One for the people good at calculating geometric shapes and the like.

I’d like to know the process of how to generate the tri-lobe shape in the picture below. As it spins, the roller bearings on either side move left/right. And by having roller bearings the contact points moves around because the varying ramps on the tri-lobe shape will also move around on the bearings. The difference in the upper and lower radii of the lobes is going to be 69 mm.
Is there some software that I could use?

Ain’t you in the midst of an engineering degree?

Adjust to suit.
You can probably do it in a lot of free stuff.
The free Sketchup might do it, Spiny.

Spiny Norman said:

One for the people good at calculating geometric shapes and the like.

I’d like to know the process of how to generate the tri-lobe shape in the picture below. As it spins, the roller bearings on either side move left/right. And by having roller bearings the contact points moves around because the varying ramps on the tri-lobe shape will also move around on the bearings. The difference in the upper and lower radii of the lobes is going to be 69 mm.
Is there some software that I could use?

Heard of Excel? :)

There’s probably other stuff that would make it easier though. It looks like there is a variable radius in between the curves, so you’d need more details to get exact coordinates.

Peak Warming Man said:

Adjust to suit.
You can probably do it in a lot of free stuff.
The free Sketchup might do it, Spiny.

How did you do that?

The Rev Dodgson said:

Peak Warming Man said:

Adjust to suit.
You can probably do it in a lot of free stuff.
The free Sketchup might do it, Spiny.

How did you do that?

5 minutes in Inventor.

Peak Warming Man said:

The Rev Dodgson said:

Peak Warming Man said:

Adjust to suit.
You can probably do it in a lot of free stuff.
The free Sketchup might do it, Spiny.

How did you do that?

5 minutes in Inventor.

did you pull it?

The Rev Dodgson said:

Peak Warming Man said:

Adjust to suit.
You can probably do it in a lot of free stuff.
The free Sketchup might do it, Spiny.

How did you do that?

ROFL.

The Rev Dodgson said:

Spiny Norman said:

One for the people good at calculating geometric shapes and the like.

I’d like to know the process of how to generate the tri-lobe shape in the picture below. As it spins, the roller bearings on either side move left/right. And by having roller bearings the contact points moves around because the varying ramps on the tri-lobe shape will also move around on the bearings. The difference in the upper and lower radii of the lobes is going to be 69 mm.
Is there some software that I could use?

Heard of Excel? :)

There’s probably other stuff that would make it easier though. It looks like there is a variable radius in between the curves, so you’d need more details to get exact coordinates.

Ta to PWM & Rev.
I can easily draw a shape like that, but the question is not that simple – The shape needs to just touch the two roller bearings all the time as the tri-lobe section spins around. I could do it easily enough (maybe …) if it were just two points that were touching the lobes, but for what I want to use it for I have to use roller bearings and so the contact point between the bearings and the lobes will vary, depending upon the angle of slope of the lobes and the diameter of the bearings.
I could come up with something close by rotating a rough drawing (in CAD) around in something like 5° to 10° increments, but there must be a simpler and more accurate way to do it.

Peak Warming Man said:

Adjust to suit.
You can probably do it in a lot of free stuff.
The free Sketchup might do it, Spiny.

That may not be the right shape. I’ll have to think about it. It could also be that there are several slightly different shapes that fit the criterion, user selectable by varying a parameter. My way would be to calculate the shape on Fortran to get a csv and display it in Excel.

mollwollfumble said:

That may not be the right shape. I’ll have to think about it. It could also be that there are several slightly different shapes that fit the criterion, user selectable by varying a parameter. My way would be to calculate the shape on Fortran to get a csv and display it in Excel.

Why the heck would you do that?

That would be like writing stuff out by hand, scanning it, and doing character recognition, rather than just typing it in.

The Rev Dodgson said:

That would be like writing stuff out by hand, scanning it, and doing character recognition, rather than just typing it in.

my favourite way

I have added a function to draw arcs to one of my spreadsheets, and used it to plot the SNT shape:

You can change the centre of the shape, and the angle.

You can also change the radii, but that doesn’t work properly at the moment.

Download:

IP.xls

See the Arc sheet.

The Rev Dodgson said:

You can also change the radii, but that doesn’t work properly at the moment.

Download:

IP.xls

See the Arc sheet.

Changing radii now fixed.

Same download

Another update:

It now plots a line outside the tri-lobe shape where the sliding bearing centre cannot pass, and calculates the intersections of that line with the x axis.

It then plots a circle at those two locations.

Download:

IP.xls

See the Arc sheet.

The Rev Dodgson said:

mollwollfumble said:

That may not be the right shape. I’ll have to think about it. It could also be that there are several slightly different shapes that fit the criterion, user selectable by varying a parameter. My way would be to calculate the shape on Fortran to get a csv and display it in Excel.

Why the heck would you do that?

That would be like writing stuff out by hand, scanning it, and doing character recognition, rather than just typing it in.

Agree.

The Rev Dodgson said:

Latest (and probably final) update. It now does an animation:

Seems the upload here doesn’t like mp4’s, try the link below.

Download:

IP.xls

Animation animation.mp4

The Rev Dodgson said:

The Rev Dodgson said:

Latest (and probably final) update. It now does an animation:

Seems the upload here doesn’t like mp4’s, try the link below.

Download:

IP.xls

Animation

Excellent work, Rev.

Peak Warming Man said:

Excellent work, Rev.

Took a bit more than five minutes, but it was more fun that what I should have been doing.

The Rev Dodgson said:

Peak Warming Man said:

Excellent work, Rev.

Took a bit more than five minutes, but it was more fun that what I should have been doing.

Ha!

:)

The Rev Dodgson said:

Peak Warming Man said:

Excellent work, Rev.

Took a bit more than five minutes, but it was more fun that what I should have been doing.

I’ve downloaded the file, I’ll check it out and see how you did it.

Many thanks, Rev! It’ll help a great deal in working out the shape I need. With it, I should be able to build a test engine to see if the idea is worth pursuing.