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!

[bigred5765]

thats wicked well shot to

[mobile chicane]

thats how fast I drove in my best lap ever

[josh_smaxx]

Thats wicked!!! 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]

Originally Posted by 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.

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

[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]

Originally Posted by tonymon

only people that design gearboxes can understand that!

Originally Posted by 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.

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

[sparrow.2]

NERD BATTLE

[telboy]

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

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]

Originally Posted by sparrow.2

NERD BATTLE

LMAO!!

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

[Richard Lowe]

Originally Posted by Jonny_H

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