goduranus

Do car wheels spin fast enough to work as gyroscope/reaction wheels?

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The past few days I've been playing GTA, where you can control the car's attitude in mid air. At first I thought that was totally unrealistic, but then I remembered KSP.

On a typical car, the rear wheel have a moment of inertia, they could produce pitch torque by acting like reaction wheels.

The front wheels are usually unpowered, but while they are spinning you could get roll torque from gyroscopic precession, like with gyroscopes.

My question is, how much torque can you get out of these? If the car's catching a 5 second air time, could you somewhat control the car's attitude with throttle and steering?

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Think aerodynamic is far more important. 
You can rotate yourself or even an motorcycle by moving your center of mass around. 

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40 minutes ago, goduranus said:

My question is, how much torque can you get out of these? If the car's catching a 5 second air time, could you somewhat control the car's attitude with throttle and steering?

Its a matter of how heavy the tires are in relation to the car.

I used to race RC offroad cars, buggies monster trucks etc, and the big wheel cars have no problem making front or back flips when you hit the throttle or slam the brakes mid air. Same goes for side to side corrections using the steering. The inputs are very noticeable.

On cars with smaller wheels the effect is obviously much weaker, but still noticeable a lot. (RC sedans off small jumps)

Never jumped a real car, so no help there. But the same rule applies. Use your monster truck for best results :)

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OK so its is an real effect, very cool. 
And thinking of it it should obviously have an effect on an monster truck who is also the type of car you would jump with. 

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I think that part of a motorcycle's stability is from the rotational inertia that the wheels have, though I'm not sure how much has it been tested to be true.

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11 minutes ago, YNM said:

I think that part of a motorcycle's stability is from the rotational inertia that the wheels have, though I'm not sure how much has it been tested to be true.

Oh, most definitely. Motorcycle wheels are relatively heavy and spin at decent rates too. The effect is even noticeable on some bicycles (think downhill bikes when you jump - you feel the slight resistance in mid air when you turn the handlebar when the front wheel is freewheeling fast enough)

 

25 minutes ago, magnemoe said:

OK so its is an real effect, very cool. 
And thinking of it it should obviously have an effect on an monster truck who is also the type of car you would jump with. 

Definitely real. Imagine an RC monster truck going full pelt over a jump, airborne for what feels like seconds - if you let the wheels just coast, it flies nice and straight for half of its arc - then you hit the brakes and the truck does a quick front flip before landing. (just dont forget to release the brakes before you land) Done it myself a million times, I'm sure you'll find plenty of youtube clips. The nice thing about RC cars: you dont have to sit in them! LOL

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*Starts thinking about what to do the next time i get drunk*

Well, if the wheels are heavy, then the car can have up to 4 reaction wheels.

But you only have limited control.

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3 hours ago, YNM said:

I think that part of a motorcycle's stability is from the rotational inertia that the wheels have, though I'm not sure how much has it been tested to be true.

Definitely. Related to this, look at an mx motorbike during a jump - riders adjust pitch of the bike mid-air with throttle and or brake. A bike can also be steered by, well, steering - turning the front wheel - while the front wheel is off the ground.

 

Here are a few related demonstrations with a bicycle wheel, skip to 35:50 and 23:00 

 

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Well, I didn't think I would come across a paper like this but here we are: https://www.diva-portal.org/smash/get/diva2:893827/FULLTEXT01.pdf 

I seem to remember Travis Pastrana and/or Ken Block talking about using the brakes/gas to control attitude of a car in the air but I can't for the life of me find the video. The short version: it absolutely is a thing; although, as stated, it's much more pronounced with motorcycles (like in motocross/dirt bikes). 

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6 hours ago, kurja said:

Definitely. Related to this, look at an mx motorbike during a jump - riders adjust pitch of the bike mid-air with throttle and or brake. A bike can also be steered by, well, steering - turning the front wheel - while the front wheel is off the ground.

 

Here are a few related demonstrations with a bicycle wheel, skip to 35:50 and 23:00 

 

Sure, but keep in mind that a bicycle wheel is an extreme example. It's very light everywhere except at the rim. So an isolated wheel like this shows a lot of gyroscopic effects.

But gyroscopic forces are almost negligible when actually riding a bicycle, because the mass of the wheel is very low compared to the mass of the bike+rider.

Motocross is a bit different, because the motocross wheels are much heavier, and higher in proportion to the total mass of the bike+rider. But when the motocross rider is adjusting the pitch of the bike by using the throttle, that's not a gyroscopic effect. That's more of a pure conservation of angular momentum effect, where adding or subtracting angular momentum to the wheel means it has to be balanced by an opposite subtraction or addition of angular momentum to the rest of the bike.

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I did the bicycle wheel test in my high school physics class. While holding a typical 10 speed bicycle wheel by handles on the axle and a classmate giving it a spin there is a very noticeable resistance to changing the orientation of the axle, even when the wheel is turning very slowly. so,

5 hours ago, Racescort666 said:

it absolutely is a thing

 

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A good deal of bicycle and motorcycle stability comes, not from the gyro effect, but from the geometry and angle of the front fork.

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8 hours ago, SuperFastJellyfish said:

Castor angle is the technical term.  :)

On motorcycles/bicycles they call it rake but, yeah, same thing.

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On 1/8/2019 at 9:10 PM, Shpaget said:

A good deal of bicycle and motorcycle stability comes, not from the gyro effect, but from the geometry and angle of the front fork.

This is true then cycling, the front fork will self stabilize. It has no effect then airborne. 
But its the major effect on the ground, more than the gyro effect. 

Edited by magnemoe

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On 1/9/2019 at 3:10 AM, Shpaget said:

A good deal of bicycle and motorcycle stability comes, not from the gyro effect, but from the geometry and angle of the front fork.

Including when cornering ?

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41 minutes ago, YNM said:

Including when cornering ?

Yes. You lean when cornering so the sum of all the forces on the bike are down the bike, which means it acts the same as when you're moving along the ground.

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22 minutes ago, 5thHorseman said:

Yes. You lean when cornering so the sum of all the forces on the bike are down the bike, which means it acts the same as when you're moving along the ground.

Yeah, but you can't turn while not leaning either...

idk, this is why I'm doubting that only one effect is in play.

Although from statics perspective, a bike / motorcycle only has three reactionary forces; three less from a complete stationary condition.

Edited by YNM

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To test, ride a bike with a vertical fork. you may need to make it yourself though because it's such a bad idea :D

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58 minutes ago, 5thHorseman said:

you may need to make it yourself though because it's such a bad idea :D

E200_WH_RD_Product.png

______

 

I seriously think it's far more nuanced than that. I ride a motorcycle almost every day, I've fallen from it twice, I've seen others falling. But I just never thought anything of it !

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 These two videos give some explanation and examples.

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20 hours ago, Shpaget said:

These two videos give some explanation and examples.

I know they give steering stability, but those who fall from a bike / motorcycle usually don't fall because they can't steer.

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3 hours ago, YNM said:

I know they give steering stability, but those who fall from a bike / motorcycle usually don't fall because they can't steer.

They fall because they make poor decisions:

 

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25 minutes ago, Racescort666 said:

They fall because they make poor decisions

I've fallen once on sand (due to braking it on that, just like your vid) and once on oil spill (actually, I was able to brake to avoid colliding but I only fell after the motorcycle went really slowly); I've seen people falling due to leaning too hard while turning and due to losing a stand or getting the CoM too far from centerline.

Fun story with me falling on the oil spil is that there was another rider in front of me that didn't fall because he didn't have to brake too much whereas I have to brake more to avoid him; also, the rider that came after me also fell due to braking to avoid crashing onto me (and fell after the motorcycle comes almost to a halt, much like I do).

But I know this is not the only thing, because there are also those who fell simply from leaning too much.

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