# Whats inside the gearbox/motor?

@stuartri

Could you add this to the mechanics section of the Wiki?

Once this is complete can someone take lead to put all of this in the wiki?

Thank you

Bee,

Let me know and I will add what you need.

Stuart

Yes - A link to the video as an educational piece.

I think it’s worth keeping as at some point we should develop an education section aimed at schools to try to spark the students in to making other projects reusing the technology they already know how to use. This explains how the magic happens behind the curtains.

Thank you

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Thanks for that Bee Will do. I will add a detailed explanation of the working of the current worm gear motors into the Maslow Survival Guide as well.

Kind Regards Stuart

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Bee,
I have added in the links to the video and also added two more links that explains how to calculate gear ratio’s as well as understand the torque capabilities of gear trains. It is very we’ll explained.

I put the information in the . The data was added to the Drive Motor Gearbox page. I note that the existing text is referring to a 23:1 gearbox ratio but as this thread has shown it is actually 289.776 and some change lol. Do you want me to amend that as well and put in the actual calculation from this thread.

Regards Stuart

## PUTTING IT ALL TOGETHER

The axis motors have 3 sets of compound gear arrangements with the final stage consisting of a single gear.

The plastic wheel is the worm wheel which is set up in a compound gear arrangement.
The 25 Teeth of the Worm Wheel are driven by the Worm attached to the motor shaft. (Still need a decent picture of worm profile - assumed double start)

Stage 1 - Compound Gear (Worm Wheel plus gear)
Compound Stage 25/10 Teeth

Stage 2 - Compound Gear
Compound Stage 35/9 Teeth

Stage 3 - Compound Gear
Compound Stage 29/18 Teeth

Stage 4 - Single Gear
Single Stage 37 Teeth

Now we can cascade the gear ratio’s to work out the overall reduction ratio from the input shaft of the motor to the output shaft of the gearbox

Reduction Ratio = 25:2 * 35:10 * 29:9 * 37:18
Reduction Ratio = 938875: 3240
Reduction Ratio = 187775: 648
Reduction Ratio = 289.776: 1 [Input to output shaft relationship]

This means that the Input shaft will rotate 289.776 times for one rotation of the output shaft.
This calculation aligns with those previously calculated in this thread

The encoder coupled to the motor shaft is the ET-MY37 and has a resolution of 7ppr (7 Pulses per revolution) and uses quadrature encoding as per the diagram below

Using both Channel A and Channel B we can actually extract 7*4 = 28ppr because each transition is a distinct place in the signal. Multiplying this by the gearbox reduction ratio of 289.776 gives us a final output shaft resolution 8113.728 pulses per revolution.

Kind Regards Stuart

8 Likes

Fascinating thread. I’ve purchased a couple of the alibaba motors that have a high stall current and I’ve failed to make them work witht he maslow shield. So, I decided it probably best to take them apart and learn about the innards. Just looking on the forum for a suitable place to put them, and I discover this most comprehensive thread. I doubt there is much that my pics can add to the commentary, but I’ll post them anyway. One interesting difference is that all the gears in mine are metal and the spacers all brass. I think mine was sold as a 1:280 ratio box, but I didn’t bother counting teeth when I had it open. A word of advice to anyone taking one apart, make sure the front plate of the box comes out of the bottom of the box, otherwise you’ll end up with a lap full of cogs and silicon grease. I ended up taking the second apart to learn how it all went back together! These gearboxes appear quite well made, but I’d question how long any plastic/nylon gears would last if hauling a heavy sled/router around for a while. While apart, I noted that the motor to gearbox mounts were 22mm apart, so it is quite possible to get another motor and mount it to the gearbox. I’ll be keeping these as spares, should I have a gear strip or other gearbox failure.

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Did anyone ever tear the z-motor gearbox down? Have we determined the gear ratio?

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I will dig into mine tonight and take a look.

I disassembled it but only got the final output gear counted. It is a 40 tooth gear. I will post the pictures and if I get to it before anyone else I will post the counts as I can squeeze in the time.

Next gear down the stack

Down again

One More time

The bottom gear in the stack

The drive

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Excellent write up @stuartri! @Joshua brought up the topic of both channels transitioning to high at the same time and what the firmware will do in that case. Have you done any analysis on this (eg. is it possible? If so, how often)?

With Grey Encoding, only one channel transitions at a time, you never have the
case of both channels transitioning (either direction) at the same time.

David Lang

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Hi David, good to hear from you. This is a rotary encoder, correct? I haven’t opened this one up yet (I’ve seen others) but have one on order to tear apart. Is it possible for the switch rings to slip?

There is a single ring with two sensors, they may slip a little bit, but not
nearly far enough to overlap.

David Lang

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@kelly , if you haven’t already I encourage you to read through this thread before buying different motors. One big take away from this thread is that you can’t necessarily trust manufacturer, or amazon reseller, specs on gear ratios ( they probably didn’t count properly and the wrong info continues to spread). If you really want to know you have to take it apart, count the gears, do the math and update your GC settings accordingly; this thread explains that process. Some of the last posts here have info on the z axis gears but the question of the true stock z motor ratio hasn’t been answered, that I know of.

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Hence why my numbers are wack in GC, but it works great! Lol because it is probably not actually 131:1

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@SnailPowered and @dlang, on the above pictures from the z axis, I counted 30/10 teeth on every gear, with the last one on the drive having 12? That doesn’t seem right, although I know nothing about motor gearing. What’s going on here? I’d like to document the true z axis ratio from the stock z motor.

It would be good to see more pictures of the inside of the assembled gear box too.

ratio from the stock z motor I believe it’s 270:1
7 = ppr
4 = cuadrature encoder (rising edge and falling edge per channel)
7560 = default settings for the Z-axis encoder steps per revolution in Ground Control advanced settings.
7560/4/7 = 270

yes I understand how you get there based on the number in GC but it may not be correct (the encoder steps per rev, for x/y motors, in GC used to be wrong until after this thread). I don’t have a spare or else I would take mine apart but don’t want to risk being out of commission!

Think of this, if it’s not 270:1 then the z axis travel wouldn’t be working correctly for anyone using the stock settings with the original motors. It would mess the pitch settings (3.17)