Drive-in Descending Distance Determinator

By request on the r/functionalprint subreddit, one of my more effective-yet-arguably-unnecessary designs. Original post here.

First up, credit where it's due; much of the CAD work was derived from the stellar TUSH FT ‘Fat Tracks’ Spool Holder by wavexx. Without their generous decision to include step files in the design, this would have been a much slower process. In the same spirit, a f3d project file is included here, organised as well as I can manage.

A copy of the 'rail v2' STL is included which was unchanged from wavexx's submission, just for convenience. (Despite there being a version 3, the v2 actually suits this purpose better).

Required parts;

2x Roof Bracket Half

2x Rail v2 bearing outers

1x Pulley Housing

1x Axle Plug M

1x Axle Plug F

1x Door Anchor part of your choosing - you may need to get creative here as the location you place your anchor will differ based on your garage door and it's mechanism. I have included the design I drew to fit my own, plus a couple of generic options that might be useful as a kludge or starting point. All have either a pass-through for a zip tie, or screw holes.

2x 608 bearings - printable alternatives should be fine, the forces involved are neither fast nor heavy enough to make genuine metal bearings essential.

3x M3 screws - about 10-16mm length should be fine, or whatever similarly sized woodscrews you've got lying around.

1x length of lightweight rope to suit - simple generic polypropylene rope or braided nylon twine should be fine. I needed maybe 6 metres? Grab a tape measure - you're a maker, you got this!

1x small ‘weight’ object to use as an indicator when parking. I used a tennis ball, it's likely going to touch a car, think round/soft/highly visible.

Preparation

i) Before you begin, take some quick measurements. Find the exact spot on the ceiling you would want to have your Indicator descend from. Then measure the lowest point you would want the Indicator to go when it's lowered.

ii) Now find where your anchor point is. Measure the distance it travels between the garage door being fully open and fully closed.

iii) Compare the two measurements. If your anchor travel distance (ii) is more than twice your maximum drop distance (i), please do not proceed. Using this mechanism may cause the pulley housing to strike your vehicle and cause damage. Consider that as the designer, my only notable qualifications are a proclivity for obnoxious Hawaiian shirts and tragic Dad Jokes.

Build Guidance

a) press fit the Rail v2 outers to your 608 bearings (or substitutes)

b) install one of the bearings on a Roof Bracket Half. Snap the other half in place, and use two screws through the axles to hold the halves together.

c) attach your Roof Bracket to the ceiling in the spot you picked earlier in step (i). The bracket has a couple of holes for screws, which worked fine for plasterboard, but this is up to you. Tape is not recommended. You want it aligned as best you can with your chosen anchor location, the end with the bearing closest to the garage door. 

d) grab your Door Anchor and go attach it near the garage door. Now is a good time to run the door up and down a couple times to make sure nothing's going to get knocked off.

e) thread your rope over the bearing in the bracket, and tie it off on the anchor. Run the door again, keeping slack out of the rope, and make sure everything so far is securely mounted and nothing snags.

f) now for the descending assembly. Press axle plug M through the centre of the remaining bearing, match it with axle plug F on the other side, and use a screw to hold them in place.

g) look inside the pulley housing. There is a recessed circle on each side for the axle plugs to seat into. The raised segments inside these circles are different sizes - match them to the corresponding holes on each axle plug end. Gently prise the sides of the housing apart enough to slide the bearing-with-axle into place. It should sit there firmly enough to not rattle out with gentle movement (but would pop out if placed under sudden, high force - this is by design, better than tearing a hole in your ceiling if it were to get accidentally yanked).

h) close the garage door so the anchor point is as far as it will ever get from the roof bracket. Thread the rope through the pulley housing (under the bearing), and tie off the rope on the second roof bracket axle (the one with no bearing). You are free to run the rope short enough that the pulley housing is nearly touching the bracket, as the anchor is unable to pull the rope any further.

j) now open the garage door to let the pulley housing descend (and witness the majesty of human ingenuity!). Attach your Indicator object through the bottom hole in the housing, adjusting the length of rope/string used to your preference. If you would rather have less length below the housing, but don't mind the whole assembly sitting lower when the door is down, allow a little more length before the tie-off from the step above.

k) optional - run the garage door up and down repeatedly, today and every day for the coming week, watching rudimentary physics in action with childlike wonder while your spouse rolls her eyes and reflects on her life choices.

'Advice'

Material - anything is fine. Mine is a mishmash of PLA, ABS and PETG depending on what I had loaded at the time. If it's an option, you may find the extra flexibility of PETG useful for the pulley housing when fitting the axle.

Print Settings - using the lowest layer height you can stomach for the bearing rail will make it much smoother and friction wear on the rope.

Avoid 100% infill on the axle plugs - having a little bit of internal space to deform as the screw goes through reduces the risk of layer separation. They're small parts so even just a few perimeters will act the same, so check the preview.

Orientation - nothing here has layer lines running horizontally when in its final position. Because gravity. Keep this in mind when orienting parts in your slicer.

Indicator - you can use literally anything for this, but a replacement totem tennis ball (tetherball?) available from most department stores with a sporting section is a cheap option for a tennis ball with string already conveniently attached.

Weight - you may find that the weight of the rope overwhelms the weight of your indicator & pulley housing, and causes the rope to show slackness between the bracket & anchor. I added a stack of metal washers beneath the pulley housing to increase the weight on that side a little, which resolved the issue.

Donations

Just kidding - I do this for fun!

If you'd like to do something nice, call your mother. She cares about you.

Thanks for reading, good luck!