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4 Motors and Chains

#1

Hi guy, I’m going to be ordering my kit on my next paycheck. but anyways I was wondering if anyone has thought about getting code written and setting up the CNC with a motor and chain in all 4 corners. to me it seems that it would fix a lot of the issues with cutting in all four corner. You could keep tension on the chains and take gravity out of the equation. it doesn’t seem like it would cost much more to do so ether. also i would think if you wanted to lay it flat instead of standing up also.

Tell me what you think and let me know if I’m wrong.

2 Likes
#2

There has been discussion of this idea, and also of using pulleys and stretch cord toward the same end. Adding two more motors would add quite a bit of cost, probably requiring another Arduino, motor control board and power supply. It could solve some of the accuracy issues, though.
I think I would put a spring or bungee link in the lower attachments, so that the upper motors would have more definite control of position than the lower motors which would only provide tension.

2 Likes
#3

That sounds good,
you could then make it a table top,
I can see the benefits this will have for the extra cost,
might be worth it,
count me in

1 Like
#4

I would like to work on this also, this is one of my goals for when we’re taking a break from selling kits

5 Likes
#5

Maybe ditch the present slack management and extend the present chains and add sprockets in the lower corners to use the ‘tails’ as the tensioners?

4 Likes
#6

I believe you would still have to use a spring of some sort to adjust the length of the chains for when they go into the corners. I could see this as a problem for when you are pulling the router with force through a board. I would think that with 4 motor it would be able to pull the router in any direction instead of using gravity to move in some direction. Maybe we would be able to use a bigger router and be able to cut down on how many passes are needed to cut through 3/4 plywood.

1 Like
#7

yes, with 4 motors you would not be dependent on gravity.

These routers are very beefy, you don’t need a bigger router.

Bar is especially timid in his cut depth, there have been some tests run where
the cut is a 1/2" bit cutting all the way through 3/4 plywood in a single pass.
Bar has done some of them. :slight_smile:

try cutting deeper passes, watch for symptoms of the router not moving enough.

and please, report your findings :slight_smile:

David Lang

2 Likes
#8

New Idea - How about longer chains and an idler in one corner with a loop of chain.

Thoughts?

This means you @dlang :wink: @madgrizzle @blurfl @bar @jwolter @Gero and anyone I forgot(sorry) you want in on
this?

Second thought - magnet on a chain link as a reference point in the loop.

Constant Chain Tension System -

Thank you

#9

Not sure I can envision this… How would longer chains affect sag and elongation through wear and stretch? Wouldn’t they add to it?

#10

I am envisioning a chain that goes from some fixed point, around an idler at an upper corner, through an idler at the sled and then back up to the motor also in the corner area. I may have your idea all wrong, but I will comment on my interpretation.

  1. The idler in the corner does virtually nothing. As the sled moves around, the chain wraps and unwraps around the idler, slightly changing the chain length.
  2. Doubling the chain will effectively halve the speed of the motor and double the torque. This will help if you have a heavy sled, but remember that the Maslow is prettty slow already.
  3. You would still want a triangular kinematics setup for accuracy.
#11

I could see that to figure out if the chain is where you think it is. However, usually the reason you don’t know the chain location is because the chain has skipped on the sprocket. In that case, the cut is ruined anyway.

What’s your use case?

1 Like
#12

Constant tension on which side of the sprocket? On the slack side, well, that’s what the milk jug is for. On the sled side, the tension has to vary to balance the forces.

I feel like I’m pooh-poohing all your ideas, something I hate to do, because I want to encourage people to freely share their ideas without fear of rejection. On the other hand, the vast majority of ideas don’t pan out, regardless of who came up with them. You usually have to go through a lot of them before you hit on “the one”. So keep slinging them, Bee!

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#13

a loop doesn’t work, the loop would need to be a different length if the sled is in the center vs the corners

draw a loop with the motor on the top left and the sled in the bottom left and top right vs the center. look at the length of the chain in these three cases.

#14

The idea here and I don’t have a clear picture myself is the chain is a loop, think 8 track tape. As a loop, floating in a big circle you no longer are fighting with “slack” because it’s all the same. Forget for a moment what we are doing. Think of a belt on a 3D printer, it might have tensioner but they don’t have a Slack and uptake. Imaging one Axis instead of 2 the router is a link in a band of chain. I will try to come up with graphic at some point. But I wanted to see if some other minds would see it too and improve on it. I’m fine with being shot down. I’m egoless in this arena. I’m here to further the cause, if I skin a knee in the process so be it. I value your input.

Thank you

#15

The magnet is Indexing, at each start up you seek a known point. The mass has to be a big enough loop to reach all points, it requires two loops that probably pass behind the work area and cross over each other without interference. Again if you are not old enough to know what an 8 track tape is look it up. We are using a cassette tape at the moment, that means reaching an end, you must rewind, there are 2 sides of the sprocket if either side encounters a problem it is reflected on the opposite side. In a loop the loop even if long and complex remains constant until it breaks.

Thank you

1 Like
#16

I see advantage about four motors and in fact even 4 - 8 ?! Just look at the octa-drones. the difference is, we have a feedback loop on Maslow motors not like the stepper motors, hence the logick should know every step each motor take. In my view (but am far from expert in coding) the code could be configured for number of motor?! It would allow for more thinkering too! You would only need to add more motor controllers and use more inputs for feedback but one arduino should be sufficient.

I am too in favour of tabletop orientation and also timing belts -much lighter than the chain.

Cheers

#17

theoretically you are correct, in practice you are wrong. If we knew the right
number of steps for the motor to take, we would have perfect accuracy today.

The reason we don’t have perfect accuracy is that our model doesn’t quite match
the real world.

With the 2-motor maslow design, when we are off and the chains are shorter than
they need to be, the sled is in the wrong place.

However, with a 4-motor design, when one chain/line is shorter than it’s
supposed to be, it pulls against one or more of the rest before it can move the
sled. This can tear the machine apart if the error is too large.

I’ll say again that if you want tabletop orientation, you should really look at
building a gantry style machine. That’s going to be far simpler than a 4-motor
machine, and can be built with just slight modification to existing firmware
(like grbl)

David Lang

4 Likes
#18

I am just about starting with the router after having my (own design) CoreXY design 3d printer David. In my view, stepper motors are great for applications with consistent load on their path hence I understand the Maslow idea to have encoders, partly to help correcting ea. missed steps. As I said earlier, i am not great in the coding side but understand that the encoders return each step to the controller hence the slack, tension and PID settings could benefit from the these feedback?!
I could also imagine a giant (like on your garden lawn) 4 motor setup where the errors caused by undesired tensions are relatively minimized.

Istvan Toth