That will definitely look cool. But for the router bit to remain equidistant from the ends of the motor chains, each motor (and the brick) would have exert the same force in the loop at all times.
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i should make a mockup and see what really happens, Gero’s ‘triquad’ has in my opinion a lot going for it.
After seeing the video it seems more stable then i expected at first glance, the simplicity makes it attractive
… waiting for more video’s
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Ok,ok, I will make some cuts 
to make the theoretical drag error practically visible.
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$40 all in? Just want to make sure before purchasing. Frank
for the top mount kit shipping in the US, $40
David Lang
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I had a chance to try a symmetrically balanced weight arrangemnent with a top-mounted pantograph linkage. Unfortunately, friction of the sled against the surface and the weight of the linkage seem to have enough effect that the linkage does in fact come to rest against one of the chains, but causes a slight bend in the chain.
I think the offset weight arrangement works better than the symmetrically balanced one.
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Thanks for running that test @blurfl! That’s something we’ve been wondering for a while now and I’m glad to have an answer
Hey guys, I am definitely late to this thread. I did not read the whole thing because it was so long. I did have one idea to add to the linkage idea. The biggest issue with the linkage idea is that it appears to be huge. One potential solution to this is to make the parallel members curved. As long as the linkages are rigid, curved links function the same as a straight links. If you design the parallel members to be curved, such that they wrap around the router, the connection points can be closer to the router, which could reduce the size of the linkages overall. This is only applicable to the 45 degree version. Said another way, the four parallel links that connect to the base could be cut with a radius. They would be curved outward, such that in the extremes of the motion, the radius wraps around the router base. This would allow the links to be mounted closer to the router base, because the curved members create more clearance than the straight members. This means that the mechanism can be built smaller overall.
I apologize if this has already been mentioned. If not, hope it makes sense and is useful.
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That is an idea that has been discussed and it may have some merit still, however it appears that the limiting factor in most cases is the mounting points not the bars. The kits I’ve been sending are 9" from joint to joint, not tiny but I would not classify them as “huge”… if anything they are a little on the small side. They work great with the recommended ridgid router but if you have a router with a much larger base then things can get tight. I am working on a version for someone on these forums that will fit around a larger bosch router. I also have a semi-untested version that uses shaped bars, but not really for reaching around the router; It’s hard to explain but I hope to make one and post pictures at some point.
Just remember, even with curved members, the distance between the mounting points needs to be the same distance as the joints on the bar that the chain attaches to.
Another thought related to the ring option shown by Bar. Specifically, this is related to the chain “jumping” discussed above. I think this can be largely mitigated by changing the design of the roller attachments. Right now, the picture shows two rollers per chain; the rollers are close together, the carrier is small, and the chains mount very near the radius of the ring. The jumping could be mitigated by changing the carrier,such that it extends radially outside the radius of the ring. This would be like arms, maybe 8"-16" long, that extend radially out from the ring. The chains would mount at the end of the arms. I think of this arm as being a lever-arm; as long as the wheels don’t lift off the ring, it rotates about the router’s center. Tangential forces from friction or imperfections in the ring are opposed by the cross product of the tension in the chain, and a small angular displacement. The reason this should improve jumping is it increases the length of this lever-arm. The torque generated by this arm should be greater for any small angular displacement. Any increase in the length of this arm should correspond with a reduction in the magnitude of jumping. It is a potential improvement.
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Yes, true @Joshua
However longer arms = more flex, meaning less accuracy.
Also longer arms need more space, therefore restricting how close the sled can be drawn in close to the motors/sprockets, and therefore reducing the available cutting area on the bed.
However longer arms = more flex, meaning less accuracy.
I may be misunderstanding what you are saying, but the longer arms are replacing
chain, so they are unlikely to have more flex than chain.
Also longer arms need more space, therefore restricting how close the sled can be drawn in close to the motors/sprockets, and therefore reducing the available cutting area on the bed.
This is not likely to be a proble, there is a lot of distance between the edge
of the sled and the sprocket in the top corners (something like 9" or so)
The length of the arms would definitely be constrained by the length required to cut a 4X8 sheet of plywood.
The arms should not result in more flex. Why do you think the arms would result in more flex?
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The way I understood @Joshua’s idea was that the arms would be in line with the chain, effectively replacing the last 8-10" of chain with a rigid member that is part of the pulley assembly. In this case they would be mainly under tension, I doubt they would flex much at all.
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Ok, now I get it. You’re right, should not result in more flex.
Anyone ready to give it a test?
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@bar Have you thought about doing the following to the ring, just thinking outloud… and bending the rail around. With the roller inside.
http://s.aliexpress.com/jY77zmEv?fromSns
Not sure of the advantages 
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I like it! I thought about doing something like that but I don’t think the rail would bend smoothly. I’d love to see someone prove me wrong and bend some tho 
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I mean, places like hospitals have it bent… but sideways not around… might be hard to explain to a curtain manufacturer why you wan it bent in a circle 
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I have a pipe bender, might bend some pipe maybe cut a slit in it first got to do something while waiting for power in my shed…
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you will have trouble keeping it from collapsing.
Why is this any better than the existing approaches?
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