Manual stepper

[4odonates]

I would like to build a manual stepping focus rail using plastic toy gears and parts from either K'NEX or LEGO. My goal is to be able to manually turn a focus rail in 1 micron increments, similar to the "Walls-O-Stepper" created by Allan Walls. Problem is I have no idea where to begin. Can anyone offer advice that will help me get started? Thank you! Related Resource: https://youtu.be/bPE2eigu8C0

[physicsmajor]

Allan has done a lot of great work, but the project you're looking at is likely not fully generalizable to LEGO. K'NEX is probably not even worth considering.

LEGO has incredible tolerances, claims vary but what I read is somewhere around 2 microns. The problem is that tolerances stack in a mechanical system, so your ultimate system capability will be far worse than that. Worse, the mechanical parts in LEGO are designed to have very little friction for unlubricated use, and thus will have substantial backlash in any standard/legal build configuration. This backlash will get worse and worse as you iteratively gear down. Allan's mechanism uses some sort of scavenged plastic gears to do a good gear reduction, but note he has added spring tension to try and reduce backlash.

Beyond that, if you were looking to make the whole system out of LEGO the carriage and "rails" would end up being quite problematic.

What is your budget, and how long of travel do you need? I ask because there are surplus mechanisms available inexpensively which would leapfrog all of this and immediately give you micron level precision and far more capability. This stage in particular has 3.3" of travel, dual linear rails with 2 carriages each, comes with a stepper and quality leadscrew, an optical limit switch, and even a 0.5 micron Hall effect linear scale mounted and ready to go. The stage itself is even tapped for 1/4"-20 (standard Imperial tripod mount thread). For under $100 shipped in the US, this might be similar in price to the pile of LEGO parts you'd need but is superior in every way:

https://www.ebay.com/itm/274638872477
https://www.ebay.com/itm/374278141465

I have personal experience with this stage and like it so much I bought a 2nd as a spare. The only reason this is being sold so cheap today is because it was scavenged from a now-obsolete gene sequencer.

[phansen39]

Legos not gonna work.
Look at something like this.
https://openbuildspartstore.com/v-slot- ... ead-screw/
To get to um stepping it needs a leadscrew. .
For example with this stepper motor.
0.9 stepper motor.
https://www.amazon.com/STEPPERONLINE-Bi ... B00PNEQMLY
and this type of stepper driver at 16 micro stepping.
https://www.amazon.com/OctagonStar-Step ... ter&sr=8-5
Would give you 3.2 steps per um.
with the above 0.9 motor and a better stepper driver. at 256 micro stepping could give 51.2 steps per um. This would be a bit much.
something in between could be picked.

Also needed a small arduino, 12v power 2-3 amps and sothing to control it. buttons, encoder etc.

All that said you can buy it cheaper.
https://www.ebay.com/itm/204115302832?h ... SwYMxiiv0t

[chris_ma]

For example with this stepper motor.
0.9 stepper motor.
https://www.amazon.com/STEPPERONLINE-Bi ... B00PNEQMLY
and this type of stepper driver at 16 micro stepping.
https://www.amazon.com/OctagonStar-Step ... ter&sr=8-5
Would give you 3.2 steps per um.
with the above 0.9 motor and a better stepper driver. at 256 micro stepping could give 51.2 steps per um. This would be a bit much.
something in between could be picked.

from all I've read and from some basic test of myself, microsteps will only get you so far with accuracy. In what I've seen most setups will suffer from non-uniform step size once we go into higher micro stepping.

I also doubt that the ebay linked rail will truly get 1um accuracy.

[physicsmajor]

from all I've read and from some basic test of myself, microsteps will only get you so far with accuracy. In what I've seen most setups will suffer from non-uniform step size once we go into higher micro stepping.

I also doubt that the ebay linked rail will truly get 1um accuracy.

The stage I linked I've tested better than 2 um precision with the included 1.8 degree stepper, and that's the lowest I have bothered to set the tolerance in my closed-loop control. My crude closed-loop control might oscillate if I set it too low. If I swapped it out for a 0.9 degree stepper, I have no doubt it could achieve 1um.

The quadrature Hall effect scale on that unit measures actual stage position relative to the base, allowing true closed-loop positional control. Any other effects can thus just be corrected, unlike the vast majority of alternative systems.

[chris_ma]

The stage I linked I've tested better than 2 um precision with the included 1.8 degree stepper, and that's the lowest I have bothered to set the tolerance in my closed-loop control. My crude closed-loop control might oscillate if I set it too low. If I swapped it out for a 0.9 degree stepper, I have no doubt it could achieve 1um.

hi,
yes the parker stages look fantastic and I remember an old thread where there was more info about it, I'm tempted to get one myself, but shipping to europe is a bit of a hassle.

I was talking about the other ebay link:

All that said you can buy it cheaper.
https://www.ebay.com/itm/204115302832?h ... SwYMxiiv0t

sorry for the confusion.

[lothman]

I was talking about the other ebay link:

All that said you can buy it cheaper.
https://www.ebay.com/itm/204115302832?h ... SwYMxiiv0t

sorry for the confusion.

I agree that this will not consistently achieve 1µm resolutuion, but it is still superior to a Lego solution at a very affordable price.