# Coil Mechanism for Vending Machine

I'd like to make an animation of a vending machine. I'm looking for some pointers on how to make the coil turn and drop a snack.

I've made the coil from this link. The coil is on a hard surface and there are two walls on either side of the coil. I don't know how to approach the problem of getting the coil to turn and getting a box to move forward and then fall. Any tips would be appreciated.

• Have you enabled rigid body physics for the coil(s) and boxes? And are you using Cycles, Blender Internal or the game engine? – user7952 Jan 4 '15 at 6:12

## 2 Answers

There are two ways you could do this:

# Manually animate the coil:

1. Make your coil a passive rigid body and set the collision shape to Mesh. This will allow the concave coil to collide correctly with the object being pushed, however you may need to increase the number of Steps in Properties > Scene > Rigid body world to avoid glitches. I used a value of 120.

2. Animate the rotation of the coil. To do this, insert a rotation keyframe (I), then on a later frame, rotate the object and insert another keyframe:

You'll notice that as I have the coil tipped 2° downwards, I'll want to rotate on the local Z axis. A quick way to rotate around a local axis is by using a rotation order with the axis in question first. So in this case, either ZXY or ZYX. See Why are keyframes in global coords, instead of local coords? (Blender 2.70a)

3. Make your package object a rigid body. I used pretty much default settings.

# Use a motor constraint:

By using this method the coil will react to the resistance of the package dragging against the tray, etc.

Also see my related answer here.

1. Set up the coil as in step 1 of the animated method.

2. Add a cube to act as the "motor" and mount point. I've rotated both the cube and the coil 92° so that they tilt downwards slightly:

3. Select the coil and then the cube (so that the cube is active) and press Connect in 3D view > Tool Shelf (T) > Physics > Rigid Body Tools > Constraints, then set the constraint type to Hinge:

4. Rotate the empty created by the Connect operator so that it's local Z axis is aligned with the axis around which you want the coil to rotate. In my case I've rotated it 92°:

The hinge constraint will act as a mount, holding the coil in place but allowing it to rotate around a single axis (defined by the local Z of the empty).

5. Again select the coil and the cube (with the cube active), and press connect. This time set the constraint type to motor to add a Motor constraint:

6. Select the new empty created by the connect operator and enable Angular Motor in Properties > Constraints:

Adjust the Target velocity to control the speed of the coil rotation.

Also note that I've rotated the motor empty 2° so that it's local X is aligned with the same axis as the hinge's local Z (for some reason the motor constraint rotates around the empties local X, while the hinge uses the local Z)

7. Optionally hide the cube.

## Result:

Once you have the coil, you need to set it in motion by adding keyframes. Go to the first frame press I and select rotation. Move to a different frame, rotate the coil and set a new keyframe by pressing I again.

Now set the coil to a passive rigid body.

Add the object on the vending machine and the rest of the collision objects. Set all of them, except for the box to be dispensed, as Passive rigid bodies.

Then set your dispensed object as a Rigid body but make it active. The big problem, as you'll soon see, is that the coil does not work correctly as as rigid body to interact with the dispensed box. The box goes out flying out at at the beginning of the animation.

The issue is that the physics for collision objects and rigid bodies is far from perfect and does not follow the real geometry of the object, but creates like a bounding box: The Coil becomes almost like a big solid object with no gaps in between.

The solution is then to turn the dispensed object into a rigid animated object for part of the interaction to force it to follow the turns of the coil, thus simulating the real motion of a vending machine.

Animate the object so it follows the movement of the coil.

Now all that's left is to animate the animate button. To do that go to a frame where the dispensed object has reached the edge of the dispenser. Hover with the mouse over the animate box and press I to set a key frame, Then move one frame in the time line, uncheck the animate button and press I again to add another keyframe. What you are doing is deactivating the animation settings for the rigid body and letting it act just with the physics engine. Press AltA to cache the physics and watch a preview of the object falling over the edge of the dispenser.

Here's the .blend file

• Wow!! This is incredible. Thank you so much for this. I appreciate you showing also what did and didn't work. That was helpful. The "animate the animate button" part now is brilliant. Thank you again. – Alexis Jan 4 '15 at 9:38