I thought I would offer some ideas on different ways to open box lids. My main motivation has been finding a good way for lifting the lid of small Halloween coffin props, but the techniques can be used for many other applications as well.
I love to play around making these things as a hobby, but I need to make smaller versions of these because I don’t have enough room for full-sized ones. Here’s an example of a nice full-sized one by MrTmartindale on YouTube.
Seeing as I was recently playing around with pulleys I thought I would start with probably the most basic way to lift a lid — with a string!
There are a lot of potential problems with this arrangement:
You need to reverse the polarity on the motor for up and down directions.
It takes up a lot of space.
It needs a lot of parts: string, string pulley, pulley support, motor, motor pulley, motor mount, and some way to reverse the motor direction.
Today I’m starting to experiment using pulleys. They’re not used all that much in animatronics. I’m guessing it’s because they’re not as strong, predictable, or reliable as gears. But sometimes they can be useful. I see them a lot on the outside of gearboxes like this one, where the inside is chock full of gears (click photos to open larger versions in a new window):
I’m guessing this is the case when they don’t have room inside a standard gearbox (if there is such a thing in animatronic toys) and when speed, direction, or power transfer are not critical. Although, I wonder why they just don’t re-design the gearbox to accommodate this arrangement with gears? I have come across two toys where the drive belt has broken and rendered the toy’s animations useless.
Now these little gearboxes are tremendous to use in small animatronics, but it’s not possible for most of us to design our own gearboxes on this small of a scale. So pulleys are one way to drive our own hobby animatronics.
Enter my beginning learning design!
The first thing I had to do was get myself a little hobby motor. They are easy to find in just about any animated toy. They are pretty generic can usually run on anything from 1-1/2 to 6 volts DC or so. The problem with using just the motor is that they spin way too fast (around 10,000 RPM), and they have no power. Gears, or pulleys, are used to slow down the rotation and increase power.
In my previous post I talked about using a motor, a cam, and a switch to fire a solenoid. That just wasn’t going to work because it was too hard to get the right pace of the solenoid firing. The motor voltage changed its speed, and the cam idea was too difficult to adjust the cam shape and location.
In this post I’m showing how I switched to the Arduino Nano to control the firing rate of the solenoid. With the Arduino, it’s a 30-second program change to change the rate of the solenoid firing as opposed to the ridiculously difficult process with motor and cams.
The first video below shows the solenoid firing using the default settings in the sample ‘Blink’ program in the Arduino IDE.
The video below shows the solenoid firing after I modified the delay settings in the ‘Blink’ program.
Trying to find a way to mount things like motors, solenoids and switches is often a big challenge. Trying to find the right bracket, the right screws, and the right locations for those items in your experimental projects can be tough.
So I thought I’d show a few tips and tricks that I use.
First, my goal: I was trying to set up a little solenoid to bang against a miniature box to make a ‘chattering’ effect for a mini ‘monster in a box’ project, kind of like this Halloween monster in a box video (fast forward to about 1 min, 25 seconds to see the box chatter).
I started by experimenting with a little hobby motor. It wasn’t powerful enough to attach a cam straight away to rattle the box on its own so I had to find gears or levers, or something, to get some mechanical advantage.
The box in the video uses a cam attached to an electric drill, but I wanted something much smaller for my little project.
I started out using a cam to trigger a micro switch, which would energize a solenoid in rapid succession. (See my next post to see the solenoid fire.)
Instead of trying to find the right size and shape of a motor mount for my initial testing of things, I just used hot glue to secure some little blocks of wood to my test base (a 12″ square piece of press board). Then I put a little dab of hot glue on the motor and on the micro switch to secure them to the proper height of wood blocks.
Click on the photos to see larger versions.
Using blocks of wood is a fantastically simple way to make the right heights and locations. I was able to put away my box of sheet metal, tin snips, and other miscellaneous hard-to-use metal mounting hardware!
You can see my little blue cam that I also used hot glue for. I glued it to the motor shaft for a temporary attachment. Hitting the switch with the first cam — the brown pointy one you can see laying there — didn’t keep the switch activated long enough to fire the solenoid properly so I made the blue cam that kept the switch activated for about 5 times as long.The hot glue made it very easy to swap cams and re-glue.
The motor rotates at 300 to 600 RPM depending on the voltage applied (3 to 6 volts). That was way too fast with either cam, so I had to find another solution (see my post about using the Arduino instead of a motor). But the mounting techniques of wood blocks and hot glue have been a big headache-reliever for me over trying to find or fabricate metal mounts.