Is this a bug, or do I need to adjust my thinking about gear ratio constraints?

[Ken226]

Sprocket 1 is the 60 tooth camshaft sprocket and gear 2 is the 30 tooth crankshaft sprocket. Logically, I should be setting gear #1 (60t) to .5 rotations for each rotation of gear 2 (30t). But, when I set it that way, the camshaft sprocket rotates twice per crankshaft rotation.

To get the correct ratio, I have to set gear 1 to a full turn per half revolution of gear 2. That seems exactly backwards, or am I thinking about this wrong?

 

[HaroldL]

I notice that too and thought it odd that it seems like the ratio has to be entered in reverse. I made a short video to illustrate, maybe Support can shed some light on this. As I note in the video, Help is not clear which gear is #1 or #2, I suppose it depends on which one is picked as the driving and which is the driven but that is not clarified.

What Is Wrong With Gear Constraints.mp4

Shared from Screencast.com

www.screencast.com

Here's what the Help has:

 

[idslk]

Hello Colleagues,

sorry typo made a rough gear and wheel 1 has to be turned 2 times for one round of wheel 2:
corrected: made a rough gear and wheel 2 has to be turned 2 times for one round of wheel 1:



Regards
Stefan

 

[Ken226]

Hello Colleagues,

made a rough gear and wheel 1 has to be turned 2 times for one round of wheel 2:

View attachment 35956

Regards
Stefan

Yes, that's what had me scratching my head.

In a real world gear set, if wheel 1 were turned 2 times, then wheel 2 would have turned 4 times.

 

[albie0803]

So it seems which ever gear is nominated as Gear 1, enter the number of teeth it has in the Ratio Gear 1 box and the same for Gear 2.
The Ratio label maybe needs to be changed to "Number of Teeth" which would clear up what value is required.

 

[idslk]

Yes, that's what had me scratching my head.

sorry i had a typo above and corrected it, please try package to test

 

[Ken226]

So it seems which ever gear is nominated as Gear 1, enter the number of teeth it has in the Ratio Gear 1 box and the same for Gear 2.
The Ratio label maybe needs to be changed to "Number of Teeth" which would clear up what value is required.

That would make sense and avoid any confusion.

sorry i had a typo above and corrected it, please try package to test

Thank you.

I got everything working as it should be now, I didn't realize it was asking for a tooth count rather that a turn/turn ratio.

 

[HaroldL]

The Ratio label maybe needs to be changed to "Number of Teeth" which would clear up what value is required.

No it wouldn't. What about pulleys? They have no teeth so you still need ratio. It just needs to be clarified what to enter where and Help is sorely lacking that information. Once you figure it out then it's fine but for someone new to the tool it is a bit confusing.

With Stefan's example I was able to get the same results by changing the number of teeth to a ratio. And my previous example has no teeth either so....

 

[albie0803]

Oh you're right, I forgot that constraint applied to pulleys as well. Maybe make the label "Ratio / Gearteeth"

 

[Ken226]

Or two sets of fields perhaps, where entering data in one set of fields grays out the other.

Gear 1 tooth count __ / gear 2 tooth count __

And

1 revolution of gear 1 = ___ revolutions of gear 2. For an actual ratio of turns per turn, there only needs to be one data point.

 

[HaroldL]

It just needs to be clarified how to enter the ratio. Is it "turns' of gear #1 to "turns" of gear #2 as in 1:2 or is it reversed which is seems to be, i.e.: 2:1

When you're designing your gear sets how do you specify the gear ratio? Do you use the number of teeth or the rotation? In the post that you're helping out with a gear set I see that you are working on the number of teeth but the end result you are working toward is a ratio. It should follow industry norms and not "invent" something new.

 

[albie0803]

They are related but not the same. 40T/10T has the same 4:1 ratio as 80T/20T but would produce different sized gearboxes.

In this case its all about knowing what value the equation is looking for to give the result that you want first time. The labels need to be clear as to what is expected.

 

[HaroldL]

In this case its all about knowing what value the equation is looking for to give the result that you want first time. The labels need to be clear as to what is expected.

I entered a Support ticket on this subject and hopefully we'll get an answer to clear up what data goes where in the Ratio fields. And have Help updated as well.

 

[DavidJ]

The fields expect Pitch Diameters (applicable to gears and pulleys). This is clearer if you look at the UI for the Rack option. For gears you can use tooth count - (you can actually use any numbers that follow the correct ratio).

It seems that some people naturally think in terms of speed or turn ratio, rather than diameter or teeth ratio. Neither is wrong, they are just inverse of each other.

A small wording change has been made in the Help. A request has been logged to make the labelling of the fields in gear/pulley constraint consistent with those for the rack.

 

[HaroldL]

@DavidJ, Thanks for clarifying the Help and putting in the labeling request. Now that I know what is expected it won't be a mind-bender when I use the gear constraint.