Close

First Pass at the Digital Design

A project log for Witch-on-a-Wire Cable Bot

A cable-cam-inspired robot to fly a witch, or other lightweight ghoul, over unwary tricksters.

GageGage 10/10/2021 at 23:390 Comments

I started out with with an OnShape model that HyGy uploaded. I don't have any details on how his build went, but by the time I was ready to make the first prints of my design I'd changed just about every part.

https://cad.onshape.com/documents/bae5e66ca160bb79fc7c6b50/w/eff1d0090016b902a8df9f3e/e/e265e861b78752b208c12b3a

With the basic shape set, I started making decisions to simplify my build time and design effort, like swapping what appeared to be a plain DC motor driving a 3D printed gear-set for an off-the-shelf 24V gear motor. Given that voltage of motor and my Dad's existing collection of 20V Dewalt cordless tools, I chose to use a 20V Dewalt battery for power. No need for a special charger or batteries, and he already knows how to use them.

I also needed a way to make this thing "autonomously" fly back and forth across the wire. I explored several ideas, such as limit switches on either arm, but in an effort to keep electronic complexity down, I went with a single DPDT on-on toggle switch and a momentum driven slide mechanism to actuate it. A "momentum switch" if you will.

I also couldn't bring myself to break with the cool folding arm idea, so, to actuate the switch, I plan to use a hopefully-clever application of inertia against user-set "stops" in the rope.

This design includes a support and bearing for the motor, a snap-in mount for the battery switch, locks to stow the arms in place (and tie on the prop), and the lower half (with battery) slides to actuate the toggle switch (which it does when it hits a rope stop).

Around the same time I did the first print of this, I attended the retirement party of a wizened electronics tech. In his 30 years of experience he'd only had one project whose PCB was "flawless" on the first try and many who had been there still disbelieved the claim. I know better than this, but I really did think the first Cable-Bot print would "just work".

Spoiler: It didn't

Discussions