A toy claw machine!
Of all things, while intending to make my own claw machine, I ran across this at the thrift store:
I had no idea of its condition until I started pulling it apart. First step: the batteries. Fully expecting ancient batteries and corroded terminals, I was very surprised to find 3 healthy (1.5V or higher) D-cell batteries within, and no signs of corrosion.
So, obviously, next step: turn it on, and put a coin in.
The machine came to life making quite a racket. The left-right motion worked well. The front-back motors were slow.
The drop bucket was completely inoperable, because the stick for it had become detached.
It went through its play sequence and gave me a wah-wah-wah sad sound for failing to grab anything.
Other observations: the top lid was missing a red panel. Presumably, that was there so you could put objects in, and then seal it up.
The rear and right clear panels were busted, most likely due to harsh conditions at the thrift store.
A view from below
This is the bottom area with its two panels removed. The smaller one allows you to retrieve coins. The larger one is for the batteries.
Ten screws (2.67mm OD, 8mm long) later, and I had the bottom panel off.
What a horrible rat's nest of wires! These pictures also don't show the trails of hot glue that were left wandering about, either. Very messy.
The bottom panel holds connectors to power, the power switch, and the speaker.
I then removed the four short screws (2.81mm OD, 5.65mm long) that held the circuit board in place. It turns out it's a simple, single-sided board. The "up" non-conductive side holds three DPDT momentary switches.
The joysticks were a very simple, clever mechanism. Each is a gray stick that has a T-shaped peg on the end. The holes mate to the pegs of the circuit board switches. In between, there is an oval red piece that provides a way for the stick to pivot. You can remove the grey joysticks and red oval sliders by pivoting the stick and tipping it through, and then simply lifting out the slider.
Fixing the claw joystick
This is the top side of the control board. As you can see, the peg is missing from the up-down switch. After a little shaking, I found the missing peg, fortunately.
I de-soldered the switch so I could work on it. Here are the bottom and top views. If I were to replace this, I'd need something where the switch holes were 0.2" apart, and ideally it'd have the same stabilization mounting hole separations (0.4" x 0.8", roughly).
You can see where the peg snapped off of the switch. Someone probably was too rough with it, but the peg really didn't have reasonable strengthening supports. From a 3d-printing perspective, it'd be like having a circular peg on top of a cube of plastic -- very easy to break.
I wasn't quite sure how to fix this. I could order a new switch, and hope for the best. But that seemed like it'd take too long. I also considered drilling a hole and putting a metal peg in place, but figured that wouldn't hold. Plus, the plastic in the switch wasn't all that thick, so there wouldn't be much for the metal to bite into. Gluing the peg back in place seemed like a path to rapid re-breaking.
Taking a chance, I assumed the plastic to be ABS and decided to try to melt the two pieces back together again. I set my soldering iron to 235 C. On my first attempt, I just hit the edges and it didn't provide a strong bond. It snapped back off again quite quickly. But I succeeded on my second attempt. I melted the peg bottom and the switch plastic briefly, then held the two parts together and touched around the edges. Then, I let it cool. It came out ugly, but strong and functional.
After re-soldering the switch to the control panel and putting things back together again, it worked!
Other functions
I found out during testing that the toy also has an "electric eye" beam -- an LED and an optical sensor -- near the bottom of the drop chute. So it assumes you've won if something crosses the beam. (If you leave a toy in there and start the game over again, it waits until it sees a new signal, so it's a leading edge kind of detection.)
The coin detection mechanism is also quite poor. Most often, when I insert a quarter, it would start the game, but the coin would not fall through. I also could just start the game by putting the coin halfway in, and then would take the coin back out again.
In any case, I found a nice test sequence, where I'd start the game by pushing the coin detect with a small screwdriver, and then wave my finger across the light beam to stop it.
Linear motion mechanism
Onward. The toy worked, but I was still curious about how it did its linear motion, and why the Y axis movement was so slow.
I removed the ten screws (2.75mm OD, 5.7mm long) that held the lid in place, and then removed the lid. Getting those screws off was a little tough. They were screwed down tightly, and I had a limited range of motion because of the clear panels.
Removing the motor cover gave me a little more insight.
So... a few things to point out here.
First, it's a rack-and-pinion mechanism in both X and Y axes. The X axis motion has two racks. There is a metal rod connecting both X axis pinions at once, and that's connected to the motor mechanism via gears.
The Y axis movement (front-back) also uses a rack-and-pinion system with dual racks. I think for that axis they just used two motors, one for each rack. I think that means it's possible that they used the available voltage without amplification and thus lost speed on that axis. It's hard to tell and I didn't want to tear apart the motor carriage further.
There are limit switches for both X and Y axis movement. I think they're wired in series. Certainly that's what's happening on the Y axis. It's possible all four switches run off the same wire in series, thus reducing the wire count going back to the PCB.
The overall motor carriage was askew when I opened it up. It took some clever loosening and re-tightening in order to adjust that.
The claw
The claw motor is running two sprocketed gears that hook into the chains that hold the claw. But, interestingly, the chains don't both release and lift at exactly the same time. One precedes the other by a bit, allowing the claw to open upon initial descent, and then close before coming up. I think that means there's a rotating peg on one gear that hooks into an arc slot on the other gear. Clever.
Next steps
I'm going to need to take the top lid off again in order to remove and fix the rear and right clear panels. Those appear to be held on by the screwed-on corner brace columns. But they also look like they're bent at the edges, so I might have to figure out how to bend acrylic before I'm done.
I might also investigate the Y axis motors a bit more.
Otherwise, I think this toy is a decent fallback if my "real" claw machine build takes too long or goes sideways.
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