Witch-on-a-Wire Cable Bot

Description

My dad is crazy about Halloween. I think he's secretly a little undead - or maybe it's his late October birthday - but either way, his decorations get steadily more elaborate every year. For 2021, in addition to building a Gorilla-infested tree house, he asked me to figure out how to make a witch fly through his yard over his unsuspecting trick-or-treaters.

I immediately thought of the then-recent Hackaday article featuring an RC car turned cable cam and looked to cable cams as inspiration for this design: https://hackaday.com/2020/07/19/rc-car-becomes-cable-cam/

I want to make this project simple enough for my dad to use (and troubleshoot) without me and not something that would have to be manually controlled by remote all night, so I need to make it's electronics as minimalist as possible.

Components

Project Logs

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Round Two
Gage • 10/10/2021 at 23:48 • 0 comments

Ok, so this one isn't as pretty (yet) , but before I went down a rabbit hole to make it look pretty I wanted to validate the new 12VDC motor, lock-up arms, and new momentum switch (which is possible to assemble now). I also added a "safety" hook above the drive wheel in the hopes that it would prevent a fall during a derail event.

The blue thing is my second pass at a rope-stop, which still isn't immovable enough to act as the "stop". However, when I held it in place on as the cable bot approached the impact easily actuated the new momentum-switch. Double win on the new switch and motor.

The new lock-up arms work nicely too.

Now to get rid of the duct tape and add under voltage cutoff. Actually my brother, Kyle, had a great idea that I should connect the cut off circuit in to only "kill" power in one motor direction. This would increase the chances that the battery cuts out with the cable bot on one end of the run, instead of in the middle somewhere.
Ideas Meet Reality
Gage • 10/10/2021 at 23:48 • 0 comments

Alright, so the first print shows promise, but also decidedly did not "just work". For one it is technically impossible to assemble, a rookie mistake. I actually broke a piece of the momentum-switch slide assemble it. Separate from that, I need to buy a better toggle switch. The first one broke surprisingly easily and the other two of it's 3 pack were DOA. Not all toggle switches are created equal.

The folding arms work nicely, if a bit snug in their "snap" closure. A feature to hold them in the "deployed" position would help in mounting it onto the paracord.

The motor support bracket seems to introduce a lot of friction without adding much benefit. The bot ran ran much better when I removed the support bracket, but even then it's slower than I want. My orignal speed estimates didn't take into account that I am driving a 24VDC motor with a "20V" battery. Next round I'll try an equivalent 12VDC motor.

Over all I'm actually quite pleased and like enough of the core ideas have been validated that I'm *probably* not going down a dead end road.
First Pass at the Digital Design
Gage • 10/10/2021 at 23:39 • 0 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