Thread: hair-brain half-baked idea coming right up

Originally Posted by F4Phantom

Please dont flame me too much for this idea BUT... why would this not work

machine a box 300mm long 200mm wide and 150mm thick (I mean properly machined not hammered and welded and hacksawed in the backyard) with two shafts in bearings about 150mm apart with a triplex chain. The box is bolted to the axle stubb and the alxe fit to the top shaft so the drive is offset 150mm down to where you attach the wheel. You now have a portal axle for a reasonable cost even when including proper machining.

I can see fitting the disks a problem but obviously not to many others or I would not be entertaining the idea.

anyone care to comment?

Yep you have a serious fetish there

Chain driven portal... I guess it would be a trade off between lash and chain wear?

Got a mate who has 6x6ed an old rangie and has used chain drive from 2nd to 3rd diff?

Anythings possible - but surely the hassle of machining for good chain tolerances could be spent making a gear housing and gear set a la "normal" portals?

S

Yeah, I think the same, there chain as it wears could become a problem... But then again the rover transmissions have that much play in them already that it probably won't make it much worse.

If you were considring doing this with bearings and what not, you might as well use 3 spur gears or helical gears to make it more durable (I was a little bored):

why bother with that...

take a planetry gear set retain the anulus and planetry carrier.

put the wheel on the anulus and then drive the anulus from one planetry gear as opposed from the carrier. Instant portal with substantial reduction and less moving parts allowing you to fit those extra huge "why does that unimog I parked next to have licorice strip tyres?" rubbers you never knew you always wanted without reducing your diffs innards to swarf of increasing the parts count of your halfshaft.

I think I would be looking at the maximum allowable torque loads for chains before getting two far with the design. I suspect you would be looking at at least a four row chain, and possibly wider, which is likely to find your tyre centreline moving well out from the swivel. Also, you need to have some means of tensioning the chain, suggesting an idler. Whole thing is beginning to get complicated - I think I prefer Dave's plan. But still be a lot of work.

And at the risk of again usurping Ron's job, that is hare-brained, not hair-brain. The term comes from the erratic behaviour of the animal, nothing to do with the stuff on your head.

John

In the fifties and sixties there was a tandem drive conversion for single axle drive trucks using v-belts from the driven axle to the rear additional axle. Had some limited popularity with tipper operators. Most likely on the basis of price, being a cheaper way of increasing carrying capacity of an existing lighter duty truck than buying a tandem drive truck.
Chain drives were common in veteran, cars and on trucks right through the thirties.

I have had similar setups on machines such as coring machine and scarifier.

They are light weight and slow moving and they still wear out tripple chains and sprockets regularly.

I dont think it would take any amount of Hp with any real success.

The tripple gears would work well and wouldnt be that expensive, I just had 3 gears and a carrier made up for a planetary set in a bobcat trencher which cost $320, but I did have the original bits of the old ones for him to copy.

I did think of helical gears at first but figured having 3 in a row with reasonable teeth and outer diameter the size would be to big, but I now think it would be ok given that a chain is not strong enough. I even thought a wide timing belt would be ok. I have not got my head around the "annulus and planetary carrier" idea yet.

The biggest problem would be alignment and vibration. Strength is easy, just use something tougher and harder than mild steel.

I was thinking of attaching a bolt on portal device to my weekend tyres permanently as I got some 35 baja claws.