science in suspension

morleyman200 · February 2011

Im doing my A2 coursework, and decideed to do it about mountain bike suspension, prefereably air suspension, forks and shock, so if anyone knows the physics/science behind suspension platforms, some help would be most appreciated.

Tom

njee20 · February 2011

So you want us to do your work?

What exactly do you mean by the science behind them!?

jmj · February 2011

It's VOODOO!

J

bails87 · February 2011

Read the technical manuals to try to figure out how everything fits together, and what does what.

cooldad · February 2011

bails87 wrote:

Read the technical manuals to try to figure out how everything fits together, and what does what.

Sad that you even have to suggest that.

nicklouse · February 2011

have a look in the tech links above for linkage.

Daz555 · February 2011

morleyman200 wrote:

so if anyone knows the physics/science behind suspension platforms, some help would be most appreciated.

Tom

The science behind suspension platforms is physics.

Anonymous · February 2011

Daz555 wrote:

morleyman200 wrote:

so if anyone knows the physics/science behind suspension platforms, some help would be most appreciated.

Tom

The science behind suspension platforms is physics.

Job done. Sounds like a pretty comprehensive essay, and very succinct

rhext · February 2011

It's all different branches of physics:

- Hook's law for coil springs
- Gas pressure/volume/temperature equations for air springs
- Classical mechanics for levers
- Fluid dynamics for damping (good luck with this one by the way).

If you start there, the internet will be crawling with stuff which can help!

bike-a-swan · February 2011

It's all fairies.

There are little fairies in the air chamber (which is just so they don't suffocate- fairies rights and all...) and they fly up to push up on the bottom of the stanchions. When you hit a bump it increases the amount of force they're pushing against, and the time lag between that and them increasing the pressure differential as they flap their wings harder is what allows the fork to move. Bottom out is a load of cushions that protect the fairies when you over compress the fork, and when you over compress it too hard, it crushes the fairies at the bottom, which is how forks get damaged.

In the damping circuit you have more highly trained fairies who react faster and can control the rate at which the fork descends. Turning the compression and rebound damping is much like the 'all ahead/half ahead/ all stop' wheels on old timey ships, it lets them know what's going on outside. This is why budget companies can't do good damping- they haven't built up the necessary experience in fairy training and motivation.

Rear shocks work in much the same way, but the fairies are packed in much more tightly.

bike-a-swan · February 2011

That should have been brief. I think it's time to go to the pub.

mattv · February 2011

Get your cad out, model a few of the popular suspension platforms. Always look good!

pilsburypie · February 2011

bike-a-swan wrote:

It's all fairies.

There are little fairies in the air chamber (which is just so they don't suffocate- fairies rights and all...) and they fly up to push up on the bottom of the stanchions. When you hit a bump it increases the amount of force they're pushing against, and the time lag between that and them increasing the pressure differential as they flap their wings harder is what allows the fork to move. Bottom out is a load of cushions that protect the fairies when you over compress the fork, and when you over compress it too hard, it crushes the fairies at the bottom, which is how forks get damaged.

In the damping circuit you have more highly trained fairies who react faster and can control the rate at which the fork descends. Turning the compression and rebound damping is much like the 'all ahead/half ahead/ all stop' wheels on old timey ships, it lets them know what's going on outside. This is why budget companies can't do good damping- they haven't built up the necessary experience in fairy training and motivation.

Rear shocks work in much the same way, but the fairies are packed in much more tightly.

I was told it was frogs.

RevellRider · February 2011

pilsburypie wrote:

bike-a-swan wrote:

It's all fairies.

There are little fairies in the air chamber (which is just so they don't suffocate- fairies rights and all...) and they fly up to push up on the bottom of the stanchions. When you hit a bump it increases the amount of force they're pushing against, and the time lag between that and them increasing the pressure differential as they flap their wings harder is what allows the fork to move. Bottom out is a load of cushions that protect the fairies when you over compress the fork, and when you over compress it too hard, it crushes the fairies at the bottom, which is how forks get damaged.

In the damping circuit you have more highly trained fairies who react faster and can control the rate at which the fork descends. Turning the compression and rebound damping is much like the 'all ahead/half ahead/ all stop' wheels on old timey ships, it lets them know what's going on outside. This is why budget companies can't do good damping- they haven't built up the necessary experience in fairy training and motivation.

Rear shocks work in much the same way, but the fairies are packed in much more tightly.

I was told it was frogs.

That's only in BOS forks as they're French

cavegiant · March 2011

A2 is A-level for dummies, so you will not have to be advanced.

Just doing a comparison on how springs and air compresses would probably be enough.

You can mention how hydraulic damping works as an after thought (fluid sucked through holes limits speed, more advanced versions involve shims, but keep it simple).

A well explained simple idea will probably go down better than over complicating things.

If you need it to be long you might add in thermal effects.
compression of air/springs is work, things get hot.
pv=nrt for gas heating/compression.
the spring rate of air will change as it gets hotter (pretty negligible as it is off the baseline of 0k, but maybe enough for a bit of credit).
damping fluid gets energy out of the systems by converting to heat.

If you have any specific questions, or something you don't understand after reading up a lot feel free to PM.

The simple approach is that hundreds of people already have done this project, google is your friend.

ThanksBye · March 2011

cavegiant wrote:

A2 is A-level for dummies, so you will not have to be advanced.

And A2 is ''proper'' A levels your thinking of AS being the Easy ones

Jon

FBM.BMX · March 2011

ma+cv+kx

Look at control theory. free vibration, damped vibration.

Stiffness x Displacement = Spring Force

Damping x velocity = Damping Force (damping is considered linear for ease of cals, but in fact is v^2)

mass x acceleration = force

you're opening a big can of worms looking at air spring instead of mechanical spring. Mechanical spring is linear and the mechanics is straight forward.

With an air spring, you'll be getting into thermodynamics, a whole new area you will not have touched on.

Basically, you have chosen a far too big of a topic to do for A2, you'll get nothing out of it, no understanding, just skimming the surface.

cavegiant · March 2011

tomatoevousparlour wrote:

cavegiant wrote:

A2 is A-level for dummies, so you will not have to be advanced.

And A2 is ''proper'' A levels your thinking of AS being the Easy ones

Jon

These new fangled qualifications confusing me!
Much easier in my day, you just did a-levels.

As FBM says, keep it simple, you will not have enough time to cover more than a few points in detail.

Anonymous · March 2011

go on, take these guys' advice, then you can be special like them. Or maybe consider that what you read on the internet may or may not be true, and that just possibly, someone is messing with you.
Then once you've done that, get your head down and do your own work, you cheating little scrote.

cavegiant · March 2011

cheating little scrote?

That is a bit harsh.

A key part of a research project is research.
His first step was contacting 'pillars of knowledge' aka forumers to see what areas he should be reading up on.

We didn't give him the answers, but gave him a few good ideas on what topics to look in to eg springs, fairies, damping.

I can't remember if you have to quote sources at A-level, but if he does, he should mention this as a stage of research.

I made a friking powerful crossbow for my a-level physics, it was fun.

morleyman200 · March 2011

thanks cave giant, most appreciated. and yea A2 is the hard part of A levels, AS is the easy bit

Im not asking anyone to do my work for me, im just asking for a few ideas and a little help into what would be worth while, i think ill concentrate on coil springs and then dampening systems as i can relate this to simple harmonic motion and critical dampening.

Anonymous · March 2011

Pah, i see your puny crossbow and raise you a railgun

We made a crossbow from a tractor leafspring, a construction girder and a chainblock when we were around 15, it was AWESOME! It shot scaffold poles through trees

idiotdogbrain · March 2011

It's damping, by the way.

Unless you're talking about getting it wet, in which case dampening could be used, albeit somewhat incorrectly.

Oh, and this ' is an apostrophe - it fits neatly into such classic favourites as I'll and I'm.

Good grief, I learned this when I was in middle school; surely people taking A-Levels should know this? Oh, that's right, everyone's dyslexic these days...

The Rookie · March 2011

yeehaamcgee wrote:

Pah, i see your puny crossbow and raise you a railgun
We made a crossbow from a tractor leafspring, a construction girder and a chainblock when we were around 15, it was AWESOME! It shot scaffold poles through trees

Pah, I had progressed to firearms by then, firing marbles or ball bearings from aluminium cigar tubes using french 'petard', once shot a BB right through my Dad's shed, 2 sheets of corrugated and a piece of 2x2 frame, he wasn't overly impressed, the tubes used to distort quite badly (never blew one up) and needed some reinforcing to cope as my charge levels went up and the BB's got heavier and better fitting.

Back on topic, is the OP trying to work out how the individual components (springs, arms and damping) works or how they make the bike respond, which is all about weight distribution and how spring and damper rates change it transiently and under pseudo steady states such as cornering and braking.

Simon

cooldad · March 2011

@idiotdogbrain - grammar nazi, and you forgot to mention BIG letters.

Anonymous · March 2011

We never made firearms bit we did make a ball bearing machinegun from a jackhammer. Fun, but not much use apart from scaring cows

Made a few small explosives though, which we used to demolish old sheds or "remove" dry Stone walls, so my mate's dad could build more sheds!

cavegiant · March 2011

yeehaamcgee wrote:

Pah, i see your puny crossbow and raise you a railgun
We made a crossbow from a tractor leafspring, a construction girder and a chainblock when we were around 15, it was AWESOME! It shot scaffold poles through trees

My crossbow has been humbled.

The Rookie · March 2011

yeehaamcgee wrote:

Made a few small explosives though, which we used to demolish old sheds or "remove" dry Stone walls, so my mate's dad could build more sheds!

Yes we did the old nitrogen fertilizer and big bang a few times, once when digging a big hole to build a 'tank trap' to stop the delivery lorries for the farm next door reversing 'through' our holly tree, French bangers made a great detonator!

Simon

cavegiant · March 2011

Nitrogen triodide was always a fun one, more for practical jokes than demolition (far to dangerous to make more than a gram or two a go).

Same stuff that goes in those bangers that chavs throw at the ground, difference is the chavs are 0.1% NI3. You pour it on stuff when wet, then when it dries it is amusingly unstable. Very funny to pour on the floor. When someone steps on it the floor sets on fire =-)

Always wanted to make ammonium fulminate, but never had the balls...or had too much common sense depending on how you look at it.

Most of the explosives I made I used to 'upgrade' fireworks with.

Nothing like flaming metal shrapnel to brighten up your day.

Anonymous · March 2011

cavegiant wrote:

yeehaamcgee wrote:

Pah, i see your puny crossbow and raise you a railgun
We made a crossbow from a tractor leafspring, a construction girder and a chainblock when we were around 15, it was AWESOME! It shot scaffold poles through trees

My crossbow has been humbled.

I am almost certain that yours was more portable though. We needed a Toyota hilux to move ours

Oh, and for what it's worth, we used to use broken bulbs as detonators, hokked up to a car battery.

cavegiant · March 2011

I used firework detonators, cheap, easy and reliable.

I wanted stuff to be reliable!

I tried to make a two stage hyperbaric device while at uni too, but could never get the fuses correct. When I did the maths later on the energy release, I was quite lucky not to get it right.
My protective screen was a double glazed window 10 metres away, if the bomb had worked it would have taken a wall down.

If was fun to watch, mist of explosive goes up, then you cross your fingers for the second charge, mist lands/disapates, second charge goes.

Using your car battery to control the secondary would have been good (apart from I could have killed myself if it had worked).

science in suspension

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