# drawing a belt around a gear

Hello, I am having a hard time creating belts and chains around a pullies and gears. I usually use a Nurb curve or the the Array modifier, but they usually end up not coming straight.

*** is there an easier way to create a belt/ chain around these gears?

Thank you for your time :)

• what do you mean by "not coming straight"? Commented Sep 14, 2018 at 12:27
• when I use the curve to draw the belt, the vertices are not always straight, the belt ends up looking like its slipping off the gear, and perfect in other places. I am really sorry but that's the best way I can explain it. I wasn't sure if there is away where you select an area and the curve fallows right on top of the surface. Commented Sep 14, 2018 at 13:19
• Your usual way to do that is pretty good but instead of nurbs use path or object edges turned to path (Alt+C - Curve from Mesh), then turn on Curve Tools addon if you don't have it on yet and in edit mode set spline type to nurbs. That will give you straight smooth path of your liking every time. Commented Sep 14, 2018 at 14:49

A constrained shape like a belt or chain on a complex path can be generated using softbodies.

This solution is similar to "attract part of a mesh around an arc"

Procedure (tested on Blender 2.79)

1. Create geometry for the upper gear, lower gear, right guide, left guide, and belt. Make sure the gear geometry is inside the belt geometry and the guides are outside. This is important because collision between the objects will be used to shape the belt.

1. Set the top gears a guides as collision objects.

1. Set the belt as a softbody. Follow the setting below. The changes to setting are to get the belt to smoothly follow the forces applies. This is done by applying a large aerodynamic force to slow down the movement of the belt as it collides.

1. Animate the movement of the gears and guides to their final position. To fit the belt to the path from these parts, they need to move relatively slowly from their initial position to the final position.

2. Run the animation and the belt will be stretched to follow the part shapes. (Note: A modifier was added to make the belt appear thicker) The final geometry can be applied following this method - "Saving the deformation"

A blend file for this is available at

• Nice solution - and well presented answer. You could try increasing the Soft Body 'Friction' setting to calm it down - rather than aerodynamics. Commented Sep 19, 2018 at 8:04