Shocking
 

I've been considering making some internally-sprung shocks for my truck and looking for some insight. The first idea that came to mind is to duplicate an existing 1/10 design, and then just scale it up to fit. Around a 6" overall open length with 2" or so of travel should be fine. Materials and such are already worked out - steel body (no, I don't want any more aluminum, and weight doesn't matter), chrome shafts, buna o-rings, steel rod ends, stainless springs, etc. The bodies will be threaded and capped with a plug at the chassis end to fill and bleed.

In order to keep the springs inside, I'm not sure of how they would interact with the piston. I figured that when the piston is compressing the spring it should also be able to dampen. Now, keep in mind that the amount of dampening is not critical, and the main purpose for the internal spring is purely for the look. I believe that the piston should always remain outside the spring coils. The preload will be adjusted by way of a screw at the chassis end of the shock body.

It's important that they do the job throughout at least some of their travel. I don't expect performance, just decent movement and adjustability. I will have many different springs and rates from which to choose.


My question is this: Does this operation sound feasible? Feel free to disassemble my idea if necessary. I have no wish to dive in and then find a problem [&:]:D

RE: Shocking
 

I'll tell you what... It sucks out loud when I have to step on the policy that I am always harping on and come in here bumping my own freaking thread.

Two weeks and no responses. I am going ahead with this shock build, so if anyone wants to HELP :D maybe just a little bit, that would be nice.

Scaling up a 1/10 shock as I said is the only thing I have to lead me off. We all know how shocks work, right? I want the spring on the inside, that's all. I did decide to leave out any adjustment since it will be tough to do from the outside. There are many droop setups like this, so it should not be a problem with no adjuster.

Comments are welcomed! (and downright desired ;))

~R

RE: Shocking
 

Should I delete the above post for bumping, guys? What do you think? :)

In all seriousness Reiko, I never heard of anyone trying to do what you're trying to do at any scale smaller than 1:1. Good luck with it, I'll be very interested to see if you can make it work, would make the shocks much more scale looking.

RE: Shocking
 

Reiko,
I have some ideas on how to achieve the internal springs and provide some external preload adjustments. I will put together some quick sketches tonight after work.

RE: Shocking
 

There are a few scale shocks in the Crawler forum with internal springs. It is purely for looks, and most are used for droop. Nothing on a larger scale, however. I need big fat ones! ;):D

I'll get some work started and then slap some pictures up here.

RE: Shocking
 

Here's a quick and dirty. 2 vertical rods go through the spring tensioner (to prevent it from rotating) and the shock piston. Rotating the shock shaft adjusts droop.

RE: Shocking
 

That is a great method for easy adjustment. I had not considered anything else inside the reservoir besides the shock shaft! Great idea, and thanks for the tip [sm=thumbs_up.gif]

RE: Shocking
 

If I understand well the spring is in the oil itself and not easy to change?

People talk mostly about pre-load but you are actually not adding or taking away pre-load or changing the charecteristics of the spring.
You are just changing the ride height of your vehicle.
(presuming the travel limiters / droop stops are still free when the car is not moving)

Interesting project but I do not see any advantage to be honest.
As I wish to be able to swap a spring fast and easy when I want to. Same with adjusting pack and rebound by another piston and/or oil.

Also i like a nice shock with the sprig visible, i personally like that look better then a naked tube.
But that is a matter of taste.

If it is just the naked tube view you are after. Then I personally would opt for some telescope system around a normal shock and cover it up like this.

RE: Shocking
 

There is no reason why it wont work, it will work fine if you get the sizes right so everything fits good, but an internal spring/shock set up isnt new, l cant see why it wouldnt work, the top of the shock housing has to be strong, if its threaded on the thread needs to be a deep one so you get massive strength through the threads surface area.
It will work, what you loose is some distance your shock can move, the room the spring takes up when compressed, these designed shocks are used in rally cars and on road cars, there is NO need for a stainless steel spring, its covered in oil 24/7, a normal rated spring will do. If your worried about the shock absorbancy of the shock, maybe think about resovars for em, gets pretty complex but then, your basic design will work fine, be tough as any you can buy, as adjustable as any, just cant seee a reason why it wouldnt work as good or better than the Rc shocks you buy, lets face it Rc shock systems are pretty basic, compared to real shock absorbers !

RE: Shocking
 

Wow, all the replies come flying in!

These are all good points. Let me address Apache first. As for the manner in which we speak about preload, you're right. The spring will just hold up the truck. In my experience, there is a fine line between full compression and full extension in that the truck will eventually just sag without enough tension. The springs actually need to be cranked up beyond just holding the truck up in order to alleviate the sag. Also, I do not need to change the springs at all. Once the tension is close to what I need, I will then fill the shocks and leave them alone. If more support is required I will add some small torsion bars to assist (please don't ask why I do things so complex! ;)). I understand you not seeing an advantage - I only want them like this for the look. They will not likely function terribly well, and it doesn't matter anyway. Heh.

Beer, you're right about the spring material. I just like the stainless on the truck (I also wear stainless jewelry, if that helps [&:]). The compressed spring length will be factored in before I have a final length dimension. It really makes little difference because I can make these as long as necessary.

Thanks everyone for the comments and insight!

RE: Shocking
 

Ok clear Reiko.
Maybe you overthought the remarks below already, when not I hope it helps contributing to a good end product.

1st remark is you need a volume compensation.
When the shocker rod is moving inwards the volume inside needs to be absorbed by some volume compensation.
Fluids are not compressible, neither is your piston rod. Air is compressible but you do not want to have the air being mixed with the oil.
So you need some kind of closed air part which can dispisate the incoming volume of the shocker rod.
Without a vol.compensation, when the shock is properly filled and closed it will bump back instead of providing any dampening.
You wish to keep your oil medium without air to get a most stable dampening.
Proper sealing is the key here.

Another point you should think about is the movement of the spring.
When compressed the spring will also rotate on the ends + when compressed the outer diameter increases.
These are minor movements but they should be taken into consideration.
You could for example place on bottom and top some simple ring from for example delrin material to absorb rotation movements. Otherwise your top/bottom lid might work loose.
Ensure enough clearance to the cilinder wall so the spring won't touch the wall when compressed.

I am curious on the end effect.
Show some pics when done.

I fully agree that these shocks can work just as good as the ones we know with springs on the outside.
It is just that you loose the option for swift spring change. But if that ain't bothering you you should be able to make a fine shock.
Good luck mate.

RE: Shocking
 

Never thought about the shaft's volume. makes sense. Guess that's why a res would b a good idea. And the spring may expand a little. But once it hits the cylinder walls it will then rotate at ends instead of expand.

I had 2 different ideas for adjusting......but would most likely leak considering this shaft volume thing. Hmmmm.......

RE: Shocking
 

Ok....what about a screw coming though the top cap. Hole is not tapped. An e-clip keeps screw from spinging out. Screw threads through a nut welded/fastened to a washer which rides on the top of the spring. I'm not too familiar how resaviors work or what they really do other than look cool....but could fill oil say 80% full (because I don't hink you're a 20% empty type of gal). Air space would compress rather than excess pressure blowing threw the screw hole. An o-ring or neoprean washer between e-clip / cap and cap / screw head to help seal.

Just an idea.

RE: Shocking
 

Very complicated for a volume compensation.
Much easier is.

1)
Take a CLOSED celrubber.
These are all small captured air bubbles.
The celrubber with its captured air can compress when the shaft is going in.
Look at the elcon shocks.
Simple and very effective.
Located in the top it will always float upwards and can never get jammed between piston and cilinder wall.
No need to fix it even as it will always float in the oil and stays in the top (unless your car is upside down..).

2)
Take a simple rubber hat like fg has.
Mount it upside down with air above so it can be compressed as well.
Bit more vonerable then option 1 as now air might be possible to slip through and get into the oil medium where option 1 will prevent this at all time.

3)
double piston which seperates air and oil.
You can add even a small spring between the top and this seperating piston.
It gives the option to easily change this small spring for a stiffer or softer one, to play a bit more with the dampening characteristics. Basicly the same as the cad shockers.
As an extra you could drill a hole in the top cap and mount a pneumatic restrictor, then you can play from the outside even more with the dampening.
Key is to make a good seperation of the air/oil.

There are even more complicated options possible but I think this is beyond what a scale model needs.
Been there, done that, tested each option even with pre-pressurized compartiments.
I would opt for no. 1. and would first focus on closing your ingoing piston rod.
Other things are all fairly easy to solve / addept.

The closing of the constant in/outgoing movement together with the dirt that will help to damage the seal will be your main concern.

RE: Shocking
 

I have some simple concepts for externally adjusting spring rates through varying the number of coils allowed to compress during the shock's travel. While it doesn't follow the same methodology as NASCAR, the concept is similar. They use "spring rubbers" to adjust spring rates. Adding a spring rubber reduces the number of coils that can compress, effectively stiffening the spring. Removing a spring rubber increases the number of coils that can compress, softening the spring. The schematics would be a little more complex than my solution to adjusting pre-load, but nothing I couldn't machine in my garage with my metal lathe and 3 axis mill.

If you're interested, I could draw them up.

RE: Shocking
 

It is true that the spring will need to move around a bit, but there does not need to be a tight clearance between the OD of the spring and the ID of the shock body. The spring will be encapsulated and as a result it will be forced to move without argument.

Also, I believe that the oil reservoir will not be totally void of air. I don't believe that an outside reservoir will be necessary. During shock bound and rebound, the oil will only travel through the piston. Leaving some air (say just a very low percentage) in the volume of oil will allow for easier flow back and forth. I don't see how there can be any compression of the fluid at all. The shock performance will not be optimal, of course, but then again does anything I build work correctly?? [:'(]:D

Tweety, I would appreciate any insight or drawings that you could provide. Please don't go to too much trouble! The first drawing that you posted above really helped me to take a hard look at what will be necessary inside the shock to make this work.

Mojave, I think the adjustment that Tweety described upthread is the best idea so far. It is simple, seems straightforward to make, and effective enough for my needs. If that proves to be a pain, I'll work with the idea of an adjustment screw.

Again, all of the ideas are much appreciated!

RE: Shocking
 

Here's a quick and dirty sketch of one of my concepts on spring rate adjustment. The thumb screw on the top cap is used to rotate a hollow shaft (to allow for overlap between the ride-height adjustment threads and spring rate threads). This hollow shaft is externally threaded, and when rotated, the auger shaped plug moves up or down, preventing the spring coils above it from compressing under load. This effectively adjusts the spring rate, making it stiffer as you rotate the plug down (softer as you adjust it upward). The plug is also prevented from rotating by the same 2 shafts used in the pre-load adjustment system.

RE: Shocking
 

That is a great idea. It is becoming more complex, but nothing I can't build (you won't ask if it works right, I hope! :D).

If I am seeing this and understanding correctly, there are separate capabilities of spring rate and ride height. Your design is certainly workable. Have you made something like this in the past?

RE: Shocking
 

Yes, the design allows for separate ride height and spring rate adjustments. It's also a modular concept. You can start with ride height adjustment with conventional top cap and get that portion working properly. Then modify the top cap to incorporate the spring rate adjustment. I also have a concept for external shock reservoirs with no trapped gasses. I can make things as complicated as you'd like :D.

Finding this thread was the first I thought of this problem. Being a manufacturing engineer with a small metal shop in my garage has it's advantages [sm=wink_smile.gif]

RE: Shocking
 

It certainly does.

I think I'll leave out any reservoirs for the time being. I'll do some work on the ideas you've provided and see what happens. The ride height adjustment may end up being a threaded rod that moves the chassis-end of each pair of shocks. Just dial up and down.

Thanks Tweety! I appreciate the inspiration.

RE: Shocking
 

Reiko, you truly need a volume absorbtion.
When you do not ad it be sure to blow out the seal after landing the car or brake a piston rod when the seal holds as the piston simply cannot move inwards if you do not add a volume compensation.
Without it does not work.
Just drop in the option 1 I adviced you, cheap, and simple, made in less than 3 minutes by hand.

Also as I mentined before, focus on closing your piston rod. That will be your main concern.

RE: Shocking
 

Apache, since Reiko has indicated that optimal performance is not a key requirement, then having some air in the shock body should handle the volume absorbtion issue. Some foaming of the oil will result, but it isn't a big deal. Associated has used this very method in their competition racing shocks for years with NO isolation bladder or closed cell foam. If it's good enough for Associated, who are racing and always looking for handling advantages, then I see no issue on a fancy dancy show truck.

Additionally, with the internal spring setup, there is less room for bladder or foam block.

RE: Shocking
 

Or a convoluted shelf queen :D

I think you're right, and I don't see any reason why a nearly-full reservoir will be a problem. Even if the vehicle eventually runs, it will not be going very fast.

RE: Shocking
 

Go and try without a foam block which is costing you less than a dollar and made in less than 2 minutes and have oil with bubbes in there.
Comparing the associated shocks with shocks for bigscale is IMO not correct. The weight is way lower of a smaller scale car and the absorption needed then is less.
I run in my 1/10th on-road without oil in races. Doesn't mean that it is the best.
You can also mount no shockers and your car will still drive... :eek:

RE: Shocking
 

Apache I understand your point about the 1/10, and I very much appreciate the insight and suggestions. However, comparing my truck to your average large scale is quite a contrast. Right now it is in excess of 19lbs and has no engine, radio gear, body, batteries, transmission, servos, cooling system, generator, power supply, or steering drive. By the time I add the items that are in the works, it will be extremely heavy, so the ability of the shocks to actually dampen will be minimal. I think the best idea is to proceed as Tweety suggested and see what happens with just oil and springs. I am confident that they will be fine.

Also, keep in mind that my intention was to crawl this monstrosity, and the planned gearing will not allow for anything over just a few mph.

~R