, and good luck.

[JThiessen]

Jerry - per the MT speed rules your body cant cover the wheels, so he's stuck with something close to standard width. He may be able to extend one out to almost touch the wheels though.

River - I would almost think that a light diff fluid may help with the torque steer. If not, you may have to get good at setting up your chassis to compensate. I'm going off memory here - can you adjust the maxx arms front to back at all? You may have one wheel sitting slightly forward of the other which could cause a slight drift.

Maybe also try adding a shim to the spring on the uphill/crown side of the truck.

[Rivermaxx]

Originally Posted by JThiessen

Jerry - per the MT speed rules your body cant cover the wheels, so he's stuck with something close to standard width. He may be able to extend one out to almost touch the wheels though.

River - I would almost think that a light diff fluid may help with the torque steer. If not, you may have to get good at setting up your chassis to compensate. I'm going off memory here - can you adjust the maxx arms front to back at all? You may have one wheel sitting slightly forward of the other which could cause a slight drift.

Maybe also try adding a shim to the spring on the uphill/crown side of the truck.

The body cant cover the tires in the open wheel class. I was told by Nic Case that a spool or locked front diff is what I want thin dif fluid will have the opposite effect I want. The front will unload one tire quicker causing drift or torque steer. If its locked or close to it, both tires have to spin the same speed no matter what causing the truck to pull itself straight. I dont know if you guys noticed the arms are the short old style rpm arm so they are not adjustable. I did put some more toe in in the front to help with high speed stability, I will lyk how it works out. Not sure if a shim will help either the truck is pulling toward the side with the most traction. It was pulling toward the crown so if I shim that side it will put more pressure down causing more traction and more pull now if I put it on the other side it might help. My springs are adjustable so no need for shims just preload one side more than the other.
Jerry, I have seen plenty of open wheel cars go fast. Look @ the fastest top fuel cars, 230+ mph indy formula 1 cars, and outlaw cars. I also have seen a few open wheel buggies go 100mph+ and a few 80mph revos, and 1 that went 91.2mph . So I know it can be done it just getting everything set up just right and lots of testing like you said. Remember this is my first real test with the proper tires and I allready am doing 67mph. How many maxxes have you seen, heardor read about going that fast on radar? I know I might have read about 1 or 2 and thats it.
How do you guys like this open wheel design? I am thinking of stealing the front wing design. Will more smaller stablizers front and rear be as good as big ones on the rear. Kinda like a indy car.

[brushlessboy16]

Go with spools all the way around. Maximum power transfered. and your not turning much.

[Rivermaxx]

Just the front, rear really dont need it especially with the weight transfer.

[ZippyBasher]

Hey did you happen to Catch last nights episode of the "Mythbusters". It was about aerodynamics and creating less drag on a car with the addition of dimples. (IE. Like a Golfball) they were able to prove a 12% gain in gas mileage just by adding dimples across the entire car. They were using the science of a dimpled golfball will fly farther than a non-dimpeled using the same amount of thrust. (which is about 40%)

After reading through your thread last night I watched the epsidoe and thought that I would pass this info along. As I thought this might help you out with your goal. Wind is going to contribute in a huge way and every little bit would count when trying to break a new record. You should check it out. It may just give you that little bit extra of an edge over the comp. if you were to design the body correctly. Anyhow Good Luck.