# shooting object by using a DC motor

This is not directly electrical, but I am working on making a real life version of a coin block from Mario. Basically I use an LDR and to detect if someone punches the block and then use a transistor to turn on a DC motor.

The problem is that I want to be able to 'shoot' a coin up from the box using the motor, but I am not sure how I could achieve this. I have tried attaching some objects to the motor, which then hits a stationary coin, but that isn't very effective.

In summary, I want to be able to use a motor to shoot a coin up against gravity,

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This is more of a physics question. The motor doesn't have enough impulse to do what you want, you're going to need some sort of energy storage. Think of a bow - you put energy in using your arm, but the effect isn't the same as pushing the arrow manually. The bow frame stores the energy and then releases it all at once. – Optimal Cynic Oct 21 '11 at 10:47
Were all supposed to know what "a coin block from Mario" is!!? – Olin Lathrop Oct 21 '11 at 12:07
@olin yes, and I'm surprised you don't. – Majenko Oct 21 '11 at 12:22
The down votes will all be because it's off-topic. Shame really, as it's a fun question. – Majenko Oct 21 '11 at 12:40
@Olin What does rediculous mean? – Rocketmagnet Oct 21 '11 at 14:22

To shoot a coin, you need a fair amount of speed. A DC motor will probably accelerate too slowly to achieve the required speed in such a short distance. My advice would be to use something with less travel but more speed.

A solenoid can be used punch something pretty hard. They typically travel less than an inch, but with a good current pulse, will kick pretty hard. If you don't have enough current available, then you can charge up a large capacitor, and discharge it suddenly into the solenoid.

Alternatively, you can mount the coin on a spring which is held back by a little solenoid. When you energise the solenoid, it pulls back a catch which releases the spring which fires the coin. The down side is that you would have to re-set the mechanism each time. (or you could use a motor to pull the catch).

Lastly, as David Kessner suggested, you could have a pair of counter-rotating flywheels. Whacking the box pushes the coin into the wheels, which grip it and throw it skyward. The downside to this is that you need to keep the power on to keep the wheels spinning, which is a bit of a waste.

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Oy yea! Shooting coins using spinning wheels can be the wicked! Crank those motors up and stand out of the way! – ppumkin Oct 22 '11 at 12:53
I've seen a lego version of the flywheels idea work pretty well with ping pong balls. I don't recall if the wheels were geared together or driven by separate motors (no synchronization of speed, but simpler to build). The problem with this though is that you need something like a solenoid to feed the projectile into the already-spinning motors. A solenoid with a long stroke to directly fire the coins might be simpler. – Chris Stratton Oct 23 '11 at 1:29

How about a leaf spring underneath the coin, and the motor has an armature which presses against the end of the leaf to move it down. Once the armature slips off the end of the leaf the energy is released causing the coin to fly upwards.

With some gearing of the motor you can get quite a lot of torque out of it, thus allowing a relatively stiff leaf spring to be used to give you a nice powerful flick.

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+1 for the diagram. – mjh2007 Oct 21 '11 at 12:38
It's based on the age-old ruler + chewed-up paper from my school days :) – Majenko Oct 21 '11 at 18:50
Great diagram! +1. – abdullah kahraman Dec 15 '11 at 13:54
As always, Pictures = Votes. – Kortuk Jan 26 '12 at 19:12

Have you looked into an electric cordless nail gun? These are standard nail guns that use electricity instead of compressed air to fire the nail. It basically works like this: There is a flywheel that is spun up. Once the flywheel is at speed, some mechanism forces the nail in contact with the flywheel and it is then forced into the wood (or brain). The diameter, weight, and speed of the flywheel is changed to match whatever the nail/wood is.

You could do something similar. Have a flywheel with two posts or whatever sticking out. There are two to keep the thing balanced. A motor gets the flywheel spinning, and keeps it spinning. When you want the coin to pop, a small solenoid drops the coin so it hits a post on the flywheel and gets launched. Of course you would need some guides so the coin goes in the right direction.

Using this method you could use a relatively small motor to launch the coin. And if you are inventive enough, you could auto-load the next coin and be ready to fire again in 10-ish seconds. This would also work well if your coin was large (6 inches?) or you needed it to go far (across the room). The main disadvantage of this is that you have a flywheel spinning all the time, consuming power and making noise.

Another super easy approach is the slingshot method. Basically you use some rubber band or surgical tubing to make a slingshot, then just have a simple solenoid to release the thing. Super easy, good "firepower", low power consumption.

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