MarkusOSX

Which is the better gear transmission ?

23 posts in this topic

Hi folks,

short question plz:

Which is the better, more stable gear transmission?

8173347493_d8aa320023_c.jpg

I guess the yellow, right ?

Greetz

Markus

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

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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;-)

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

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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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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).

tim

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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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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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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.

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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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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.

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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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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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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.

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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)

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To get a strong but still smooth power delivery you can use these old gears:

g9.gif

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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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 :)

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

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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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