low and high speed damping

[MHeadling]

It seems there are already these adjustable shocks out there, I know the 5th scale lads run similar shocks to these but they are about £400 a set for the 5th scales:

http://www.neobuggy.net/modules/news...p?storyid=6654

http://www.expertmodel.com/

[MHeadling]

English link to website:

http://www.expertmodel.com/eng.html

[Apricot Slice]

Originally Posted by Mark Headling

It seems there are already these adjustable shocks out there, I know the 5th scale lads run similar shocks to these but they are about £400 a set for the 5th scales:

http://www.neobuggy.net/modules/news...p?storyid=6654

http://www.expertmodel.com/

These are some pretty cool looking shocks.
look like a solid piston. with all of the oil passing the needle valve.

[Apricot Slice]

Originally Posted by The Pookster

Without question RC dampers could be much more advanced in terms of how the damping forces are achieved and in what direction. I also think it would not be too difficult to make some real gains on the track as it would improve the handling/large jump/bumpy track compromise.

But this needs to be developed carefully using real data as a guide and using real road/race car damper experience. Not wishing to upset anyone but it is plainly obvious on this thread that no-one has this understanding. I feel in a position to say this as I'm currently employed as a steering/handling technical specialist for a major car company.

Lastly, gains that could be made with the dampers would be at the expense of complexity, i.e. the number of options and interactions of damper internals would be so complex most racers would struggle to get a good balance. Sometimes keeping it simple means you get slightly less performance but for more of the time.

I think there is a sensible compromise between complexity and better results. (not forgetting that everyone is using piston damping in its most basic form) and that this avenue is ripe for development.

Of course my designs may be doomed to failure because of a lack of understanding and bad design, etc.
If my designs are good and my understanding is on track, no pun intended, as you say, careful development would have to take place of which I have little experience.
Were i to do it on my own, a hands on, trial end error type testing is the only way forward as maths and science isn't what I'm good at.

Ultimately I'd like to be able to make a manufacturer/team an offer they would find hard to refuse and see them get big results.

[gps3300]

Originally Posted by smOkin

bump stops would have to be used in the absence of pack to survive heavy landings.

I very much dont like this ^^

Technically speaking, modern full size cars don't have bump stops anymore but "spring aids". On older vehicles a bump stop was simply a lump of rubber placed to stop a metal to metal clash at full jounce. Modern suspension designs tend to use a carefully tuned tapered cone of elastomer which engages much earlier than a bump stop and as I understand it works a bit like the concept of a dual-rate spring as the suspension arm loads up.

This idea can easily be recreated on a 1/10th buggy, however I'm not sure if a full size car uses them for handling or ride comfort (or perhaps both?).

[Apricot Slice]

Originally Posted by gps3300

Technically speaking, modern full size cars don't have bump stops anymore but "spring aids". On older vehicles a bump stop was simply a lump of rubber placed to stop a metal to metal clash at full jounce. Modern suspension designs tend to use a carefully tuned tapered cone of elastomer which engages much earlier than a bump stop and as I understand it works a bit like the concept of a dual-rate spring as the suspension arm loads up.

This idea can easily be recreated on a 1/10th buggy, however I'm not sure if a full size car uses them for handling or ride comfort (or perhaps both?).

I like this red one http://www.off-roadweb.com/tech/0904.../photo_11.html
Its a very agreeable colour yes?

[Matt Airbrushing]

Does anybody know if gas shocks have ever been tried on an RC car?

I did some designs for oil shocks but they will be very complicated (similar to the design shown in the link above)

A gas shock might be simpler to manufacture, but im not sure if they would work very well (if at all)

[The Pookster]

Originally Posted by gps3300

Technically speaking, modern full size cars don't have bump stops anymore but "spring aids". On older vehicles a bump stop was simply a lump of rubber placed to stop a metal to metal clash at full jounce. Modern suspension designs tend to use a carefully tuned tapered cone of elastomer which engages much earlier than a bump stop and as I understand it works a bit like the concept of a dual-rate spring as the suspension arm loads up.

This idea can easily be recreated on a 1/10th buggy, however I'm not sure if a full size car uses them for handling or ride comfort (or perhaps both?).

Spring aids is the correct modern term and they create a compound spring rate curve in combination with the spring. They are better than having a progressive spring as you have more options in terms of their characteristic and where they contact in the travel.

They perform multiple functions for handling in terms of balance and smoothness of breakaway as well as ride control on large bumps and providing the end stop for the suspension on potholes and such like. Quite time consuming and complicated to develop.

For an RC application the material simply can't be made soft enough to act as a spring aid but if it could then they would be quite advantageous.

[The Pookster]

Originally Posted by Matt Airbrushing

Does anybody know if gas shocks have ever been tried on an RC car?

I did some designs for oil shocks but they will be very complicated (similar to the design shown in the link above)

A gas shock might be simpler to manufacture, but im not sure if they would work very well (if at all)

Not sure what you mean?

Gas shocks have oil in them, they provide the damping as normal with a piston moving through oil. The gas part is a seperate chamber that is pressuized with gas and has a floating piston that pushes on the oil. Basically it means the damper is capable of producing higher forces without the oil cavitating as it moves though the piston at high speed.

Practically all cars sold these days have gas shocks of this type. Some cheaper aftermarket dampers use the gas dispersed through the oil.

[The Pookster]

Originally Posted by Mark Headling

It seems there are already these adjustable shocks out there, I know the 5th scale lads run similar shocks to these but they are about £400 a set for the 5th scales:

http://www.neobuggy.net/modules/news...p?storyid=6654

http://www.expertmodel.com/

This discussion thread is about shocks that are much more complicated than those on the link.

They basically have an adjustment that bleeds off oil during the stroke so you can have a finer control over the amount of damping, rather than just step change between piston hole size. But they don't offer any advantage in terms of differences between bump and rebound or low and high damper speeds.

[SlowOne]

The bump stops idea we used (back in the day!) by putting fuel tubing over the shock shaft. The tubing could be adjusted for length, and by taking 'nicks out of the sides with a scalpel, we could change the 'rate' of the bump stop to be more like the spring assist.

The 'gas' shock Pookster describes we already have, albeit only at atmospheric pressure. The bladder in the top of a lot of shocks acts like the gas piston on top of the oil, its just that we don't put any pressure behind it above atmospheric pressure.

[Apricot Slice]

If only one of the damper speeds can practically be made to have differing rates of bound and rebound. which would you say is the most important to have it on?
(I would assume that the high speed side would be far more important.)

[The Pookster]

Originally Posted by SlowOne

The 'gas' shock Pookster describes we already have, albeit only at atmospheric pressure. The bladder in the top of a lot of shocks acts like the gas piston on top of the oil, its just that we don't put any pressure behind it above atmospheric pressure.

Actually this isn't quite right. The diaphram is there to prevent the damper from hydraulically locking when it is compressed. This is because as the piston rod enters the damper it takes up space, and oil is incompressible, so the diaphram and air behind it allows for this. Any change in pressure is so small is has pretty much no effect.

If you take a bleed type damper like an AE with bleed cap and lock the bleed screw before the damper is compressed fully you won't be able to push it in any further.

[The Pookster]

Originally Posted by Apricot Slice

If only one of the damper speeds can practically be made to have differing rates of bound and rebound. which would you say is the most important to have it on?
(I would assume that the high speed side would be far more important.)

You need to think about this a bit more and understand the damper.

All dampers produce different damper forces at different damper speeds, so they are already variable. Best practical way to experience this is simply to take the damper off the car and push the rod in and out at varying speeds to feel the difference.

The events on the track happen at different damper speeds, handling is fairly low speed, bumps can be mid to high speed and landing off a big jump is high speed.

The compromise with an RC damper is there because this relationship is fixed, i.e. it produces more force as you move it faster exactly the same way no matter what oil and piston you use, it's just the overall amount that changes. If you had a more complex piston you could start to change these relationships to tune one bit for handling, one for jumps and one for ride on the bumps based on different dampers speeds on different events as above.

[ghea]

Hi Guys,

First I like to say this thread is awesome.

When we first started making pistons I was not sure how they really worked,so I figured that I had to measure them to fully understand what happens.

With some help from a friend we started to build this machine for measuring low to high speed damping forces and we can also simulate different pack situations.

When you measure for example a 16mm big bore piston from low to high speed you will find them to be quite linear up to the high speed area where the damping force gets more progressive.

With our pistons we make the damping force more linear than standard pistons and that's what make the cars calm down.

Today we are testing what we call "pack control" that means you just change oil with outside temperature to get the right low speed damping and choose the piston depending on what high speed damping you need.

Thanks/Ronny Guta
GHEA

[Apricot Slice]

Hi Ronny,
That's a great looking workshop you have.

The first thing that came to mind for a test rig was a large rolling road. and have a camera mounted so results can be examined in slow motion.
Not very scientific.

It would be very interesting to hear about your machines.

Phil

[TSewell]

I agree with Ghea, this thread is awesome.

To me, the aspect that is missing in all of this is real data. Having a shock dyno is great, and they are fairly straightforward (but not cheap) to build for RC use ....However the missing components are things like damper speeds (how often does the shock go up and down in 1 second on the track? Some 1:1 road race cars have damper speeds of 20in/s!) and how they relate to lateral accelerations.

The way to get this is with an onboard datalogger with 3 axis accelerometers and shock position measurement (probably linear potentiometers as used in full scale). With this, and a shock dyno, real repeatable results can be attained.

Sound impossible? A few years ago it might have been, but digital electronics have made huge strides in the past few years. I am attempting to do this very thing. I have the following so far:


http://www.sparkfun.com/commerce/pro...oducts_id=8627

http://www.sparkfun.com/commerce/pro...oducts_id=9431

I am still looking for a way to measure shock position in real time. Linear pots are expensive..anyone want to whip me up some custom hall sensors that I can run in the preload collars ?

Travis Sewell
Mechanical Engineer

[SlowOne]

Originally Posted by The Pookster

Actually this isn't quite right. The diaphram is there to prevent the damper from hydraulically locking when it is compressed. This is because as the piston rod enters the damper it takes up space, and oil is incompressible, so the diaphram and air behind it allows for this. Any change in pressure is so small is has pretty much no effect.

If you take a bleed type damper like an AE with bleed cap and lock the bleed screw before the damper is compressed fully you won't be able to push it in any further.

Mmmmm... So what's the difference between a piston sat on top of the oil with gas pressure behind it (as described in your earlier post), and a diaphragm sat on top of the oil with atmospheric pressure behind it? I get that the road damper has a pressure greater than atmospheric which helps, but...

Isn't the theory the same? Without the compressible gas behind the piston, the increasing volume in the oil of the advancing piston rod would cause both systems to hydraulic, wouldn't they? I think you're confusing application with theory here...

One thing's for sure; once someone does come up with a more tunable damper, that particular genie will be out of the box and may well turn into a source of regret for your class. Whenever things get more technically complex, and makes it more difficult for the average Joe or Jane to go racing, the class suffers. Off-Road is the ideal class right now, since you have that greatest of all levelers - more power than grip. As I said before, be careful what you wish for!

[Apricot Slice]

Originally Posted by SlowOne

Mmmmm... So what's the difference between a piston sat on top of the oil with gas pressure behind it (as described in your earlier post), and a diaphragm sat on top of the oil with atmospheric pressure behind it? I get that the road damper has a pressure greater than atmospheric which helps, but...

Isn't the theory the same? Without the compressible gas behind the piston, the increasing volume in the oil of the advancing piston rod would cause both systems to hydraulic, wouldn't they? I think you're confusing application with theory here...

One thing's for sure; once someone does come up with a more tunable damper, that particular genie will be out of the box and may well turn into a source of regret for your class. Whenever things get more technically complex, and makes it more difficult for the average Joe or Jane to go racing, the class suffers. Off-Road is the ideal class right now, since you have that greatest of all levelers - more power than grip. As I said before, be careful what you wish for!

the main difference is that the nitrogen filled jobs of full size car shocks prevent cavitation as oils passes through the various valves and holes etc. as the Pookster said.
i suspect that if you tried the same thing on tenth scale shocks, the rods would get shoved frimley out to their fullest extent. i suspect also that forces aren't big enough on model cars to get cavitation.
other than that, i think the purpose is very similar.
But I aint no expert..

[elvo]

Originally Posted by SlowOne

Off-Road is the ideal class right now, since you have that greatest of all levelers - more power than grip. As I said before, be careful what you wish for!

Or more power than thumbs

I'm not wishing for scaled down adjustable 1:1 shocks. As someone posted before, the cars scale down, but the physics don't. 1:5 scale cars and planes are still close to realistic - I think wind tunnel tests are often done on scale models that are ~1:5. But anything 1:10th or smaller, forget realistic shapes or realistic handling. Water especially doesn't scale. For example: a 1/10th model of a speed boat doesn't work. A 1:10th speed boat that does work, does not look like a boat at all. Dirt doesn't scale either: realistic-looking dirt tyres don't grip, and real off-road trucks don't use spikes or pins.
Oh, and it works the other way as well: I don't think the jumps we have in off-road racing scale up

I don't think we want shim stacks to soften high-speed damping.

Needle-adjusted low speed damping and a floating piston look interesting, but sealing any kind of pressure on a 3mm shaft will be challenging...