Miles wrote:Okay engineers I need your help. I can't use a pushbutton to engage a motor because it requires too much force (I'm using jellybeans as "water balloons" that will be propelled at the target with a rubber-band) so I'm going to use a counterweight which will lift the garage door when it's lowered. Now I just need to figure out the mechanics for releasing the counterweight. I had thought of using a mousetrap but it may be too bulky.
The problem is that Santa's face is front of the area where the garage door will lift. That means I can't have anything too thick behind the face/target or it will prevent the door from lifting. I suppose I could build a track, much like a real-life garage door, but that seems like a lot of work.
Here's an illustration (semi-exploded) showing the position of the posts, target and garage door. Any ideas would be welcome.

Miles, instead of using the motor to open the door which is a cool idea, have you considered the possibility of just having the door magnetically stay closed and when the santa face is hit, it pushes a switch that releases the magnet causing the door to flip open with a little spring assembly or even top weights inside at top of door causing gravity to flip the door open outward from the bottom up towards the stakes when the magnet is switched off.
Here is a way to make a battery operated magnet and you could test it over and over, but I'm not sure off the top of my head whether this will give you the strength to hold the door shut until the switch is hit, but inexpensive to try. You just need to obviously push the switch again to turn on magnet and push the door down to catch manually when repeatedly testing.
You just need a wire, bolt, battery and on/off switch for your mechanism.
1. Using your long wire place the bolt in the center of the wire and press the wire just under the head of the bolt.
2. Start coiling both ends of the wire in a compact fashion to the other end of the bolt.
3. Connect one end of the wire to the positive end of the 9 volt battery
4. Connect the other end to the (on) portion of your switch.
5. Connect a second piece of wire from the other negative terminal on the battery to the on (off) portion of your switch.
That's all, now you have an battery operated switch magnet.
I'll think about some other ingenious and low cost solutions to offer up on the DC powered hobby motor, but how are you thinking of opening it and automatically stopping it without the use of sliding track and I'm thinking you'd need a stop and start sensor also to engage when the door reaches the fully open state.