Mechanics and Construction > Mechanics and Construction

Independent Suspension System

(1/2) > >>

Sylvestre:
Hello,

I'm building a robot with tank tracks and I'm using a independent suspension system where each idler is connected to a shock absorber. There are issues with the shock absorbers though.

1) It is a 1/2" too long so the track is very tight, which is drastically decreasing the efficiency of the track.
2) They require too much force to compress.  I probably only need 3/4 the required force needed. 
3) They are very hard to find.  I don't know if I'm searching for the right terms or not, but I only could find one http://www.pocketbikeparts.com/Shock_Front_Adjustable_11_1_2_inch_6mm_spring_p/atsh303238.htm
And there are hardly any specs regarding the force needed to compress

I've determined that my tracks aren't running as smoothly and efficiently because the track is too tight so I think I could kill two birds with one stone if I purchased new shock absorbers or gas struts or whatever they're called.

So my question is do you guys have any suggestions on what terms to search for if I want to replace the shocks? What should I be looking for? Gas struts? Shock absorbers? Hydraulic shock? I dont know. It just seems like the shock absorbers I have would rebound too quickly also. 

When I look at high speed tanks like this, it looks like they use hydraulics, but I'm not sure.  Something like that except if it were 11-11.5 inches (hole to hole) would be perfect.
http://waronterrornews.typepad.com/.a/6a00e551d9d3fd883301156fca796f970c-pi

And do you have any suggestions where I could buy these?  I'm a student too so I would prefer not to spend a fortune on these.

Below is a video describing my problem in further detail 
Track Analysis

Thanks for taking the time to read this

jwatte:
Shocks are typically only movement dampers; the extending force comes from springs. if your shocks come with built-in springs, you may be able to find different springs that have the same dimensions.

Another source for suspension parts is Go-kart places (for heavier parts) and RC car/truck places (for lighter parts.)

bdeuell:
While a shock adsorber technically only refers to the damping element, in practice the entire assembly including spring is commonly referred to as a shock adsorber. I think think you are on the right track with searching terms like "strut", "shock adsorber" and "shock". The key will be finding a market where something with the specs you want are used and produced in large quantities. Based on your link it looks like you have been searching in the ATV market. You might find some good products in the mountain biking market as well but I know things can get really pricey there. Try searching by specific applications that use similar products such as "mini ATV strut" or "rear mountain bike shock".

If you can disassemble them or even  get them apart in a manner that you would be able to reconstruct them replacing the springs might be a good way to go and keep costs down.

As far as specs go there are a lot of variables but the main ones I can think of are: spring rate (which may vary along the stroke), preload, damping coefficient (may be different for extension and compression). Any of these may also be adjustable depending on what shocks you have. I'm not surprised you are having difficulty finding specs as I suspect most of the shocks for ATVs have had little testing outside of does the thing work in application (if they are made in china the manufacturer may not even have an idea what the target specs are ... just what the design they copied looked like  :)) It looks like the ones you are currently using have a progressive spring rate as well as an adjustable preload. Have you reduced the preload to the minimum setting?

Another idea is to change the mechanical advantage of the suspension mechanism. You could move the mounting point of the shock closer to the pivot of the suspension arm. You could also mount the shock so its axis is more perpendicular to the path made by the point where the shock attaches to the suspension arm.

It sounds like the track is putting a lot of perload on your  shocks, can you make the tracks longer?

Sylvestre:
Thanks for the response JWatte and Bdeull.


--- Quote ---Shocks are typically only movement dampers; the extending force comes from springs. if your shocks come with built-in springs, you may be able to find different springs that have the same dimensions.

Another source for suspension parts is Go-kart places (for heavier parts) and RC car/truck places (for lighter parts.)

--- End quote ---

I'm wondering if the rebound is almost too fast with the shock absorbers that include the coils.  Howe and Howe Tech which is a company known for the high speed track systems looks like they don't use coils in their suspension system. Take a look at this video and you can see what I mean Mini Ripsaw UNREAL CRAZY VIDEO of the Most Kickass ATV EVER Built! Newest Vid never released

Maybe its good to not have much rebound?


--- Quote ---The key will be finding a market where something with the specs you want are used and produced in large quantities. Based on your link it looks like you have been searching in the ATV market. You might find some good products in the mountain biking market as well but I know things can get really pricey there. Try searching by specific applications that use similar products such as "mini ATV strut" or "rear mountain bike shock".
--- End quote ---

Yeah its very tough to find shock absorbers that are just the correct size.  Its right inbetween standard sizes for rc vehicles and atvs and go karts


--- Quote ---If you can disassemble them or even  get them apart in a manner that you would be able to reconstruct them replacing the springs might be a good way to go and keep costs down.

--- End quote ---

I agree. I'm trying to figure out how to disassemble these to see if that's an option. It is very cumbersome and requires some advanced tools that I don't have.


--- Quote ---As far as specs go there are a lot of variables but the main ones I can think of are: spring rate (which may vary along the stroke), preload, damping coefficient (may be different for extension and compression). Any of these may also be adjustable depending on what shocks you have. I'm not surprised you are having difficulty finding specs as I suspect most of the shocks for ATVs have had little testing outside of does the thing work in application (if they are made in china the manufacturer may not even have an idea what the target specs are ... just what the design they copied looked like  :)) It looks like the ones you are currently using have a progressive spring rate as well as an adjustable preload. Have you reduced the preload to the minimum setting?

--- End quote ---


I have put it to the minimum setting and it is still extremely stiff for my application.


--- Quote ---Another idea is to change the mechanical advantage of the suspension mechanism. You could move the mounting point of the shock closer to the pivot of the suspension arm. You could also mount the shock so its axis is more perpendicular to the path made by the point where the shock attaches to the suspension arm.

--- End quote ---

Right now, the shocks are mounted perpendicular to the doglegs and there is hardly any wiggle room in terms of creating a new mounting point on the suspension arms so I don't think this is really an option.


--- Quote ---It sounds like the track is putting a lot of perload on your  shocks, can you make the tracks longer?

--- End quote ---

Its one of those things where one more link would make it too loose and one less link would make it too tight.

bdeuell:

--- Quote ---I'm wondering if the rebound is almost too fast with the shock absorbers that include the coils.  Howe and Howe Tech which is a company known for the high speed track systems looks like they don't use coils in their suspension system. Take a look at this video and you can see what I mean
--- End quote ---

I am not able to see exactly how the suspension in the video operates but my guesses are:

- they may be using a torsion bar  for the spring, which is not uncommon in larger tanks

- the strut may have an internal spring (like a screen door closer)

- the strut may actually be a gas spring (this would mean they do not have a damping element) ... at first i thought this would be unlikely but then i  realized they also have a couple of "boogies" in their suspension which most likely pivot freely and have no damping. Thinking about this a little more the lack of any damping component (at least in the extending direction) may work well on tracked systems as it would allow for the fastest return speed when the load is removed making sure the track remains taught.



--- Quote ---
--- Quote ---If you can disassemble them or even  get them apart in a manner that you would be able to reconstruct them replacing the springs might be a good way to go and keep costs down.
--- End quote ---

I agree. I'm trying to figure out how to disassemble these to see if that's an option. It is very cumbersome and requires some advanced tools that I don't have.
--- End quote ---

It looks like there is a hex on the bottom of the rod eye (inside the spring) is the rod eye threaded onto the rod? If they are permanently attached (or require tools you do not have access to) perhaps you could cut the end of the rod off and either modify the rod eye, manufacture a new one, or purchase an off the shelf component and then reattach the parts.

Navigation

[0] Message Index

[#] Next page

Go to full version