tat ty wrote:The explanation of the loop factor did effectively loop my brain. I do have a reasonable mathematical ability, but I'm sure I'll need to read it at least 5 more times before there is a chance that I may "unloop"
I dip my helmet to JC1.
So here is the question that I've needed resolved and I suspect JC1 may have the explanation.
In the mid 1980s an American company named ATK produced a revolutionary dirt bike. Either side of the swing arm pivot (above and below) was an idler pulley, which ensured that the chain ran parallel to the swing arm.
My hunch is that the system (Anti-Tension Kettenantreib) had to do with the loop factor. So the question is out.
Alastair.
When I first wrote that post many years ago I thought of that design too Alastair.
ATK called it a parallelogram system that was marketed as isolating the chain torque reaction from the suspension so that they were independant from each other - ie it was supposed to make the suspension more supple and responsive: no effect on the suspension from the chain pull force because, according to ATK, the chain pull was parallel to the swingarm.
I immediately realized that the ATK designer didn't understand how chain-pull torque worked, since the chain-pull torque has nothing to do with whether or not the chain-pull direction is parallel to the swingarm.
Look at the diagram again and compare it to the ATK in David's post.
(Or google-image ATK406 and you can see some pics where the configuration of the system is more apparent.)
- Chain Torque JPG.JPG (14.08 KiB) Viewed 2300 times
In his system the dimension 'a' is huge (and constant) compared to a normal system, so the squat torque from the chain pull is also constantly huge. To compensate he is forced into having an extreme swingarm angle (and a hi swingarm pivot location) so that the dimension 'b' is even more huge to counteract it.
To some extent it did counteract loop factor (anti-squat) a little because 'a' is so large causing squat, but at the cost of actively softening the rear suspension when under power (which was what my next post was about back then on page 4 of this thread).
It did achieve more or less constant chain tension but at the cost of extremely hi wear of chain and front sprocket since the chain wrap-around of the front sprocket was barely 90deg, so all the power was transmitted thro just a few teeth. And I suspect it would be prone to the chain jumping teeth whenever the system is slightly out of adjustment.
There was also an accessory marketed, called the AMP Link if I recall correctly, which was also based on the parallelism claims, which tried to emulate the ATK system but is long gone.
They both were little more than a novelty which soon wore off as it didn't achieve what was claimed. It's noteworthy that nobody else took it on board.
For good reason.
"Men are never more likely to settle a matter rightly than when they can discuss it freely"