MITERS is the greatest thing that has ever happened to the world (or specifically just me), but while it has copious amounts of tools, test equipment, machinery, and an almost gratuitous amount of parts, it lacks space. Having been to other non-academically affiliated hackerspaces (such as Freeside Atlanta), I realize how outclassed we are in our capacity to host projects. Despite that, we’ve stacked up a whole bunch of “large”, generally vehicular contraptions, including the beloved LOLrioKart.
LOLrioKart takes up a good portion of floor space in the back half of the room and is occasionally used to store all my crap. It’s also a pain to move around because of its mass, and a pain to work on the electricals because they are all very low to the ground. If I want to test the drivetrain, I had to lift the kart and balance it on a set of automotive jacks. Don’t even mention that time I had to swap the battery packs…
So for a while, I had wanted a lift or crane to suspend the kart from. I didn’t take the idea seriously until Spring term ended, when I started looking for options. I became partial to a ceiling-mounted hoist because of the ability to send the kart all the way to the top for storage and extra floor space.
The kart only weighs about 200 pounds empty, which is a essentially trivial load in the world of winches and cranes. MIT building N52 used to be a factory, and factories in the early 20th century were built to last forever. The ceilings are all solid concrete, more than a foot thick. Essentially, almost anything would have worked, and I briefly considered just gearing down a beefy DC motor instead of buying a specifically designed winch or hoist motor.
But as luck would have it, Craigslist produced a pristine example of an ATV winch for sale locally, so I quickly jumped on it.
This Master Lock (I thought they just sold locks, but I was wrong) unit seems to be a pretty standard offer in the world of cheap generic utility winches. It made some substellar sounds when loaded and the drum finish was pretty rough, but I’m going to assume that it won’t kill me. Too badly, anyway.
The mounting holes in the winch frame were located in a place where I couldn’t access them with a powered screw driving tool. They were designed to be mounted to brackets first, which are in turn mounted to your choice of stationary reference frame.
…so I had to devise my own. This 3/8″ aluminum plate was just hanging out in the cave of materials. I could probably have waterjetted any number of small robot parts from it, but hey.
The two large middle holes are countersunk on the other side to fit 5/16″-18 socket head cap screws. The six surrounding holes are countersunk to fit some 1/4″ flathead concrete bolts. MITERS had a large stock of “tapcon” style concrete screws (which do not use anchors), probably from back when we bolted stuff to the ceiling all the time.
Because bolting things to the ceiling isn’t exactly a precision machining activity, I used spraypaint and sprayed a pattern into the ceiling, using the mounting plate as a template.
The winch itself is mounted using two 5/16″-18 socket head cap screws and grade 8 nuts and washers. This should not be the first failure point.
A little while later…
I borrowed a hammerdrill and a 5/32″ concrete bit and went to town on the ceiling. Reportedly, the hammering noise was ungodly loud, even on the third floor. I guess that’s what happens when you bang on a solid concrete building.
I learned that a hammerdrill is best used not under intense drilling pressure, but rather under modest pressure. If you push too hard, you dampen the chiseling action and the effect is diminished. This was well reflected in me taking almost half a minute to drill the first hole – but the last only took 5 seconds.
Unfortunately, attempt #1 to mount the winch didn’t go well. I made the mistake of reading a different box of screws (which specified a 5/32″ drill). 1/4″ tapcon screws need a 3/16″ drill. The difference meant that I managed to shear off the screw halfway into the final depth.
I quickly went back with a 3/16″ bit to expand the other holes, and the rest went well. Friends and cohorts spotted the high-altitude work and helped hold the 25 pound winch up while I drove in the screws.
But after much sweat, concrete dust, and loud construction noises…
Well, at least I know my five-bolted rig can hold up 1 LOLrioKart. The only power supply strong enough to supply the current demand of the winch was a big Optima lead-acid battery.
Because this is a shady winch being held up by shady screws into shady century-old concrete, we started piling heavy things into the kart to see if we could find the maximum load. Helmets and face shields were aplenty during this exercise, because even if the kart was only 1″ off the ground during it, the falling 20-odd pounds of steel were a concern.
Things piled into the kart include two truck disc brakes (60 pounds), the lead acid battery (50 pounds), the Defibrillator (a.k.a the kart charger, 25 pounds), one brushless Etek (25 pounds), a huge linear power supply (25 pounds), and a milling vise (40 pounds). Powered lifts and interrupted drops were attempted to put force on the mounting, but it was solid. I think it’s proved itself.
Assuming I did install the screws correctly and that the concrete is not crumbly, each 1/4″ concrete screw is rated to a maximum of 1,100 pounds assuming a 1.5″ depth. There are five holding the plate to the ceiling for a cool ultimate tensile strength of 5,000 pounds. Even accounting for imperfections, the winch should stall long before the screws pull out. It’s still unlikely that I’ll ever allow anything more than the kart by itself to be hoisted, or items of similar weight, because it can get overhead and that can end badly.
Yup, it’s a hoverkart. Any questions?