Post by Admin on Oct 18, 2018 7:53:20 GMT -5
Liteway started this thread
Liteway
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Posts: 664
Aug 20, 2017 DaveJ98092 likes this
Post by Liteway on Aug 20, 2017 at 3:46pm
Have you guys seen Adam's new Video? Not a big fan of the trike, as the suspension at both ends is suspect. None the less, the driver is diggin it. Adam posted the trike here several years back, but did not hang around. The video itself is better produced than any other trike vid I have seen on You tube and its inspiring a lot of viewers/followers. Worth a look.
Youtube of AMT3 Trike
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didjeffects
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Aug 20, 2017 at 6:07pm
Post by didjeffects on Aug 20, 2017 at 6:07pm
Huh, I'd like to hear your critique of the suspension, looks like fairly standard stuff (and surprisingly stiff in the corners) so what am I missing? My favorite detail is the gas tank in the dead space under his legs, was thinking of doing that for my build and his execution is super clean.
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Liteway
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Aug 20, 2017 at 8:05pm didjeffects likes this
Post by Liteway on Aug 20, 2017 at 8:05pm
On the front:
Upper arms, inboard to outboard, slant down. This means as the outboard spring compresses under load in a curve, the resulting geometry will result in a gain in positive camber which means the wheel/ tire will lean to the outside diminishing the contact patch.
This could have been partially countered by making the upper arms shorter, but instead he made the lengths even more equal than normal which deepens the problem.
In comments he seems to get that but says there is little travel to the suspension so its not so much a problem. As you observed, it doesn't lean much and that is why. He made it stiff, likely very. He forced himself into an unnecessary compromise that I would bet results in a rough bouncy ride. I also see a lot of static neg. camber. That will help to work against the positive camber gains in the corners but will result in uneven tire wear.
At the back, the swing arm looks similar to ones used on motorcycles in the old days before engineers knew or cared about what their flexing did to handling and stability.
Small main tubes, no bracing.
If you look at any modern mid/large sport bike swing arm you will see they are heavily braced or have large main tubes to prevent twist/flex under the relatively light lateral loads a street bike generates. Flex is bad news that will result in inconsistent/squirrelly handling.
The lateral loads induced on the swing arm of a heavier trike are going to be a lot more demanding. It should be beefier than on a bike, not the spindly looking thing Adam made.
edit 8/26. I also noticed juddering when trike accelerates. That's from improper swing arm geometry. It can be seen at a glance, the front pivot is too far from the counter sprocket causing a change in chain tension as the springs compress. That sets up an oscillation you can hear in the engine note.
Having said all that, Adam's trike looks like a ball to drive , and I wouldn't mind a go if so privileged.
Its still a more attractive proposition than the more popular production trikes. I would not ride it without a full face helmet and jeans or leathers taped closed at the ankles.
Tank placement is unusual. I could not get a 2 gallon tank in there, though I have managed a 6-pk of Modelo or 3 liters of Carlo Rossi.
Later: Adam has responded to my swing arm critique (not so detailed as above) posted to comments on his video.
He states the side tubes are "1 3/4" DOM, pivot is 1" shaft, axle is 3/4", there is no flex".
I'll leave it there
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didjeffects
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Aug 24, 2017 at 11:31pm DaveJ98092 likes this
Post by didjeffects on Aug 24, 2017 at 11:31pm
Huh, my understanding of all these principals is fuzzy, I get that roll stiffness in 3ws is a big deal (good breakdown here - ismasupers.com/downloads/tech-talk/Tech-03%20Springs-Roll%20Stiffness-4.pdf) and that's why sliding pillar suspension worked on the old Morgans (tho they abandoned it for a-arms eventually). One of the things I like about my project, recycling the Unisport front end, is it uses sliding pillar but I can bolt in a-arms down the road when my understanding improves.
So it seems in Adam's design that he's added stiffness by making the top a-arm longer than most? And I assume that solution would be more popular if others agreed w/ the compromises involved, which they don't? Adam's design is also super low, yes? Lower than the kinda-similar t-rexs? Looks too low to handle the country roads where I live.
And, in case any of this comes off as overly-critical, cheers to Adam for getting a driveable vehicle on the road, that's a huge accomplishment that everyone here can appreciate.
Liteway
Exalted Member
Posts: 664
Aug 20, 2017 DaveJ98092 likes this
Post by Liteway on Aug 20, 2017 at 3:46pm
Have you guys seen Adam's new Video? Not a big fan of the trike, as the suspension at both ends is suspect. None the less, the driver is diggin it. Adam posted the trike here several years back, but did not hang around. The video itself is better produced than any other trike vid I have seen on You tube and its inspiring a lot of viewers/followers. Worth a look.
Youtube of AMT3 Trike
_____________________
didjeffects
Tadpole
Posts: 5
Aug 20, 2017 at 6:07pm
Post by didjeffects on Aug 20, 2017 at 6:07pm
Huh, I'd like to hear your critique of the suspension, looks like fairly standard stuff (and surprisingly stiff in the corners) so what am I missing? My favorite detail is the gas tank in the dead space under his legs, was thinking of doing that for my build and his execution is super clean.
____________________
Liteway
Exalted Member
Posts: 664
Aug 20, 2017 at 8:05pm didjeffects likes this
Post by Liteway on Aug 20, 2017 at 8:05pm
On the front:
Upper arms, inboard to outboard, slant down. This means as the outboard spring compresses under load in a curve, the resulting geometry will result in a gain in positive camber which means the wheel/ tire will lean to the outside diminishing the contact patch.
This could have been partially countered by making the upper arms shorter, but instead he made the lengths even more equal than normal which deepens the problem.
In comments he seems to get that but says there is little travel to the suspension so its not so much a problem. As you observed, it doesn't lean much and that is why. He made it stiff, likely very. He forced himself into an unnecessary compromise that I would bet results in a rough bouncy ride. I also see a lot of static neg. camber. That will help to work against the positive camber gains in the corners but will result in uneven tire wear.
At the back, the swing arm looks similar to ones used on motorcycles in the old days before engineers knew or cared about what their flexing did to handling and stability.
Small main tubes, no bracing.
If you look at any modern mid/large sport bike swing arm you will see they are heavily braced or have large main tubes to prevent twist/flex under the relatively light lateral loads a street bike generates. Flex is bad news that will result in inconsistent/squirrelly handling.
The lateral loads induced on the swing arm of a heavier trike are going to be a lot more demanding. It should be beefier than on a bike, not the spindly looking thing Adam made.
edit 8/26. I also noticed juddering when trike accelerates. That's from improper swing arm geometry. It can be seen at a glance, the front pivot is too far from the counter sprocket causing a change in chain tension as the springs compress. That sets up an oscillation you can hear in the engine note.
Having said all that, Adam's trike looks like a ball to drive , and I wouldn't mind a go if so privileged.
Its still a more attractive proposition than the more popular production trikes. I would not ride it without a full face helmet and jeans or leathers taped closed at the ankles.
Tank placement is unusual. I could not get a 2 gallon tank in there, though I have managed a 6-pk of Modelo or 3 liters of Carlo Rossi.
Later: Adam has responded to my swing arm critique (not so detailed as above) posted to comments on his video.
He states the side tubes are "1 3/4" DOM, pivot is 1" shaft, axle is 3/4", there is no flex".
I'll leave it there
_____________________
didjeffects
Tadpole
Posts: 5
Aug 24, 2017 at 11:31pm DaveJ98092 likes this
Post by didjeffects on Aug 24, 2017 at 11:31pm
Huh, my understanding of all these principals is fuzzy, I get that roll stiffness in 3ws is a big deal (good breakdown here - ismasupers.com/downloads/tech-talk/Tech-03%20Springs-Roll%20Stiffness-4.pdf) and that's why sliding pillar suspension worked on the old Morgans (tho they abandoned it for a-arms eventually). One of the things I like about my project, recycling the Unisport front end, is it uses sliding pillar but I can bolt in a-arms down the road when my understanding improves.
So it seems in Adam's design that he's added stiffness by making the top a-arm longer than most? And I assume that solution would be more popular if others agreed w/ the compromises involved, which they don't? Adam's design is also super low, yes? Lower than the kinda-similar t-rexs? Looks too low to handle the country roads where I live.
And, in case any of this comes off as overly-critical, cheers to Adam for getting a driveable vehicle on the road, that's a huge accomplishment that everyone here can appreciate.
