I found this wonderful broken excavator toy while thrifting, and took it apart today to see if I could reuse the entire movement assembly, or parts of the motion works, or just the motors in another build.
First, the treads came off along with some little supporting wheels.
After that there were several (six? eight?) screws that held the base plate up. Here's what it looks like with the plate removed.
Just by the wiring, you can see there are just two wires going to each of the front wheels. The rear wheels spin freely as idle gears. The front motors appear to be geared DC motors, given there are only two wires going to each. That makes sense for a basic toy.
By the way, these things retail for around $60. But this one is missing the entire front bucket assembly and the remote control.
The tread motors came off with the removal of four more screws each. One thing I like about this toy is that, unlike things like H-P printers, they use normal screws, and I think there were only two or three types of screws in the whole assembly.
At this point, I hit a problem. I wanted to remove the wheel base from the cab assembly, but couldn't get to its screws. The screw heads were blocked because the cab couldn't pivot, being on a gear assembly for swiveling, and I couldn't activate the motors, lacking the remote control.
I did a quick power test, hoping that maybe the boot cycle would rotate the cab. The power area was missing the battery, but was labeled 4.8v and had clear black and red wires. So I hooked it up to a USB wall wart and breakout wire. The cab lights lit up and flashed, but there was no movement. That wasn't entirely surprising.
So to get the cab parts off of the cab baseplate, I had to sneak a #1 Philips (or smaller) screwdriver bit into the hole, and use an adjustable wrench to turn it until the screw came free. Then, I was able to turn the bit with my fingers.
Fortunately, that's all it took. The cab top came off of the cab baseplate cleanly. There weren't any tricky, easy-to-break plastic tabs to fight.
Here it is with the cab top removed, revealing the circuit board and motors.
After looking around a bit, I found that it had the following:
- Six thin wires going up into the arm. I could only see two, where it was broken, but there were six originally.
- Two wires to each front wheel/tread motor
- Two wires to a speaker
- Three wires to the cab so the LEDs could flash independently
- Two wires to the cab swivel motor
- Two wires to the arm motor
After removing a few more screws here and there, I had the arm off
and the swivel motor out (the black box at the bottom, now away from the swivel gear).
From there, it was just a matter of taking lots of pictures of the circuit board, removing it, and de-soldering.
The top left chips are marked MX1508 / 1842HS. A quick google shows those are DC motors controllers, but it's hard to find a clean datasheet without looking at breakout boards. The breakout boards might have flyback diodes and PWM control.
They appear to be dual H-bridge chips, thus allowing bidirectional movement in each motor. Each chip can control two motors.
The motor connections had labels and were easy to trace.
MXB = yellow/green, thin, going up into lift arm
MDB = yellow/white, thick, for lift arm
MWX = blue/red, thin, going up into lift arm
HYM = black/dark blue, thick, for swivel motor
MZS = white/black, thin, going up into lift arm
MLFB and MFRB = traction motors (presumably LF = left front, FR = front right).
The top-left one MX1508 (I'm viewing it upside-down, based on the silkscreen labels) controls motors MXB and MDB, so a mixture of arm stuff and the arm lifter.
The next MX1508 controls MWD and HYM, so lift arm something and swivel.
After that is the MZS motor, and it appears to have its own dedicated chip, maybe for layout or power reasons. It's another where the wires went up into the lift arm, so I don't greatly care. The chip is labeled MX08E / 1923H and aliexpress says it's a motor driver, but datasheets aren't easily findable.
I think it's reasonable to assume it does a single H bridge, kind of like getting half of a MX1508.
Here's a reasonable page that talks about the 1508:
https://arduinodiy.wordpress.com/2019/11/02/mx1508-vs-l9110s-vs-l293-motordriver-board/
Finally, there's one last chip at the top right. Its label said MX1616 / 1851H but has since worn off. It's wired similarly to the MX1508. It controls the MLFB and MFRB tread motors. The layout on the board is a little different, just because the MLFB connectors have to avoid the mounting hole.
There are two chips in the middle. One is 14-pin
and the one next to it is 16-pin
The 14-pin chip talks to the first two MX1508s.
The way the board in the toy is set up, it sends GND and VCC under the whole bank of motor drivers.The 14-pin chip appears to connect to the first MX1508's INA and INB directly. MX1508 Pins 6 and 7, INA2 and INB2, are connected via 102 (1k) resistors, so I suppose they're limiting current to both motors.
I'm kinda thinking that they did this to intentionally stall the motor that controls the lift arm. It sort of suggests that another articulating motor on the arm was connected to MXB.
For the second MX1508, the 14-pin chip connects directly without 1k resistors. I'm not sure why they wouldn't force-stall those (if my earlier assumption is correct) but maybe they need more power to swivel the whole body, and perhaps the other thing in the arm similarly needed full power.
In any case, at least four pins are being used for INA/INB and INA2, INB2 of each MX1508, meaning 8 of the 14 are consumed, leaving 6 to be explained. Another two go to L- (LED light) controls. So now we're left with 4 to explain. Two more must go to logic + and - so there are two left.
I'm wondering if it's some kind of serial multiplexer, but that'd be hard to explain. It would need addressing to four motors, and directional control. I'm thinking maybe one pin is a clock signal, and the other is a serial input, and it has some kind of internal protocol that knows what's going on.
The 16-bit chip uses 6 pins for the remaining three motors, uses 2 for the speaker +/- points, and uses 2 to talk to the 14-bit chip. Then giving 2 more to Vcc and GND, we're left with 4. Of those, 1 certainly ties to the right side chip, which presumably is all about radio control. The other three aren't clear.
I think this means that if I want, I could remove the middle-level chips entirely, cut a bunch of traces, and have access to the MX1508 inputs.
Or, I could just ignore the whole board, and wire up the motors to something where I can get actual datasheets.
I think I'll start by removing the existing, undocumented chips and see where that leads.
Here's the whole of the disassembled toy, minus screws and control board.
And videos of the motors and how they sound (direct 5v connection):
Tread motor:
Arm motor:
Swivel motor:
Arm motor, connected and counter-weighted:
There are two uses, or a combination of the two, that I'm looking at for this.
1. Just rebuild is using my own motor mechanism and Arduino or Raspberry Pi. Tie in some kind of communication, perhaps using a simpler motor control from a different toy.
2. Take advantage of the tread assembly and use the whole thing as one linear motion mechanism of a claw machine. That is, instead of having a claw hung from a carriage along an axis, drive the whole toy as that axis, and somehow keep it from tipping over with the weight of the claw.
3. Make it the center point of a rotating crane-type claw machine. That is, pretend it's a crane instead of being an excavator. Mount it on a center post, use the existing swivel mechanism, and fix the arm. (Perhaps strip out the existing arm wiring and replace it with strong fishing filament, hide the winch somewhere, and put idle pulleys in to avoid abrasion.) Extra credit: find a way to make the crane arm extend and retract.
More on the board
Here is an image of the board with some of the signal distribution chips removed, and 1508 (or 1616) pins labeled and traced.
VCC (red wire, left side) connected to Vdd1 and Vdd2 on the motor boards. That means the motors are all driven off of the same power source as the logic controls.
GND goes through a few capacitors (C3 north-northeast of GND, C4, C5), before arriving at the Vcc1 and Vcc2 pins on the motor boards. Note: the C3 label appears twice.
The InA1/B1/A2/B2 pins are used to control the motor power feeds. These are fed from the 14- and 16-pin signal distribution chips.
There are 000 "resistors" working as jumpers across traces on the board.
Interestingly, there are terminal points for U+/- and D+/-. They weren't wired originally. I think perhaps a higher priced version of the toy has other capabilities, or maybe it's a multipurpose board that allows for use in different kinds of toys.
The chip power actually goes through what appears to be a 2.8v or 3.0v voltage regulator. It's marked 7560-1 but good luck finding a datasheet. I just measured the three terminals on one side and got 0V, 5V, and 3V, when GND and VCC were connected to USB power. So that means Vcc pins are at 3V. The datasheet mentioned earlier says the MX1508 can run in the range 1.8-5V.
The 3V line from the regulator connects to the LED+ terminal and also to the pins feeding the 14-pin and 16-pin chips.
14-pin board:
14p1 - R13 (102) - U+ terminal - 1508a InA2 (MDB)
14p2 - 1508a InB1 (MDB)
14p3 - 1508a InA1 (MDB)
14p4 - missing component - 5
14p5 - 16p-6
14p6 - (16p-7) and (14p6 - 103 - 3.0v) -- so perhaps a shared pull-up resistor?
14p7 - 102 - L- (LED A) (damaged pad) -- small current-limiting resistor; assume 1.8v voltage drop in LED and we have about 12mA going through?
14p8 - 102 - L- (LED B)
14p9 - 1508b - InB2
14p10 - 1508b - InA2
14p11 - 3.0v
14p12 - 1508b - inB1
14p13 - 1508b InA1
14p14 - R14 (102) - D+ terminal - 1508a InB2 (MDB) -- presumably the 100 ohm resistor weakens the lift arm so it can stall without grinding gears off.
No comments:
Post a Comment