Has anyone ever made the motors on the sled? how to deal with extra chain?

Here are some design considerations that I see:

  • for a triangular linkage, the motors will need be free to move so that the line of the chain (a line halfway between the to- and from- chain paths and through the center of the motor shaft) intersects the center if the router bit. If I remember right, the smaller that radius, the better the chain stayed truly aimed.
  • does the point which represents the upper corner of the motor-sled-XY right triangle move as the sled travels to different corners? How to calculate exactly where it is and measure between the left- and right- ones?
  • the chain-to-cable splice cannot pass over the motor sprocket or the tensioning pulleys
  • the encoders on the motors will be much closer to the electrical noise of the router

All that aside, having the motors on the sled could make the whole machine easier to pack away and set up again.

that’s a great question. I have to brush up on high school geometry! Probably the easiest way to make it sureproof is to have a 10 tooth sprocket right above the permanent chain attachment point. The further distance away the permanent point and the take up sprocket are then the more chance to introduce error?

looks like by getting rid of 25 feet of cabling this alternative adds a lot more chain and you are right sprockets would have to be used instead of pullies.

Doesn’t the tension cable become part of the equation as well? It adds some force to the motor position so it affects the pivot point too. The geometry of that corner looks complicated to me.

maybe you are right, wil have to think about it more.

which is why I wanted to have the spring loaded “collectors” on the sled to begin with.
in that situation the top tanget point of the motor sprocket because the center line of the triangular kinematics. And their is only a single well defined top chain attachment point on the top beam.

Pics are in this thread:


edit: link corrected, thanks to Gero.

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The concept and springs of this blinds rollers would do the job on taking the chains. A new and larger housing would need to be made.

Pic from Maslow without Stretchy String, bungies or elastic cord only blind rollers

The sled was build around a Lazy Susan I think. The first triangular before we had it in the software.

The interesting pics are in -> Posted on 2017-03-28 14:07:53 by jessbussert :

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I have a 3d design of a 3 part slew bearing somewhere in my archives from those days. I need to dig.
The middle part would hold the router with a pendulum to keep it straight and the 2 outer part would hold the chains. Slew bearings can take the load and can be made sealed from dust.
I’ve frozen the concept as I have no idea who to manufacture the design.

thanks but slew bearings tend to be expensive. and I already have a solution using cheap roller bearrings.
I will buy some of those blind rollers on ebay or some retractable cords and test them out.
I am not sure either one will hold about 9 feet of roller chain which is the minimum needed.

Gero,

The constat force is not enough, you need a powerfull constant forcé spring, I use it only with the strap.

what is the strength of the spring you recommend? I thought you were using mini blind springs in your frame build? did you switch the out for more powerfull constant force springs?

To roll up the slack chain not in use, this springs should be sufficient. But I have not tested it. To keep my slack chain horizontal across the top beam I need 2kg (~ 4.4 lbs)

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So I drew up a standard maslow motor mount configuration and the math on the standard everyone is using seems just as complicated. as the sled goes from the top
to the middle the distance between the pivot points on the chain sprocket changes by about 1/8" on each end or 1/4" total. does the software compensate for this. or is it just considered close enough for horseshoes and hand grenades?


2nd drawing shows the entire scale of measurements.

I do know it compensates for how much chain wraps around the sprocket based upon where the sled is. I haven’t figured out the math to it though from just reading the code. A diagram of how it all works would be helpful to have.

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I was wondering if you could 3-D print a chain guide that always has the chain coming out at a single point… something like this…

image

bottom right corner is where the chain feeds out and right side is where the chain feeds in (from the takeup).

I guess one could, but you would have to tension the chain so it wouldnt’ jam. PERSON WHO tried this before specifically said chain jamming was an issue.
since maslow software already accounts for chain wrap it would be easiest to just add an extra 10 tooth sprocket up where the motors are at and in essence it would work the same way mechanically as the exsisting setup so no new math would need to be figured out

I was envisioning the motors and chain takeup on the sled (say mounted on top of the bearing rollers of a ring kit) and so you needed the chain to feed off the motor directly in line with the router bit.

I don’t think there will be any real solution for storing the excess chain on the sled without using a separate motor for it.

a spring loaded cansister like those used in retractable power cords would work, but the above drawing is probably cheaper, only requires two extra chain sprockets bolted to the top two corners which is $9 more. About what the L brackets would of cost anways.

I still think having the chains collect on the sled somehow is cooler.

How does the chain wrap around the sprockets/motors on the sled? I’m having a hard time picturing what is happening there.

sorry updated drawing with the missing fixed chain end point

I don’t think the diagram correctly captures the force on the sprocket - i think it is divided between the chain to the fixed point and the chain to the slack turning point, though not equally. I think the chain to the fixed point will have the greater effect, and more during upward travel that during downward. I think this varying effect would make calculate even messier.

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