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Which is the better gear transmission ?


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#1 MarkusOSX

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Posted 11 November 2012 - 12:05 AM

Hi folks,

short question plz:

Which is the better, more stable gear transmission?
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I guess the yellow, right ?

Greetz

Markus
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#2 dandexter

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Posted 11 November 2012 - 12:10 AM

As far as I know the 'yellow' gears would be stronger/less likely to spill or come off the axle.

#3 Sariel

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Posted 11 November 2012 - 12:42 AM

Knob gears, obviously. They don't snap.
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#4 D3K

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Posted 11 November 2012 - 01:05 AM

I would imagine that especially for the steering of your 8x8, you would be better off with the knob gears, as slippage of the bevel gears you currently use, would probably make the four linear actuators to become misaligned..?
That was actually a thing I noticed when I looked over your render of the new steering system;-)


#5 Alasdair Ryan

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Posted 11 November 2012 - 01:46 AM

The knob gears are better in a gear transmission.
The small bevel gears should be used were you need to change direction that does not have high torque going through them like in linear actuators.
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#6 pluto7443

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Posted 11 November 2012 - 01:48 AM

Yes, definitely the knob wheels. I've snapped the others before, inside a differential. Of course, that was with 3 NXT servos :blush:

#7 Alasdair Ryan

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Posted 11 November 2012 - 01:50 AM

 pluto7443, on 11 November 2012 - 01:48 AM, said:

Yes, definitely the knob wheels. I've snapped the others before, inside a differential. Of course, that was with 3 NXT servos :blush:

Hence why some of us make our own differentials using knob gears........ :laugh:
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#8 Phoxtane

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Posted 11 November 2012 - 02:00 AM

 Alasdair Ryan, on 11 November 2012 - 01:50 AM, said:

Hence why some of us make our own differentials using knob gears........ :laugh:

In fact, "The Nxt Step", a Lego NXT blog, put up a post recently on how to make heavy-duty differentials: http://thenxtstep.bl...ntial-just.html
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#9 Alasdair Ryan

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Posted 11 November 2012 - 02:10 AM

 Phoxtane, on 11 November 2012 - 02:00 AM, said:

In fact, "The Nxt Step", a Lego NXT blog, put up a post recently on how to make heavy-duty differentials: http://thenxtstep.bl...ntial-just.html

Yeb we also saw some on here too.....Idea 1 Idea 2
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#10 timslegos

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Posted 11 November 2012 - 02:12 AM

As explained in Sariel's book, the knob gears do have a tendency to wear down much faster as well as not transmit power at a constant rate (because only 4 spokes).

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#11 sama

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Posted 11 November 2012 - 02:44 AM

Knob gears are used if you are inputting a large amount of force and you need to exert a lot of force (transmission for slow crawlers) because they don't break or slip but the 12t bevel gears are used for smaller application (quick cars or lifting light loads). However, there is a lot more friction in the knob gears than the 12t bevel gears.
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#12 jorgeopesi

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Posted 11 November 2012 - 02:54 AM

 sama, on 11 November 2012 - 02:44 AM, said:

Knob gears are used if you are inputting a large amount of force and you need to exert a lot of force (transmission for slow crawlers) because they don't break or slip but the 12t bevel gears are used for smaller application (quick cars or lifting light loads). However, there is a lot more friction in the knob gears than the 12t bevel gears.

Completely agree.
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#13 Front

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Posted 11 November 2012 - 08:15 AM

The "knob gears" also gives a highly uneven output rotation, with four cycles of rotation variation, overlaying the input translation.

In the same way as a chain on a chain wheel has a "polygon effect" giving uneven rotation. For chain wheels with more than about 15 teeth, the effect is minimal.

#14 MarkusOSX

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Posted 11 November 2012 - 08:31 AM

 D3K, on 11 November 2012 - 01:05 AM, said:

I would imagine that especially for the steering of your 8x8, you would be better off with the knob gears, as slippage of the bevel gears you currently use, would probably make the four linear actuators to become misaligned..?
That was actually a thing I noticed when I looked over your render of the new steering system;-)

First thx for all the answers.

I'm thinking about to use the knob wheels for transmission, not for steering. The steering of my 8x8 works really well with the bevel gears.

Greetz

Markus
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#15 skppo

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Posted 11 November 2012 - 10:18 AM

 D3K, on 11 November 2012 - 01:05 AM, said:

I would imagine that especially for the steering of your 8x8, you would be better off with the knob gears, as slippage of the bevel gears you currently use, would probably make the four linear actuators to become misaligned..?
That was actually a thing I noticed when I looked over your render of the new steering system;-)

The acuators built in clutch can cause this too.
I guess going full lock would fix it if it were a big problem.

#16 allanp

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Posted 11 November 2012 - 10:52 AM

I don't like knob gears due to their uneven power transmission, innefficientcy, uglyness and lack of realism. I have never used them in a MOC.
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#17 Zblj

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Posted 11 November 2012 - 12:55 PM

I wouldnormally  use a 12:20 or 12:12 transmission, and not knobs. Also dpends on speed. If its a low speed high torque tranmsission thank knobs may be used, but for high speeds I woul deffinatelly use normal gears, because the knob wheels dont spin smoothly at all!

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#18 hrontos

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Posted 11 November 2012 - 02:08 PM

If you have enough space for knob wheels, but you do not want to use them because of what was written here, use largest possible bevel gears.
Small and larger bevel gears have the same shape of teeth, so they snap at the same certain force applied on tooth.
When input torque is given, force applied on each tooth depends only on the diameter of the wheel.
This means, that for smaller gears this force is larger and for larger is smaller. So for 20 tooth bevel gear the force applied on each tooth is 12/20 compared to 12 tooth bevel gear. Which is 60%, a bit more than a half of the force present in case of 12 tooth gear.
As a consequence, you have almost double chance of snapping to occur with 12 tooth than with 20 tooth bevel gear.

#19 Ape Fight

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Posted 11 November 2012 - 02:29 PM

 Sariel, on 11 November 2012 - 12:42 AM, said:

Knob gears, obviously. They don't snap.

They do : (

But yes, they are stronger, although less smooth in their power delivery (as they only have 4 teeth vs the many on most other cogs)

#20 F0NIX

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Posted 11 November 2012 - 03:25 PM

To get a strong but still smooth power delivery you can use these old gears:
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They are though and have more teeth that make the transfer smoother. But they are a bit hard to get hold on (probably expensive too). I have some from my childhood. I have the red (9T), the blue (15T) and the yellow (21T).
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#21 Erik Leppen

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Posted 11 November 2012 - 08:15 PM

Gear up, then go around the corner, then gear down. That way, there is less torque on the bevel gear transmission. Spur gears can handle more torque, if they're not 8t's ;)

...just to give an idea that hasn't been mentioned before in this topic :)

#22 Tadej

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Posted 12 November 2012 - 12:40 AM

Gearing up and then down is a good idea if you have the space for that.

#23 kieran

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Posted 12 November 2012 - 03:56 PM

The other issue with changing the torque using gears all over the place is that you increase friction in the drive chain and as such limit the total machinable power delivered to the wheels, but as you say Erik this is a novel solution that may work out. In any case it will be less lumpy than using knob gears



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