rod ends

[D J Yates]

Am i right in thinking that most teams are using 8mm (or 5/16) rod ends? Anyone use anything smaller? My calculations suggest that i could use 6mm, maybe even smaller. Aside from the single shear issue (more of a design issue IMO) are there any other reasons why larger rod ends are used?

[Cement Legs]

I think most teams are using 5/16 and 1/4 for lighter loaded beams. Going smaller is really gambling and the return is minimal...

[TomF]

Delft is looking into 5mm rod ends to replace the current 6mm ones.

[adrial]

IMO the weight savings is negligible in going below 5/16. We use 5/16 at all inboard a-arm mounts and between 3/8 and 7/16 for outboard mounts.

[TomF]

The lighter your car becomes the more dominant are even those small weight savings http://fsae.com/groupee_common/emoticons/icon_wink.gif

[Cement Legs]

Absolutely, no one would suggest adding weight for no return would make your car go faster. But I would agree with adrial, going smaller than 5/16 and 1/4 on the rod ends saves a small amount of weight compared with the strength lost. Unless you have extremely detailed stress analysis and have accounted for all of the variable (who can actually do that?), I would think that there are more suitable places to shave grams off of your car.

[D J Yates]

Smaller rod ends means smaller/lighter nuts and bolts, which can be packaged easier and in turn require less material for mounting. The weight of 30 rod ends with nuts,bolts,spacers and washers etc is significant (~2kg?). If you can save half by going for smaller rod ends, i'd say that's significant.

The max force i'm expecting to see in any of the suspension members is around 6kN. The 6mm can handle 18kN so is easily strong enough. 8mm is overkill at 33kN. Some of the members will only see forces that are a fraction of the maximum, so using 5mm for these would be ok, but i'll stick to 6mm all round for ease of manufacture and assembly.

[Cement Legs]

Yeah I think that would be a good choice. I would always tend to compare 8mm to 5/16 and 6mm to 1/4 even though there are decimal differences.

[Kevin Hall]

Our car came in at 483 lbs (a bit of a hog) with 1/4" inboard, and 5/16 outboard. Works great! The cheapest 1/4" ones i tested easily hold 3000lbs, which is way more than the calculated suspension loads.

[Ben Beacock]

We calculated to use 6mm inboards, but we decided to go with 8mm rod ends with a spacer/insert for a 6mm bolt. It gives us more angular clearance for suspension travel.

[Cement Legs]

Interesting Ben... we are doing the same thing but because of an overcalculation on my part ealier on when we ordered the rod ends. so we will get the extra strength of the rod end (woopie... the next size down would work for us) but we dont suffer the biggest weight penalty which is the hardware...

[Daves]

We have no a-arm rod ends. Isn't it bad practice to use rod ends in bending, or am I misunderstanding the location of your rod ends?

Our pullrod rod ends are #10-32 (4.76 mm) on both ends. I think our steering rods and rear tie rods use 1/4"-28 rod ends.

[TomF]

Originally posted by Dave @ L.U.:
We have no a-arm rod ends. Isn't it bad practice to use rod ends in bending, or am I misunderstanding the location of your rod ends?


Yes it is bad practice. But that just means you have to design your suspension in such a way that your rod ends are not loaded in bending. Allthough this is some nights of work it can be done. Just make sure your cupbearing is located in the point trough which all (extended) A-arms and push/pull rods go.

[Daves]

The #10-32 rod ends for our pullrods were ditched in favor of 1/4"-28 rod ends. However, the spherical balls in the 1/4"-28 rod ends broke today! Time to order the higher grade ones.

[Denny Trimble]

What's the angle of your pullrods from vertical? Do your "1/4"-28" rodends have 1/4" bores in the balls, or are they actually .1875 balls with "heavy duty" 1/4-28 shanks?

I've never seen a ball break... sounds like you've found a nickname for your car.

[Daves]

<A HREF="http://www.letu.edu/_Academics/Engineering/engineering/student-projects/formula/images/pullrod.jpg" TARGET=_blank>
http://www.letu.edu/_Academics/Engineering/engineering/student-projects/formula/images/pullrod_t.jpg
</A>

Denny, please click the image to see the angle of our pullrods from vertical. The rears are also at about the same angle. When we enlarged the rod ends to 1/4"-28, we also enlarged the bolt that goes through the rod end ball to 1/4". We were concerned that the bending moment might be too great on the .1875" bolt. Therefore, our 1/4"-28 rod ends have 1/4" bores through the balls.

We noticed it today because the ball froze inside the rod end due to 3 cracks in it, and the rod end actually broke in bending at the thread due to the ball constraining its movement. Our rod ends should never see a large bending or shear load -- only tensile.

After inspection, a few of the other 1/4-28 rod end balls were also cracking. From what I hear, the manufacturer was not surprised. They recommended their higher grade rod ends.

[Infinity]

In regards of the Suspension rod ends,wat are the standard sizes of washers used on both sides of rod ends? The clearance need to be decided from that so i need that. Also wat type of Washer shuld we used. I have heard of some conical shaped? Are these available? Shuld i Use them?
Also How do we decide the distance between brackets?( Thats y i need the Washers dimensions for)
what are zerk fittings?how are they installed?

[James Waltman]

"Zerk"� fitting: Connection allowing passage of grease into bearing for lubrication. Sometimes known as a grease nipple, greaser, or zert fitting.
From here: http://www.aurorabearing.com/technical-resources/terms-...nitions/default.html (http://www.aurorabearing.com/technical-resources/terms-and-definitions/default.html)
A pretty good resource.

http://grease-fittings-grease-nipples.electrical-brass-components.com/grease-fitting-grease-nipples.jpg

[Bill Kunst]

Wow (salivating), that is a big assortment of nipples.