Slow motion movie of an rc car

[bbq]

Mr.Pink here in sweden shot this movie.
Its from the track were we are gona have the swedish nationals next month

http://www.youtube.com/watch?v=_k4B5KceyQo

[ben]

Thats actually really cool. Its nice to see how much the suspension actually moves and how the car goes through the air. GOOD JOB!:thumbsup:

[bigred5765]

thats wicked well shot to

[mobile chicane]

thats how fast I drove in my best lap ever:woot:

[josh_smaxx]

Thats wicked!!! :thumbsup: very well done, would like to see an on board version as well.

[Jonny_H]

Way cool! How much is it slowed down by? 10:1?

I'd love to see a video of 1/10th slowed down by ~3.2:1 (sqrt(10)) as I have a theory that it would look like full size...

[Lee]

But speed is not scaled, it is a constant, 1mph is 1mph regardless of the size of the object.

[Jonny_H]

<grin> Who said anything about speed? I just said "it would look like full size"...

The problem is acceleration. Basically a 1/10th car still accelerates (in any direction) at about 1g - but the size is scaled, so if it falls (after jumping) at 10 m/s^2, it looks like 100 m/s^2 or 10g, because it's ten times as many car lengths per second.

Similarly for cornering, assuming the tyres produce about 1.0 coefficient of friction.

Slow it down by the square root of the scale, and the acceleration (jumping/falling and cornering) should make it look like it's full size.

[tonymon]

only people that design gearboxes can understand that!

[Lee]

<grin> Who said anything about speed? I just said "it would look like full size"...

The problem is acceleration. Basically a 1/10th car still accelerates (in any direction) at about 1g - but the size is scaled, so if it falls (after jumping) at 10 m/s^2, it looks like 100 m/s^2 or 10g, because it's ten times as many car lengths per second.



Are you sure though, the car will still fall at the same speed, it will accelerate at a different rate due to its weight but i dont think the size has anything to do with it. i may be wrong though :blush:

[LEGEND]

I totally agree, completely confusing. What i would try first would be slowing it down by a scale factor of 10 and work from there. Seems like a reasonably number to me.;)

[Lee]

Why?

The speed is a constant regardless of the size if you dropped a big rock and a small rock off the top of a cliff, would you want to slow the small one down so it looked real?

[Jonny_H]

only people that design gearboxes can understand that!:p :p :p

I totally agree, completely confusing. What i would try first would be slowing it down by a scale factor of 10 and work from there. Seems like a reasonably number to me.;)Nope, 10's too much - that would slow the 'scale' acceleration down by 100, because it's metres per second squared.

Try this then: you know how you used to hear "my car does 25 mph, so that's a scale speed of 250 mph"? Yeah, right... have you ever heard of a (1:1) off-road race car doing that speed? Instead, try multiplying actual speeds by about 3.2 (square root of 10):

Buggy: 35 mph => 112 mph 'scale'. WRC cars go how fast?
Touring car: 45 mph(?) => 144 mph 'scale'. Sound about right?
Velodrome / oval racer: ~60mph => 192 mph. NASCAR?
'Insane Run' record: 100+ mph => 320 mph. Maybe that's still a bit fast... but if you put the 1000 hp Penske-Mercedes Indycar (or a Can-Am / Group C prototype) on the bowl at Nardo, how fast could it go?

[Lee]

Johnny,
I know what your saying and in theory yes its about right.

that is one thing i hate when i hear people saying my car has a scale speed of 500 mph, even hpi are marketing cars with this claim.

I can see how you have come about your theory and i would like to see a video slowed down by 3.2 but personally i think once you have seen a 1/10th car go round a track "live" i think it would look slow or odd. Why not just give them a mabuchi 540 motor instead :D

[sparrow.2]

NERD BATTLE :woot:

http://www.bismarcktribune.com/blog/uploads/e/ExpatriateTwo/505.jpg

[telboy]

Hmm, so, what your saying is, our cars aren't really fast? :p

Anyway. I'd like to know if it was filmed with a high speed camera (which it looks like) or has it just been slowed down with software, which normally makes it look jerky.

[CraigM2610]

NERD BATTLE :woot:

http://www.bismarcktribune.com/blog/uploads/e/ExpatriateTwo/505.jpg

LMAO!! :thumbsup:

I haven't a clue what they're saying!

[Richard Lowe]

Buggy: 35 mph => 112 mph 'scale'. WRC cars go how fast?
That doesn't quite work out, 1.6kg and 400watt motors give about 335hp/ton, a WRC car would work out around 240hp/ton assuming minimum weight and 300hp.

I'm sure a WRC car geared correctly would do 150mph+, especially if it had the extra 120hp it would need to have the same power to weight as a 1:10th buggy :)

[mole2k]

Some of the WRC cars in Ireland hit max speed about 150mph, if you geared them even longer then you could get more top end if you had the right stage for them.

The video was filmed with a casio ex-f1 pro. It can do video at 300fps at a vga resolution and up to 1200 fps at a lower resolution, I want one!

[Mike Hudson]

its like a crawler on helium

[Dunc]

<grin> Who said anything about speed? I just said "it would look like full size"...

The problem is acceleration. Basically a 1/10th car still accelerates (in any direction) at about 1g - but the size is scaled, so if it falls (after jumping) at 10 m/s^2, it looks like 100 m/s^2 or 10g, because it's ten times as many car lengths per second.

Similarly for cornering, assuming the tyres produce about 1.0 coefficient of friction.

Slow it down by the square root of the scale, and the acceleration (jumping/falling and cornering) should make it look like it's full size.

There is some serious confusion going on here between acceleration and speed/velocity. The acceleration of any falling object will be equal to gravity; so how can a buggy 'look' as though it is accelerating 10 times faster than it is? You may be able to convince me its velocity appears increased, based on car lengths.

I think your main flaw is that you are trying to compare/factor dimensioned units (some of which are constant, like gravity). I suspect the only way to achieve a true comparison (assuming it is even possible) would be to use non-dimensional parameters.


Buggy: 35 mph => 112 mph 'scale'. WRC cars go how fast?
Touring car: 45 mph(?) => 144 mph 'scale'. Sound about right?
Velodrome / oval racer: ~60mph => 192 mph. NASCAR?
'Insane Run' record: 100+ mph => 320 mph. Maybe that's still a bit fast... but if you put the 1000 hp Penske-Mercedes Indycar (or a Can-Am / Group C prototype) on the bowl at Nardo, how fast could it go?


These are probably just a happy coincidence (remember you've scaled velocity by a factor 'derived' from acceleration).

.... then again, I could be completely wrong. This is just my feeling.

[MK999]

edit: nevermind, misread :p

[Jonny_H]

There is some serious confusion going on here between acceleration and speed/velocity. The acceleration of any falling object will be equal to gravity; so how can a buggy 'look' as though it is accelerating 10 times faster than it is? You may be able to convince me its velocity appears increased, based on car lengths.Exactly. If you're looking at a film of a car, which has no other clues to the size, then your brain would assume that it's about "car-sized", i.e. about 4 m long.

It will then make further assumptions about how fast it should be able to move, i.e. how many car-lengths it can cover in one unit of time - either from a standing start, or at full speed.

Based on that argument (and yes, I know not everything will scale - air is a fixed density, etc) then if you scale is time, velocity/acceleration follow.

I just think it would be interesting to try to produce a video where the cars appear to move like cars, not ferrets on speed...

[Dunc]

I see where you're coming from, I just don't think it will work. But that could be because I already know how a model car looks/behaves. You may be able to 'trick' somebody who's never seen one though.

Whilst I'm doubtful I would also be interested to see someone's attempt at it.

:)

A further thought:
Your idea may be quite effective under some conditions (e.g. when travelling on the flat), but when falling it wouldn't look right because our model cars already accelerate under gravity in the same way a full-size vehicle does (i.e. in this instance you don't need to slow it down, assuming the track/obstacles are to scale).

[Jonny_H]

A further thought:
Your idea maybe quite effective under some conditions (e.g. when travelling on the flat), but when falling it wouldn't look right because our model cars already accelerate under gravity in the same way a full-size vehicle does (i.e. in this instance you don't need to slow it down, assuming the track/obstacles are to scale).No...

The effect when falling is exactly the same. From the top of its flight (i.e., zero vertical velocity) the car will accelerate downwards at 10 (okay, 9.81) m/s^s. So, in 0.5 sec, both cars will fall (1/2 a t^2 =) 1.25m.

For the 1:1 car, that means it's fallen roughly its own height. The 1/10th car will look as though it's fallen 10 times as far - unless you slow it down.


I find it's something which is really noticeable in films with CGI, where they haven't got the gravity / acceleration quite right - there's a monster the size of a bus, and I'm left thinking "it just can't leap like that".

[Dunc]

No...

The effect when falling is exactly the same. From the top of its flight (i.e., zero vertical velocity) the car will accelerate downwards at 10 (okay, 9.81) m/s^s. So, in 0.5 sec, both cars will fall (1/2 a t^2 =) 1.25m.

For the 1:1 car, that means it's fallen roughly its own height. The 1/10th car will look as though it's fallen 10 times as far - unless you slow it down.


I find it's something which is really noticeable in films with CGI, where they haven't got the gravity / acceleration quite right - there's a monster the size of a bus, and I'm left thinking "it just can't leap like that".

Ten times as far compared to what? If you have no other references whatsoever (which you suggested earlier), then your brain won't know how big the vehicle is and therefore no idea what a car length is.

Assuming the track is approximately to the same scale as the model vehicle it will already be falling with the correct apparent acceleration; so no slow down will be necessary in that situation.

You can't have it one way and not the other.

There are many variables at play and simply adjusting one, i.e. time, isn't going to have the desired effect - in my opinion.

The easiest way to settle this would be to make a video, slow it down, and then rub my face in it when you prove me wrong :lol:

[MK999]

The height thing would only apply if driving the buggy over real car sized obstacles, since jumps are scaled down to our cars. :)

[ianjoyner]

<grin> Who said anything about speed? I just said "it would look like full size"...

The problem is acceleration. Basically a 1/10th car still accelerates (in any direction) at about 1g - but the size is scaled, so if it falls (after jumping) at 10 m/s^2, it looks like 100 m/s^2 or 10g, because it's ten times as many car lengths per second.

Similarly for cornering, assuming the tyres produce about 1.0 coefficient of friction.

Slow it down by the square root of the scale, and the acceleration (jumping/falling and cornering) should make it look like it's full size.

So a 1/10th scale car when compared to 1/1 car doing the same speed travels its own length 10 times as fast.

So when using the time a car takes to travel its own length as a cue for speed, a 1/10th car at 30mph looks like a 1/1 car at 300mph.

So if you want a video of a 1/10th car to look like a video of a 1/1 car, the speed and acceleration looks 10 times faster, why not slow the video down by 10? Why would you slow it down by the root of 10?

[Mr. Pink]

Hello!
I'm glad you like my video.:)

Here is anonther one at the Swedish Nationals.

http://www.youtube.com/watch?v=AJN8qwMm9gc

/Mr. Pink

[elvo]

Hello!
I'm glad you like my video.:)

Here is anonther one at the Swedish Nationals.

http://www.youtube.com/watch?v=AJN8qwMm9gc

/Mr. Pink

Awesome wheelie off the line. Awesome mayhem. Keep up the good work!

[Albertini]

The first corner has a substantial amount of comedy value.:thumbsup: It was probably very different at full speed but in slow motion it looks almost pathetic.:D
Great video, keep'em coming.:)

[Jonny_H]

So when using the time a car takes to travel its own length as a cue for speed, a 1/10th car at 30mph looks like a 1/1 car at 300mph.

So if you want a video of a 1/10th car to look like a video of a 1/1 car, the speed and acceleration looks 10 times faster, why not slow the video down by 10? Why would you slow it down by the root of 10?Because real cars don't do 300 mph. This is my whole point - the speed doesn't scale like that. A 1/10th buggy doing 30 mph looks like it's going faster than a Formula One car or a Bugatti Veyron, which is just wrong for an off-road car.

Ah well - like Dunc said, would someone please do a video at ~1/3 speed?

[ianjoyner]

Because real cars don't do 300 mph. This is my whole point - the speed doesn't scale like that. A 1/10th buggy doing 30 mph looks like it's going faster than a Formula One car or a Bugatti Veyron, which is just wrong for an off-road car.

Okay I see your point :).