Anyone Got Inboard suspension (bell cranks)

[ezakimak]

Just after some details as im trying to benchmark my design at the moment.

so what have you got?
What Size are the bearings?
what spring rate and travel does the shock have?
weight of car?

Thanks in advance.

Ryan

[gtmdriver]

I made my own inboard suspension for my GTM Coupe.

As soon as photobucket comes on line I'll post a couple of pictures.

I made my own pivot bushes for the bellcranks from oil filled nylon.

The spring rate depends on a lot of things. I did a breakdown of how to work it out in a recent issue of the magazine.

One of the major considerations is the lever ratio between wheel movement and spring movement. The spring rate increases as the square of the lever ratio so with a 2:1 ratio the spring needs to be 4 times stronger than it would be if it was direct acting.

My car was Mini based but had lever ratios of 2:1 at the rear and 2.5:1 at the front so I ended up with 350 lb/in springs front and rear.

[ezakimak]

wasent after a spring rate for my design, more just trying to work out how the bearing in the bellcrank is loaded. through vector addition, if one knowes what force was required to load the spring to reach full travel, one should be able to determin the load on the bearing. hence trying to work out what size bearing has worked in what condition.

[LaurenceFrost]

ezakimak said:

what spring rate and travel does the shock have?

With inboard, it's constantly variable throughout the wishbone movement. This is a design objective in most systems to give rising rate, but it can be a bugger to calculate.

[suthol]

ezakimak said:

Just after some details as im trying to benchmark my design at the moment.

so what have you got?
What Size are the bearings?
what spring rate and travel does the shock have?
weight of car?

Thanks in advance.

Ryan

Ask johnl, I'm sure he will be able to find a reference to copy and paste from

[gtmdriver]

Here's a photo of my front set up.





The pivot bolt is a 1/2" NAS bolt. The bearing is an oil filled nylon bush with end loads taken by thrust washers.

The push rod has 7/16" rod ends and the damper has a standard polyurethane cotton reel bush.

[ezakimak]

suthol said:

ezakimak said:

Just after some details as im trying to benchmark my design at the moment.

so what have you got?
What Size are the bearings?
what spring rate and travel does the shock have?
weight of car?

Thanks in advance.

Ryan

Ask johnl, I'm sure he will be able to find a reference to copy and paste from

OI - Keep it down, he might hear us over hear....LOL.
Do you think i should post it there for S&#t's N Gigles.

for thoes not in the loop we have had some wonderfully long suspension discusions over on the OZclubbies forum, which i find quite ammusing.

[ezakimak]

LaurenceFrost said:

ezakimak said:

what spring rate and travel does the shock have?

With inboard, it's constantly variable throughout the wishbone movement. This is a design objective in most systems to give rising rate, but it can be a bugger to calculate.

Yep got that. But when its all said and done, regardless of the ratios, when the shock and spring is fully compresed the force couple will hopefully be close to equal about the rocker pivot and the resultant vector force that the pivot is withstanding will be a factor of the spring rate by the dimension compresed of the spring.

im not after the wheel rate.

[ezakimak]

gtmdriver said:

Here's a photo of my front set up.





The pivot bolt is a 1/2" NAS bolt. The bearing is an oil filled nylon bush with end loads taken by thrust washers.

The push rod has 7/16" rod ends and the damper has a standard polyurethane cotton reel bush.

Thanks for that, Looks good, spring looks to be in the 400lbx range ?

[gtmdriver]

350 lb/in.

I arranged the geometry to give a slight rising rate but overall the lever ratio is around 2.5:1 giving a wheel rate of 56lb/in and a wheel frequency of 80 cpm with an unsprung weight of 55 lb on each front corner and a sprung weight of 250 lb on each front corner.

Edited by gtmdriver on Friday 30th April 07:34

[Sam_68]

As you're obviously already aware, the loadings on the pivot of the bellcrank can be quite high.

Personally, I wouldn't contemplate the use of nylon bushes, oiled or otherwise (though, to be fair, Sylva/Fisher use them for their rocker arm suspensions without too many problems). If you must use a plain bearing, then I'd use something like a Glacier DU and 'life' it for replacement at each service, but you'll find that the majority of bellcranks on race cars use needle rollers.

Once you've calculated the loads at the pivot, for your particular leverages, the bearing manufacturer's catalogue will allow you to select appropriately sized bearings.

[pigeondave]

This is an interesting topic and one that I would like to know more about.

I have been chatting with another fury owner(racer) an he seems to think that it
would be a good move to go for something like the Igus Iglidur-G bearings
and a bearing shaft.

The reason for the Igus Iglidur-G bearings over needle rollers is that only
a few of the needles are being subject to compression.

The only problem is that you'd have to machine something, out of
some other material like Delrin or Nylon-6, to hold the bearings
which are only about 1mm thick.
I dont have a lathe.

Please let us know what solution you end up using

[Sam_68]

pigeondave said:

The reason for the Igus Iglidur-G bearings over needle rollers is that only
a few of the needles are being subject to compression.

But the same can be said for any plain bearing - only a small part of the bearing area will be under compression, and hence wear will be very rapid.

At least needle rollers allow the needles themselves to rotate, to even out the wear, and of course they are lower friction and not quite so sensitive to dirt ingress or misalignment.

For those who haven't got a clue what we're talking about, incidentally, both the DU and Igus bearings are basically similar to the shell main bearings used on a modern engine - a layer of metallic bearing material applied to the face of a steel backing strip - but designed to run dry (though they can be run lubricated as well).

[ezakimak]

bit injured - so little typing


had posted hear

http://www.pistonheads.com./gassing/topic.asp?h=0&...

should be some shots in there

and on the social climber race forum in Australia as well if you want to search.

Ryan