Belt drive design and calculations

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After completing this lesson you'll be able to Generate a belt and its pulleys in the assembly,

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check the Belt design based on loads and the geometry of the belt, and Add a key to the pulley to keep it located on a shaft.

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In the Design tab, on the Power Transmission panel, there are three tools for flexible power transmission--

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V-Belts, Synchronous Belts, and Roller Chains.

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All of them use some type of wheel, whether a sprocket or a pulley, to guide a purchase-size belt,

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or a chain that can only be used in increments based on the length of individual links.

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Because of this, the type of input required to generate any of the three is essentially similar.

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We'll start by using synchronous belts.

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The type of belt that's already there by default. Otherwise select an H-Single-sided synchronous belt.

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We'll need to select the Belt Mid Plane.

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For this we'll use the front of the pulley that already exists in the assembly and we can relocate it in the Z-direction.

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We'll make that -0.49.

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When we put the belt in place we see it has a green preview of what the length of the belt itself will be.

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If we change the size of a pulley by clicking and dragging you'll see that the other pulley rephrase,

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you'll see the offset for the other pulley change based on the length of a purchasable size for that belt.

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If we click and drag on the second pulley we can see it snap from size to size.

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Let's locate the first pulley using Fixed Position by Selected Geometry.

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We'll select the shaft of the motor.

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And then for the second pulley we want to take advantage of the model pulley that's already in place. So we'll change its type to Existing.

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Selecting the face of the pulley, it will snap the belt into place,

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but the preview will turn to red because there is no belt size that's purchasable for that length.

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Because of this we'll use an idler.

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There's already an idler modeled in the assembly but several design accelerators, including this one,

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can use virtual elements to generate the geometry.

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So we'll add another pulley.

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Select one of the options, click it, and drag it to be the middle pulley, and then change it to a Virtual pulley.

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Looking more closely, if we move the Virtual pulley, we can see it will snap into position.

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When it gets to a purchasable size we can change the diameter.

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We can also use the curved arrow to switch sides. So now the idler is on the outside of the belt.

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We need the top pulley to be a 24 tooth pulley, so we can drag that increment out and you'll see the idler reposition.

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We need to have more control on the idler as well since we already have a physical assembly that we want to try and use.

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So we'll change its position, instead of being Free Sliding, to be controlled by a Rotation-driven Sliding Position.

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Selecting the radius of the idler on our model we can set the length of what the idler arm would be.

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We can double click on the arrow to set it to two which is what that is modeled as...

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And we can change the diameter.

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Right now, we'll leave it two, and we have a green preview which means our belt should generate.

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We can also tell it to create the belt as a Detailed model.

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Before we do this though we should check the belt.

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We'll go to the Calculation tab,

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input that we have a one horsepower motor,

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turning it 1750 RPMs, and click "Calculate".

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This will give us an error that one of the pulleys used in the transmission has a smaller diameter than the minimum recommendation.

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Since the existing pulley and the top pulley are based on tooth count, it must be the idler that's the issue.

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So let's drag the diameter of the idler, drag it to 2.5,

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it updates the position of where that idler would be, let's re-run the calculation, and it looks like that will work.

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Now we know we need to go modify the model for our physical idler or pulley or select a purchasable wheel with a 2 and 1/2 inch diameter,

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because we want to avoid that belt crossing to small a radius.

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With the belt requirements satisfied, we'll click "Okay" to generate it.

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We'll say "OK" to generate the files, and we'll get our belt on the screen.

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As I mentioned, we need to modify our idler but we can rough it into position.

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The next thing we need to do is add a key to keep the top pulley connected to the shaft.

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We'll go to the Key tool in the Power Transmission tab.

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We can select the type of key. The rectangular in parallel is the one that we'll want.

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We can see there's a large variety of keys available. We'll keep our rectangular or square parallel key.

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And then we'll begin to select our references.

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There are three different ways to model up a groove in the shaft.

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I use the middle one with a single rounded edge, and we'll select the motor shaft as a reference.

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Based on the diameter of the shaft you'll see that the key is changed from a 1/4 inch to 3/16 inch,

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it's looking for a second reference which would be the end of the shaft,

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and now we get a preview of a 3/8 long, 3/16 square key.

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The next step we need to do is establish where the hub is.

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We'll select the front of the pulley for reference one for the hub, and for reference two we need to find a radiused edge.

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We'll select the outside of a tooth, and now the design accelerator understands how wide the pulley is,

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what size the hole needs to be to accommodate the shaft and the key.

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Now we can drag the keys length and position.

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We use a one inch key and we can drag its angle on the shaft.

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We also have the ability to do a strength calculation on this but experience is telling us that this will work.

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So we'll click "Okay" to generate the groove in the shaft, the groove in the hub, the hole for the shaft in the hub, and the key.

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To clean up my view, I'll turn off my work axes by holding "Shift" and clicking right, and using "Feature Priority" to select the axis.

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Then using the Marking Menu to turn the visibility off.