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 Post subject: Re: PooKs trike build
PostPosted: May 20, 2009, 6:26 am 
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As I understand it the load on the top arm doesn't really push up on the arms as the lower arms is equipped with the coilover.

The weight of the car tries to continue forwards as the brakes are applied, this is stopped by the brake rotor being squeezed by the pads giving a twisting force. I always think of it as trying to stop a spinning bike tire with your hands... gloved hands.

The tire wants to pull your hand around the rim with it, pushing the front arm and pulling the back arm.

The important thing with a-arms is that as long as the strength of the arms is greater then the braking force on the rotors (which is strong enough to lock the tires under the weight of the car) then all is well, but if the arms start to distort or bend they will lose their strength rapidly. A little distortion in the chassis is expected but when it comes to the suspension it can get nasty fast.

Also bending tubes stretches the outside curvature and shrinks the inside, making the outside curve thinner and weaker than it once was. So, say you started with .095 wall tubing then bent the tube, the outside will be thinner now. How much thinner? I have no idea but that is the wall that supports the leading arm attachment so its rather important. Might want to take some of the tubing you used bend it the same way as the chassis part then cut it to check its thickness.

This is just paranoid safety stuff and I am in no way bashing your beautiful build. The trike looks great and I envy your talent.


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 Post subject: Re: PooKs trike build
PostPosted: May 20, 2009, 7:27 am 
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The twist places a fore or aft load on the upper joint.


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 Post subject: Re: PooKs trike build
PostPosted: May 20, 2009, 7:59 am 
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Location: Richmond Kentucky
cool then I will triangulate it like the rear of the upper arm for safty THANKS!
See that why I like this forum so much, I would bet there is enough talent and raw skill on this forum we could have saved Chysler!
I joined a trike forum on yahoo the other day and a member asked "How wide should the front track on his home built reverse trike be?" I tried to explain (the way you guy's tried to help me) that without knowing the cg's and component placement, seeing the susp geom etc...that it would be tough to give any type of safe MAGIC NUMBER. another guy answered 2/3rds as wide as it is long :shock: ignoring my post the guy replied "yeah 2/3rds sounds right"
PooK

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 Post subject: Re: PooKs trike build
PostPosted: May 20, 2009, 12:06 pm 
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pook wrote:
cool then I will triangulate it like the rear of the upper arm for safty THANKS!

PooK


No need, if that tube is what, 32/38mm? - 1.1/4"/1.1/2"?, and you say it's 3mm - 1/8" thick then don't bother, it's not going anywhere over that short distance, the top front Aarm mount is by far the lightest load and I'm suprised that it's mentioned before the unsupported top shock mount, if that tubes going anywhere it will be up - but it won't.


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 Post subject: Re: PooKs trike build
PostPosted: May 20, 2009, 7:37 pm 
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I was thinking of the shock mount as well, the red bar in the MSpaint would help brace the vertical loads of the shock mount and make the arm a lot stronger.

I would still just advise bending the tube and cutting it to make sure the tube is thick enough after bending. But like I said before its just paranoid safety stuff that I feel better mentioning then not.


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 Post subject: Re: PooKs trike build
PostPosted: May 20, 2009, 9:32 pm 
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OK ok, I see now, I wasn't picturing an upward bend stress on the main tube, I was thinking more of the shock trying to collapse the tube inward or worse (tearing the tabs off)....I will have this fixed ASAP and the designer/builder flogged! :D
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 Post subject: Re: PooKs trike build
PostPosted: May 21, 2009, 5:54 am 
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pook wrote:
OK ok, I see now, I wasn't picturing an upward bend stress on the main tube, I was thinking more of the shock trying to collapse the tube inward or worse (tearing the tabs off)....I will have this fixed ASAP and the designer/builder flogged! :D
g]


Theres no need as I can see now in this picture that you are using 1 1/2"+ and if it's 1/8" wall it won't be a problem. If your obseesed with it just run a 7/8" tube from in between the shock and front Aarm pivot down to the main square tube next to the batteries (in a place you can still get your batteries in and out!).


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 Post subject: Re: PooKs trike build
PostPosted: May 21, 2009, 8:59 am 
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Seems like I :BDH: with the pick up...

So I'll get onto a different line of thought.

I love the detachable roll hoop braces, I've always seen them done with clevises or eye ends, the flat flange seems way better. I think I incorporate those into my own build.

Any more beautiful pics to share?


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 Post subject: Re: PooKs trike build
PostPosted: May 21, 2009, 10:11 am 
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I was just showing the load direction, not asking you to change anything.

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 Post subject: Re: PooKs trike build
PostPosted: May 21, 2009, 10:25 am 
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oh I know, I appreciate the heads up still!

PooK

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 Post subject: Re: PooKs trike build
PostPosted: May 21, 2009, 11:26 pm 
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Pook, great build, I really hope you finish it. If I were to pick something to criticize it would be your anti-roll bar pickup placement on the lower control arm. Looks like you are directing the force to the likely weakest place possible on that arm. (near the center)
I've seen swaybars bend A arms before. See attached pic. (they speak 1000 words I'm told) :wink:


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 Post subject: Re: PooKs trike build
PostPosted: May 22, 2009, 8:09 am 
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without making a new sway bar do you think this "band aid" would help?
Thanks
PooK
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 Post subject: Re: PooKs trike build
PostPosted: May 22, 2009, 8:28 am 
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Turn the pivot axis of the swaybar lower end link 90 degrees.

Center the end link over the tube.

Add a narrow tab for one side with a tab the length of the tube for the other side. Each tab will be offset half the thickness of the rod end.

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 Post subject: Re: PooKs trike build
PostPosted: May 22, 2009, 9:26 am 
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Heres my thinking Pook,

I think a RT with a non roll setup such as the Sportcycle has is worth exploring and frankly I think your's, T-Rex and others are basically flawed in that they have any roll at all, obviously and seriously affecting the all important rear tyre contact patch.

In my humble opinion Pook if I was you at this point I would make up a largish diameter tube with short lever arms to act as a 100% anti roll bar bar (no twist). I would run links from next to your shock mounts (to give you a mind picture something similar to pushrods on a pushrod suspension) and on those links I would use common rubber bushings such as shock or panhard rod bushings. This will give you a no roll car as a RT should be but the rubber bushings will take sudden independent wheel shocks such as square edged pot holes.

Pictures at 11.


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 Post subject: Re: PooKs trike build
PostPosted: May 22, 2009, 9:54 am 
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I'm not convinced zero roll is best. Roll will cause oversteer from the rear sliding due to a decrease in the contact patch. This can be tuned with roll bar adjustment/swapping.

Whats better, carrying the inside wheel with maximum rear contact patch and a overloaded outside front tire or a lightly loaded inside front tire and a reduced rear contact patch? There are a few variables.

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