<p>This modification won't change the rate of reduction.</p>

<p>You can calculate the ratio of the angular velocities of two adjacent gearwheels as</p>

<p>i12 = w2/w1 = n1/n2</p>

<p>where w is the angular velocity and n is the number of teeth of the gears. Hence the original reduction reads as:</p>

<p>i12*i23*i34*i45*i56 = 12/20 * 16/16 * 20/28 * 12/20 * 12/20 = 27/175 = 0.1543</p>

<p>while the modified is:</p>

<p>i12*i23*i34*i45 = 12/20 * 12/20 * 20/28 * 12/20 = 27/175 = 0.1543</p>

<p>What you did is you simply removed the 16/16 and replaced the 12/20 gears, which results in the same reduction because the order of the multiplication is arbitrary.</p>

<p>To the second question:</p>

<p>You can change the 12-20 gears to 16-24 ones to fit the increased distance. In this case, the new reduction is</p>

<p>i12*i23*i34*i45 = 16/24 * 12/20 * 20/28 * 12/20 = 6/35 = 0.1714</p>

<p>Note that the new gears may intersect parts not shown in the figures.</p>

CC BY-SA 4.0
2018-06-19T10:56:11.920Z
2018-06-23T07:40:20.580Z
2018-06-23T07:40:20.580Z
BalazsToth
<p>If the only change is replacing the two 16-tooth gears with a 12-tooth gear and a 20-tooth gear, then you will <strong>reduce speed</strong> by a factor 12/20 and <strong>increase torque</strong> by the same factor.</p>

<p>If you want to increase the distance between gears by 1/2 stud, then you can experiment with using bigger gears and offsetting the motor sideways so the gears don't touch vertically. This may induce some play in the gears.</p>

CC BY-SA 4.0
2018-06-22T05:44:31.533Z
I would drop the portal axles, so the performance will be kept. The reason is for implementing this on other model with less axle height (42069). Well, I did it partially, but using a horizontal transmission and keeping a similar design, with only 2 reductions instead of 3 (as this model has). It performs acceptable - a little faster than 9398, but powerful enough to run over decent obstacles for its tracks. I couldn't find a combination of gears for that 0.5 stud displacement, though. The gears are usually too tight to work safely together.
mike
CC BY-SA 4.0
2018-06-20T07:49:12.220Z
2018-06-20T07:49:12.220Z
ShutterFreak
<p>I am studying implementation of 9398 crawler reduction.
Here is the stripped part, in order to see the gears and their relation - the image is made with the excellent tool which is LDCad.</p>

<p><a href="https://i.sstatic.net/tqTc8.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/tqTc8.png" alt="enter image description here"></a></p>

<p>My idea is to use this Lego design for other model and I need to know how would I calculate the effect of changing it a bit.
My intention is to replace the two 16 teeth gears 94925:</p>

<p><a href="https://i.sstatic.net/CPoY1.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/CPoY1.png" alt="enter image description here"></a> </p>

<p>with a pair of 12 and 20 teeth (32270 and 32269):</p>

<p><a href="https://i.sstatic.net/tg7tP.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/tg7tP.png" alt="enter image description here"></a><a href="https://i.sstatic.net/Kxzbd.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/Kxzbd.png" alt="enter image description here"></a></p>

<p>and to remove the last reduction pairs, the ones in portal axle:</p>

<p><a href="https://i.sstatic.net/p3Hhx.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/p3Hhx.png" alt="enter image description here"></a></p>

<p>so it would be as follows:</p>

<p><a href="https://i.sstatic.net/fIMuL.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/fIMuL.png" alt="enter image description here"></a></p>

<p>Would this become faster/less powerful or slower/more powerful?
My aim would be to keep it pretty close to how it performs now.</p>

<p>Also, is there a way to combine gears in order to add a distance of half of a stud between the motor axle and the next or the second one? In the image below, I have moved the parts and created a gap between the gears, in order to point what I intend to move, but the contact must be assured by some gears, obviously by replacing the existing ones. Would be there possible?</p>

<p><a href="https://i.sstatic.net/emSPZ.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/emSPZ.png" alt="enter image description here"></a></p>

<gears>
9398 reduction change
mike
# 9398 reduction change

(Asked by: username_0 on 2018-06-09)

I am studying implementation of 9398 crawler reduction.
Here is the stripped part, in order to see the gears and their relation - the image is made with the excellent tool which is LDCad.

[![enter image description here](https://i.sstatic.net/tqTc8.png)](https://i.sstatic.net/tqTc8.png)

My idea is to use this Lego design for other model and I need to know how would I calculate the effect of changing it a bit.
My intention is to replace the two 16 teeth gears 94925:

[![enter image description here](https://i.sstatic.net/CPoY1.png)](https://i.sstatic.net/CPoY1.png)

with a pair of 12 and 20 teeth (32270 and 32269):

[![enter image description here](https://i.sstatic.net/tg7tP.png)](https://i.sstatic.net/tg7tP.png)[![enter image description here](https://i.sstatic.net/Kxzbd.png)](https://i.sstatic.net/Kxzbd.png)

and to remove the last reduction pairs, the ones in portal axle:

[![enter image description here](https://i.sstatic.net/p3Hhx.png)](https://i.sstatic.net/p3Hhx.png)

so it would be as follows:

[![enter image description here](https://i.sstatic.net/fIMuL.png)](https://i.sstatic.net/fIMuL.png)

Would this become faster/less powerful or slower/more powerful?
My aim would be to keep it pretty close to how it performs now.

Also, is there a way to combine gears in order to add a distance of half of a stud between the motor axle and the next or the second one? In the image below, I have moved the parts and created a gap between the gears, in order to point what I intend to move, but the contact must be assured by some gears, obviously by replacing the existing ones. Would be there possible?

[![enter image description here](https://i.sstatic.net/emSPZ.png)](https://i.sstatic.net/emSPZ.png)

**Tags:** gears


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## 2 answers

### Answer by username_1 on 2018-06-19. Score: 1 | Accepted answer

This modification won't change the rate of reduction.

You can calculate the ratio of the angular velocities of two adjacent gearwheels as

i12 = w2/w1 = n1/n2

where w is the angular velocity and n is the number of teeth of the gears. Hence the original reduction reads as:

i12\*i23\*i34\*i45\*i56 = 12/20 \* 16/16 \* 20/28 \* 12/20 \* 12/20 = 27/175 = 0.1543

while the modified is:

i12\*i23\*i34\*i45 = 12/20 \* 12/20 \* 20/28 \* 12/20 = 27/175 = 0.1543

What you did is you simply removed the 16/16 and replaced the 12/20 gears, which results in the same reduction because the order of the multiplication is arbitrary.

To the second question:

You can change the 12-20 gears to 16-24 ones to fit the increased distance. In this case, the new reduction is

i12\*i23\*i34\*i45 = 16/24 \* 12/20 \* 20/28 \* 12/20 = 6/35 = 0.1714

Note that the new gears may intersect parts not shown in the figures.


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### Answer by username_2 on 2018-06-20. Score: 1

If the only change is replacing the two 16-tooth gears with a 12-tooth gear and a 20-tooth gear, then you will **reduce speed** by a factor 12/20 and **increase torque** by the same factor.

If you want to increase the distance between gears by 1/2 stud, then you can experiment with using bigger gears and offsetting the motor sideways so the gears don't touch vertically. This may induce some play in the gears.

> **Comments:**
> **username_0**: I would drop the portal axles, so the performance will be kept. The reason is for implementing this on other model with less axle height (42069). Well, I did it partially, but using a horizontal transmission and keeping a similar design, with only 2 reductions instead of 3 (as this model has). It performs acceptable - a little faster than 9398, but powerful enough to run over decent obstacles for its tracks. I couldn't find a combination of gears for that 0.5 stud displacement, though. The gears are usually too tight to work safely together.  

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