Motor gears stripped

kits are for sale again! yay!

I’m working on a counterweight setup right now. Id love to see what other people come up with. hurry up and buy one while you can! @2cents :grin:

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Hi dlang!

I don’t have this setup and I’m unfamiliar with the problems you guys are having.
Can you please elaborate on the problems you encounter when the sled is high on the board?

I know as high the sled gets, the more force the motors need to keep pulling
it up, as closer the sled is from the same height of the sprockets harder it
is for the motors, to the point that the motors will be pulling against each
other.

the motors are pulling against each other in the top center, and they can only
pull so hard. In addition, motors have the most torque when they are stalled, as
they move faster, they have less power.

So we’ve had cases where when you are cutting along the top, the motor closest
to the sled can’t keep up and the cut droops (and then hooks up at the end of
the cut when the far motor stops moving)

But if you add weight to the sled AND compensate it on the counterweight side,
you’re not adding any extra load to the motors, besides the extra side load on
the sprocket that i mentioned before.

do the math, the load on the motor is different depending on the chain angle far
more than the weight, adding weight to the sled significantly increases the load
on the motor high on the workpiece (the tension the motor puts on the chain has
to be split into a horizontal and vertical component, with the vertical
component matching the weight of the sled, if you add weight to the sled, you
have to add a LOT of weight the other side of the motor to compensate)

Counterweights are used everywhere, it’s a simple and effective way to reduce
loads, think of how a building elevator works. The weight of an empty elevator
is compensated on the counterweight side, and the motor is only lifting the
weight of the load in it (cargo, people, drag…).

they are not used at varying angles like this. the maslow doesn’t just lift up.

In the case of the sled, the tension of the chain is never reduced, the sled
still weights the same, chain still have the same tension and gravity still
pulling it down the same way, the sprocket is the one that has to deal with
the increased side weight due to the fact you are doubling the weight on it,
but you are also reducing the force the motor need to lift the sled due to the
counterweight, everything else still the same.

no, the tension on the chain is very different in the top center and the near
bottom corner and the far bottom corner.

In the top center, the chains are at an angle near horizontal, so since the
vertical component of the tension on the two chains is always going to be the
same, but with a stock setup, the tension on the chain can vary from ~3 pounds
of force to ~40 pounds of force.

if you add 40 pounds of counterweight, you have -37 pounds to deal with at the
low tension point (the far bottom corner), and if you have 3 pounds of
counterwight it makes effectively no difference in the high tension point.

I have no experience with step motors, but since it is worm geared, how can it rotate in any direction without being commanded by motor side?

all gears have some clearance and can be ‘wiggled’ a smidge. The maslow gearbox
is a worm gear followed by 4 stages of gear reduction, so there are a bunch of
places with a few thousanths of an inch of wiggle, and the wiggle on the worm
gear is multiplied by the remainder of the gear train (60:1 or so), and this
only gets added to by the other gears

As I said before, just came across this wonderful project two days ago, so excuse my ignorance on this, unfortunately there are no kits for sale so I cannot experiment.

kits are for sale again.

David Lang

I’m new here too and haven’t built my Maslow yet.I also haven’t cracked open a physics book in nearly 20 years so I’m sure my understanding of the issue is pretty vague. I’ll apologize if I’m way off on the topic of counterweights.
Trying to relate this to ‘real world’ examples of things that have counterweights and move in more than 1 axis at a time and I am coming up with a pretty short list. This youtube video however might offer some with a hint however: https://www.youtube.com/watch?v=rCsznpp4bsA Applying this to Maslow, I would think that the current counter weights need to move along the z-axis. The z-axis however might not be the same as the sleds cutting z-axis, it would the z-axis of the force of the current x-y axis. Everyone seems to be keeping them flat with the cutting surface thus far, which is making their force act like an elevator, when the sled is moving in a completely different manner.

no need to apologize, the entire maslow is a “experts say that won’t work”
project, and it was put together without any formal analysis of the math or
optimization beyond “this looks reasonable, and it works”

It’s only after it started shipping and the community built up that we really
started digging into things, and everyone here has advocated something that we
have later found wasn’t the best option (because we have better options in place
now that work)

so it’s not a matter of trying to beat anyone down, it’s a matter of trying to
educate. I can reply in a short time with a text reply, but if I need to draw
something the reply may be delayed months :slight_smile: so I apologize that I am less
clear than I could be.

David Lang

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Hi David

I think this is getting non constructive.

I don’t get your point here, as i said in my first post:

I know the load the router put on the gears is greater as it gets higher on the board, so ideally the counterweights would need to became heavier as the router gets higher to maintain a perfect balance, but even if we can not find a way to do this, I believe we still are taking a lot of forces out of the original motor/gears using counterweights.

Or in my second post:

“I know as high the sled gets, the more force the motors need to keep pulling it up, as closer the sled is from the same height of the sprockets harder it is for the motors, to the point that the motors will be pulling against each other.

I get it, but that does not mean you can’t use counterweights to relief some of the load on the motors.
Remember to objective here is to relief load on the motors to avoid damage the gears.

Again, I get the part that the load is variable and so is the chain tension, when I said everything is still the same (weight, tension…) I was trying to communicate that adding counterweights won’t change anything on the sled side.

I’m apologize, maybe i didn’t write it clear enough, maybe i should’ve wrote " everything stays the same at the sled at any given chain angle as it was before adding counterweights at the same given chain angle"
Is that clear now?

I don’t think there is wiggle on the worm gear when it’s spinning, only when it’s a 0 load.
The fact that you have “a bunch of places with a few thousanths of an inch of wiggle” doesn’t mean you will multiply that for every teeth of the gears, since are only 4 gears (8 tooth) contacting at any given time.

Also this dosen’t explain your post saying:

"at which point the output sprocket will rotate the wrong way (or fail to rotate the right way) until the backlash ofevery gear in the gear chain is taken up"

Just thinking…if you have +/-3 pounds at the lower point and +/-40 pounds at top (per your numbers), taking in account there is a max load on the motors before the gears start grinding themselves, adding a 20 pounds counterweight wouldn’t it leave us with a +/-20 pounds max load ON THE GEARS?

Isn’t 20 pounds load on the motors better than 40?

Before you point it, Yes… i know there will be -17 (negative) pounds on the sprocket at the sled lower point, until the sled reach some height passing 0 pounds and then increasing up to +20 at the top.

As a side note, i know you don’t like the idea of adding weight to the sled (as long as it is compensated on the cw side), but i believe this will also help with the horizontal axis stability, of course if the speed of movement is to high we my have kinetic problems, but it can be solved by trading speed for reliability.

Again, as i said before I came across this project and this post by chance, and from the top of my head I post a possible idea to solve the gears problems that I read you guys are having, but… it’s just an idea, I don’t mean to impose or push my ideas over anyone’s else.
I understand what you are doing, by pointing my misunderstanding of this contraption, you are helping others to avoid try this solution and waste their time. And i thank you for that, even if I don’t agree with your conclusions.

What are your ideas to fix this problem?

Just thinking :slight_smile:
Maybe the easiest and cleaner solution would be, bigger and better motors with correct shield and tweaking the software to the new steppers.

well, that didn’t work by e-mail let me cut-n-past it in here

On Fri, 13 Jul 2018, 2cents wrote:

I don’t think there is wiggle on the worm gear when it’s spinning, only when it’s a 0 load.

The fact that you have “a bunch of places with a few thousanths of an inch of wiggle” doesn’t mean you will multiply that for every teeth of the gears, since are only 4 gears (8
tooth) contacting at any given time.

Also this dosen’t explain your post saying:

"at which point the output sprocket will rotate the wrong way (or fail to rotate the right way) until the backlash ofevery gear in the gear chain is taken up"

you have teeth like

------------
\/\/\/\/\/\/
\/\/\/\/\/\/
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fitting together, the teeth on the top don’t make contact with the teeth on the bottom on both sides of the teeth. If you are applying force to the top one pushing to the right, you will
only make contact between the right side of the top tooth and the left side of the bottom tooth, there will be a tiny gap between the left side of the top tooth and the right side of the
bottom tooth. This gap is called the backlash of the gear.

If you then start to move the top one to the left, the bottom one will not move immediately (assuming no load on anything), the top will move until that gap is taken up.

In normal maslow operation this is not supposed to matter because there is always load on the geartrain from the weight of the sled, so when the top starts moving left, it doesn’t take
up the gap, as soon as the top starts to move it allows the bottom to move.

however, if you change the load on the bottom one, so that instead of being loaded towards the left, it starts being loaded towards the right, you will either see the bottom suddenly
shift until this backlash is taken up. If this is a gradual change as the motor moves, you will hit a period where the bottom one doesn’t move until the top gets in contact with the
other side.

This happens on all gears (even worm gears) as the load on the gear goes through zero and reverses direction.

each of the 5 stages of contact will have this play, and the play will get multiplied by the gear ratio of the other stages between the the side that moves and the worm gear that can’t
be back driven.
This isn’t much, and unless the gear train is a bit worn, it’s hard to see by hand, but if you were to attach a lever to the shaft you would be able to wiggle it back and forth a little
bit. And this little bit can affect your accuracy.

I’m actually starting to think that the stock bungee is causing problems here as it applies the most force when the chain is most extended, which is when the chain tension is the lowest.
This is probably throwing off our calibration and limiting our accuracy.

Just thinking…if you have +/-3 pounds at the lower point and +/-40 pounds at top (per your numbers), taking in account there is a max load on the motors before the gears start
grinding themselves, adding a 20 pounds counterweight wouldn’t it leave us with a +/-20 pounds max load ON THE GEARS?

Isn’t 20 pounds load on the motors better than 40?

Before you point it, Yes… i know there will be -17 (negative) pounds on the sprocket at the sled lower point, until the sled reach some height passing 0 pounds and then increasing up
to +20 at the top.

the problem I’m pointing out is that as you pass 0 the motor moves but the chain won’t, so there will be a loss of accuracy as you pass this point. If you knew exactly where this was,
you could compensate for it.

It’s not unknown for CNC machines that use lead screws to know this amount and rotate the screw an extra amount as it reverses direction, but in our case it’s not as clear that we will
know exactly when this happens.

If we had a high res encoder on the output shaft, instead of a low res encoder on the motor, this wouldn’t matter as we would be positioning based on the output shaft and would
compensate for this error.

As a side note, i know you don’t like the idea of adding weight to the sled (as long as it is compensated on the cw side), but i believe this will also help with the horizontal axis
stability, of course if the speed of movement is to high we my have kinetic problems, but it can be solved by trading speed for reliability.

I’m not sure that adding weight will help as much here as you are thinking, but we are both speculating.

Again, as i said before I came across this project and this post by chance, and from the top of my head I post a possible idea to solve the gears problems that I read you guys are
having, but… it’s just an idea, I don’t mean to impose or push my ideas over anyone’s else. I understand what you are doing, by pointing my misunderstanding of this contraption, you
are helping others to avoid try this solution and waste their time. And i thank you for that, even if I don’t agree with your conclusions.

What are your ideas to fix this problem?

Remember that there are 4-5 thousand maslows out there and there have been fewer than a dozen people who have had problems, this doesn’t seem to me to be a big problem (it seems like a
bad batch of gears got into the supply chain), but I would fix it by getting bigger, beefier motors and gears, not with counterweights.

yep (although a technical nit, these are DC motors with encoders, closed loop
knowing the actual position rather than steppers which are open loop in that you
know what you told them to do, but don’t know for sure that they did it)

Hi

This is exactly what i mean when i said "I don’t think there is wiggle on the worm gear when it’s spinning, only when it’s a 0 load."

You are absolutely right on this, I did not think of that.

I see your point, and you’re probably right, the thing would be to try this out to see how much those thousand of an inch affect accuracy, and maybe see if it is worth going in this counterweight direction just to save gears from worn out, at the end of the day is just a patch to undersized motors.

Thank you for taking the time to work with my ideas. :slight_smile:

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image

Our second Maslow, motors original from Kickstarter but only used last two months, had same failure after cutting a lot these past weeks. We already purchased a replacement from store and back up and running. FYI Top frame, chains go under to sled, 9lb counter weight system for slack in middle.

But wondering how we could get a plastic gear replacement, and if we can prevent going forward?

etomn motors said the maslow motors are only rated 30kg.cm, even though their website states they are rated at 50kg/cm.
When I told them this they said the motors that Maslow uses are not listed on their web site.
I guess they want me to believe that two gearbox motors with the exact same specs, rpm, etc have different torque values and the one people are having problems with just happen to not be on their web site?
Sounds fishy.

" The reason for the RPM question was to see if possibly changing to the black motors with the brass gears would introduce a high duty cycle situation where the now fanless motor would overheat. "

I’m pretty sure the stock maslow motors are not brushless.

one can buy clip on aluminum fans for motors.
not sure if this is exact size, but looks close
https://www.aliexpress.com/item/For-RC-Car-Aluminum-alloy-1-10-Heat-Sink-540-550-Modified-Motor-Cooling-Fan-7014/32853730268.html?spm=2114.10010108.1000013.1.7a444afcm8cHOT&gps-id=pcDetailBottomMoreThisSeller&scm=1007.13339.90158.0&scm_id=1007.13339.90158.0&scm-url=1007.13339.90158.0&pvid=73d86c26-cc53-4ad0-a212-79ac13799560

no, they are not, they are standard brushed motors.

David Lang

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so what happens when the brushes eventually wear down and need replacing? those motors don’t look very user servicable?

Right now - A rebuild them anyway, B design and build a better more serviceable body and migrate the parts, C buy a replacement in the Maslow store, D design and produce a better motor.

Etomn sells brushless version of the same exact gear motor. they are about $5 to $8 more. Seems like in the long run worth the investment. I just dont’ know how complicated the wiring comes with a brushless motor? I know they need 3 wires and a controller to make the ac pulse that the brushes used to make? not sure if that is integrated or seperate.

they aren’t, you just replace the motor.

David Lang

Which means taking apart the entire gear box and hoping the motor is attached with botls not rivets .
Wonder what is the life expectancy of the brushed motors in hours/days?

the brushless motor requires a very different controller board, and something
with a lot more processor than what we are using.

you may want to look up odrive for an example of using brushless motors (it’s
MUCH higher power than what we are using)

David Lang

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quite a long time. it’s the gears that wear out, LONG before the brushes.

think months to years of service life

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