Level-luffing crane, motorized and 3D printed [WIP]
| This is currently a Work-in-progress, expect updates to this page. |
The idea is to create a HO scale model of harbour level-luffing (also called horse-head) portal crane with 3 or 4 degrees of movement (roll the whole crane, rotate the crane, tilt the boom, raise and lower hook) and probably some hook mechanism to be controlled by a remote.
It uses combination of FDM 3D printing for large load-bearing parts and resin 3D printing for small details.
Originally I wanted the "hook" to be an electromagnet. Currently it’s a normal hook.
Similar products:
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ROCO 40110, 41290, 41296 and some other SKUs. Those look like they are from different era though (WW1 to WW2 maybe).
An in-progress video of superstructure rotation and boom elevation. Uses quick-and-dirty firmware for Arduino and Nunchuck.
Subprojects
Slip ring
This is 3-pole slip ring to hold all the superstructure and to pass electrical signals. It is expected be able to carry tilting forces caused by boom extension and load movement. This current design has 2 ball-bearings with 6mm and 8mm bore diameter and is printed with FDM.
Linear actuator
Linear actuator is used to move main crane jib. So far it’s implemented with a 6mm gear motor and 2mm threaded rod, and resin printed casing. You can see it in action in the video above.
I tried to not over-engineer it and use an ordinary servo, but it’s too large to fit.
It doesn’t have any endstops, that may cause some problems in the future (the threaded rod just falls off from the nut and the boom falls down).
Winch
A crane obviously needs a winch to lift stuff. What I’ve come up with is described in this post.
Here is it in action:
On crane lines
Turns out, it’s very difficult to make a good model of a crane line. There are some conflicting requirements for the cables, such as:
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It needs to be thick enough for realism sake
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and dark colored, also for realism,
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It must be flexible enough to go straight down with minimal weight,
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It must not be braided as those twist after some time of inactivity.
So far I’ve tried ordinary sewing thread that I had lying around (too thin and braided), waxed leather-grade thread (thick, good flexibility but braided), polyester thread of specific thickness (braided but otherwise perfect), black fishing line, number 1.0, i.e. 0.16mm (not braided, but too thin and not flexible enough). Currently I’m waiting for arrival of some "elastic fishing line", which unfortunately is white and thin, but if it is flexible enough and not braided, I’ll have to live with it.
Motor board
Electronics needed to control the crane is rather simple - an MCU, an H-bridge per motor and some LEDs. However, I realized that an Arduino Nano and motor boards will not fit into the housing of the crane, so I designed my own PCB with a STM32G0 MCU and 2 DRV8835 dual H-bridges (to control 4 motors).
The motor board has a separate project page.
Control
Instead of desktop-mounted joystick, the idea is to use handheld Nintendo Wii Nunchuck (or a cheap clone). It has a 2-axis joystick and 2 buttons, this seems enough to control 3 DoF crane, a winch and some kind of grabber. It also has accelerometer, which might also be useful.
It has a convenient I2C interface and readily-available Arduino libraries.
