My friend and I have an idea to make prototype of vending machine. We need suggestions for making strong dropping mechanism. The idea is:

  1. The user orders X item. Let's take a can of cola for example.
  2. Then the cola can drops in container.
  3. Then you place your hand below the container and the item drops in your hand.

The problems we have to solve are point 2 and 3.

How to make the dropping mechanism, strong and gentle? We have 3d printer.

Sample drawing: enter image description here

  • 2
    $\begingroup$ While you might have an interesting problem. Not sure it is related to 3D printing or anything close. $\endgroup$
    – apesa
    Commented Oct 7, 2020 at 5:24
  • $\begingroup$ Engineering forum is more appropriate. I was posted it in 3D printing, because the 3d printing enthusiasts may suggest me efficient 3D printed mechanism. $\endgroup$ Commented Oct 7, 2020 at 14:22
  • $\begingroup$ 3D printing is one way to create a mechanism. Designing for 3D printing is a subset of engineering, where special considerations are taken (as in: how it is printed). In fact, often solving a problem for 3D printing might be harder than traditional manufacturing, and the production of some mechanisms the traditional way might be both faster and more cost effective on the grand scale. $\endgroup$
    – Trish
    Commented Oct 7, 2020 at 15:13
  • $\begingroup$ Isn't this why there is often a flap at the end of the slide? To kill the momentum of the can? $\endgroup$
    – DKNguyen
    Commented Oct 7, 2020 at 18:59

2 Answers 2


Instead of a Servo, this could be very easily be done by the combination of a spring and a linear magnetic actuator. The downside is, that the setup needs a minimum weight of the item to overcome the closing spring.

Upon detection of the hand, the actuator retracts the locking bar and the weight of the item pushes the door open against the spring. As the item falls off the door, the spring pushes the door back to the start position. Once the door is back in position, it triggers the actuator to lock the door again.

Instead of springs, a second actuator could be used: a linear actuator could pull the link back via a tilting link, then return to its extended position afterward. The actuator's connection to the link rides in a slot, so the gate can fall freely. If the slot is replaced by just a hole, the actuator could also act as the lock.

enter image description here

A turning actuator could push the lid closed by simply doing about a quarter turn and having a peg that presses down the lever to return the gate to the position. And, if the resting position is down, it might even act as the Lock in the bottom position. With the tab chosen as the right length and bend at the end, a full rotation of the motor would release, then close the hatch with just one servo. Rotary Actuator to return

  • $\begingroup$ We will replace the spring with piece of elastic rubber band which will not be stretched at closed position. When the actuator retracts the locking bar the item will drop and the inertia of the rubber band will bring the door back and we will add a small magnet to it. I like this idea. edit: I will print this linear actuator: thingiverse.com/thing:3170748 $\endgroup$ Commented Oct 7, 2020 at 23:47
  • $\begingroup$ @SimeonBaltadziev rubber has the downside of aging $\endgroup$
    – Trish
    Commented Oct 7, 2020 at 23:50
  • $\begingroup$ We can stack many small rubbers and find the best stretching force. Easier to implement and find than spring. Bigger part of the focus of this project is the software. Hardware is also crucial the goal is to use maximum amount of ready modules to start testing as soon as possible. $\endgroup$ Commented Oct 8, 2020 at 0:49
  • $\begingroup$ @SimeonBaltadziev I added two alternate variants that forgo the need for springs but require different mounting of motors. $\endgroup$
    – Trish
    Commented Oct 8, 2020 at 10:42
  • $\begingroup$ That's interesting. Will consider it! $\endgroup$ Commented Oct 8, 2020 at 23:22

If you look at some common vending machines (I'm talking about the ones that hold snacks), They dont use a servo. Instead they have a motor turn a screw/coil continuously until the purchased item pushed along drops from inside the coil, tripping a simple sensor (like a limit switch) which tells the motor to stop.

Feedback ensures the purchased item is dispensed and the coil is easy for displaying product as well as loading the machine.

  • $\begingroup$ Yea, your comment is right. But I'm not asking for the pushing mechanism, my question is related about the state, when the item is dropped in the container. If it was common vending machine, the user would just put his hand in this container and take the item. Our goal is to make the whole process touchless. The user will only touch the item from the machine. The item have to fall in his hand. So the container is reverse pyramid and N number of helix with stepper motors will be rotating and till item X drops in the reverse pyramid. Then we have to open the pyramid bottom so th itemwilldrop $\endgroup$ Commented Oct 7, 2020 at 14:22

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