Thoughts on this design drawing (4 link rear)

[Aaron871]

Here is my rough sketch... anyone see any major malfunctions?
http://www.putfile.com/pic.php?img=4045619

This will be an off road BSR.
The Green is the frame and the yellow depicts suspension links.
4 link rear and IFS front.

I will have to build shock hoops for the suspension to attach to 12 inches above the shock mounts shown (tube bender and 3/4" dom). Haven't designed that part on paper yet but it should be a no brainer, should also give it that "off-road" character.

In the rear, I plan to use 2 rear axle kits, to give myself 3 attachment points (by welding the hangers to plate steel or angle iron), so that I can create a 4 link system.

I thought of using these for the suspension...

http://www.northerntool.com/images/product/images/13840_lg.gif

[moto1fast]

Hello, Looks great!! The only thing I can think of that might cause a problem is the drive chain Tension. As your rear axle moves up like when you hit a big bump the chain will tighten and if to much travel takes place it could brake the chain or maybe even snap the crankshaft off the engine. You could probably make a spring loaded tensioner so when your suspension is unloaded then tensioner would take the slack out of chain and when suspension is loaded the chain would have enough slack so it would not become maxed out! Just a thought. Going to this much design and work for suspension I would go ahead with 4 wheel drive. Polaris ATV's the older ones used a chain drive on there 4 X 4's. Take a look at how they were designed and you could come up with a better system than they had! Looks Great keep us posted!!:thumb:

[kkuenemann]

Aaron

I agree with Moto, your chain tension could be an issue. If you design your 4 link so that your IC (Instant Center, The imaginary point that the suspension links rotate around.) is that same center line as the crank shaft of the engine or the output shaft of the Tav, then you may not have the issues that Moto mentions about chain tension as the suspension moves. The draw back is the the engine cannot be moved around to put the proper amount of tension on the chain and a chain tensioner will still have to be used.

Just my 2 cents....

[Snakester]

Yo Aaron, This looks like a great idea, the design should work fine! Have you ever ridden a BSR w/suspension? Kinda like one of those mechanical Bulls!!! When you are sitting 36" in the air and have a 30" wheelbase and are probably holding on for dear life as it is already.....I rode one last summer that was built from a 4 wheeler ,the builder did an awsome job, man this thing was a handful to handle and to hold on to. BUT, this will be a super cool build , post pic's when you can , Good luck.....Snakester:me: :me: :me:

[monkey-1]

The 4 link is a cool idea, but unless your pivot point is the same as the the front sprocket, the chains tension will not remain the same. Also, and the more important of an issue you are going to have is articulation. Any articulation is going to bind the chain. In order for a chain drive to work, both the front and rear sprockets MUST remain aligned. The best thing to do for a rear suspension is a rear swingarm setup. This way you can have suspension and keep both sprockets aligned.

[Aaron871]

What is the proper chains tension?
What is a "swing arm setup"?

[moto1fast]

Even with a swing arm you will still have to deal with the Chain tension if the rear sprocket is not centered straight back from front sprocket. But a swing arm is a very simple set up for suspension. I would make it as Follows, First you would have 2 arms coming from frame brackets. The arms would be about 7 1/7" wide with a 3" pipe at the rear with your Bearing plates welded to each end of the pipe! Then welded to your arms. At the Frame ends of arms have a 5/8" ID pipe welded across (7 1/2") then run a Bolt all the way through pipe and Mounting brackets tighten snug with self locking nut. DO Not Overtighten just take out any slack so it will freely swing up and down. On the 3" pipe at rear put a shock mount on it in the center. Then mount the shock up to a anchor bracket on main frame. You would run the sprocket on the right side of rear arm and run the brake rotor on the left side of the left arm. Build a brake caliper mount onto left arm. You would now have a swing arm set up that would hold up to about any punishment you could throw at it. You could even put cross braces in it for one tough assy. I will mod one up tomorrow and post pics. Also the proper chain tension should be about one inch of slack up and down in about the middle distance from front to back sprocket.:thumb:

[monkey-1]

You could also mount the engine onto the swingarm and then you dont have to worry about chain tension. Bearings arent necessary on the front of the swingarm, you an use self lubricating bushings.