How should I build the driveline?

[mccheynebeeman]

Hello all,

I have a project I am building that has 8 wheels & 8 wheel steering. I have used 8 sprint control arm assemblies (strut towers and brakes and rotors.. etc) along with their CV axles to join up to four seperate differentials. I was origionally thinking that I would have an engine & transmission inline with the vehicle, droping the drive using CV axles to two 90 gear boxes, which will drive two sprockets with 80 size chain to each corresponding diff. The problem I don't like about this idea is that if I need to tension the chain (which I would) I'd need to either move both diffs side to side for each chain, or move the 90 gear box up and down. Since I wanted everything sealed in a custom box, this would make it really hard to seal.

So, I was thinking about using 3 carrier diff gears (same ones as on the current diffs) inline instead of chain to connect everything. The middle gear would connect to the 90. This way, everything can be secured down without needing future adjustments.

Anyway thoughts?

(to see some pictures of this machine for a reference of what I'm talking about got to

http://www.4wheeler.ca/index.php?showtopic=20755)

Thanks in advance,

Frazer RM Ross

 

[Warpspeed]

Steering the front four is going to give you a vastly more stable vehicle. Oversteer is highly unstable, some built in rear roll understeer ADDS to high speed stability, and is built into most (if not all) production cars.

The way to do it is to have the rear wheels deliberately steer very slightly with body roll, not a lot is needed. The correct rear steering direction is toe in on bump, and toe out on droop. As you will be using eight struts, the steering arms of the rear four struts will be attached by linkages somehow to the chassis. The location of the inner attachment point to the chassis can be selected to cause the rear wheels to steer with vertical suspension movement, or always point straight ahead. It is only a small refinement, but it is something to consider.

 

[GregLocock]

You can also use compliance steer to get a similar stabilising effect. Compliance steer is a bit faster than roll steer.

Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[Warpspeed]

Excellent point Greg, but it is a bit more tricky to judge. I would expect the cornering force levels to be quite low in this type of vehicle, particularly on off road surfaces.

Anyhow, if it has rear facing steering arms that are fairly rigidly located, and the lower suspension arm is rubber mounted (and therefore compliant), that would also rear steer in the required direction for improved stability.

 

[mccheynebeeman]

Thanks guys for all the help!! I'll post pictures when I'm done!