R/C car guy

[link=http://www.rcnitrotalk.com/forum/showthread.php?s=&threadid=14332]http://www.rcnitrotalk.com/forum/showthread.php?s=&threadid=14332[/link]

Check it out. I don't feel like typing it again so look at the link and see what i'm asking about.

jefx

Seems like a good idea. But it will take some time to find the right spring tension. Also it would have to be durable enough to take vertical landing. You could essentially achieve the same effect just by having a lower wheelie bar, one which would limit the height of the wheelie. If the front wheels were only allowed to lift a couple inches, then gravity would pull them back down. The reason the long wheelies occur is because of balance. Once the front wheels reach skyward, the fulcrum gets pushed toward the back of the truck and gravity doesn't have as much leverage on the front wheels.

crazypyro013

here comes a little physics for ya:

when the truck is driving along its center of balance is somewhat centered, but not completely

as the truck stands taller its center of balance is shifted to the rear, and eventually dumped on the rear wheel

now if you can find the center of gravity on the rear wheels of the truck in wheelie position, then measure and adjust

... and if the center of gravity exceeds its base(rear wheels) thats when it topples

theres a fairly simple way to find it using cardboard, a hole puncher, nail, string w/ weight attached, and a pencil, but i'll only explain it if ya want

popuptoaster

look at the wheelie bars on a drag car or bike, they all have springs on em, otherwise the shock of hitting em as the front came up would bend em or break something.

I think you would be better off with a small damper and very weak spring, it would damp the upward speed so you got a more gentle lift and more controlled wheelie.

Easy to arrange, bar comes from RC chassis hinged at the vehicle end, axle with small wheels at the other end, coil over damper runs from wheelie bar axle to rear of vehicle at a higher point on the rear of the chassis. (similar to a motorcycle rear swing arm)

simple spring changes and damper oil wieghts would make it tunable.

R/C car guy

I thought the fulcrum of the wheelie is always the same no matter how high the wheelie goes. I thought it was always the rear axle, or if it is independent suspension, it would just be the center of the rear wheels. I'm not saying that you are wrong, I'm just saying that it seems as though the fulcrum is the center of the rear wheels and it doesn't move backwards as the height of the wheelie increases. I figured the long wheelies just occur when the engine is able to lift the truck a little bit, it builds up a little momentum and gets higher, thus getting a little more momentum and moving even higher. This happens until the truck is at its max wheelie height, that is set by a wheelie bar. The wheelie then stays at its max height becuase the wheelie bar prevents the front from rotating any more around the fulcrum(rear wheels) and they don't fall becuase of the force of trying to be pulled backwards, for it is trying to rotate around the fulcrum(rear wheels) that way. The force that is pulling the front around the fulcrum after it is at its max wheelie height is no long momentum, for it isn't moving any more. The force is from teh front end trying to move forward and under the front end becuase it is being propelled, but the front no longer is becuase the tires aren't on the ground. The reason that the wheelie bar stops the wheelie is, if the front were to continue going up, it would cause the wheelie bar to go forward from being on the other side of the fulcrum. If this were to happen the rear wheels would come off the ground and the truck would no longer be geting propelled forward and would fall onto all four of its wheels, directly back into the wheelie, or continue rotating all the way onto its roof. This is why if the truck has an awsome amount of torque and ability to wheelie, it will sometimes look like the truck is jumping all four of its tires completely off the ground during a wheelie, even though the truck is on a flat surface.

I do agree the having a wheelie bar that limits the wheelie to only a couple of inches would have a similar and maybe even a better effect than my brothers idea of a reactive wheelie bar. Not only that, but it's also simpler, and most likely more durable. If the wheelie can only go to a couple of inches the wheelie would get to it's max height, lose its momentum, and fall soon after the wheelie started.

Keep in mind that I'm no expert in physics, and these are just my assumptions/opinions. So don't flame me if these ideas are completely off the wall.

If this post seems a little off, it's becuase I was typing it while there was only jefx's response.

crazypyro013

b/c wheels are round it is..... my explanation is the basis for all things, that i can think of atleast

well as the truck tilts backwards its mass is then re-centered, where depends on the height of the truck
if you lock the rear wheels then stand the truck up straight up and down perfectly level it'll sit there till an outside force acts on it, now if that mass is just a 1/32 of inch back, then it'll topple, if that 1/32 is the other way it'll fall on all four

the added troque from the motor lifting the wheels, causes the truck to lift, and all the wheel bar does is prevent it from going all the way back, so in simpler terms:

the motor lifts truck using torque
wheel bar opposes torque
torque pushing against wheelie bar + speed = the effect of "riding a wheelie", instant you let off the throttle the truck returns to all 4


your bros reactive wheelie bar is a neat idea, by using different spring tensions you can achieve certain affects
i.e. stiff springs means it'll get shot back to all 4.... soft springs can ride wheelies
its a neat idea i'd like to see it

popuptoaster

a sprung wheelie bar (however its deigned) will give more control as it would help to stop the rear wheels jumping off the floor as it hits the ground, easier to keep it nice and smooth, i can wheelie a push bike or motor bike all day, its all in the throttle, MUCH harder to do on a RC, everything happens much quicker and you dont have the "seat of the pants" feel for what its doing.

RC Jack

I went one further, by adding shocks to control the spring and eliminate any bounce. I did these a few years ago on my EK & MP.

Spudnik

rc jack can you please post some pics of the pie wagon. i have heard sooooooooooooo much but have seen nothing.

thanks

jefx

RC Jack, I think that's pretty much the same concept as R/C car guy was talking about.

R/C car guy, you are probably right about the fulcrum, it's been a while since my shcoolin was fresh. Maybe I used the term wrong.

Spudnik

jefx a fulcrum is the point on which a lever or anything eles pivots.
r/c guy, the fulcrum is actulay the bottom of the rear wheels but becase the truck is moving is seams like it is the axle

and don't ask why i know because i am a nerd when it comes to science (but not spelling lol) 98% in school

jefx

Cool, thanks for clearing that up, sorry if I caused any confusion.

Spudnik

not to me anyway

by the way i like the "what is taters" under your name.
it is nice to know that some eles like the Lord of the Rings other then me

R/C car guy

I still think the fulcrum is the center of the rear wheels. Think about a truck that has solid axles. When it wheelies the axle doesn't spin around the bottom of the wheel, it stays in place as the truck rotates around it.

So instead of saying don't ask how you know, just explain why it is the way you say.

jefx

It's from the sceen where Sam is cooking rabbit stew.

RC Jack

I'll start a Pie Wagon thread this weekend, with several pix & a couple of vids. The vids are a few months old cuz I haven't run it this winter; too damn cold out!!

popuptoaster

Pretty much exactly what i was trying to describe! lol

Spudnik

R/C car guy think of it this way. when you aclerate the force of the engine is transfoured to the ground throw the bottom of the wheels. the front end then lifs up. the truck goes forward and the front continues to go higher. the way a wheelie works is that the tires need to keep on moving in order to keep the front end of the truck in the air. your way would mean that a truck could wheelie and not move forward and hold the wheelie, imo

jefx you might want to change the phrase to "stupid fat hobit! we hates you!!" or "eyes always watching" or change the picture to Gimly and put "we dawfs are natural spriters, vaery dangerous over short distances"

but it is fine as it is now.

R/C car guy

You are correct in saying that the force from the engine gets tranferred through the bottom of the tires to the ground. But first, it goes from the axle to the center of the wheel. This is when the truck wheelies. If the truck were to wheelie with the bottom of the wheel as its fulcrum, the tire and wheel would end up going into the ground. You can demonstrate this to yourself using any round object. Just take a quarter, place it on a table as if it were a wheel, and rotate it around the bottom of itself where it touches the table. This is excactly what you are saying happens when a truck wheelies. When you try to do this, you will see that it is impossible. The only points at which it can rotate are the exact center and above, otherwise it cannot rotate, for it would be going through the table.

And once again, if you are correct, then why doesn't the axle on a solid axle truck rotate around the bottom of the wheel when it wheelies.

Spudnik

BECAUSE THE TRUCK AND THE WHEELS ARE MOVING. i said that twice already to and i also said "your way would mean that a truck could wheelie and not move forward and hold the wheelie" did you even read my post? and don't get all [:@]

R/C car guy

savage14,

It does not matter if the truck is moving or not, the axis at which the truck rotates stays at the same height. And the height difference between the axle and the bottom of the wheel prove my point correct. Becuase if the truck were to rotate about the bottom of the wheel, the gap between the axle and bottom of the wheel would also rotate and no longer be vertical between the two, but it doesn't do that, the axle stays in the same spot and the gap remains verticle.

Please relate your explanation to another example of something that would prove you point correct. This may help me understand your point if you are correct, or help you realise that you are incorrect when you cannot give an example that would support your point, whichever way it is.

What is the source for your information? I am still not convinced that the fulcrum is the bottom of the wheels. If I see some hard evidence, then I will concede to you and say you are correct. But until then, this debate is not over.

Spudnik

i am not debating about it. i don't care if i am wrong or right, i am giving how a imo wheelie happens end of the story