Rear-End/Driveline

[markocosic]

Evening all,

How daft a proposition would it be for a car with a 'spool' to run only two CV joints?

The solid rear axle cars:
http://www.cosic.org.uk/galleryv2/main.php?g2_itemId=670
show that the chain will tolerate the misalignment caused by suspension travel.

Could you (with an independently sprung/spool diff) car add just two CV joints/flexures at the wheel ends, and have a solid beam with sprocket for the centre do we think? As far as I can see you wouldn't be loading the tripods with anything they'd object to.

[Steve Yao]

Take a closer look at Obisbo's uni-bellcrank, Marko. http://www.cosic.org.uk/galleryv2/main.php?g2_itemId=679

It is designed such that the axle only has one DOF. The axle does not twist...well it does, but very little since that bellcrank amounts to a practically rigid anti-roll bar. The driven wheels do not move independently. There is no misalignment of the chain like Lehigh had in 2005. Thus they do not destroy chains like Lehigh did...of course the car had almost no track time before competition so that is really hard for me to say for certain.

[kwancho]

Basically, you're saying chassis roll angle = live axle roll angle, right?

[markocosic]

Gotcha Steve.

Lehigh - that was the other name I was looking for. How quickly did it eat it's chains?

Are belts any better at handling misalignment than chains? Initial gut feeling says yes given their torsional flexibility (provided you can keep the buggers on the pulleys) but I've no real clue. Any good texts out there folks know of offhand? (searching the Gates site as we speak)

Kwancho - yes, although the "live axle" would be between two independently sprung rear wheels. seeing as things want to be stiff for wheel location, thoughts wandered to re-using those stiff points & bearings to eliminate a pair of CVs/set of splined or bolted joints and the 'diff' bearings you'd normally see:

http://www.cosic.org.uk/galleryv2/main.php?g2_itemId=9991
http://www.cosic.org.uk/galleryv2/main.php?g2_itemId=10066

Braking through the belt/chain might not be so brilliant mind.

[murpia]

Originally posted by markocosic:
Could you (with an independently sprung/spool diff) car add just two CV joints/flexures at the wheel ends, and have a solid beam with sprocket for the centre do we think? As far as I can see you wouldn't be loading the tripods with anything they'd object to.

An interesting concept! You need to think of a cool name for it, 'Dion-de' doesn't give you enough personal credit, Marko...

Either you restrain your 'diff-axle' radially with respect to the hubs or the tripods are loaded radially too. With a chain drive this radial load will be similar in magnitude to the chain tension. Tripods will handle radial loads, but you might need to upsize them. You also need to consider how you accomodate the required plunge travel, and with a chain you will need to keep your 'diff-axle' lined up with the sprocket.

You could use bevel gears and a stub shaft to transmit torque to your 'diff-axle', maybe in conjunction with a longitudinal engine. Use a version of any of the well known beam axle location techniques (radius rods, panhard rod, Watt's linkage etc.) to react your housing torque and the tripods themselves can be relieved of some of the radial loading. Be careful not to over-constrain though...

Regards, Ian

[LU-Bolton]

Hey guys,
We ran the solid rear for two years ('04, '05). In '04, we did not align the swing arm pivot point with the pinion on the engine. Thus, we had ridiculous amounts of chain length change through suspension travel. The swing arm was moving on one arc, and the chain was moving on another. Chain tensioning was the problem that year, as opposed to eating chains. We used a 5-20 by the way.
In '05 we fixed the problem. Aligned the swing arm pivot with the pinion on the WR-450 and we were good to go. No real chain length change observed. One thing that was a problem was that we had absolutely no chain tensioning. Imagine it, bolt the rear swing arm up and the engine. Now you have no chain tensioning device whatsoever. We had to wait for the chain to stretch before we could half-link it and tighten it up. Those were the good old days... However, there were no chain wear issues whatsoever. It can be done quite easily if you plan your design well. The other design flaw would be that it handled like a Mustang to put it bluntly. It was hard to bring that car back due to some oversteer issues and poor rear grip.

Aaron Cassebeer

[markocosic]

Originally posted by murpia:
'Dion-de'

Like the description!


Either you restrain your 'diff-axle' radially with respect to the hubs or the tripods are loaded radially too. With a chain drive this radial load will be similar in magnitude to the chain tension. Tripods will handle radial loads, but you might need to upsize them.

Good good! http://fsae.com/groupee_common/emoticons/icon_smile.gif Initial looks suggest that upsizing would be lighter than radial supports (most tripods we see are overkill as it stands - we'd just be making better use of the existing material)


You also need to consider how you accomodate the required plunge travel, and with a chain you will need to keep your 'diff-axle' lined up with the sprocket.

Plunging CVs are easy enough, but allowing the whole sprocket-axle (spraxle?!?) to float around of it's own accord sreams bad idea. Perhaps a floating 'spraxle' with two nylon rubbing blocks on that compulsory chain-guard would do the trick?


You could use bevel gears and a stub shaft to transmit torque to your 'diff-axle', maybe in conjunction with a longitudinal engine. Use a version of any of the well known beam axle location techniques (radius rods, panhard rod, Watt's linkage etc.) to react your housing torque and the tripods themselves can be relieved of some of the radial loading. Be careful not to over-constrain though...

All starts to sound rather heavy - adding bits rather than deleting them? Food for thought though!

Thanks for the notes Aaron, doesn't seem quite such a daft idea if the chains can survive it. http://fsae.com/groupee_common/emoticons/icon_smile.gif

[Steve Yao]

I stand corrected. My apologies to the Lehigh team for making comments on their systems in ignorance.

Aaron, why did the car not finish endurance in Detroit 2005?


Originally posted by LU-Bolton:
Hey guys,
We ran the solid rear for two years ('04, '05). In '04, we did not align the swing arm pivot point with the pinion on the engine. Thus, we had ridiculous amounts of chain length change through suspension travel. The swing arm was moving on one arc, and the chain was moving on another. Chain tensioning was the problem that year, as opposed to eating chains. We used a 5-20 by the way.
In '05 we fixed the problem. Aligned the swing arm pivot with the pinion on the WR-450 and we were good to go. No real chain length change observed. One thing that was a problem was that we had absolutely no chain tensioning. Imagine it, bolt the rear swing arm up and the engine. Now you have no chain tensioning device whatsoever. We had to wait for the chain to stretch before we could half-link it and tighten it up. Those were the good old days... However, there were no chain wear issues whatsoever. It can be done quite easily if you plan your design well. The other design flaw would be that it handled like a Mustang to put it bluntly. It was hard to bring that car back due to some oversteer issues and poor rear grip.

Aaron Cassebeer