The Make Something Every Week Contest

[ceptimus]

They do generally. Most model helicopters use simple, single-stage spur gears.

I wonder what is the efficiency of Corona688's gearbox? I suspect that it wastes more energy in friction losses than the standard designs - but of course it is more space-efficient than those. It's an interesting physical law that any gearbox that 'wastes' more than 50% of its power input won't work in the opposite direction - so a 49% efficient 10:1 reduction box can't be used as a 10:1 speed-up box by swapping the input and output shafts. For some applications, such lossy gearboxes are desirable: a good example is one of those chain hoists used in factories to lift heavy machinery - because it is less than 50% efficient it doesn't need a ratchet to prevent the chain running backwards, so the operator can let go of the chain at any time and the load being lifted remains suspended and doesn't fall back down. A mechanical car-jack used when changing a tire is the same - you can let go of the handle and the weight of the car won't cause it to spin back down. You have to put more energy in to the jack when you are ready to lower the car back down, although it's generally much easier than lifting up the car was.

[thedoc]

Originally Posted by Chris Porter

Why don't helicopters have more simple, belt driven rotors?

Perhaps belts slip and require more sophisticated software to keep track of the changes.

[S.Vashti]

Or maybe it's a design that will let the blades keep spinning even if power is removed?

[Corona688]

There's more output torque involved here than might be obvious, the 10:1 reduction isn't for nothing. At these speeds and forces a tiny belt would vibrate, slip, jump, melt, and burn -- in that order.

Slipping is a problem I'm already fighting, attaching the off-center cam (the bit which pushes the gear in its wobbling circle) to the little motor. Plastic cams can work if you *REALLY* cram them in there, but getting one on without wrecking it is difficult. It's too small for set screws of any sort, even parallel. And if it does start to slip, or you ever need to remove it for any reason, it's destroyed. I've made metal cams by drilling off-center into a metal rod, but I don't have the exact right size drill bit to do a proper interference fit, and not even locktite can hold those on except for one miracle I've never been able to duplicate.

This morning I had an idea and spent 30 minutes with a 5mm bolt and triangular file:



So far so good. (Yes, most of the rest will get cut off.)

[Corona688]

Originally Posted by ceptimus

They do generally. Most model helicopters use simple, single-stage spur gears.

I wonder what is the efficiency of Corona688's gearbox? I suspect that it wastes more energy in friction losses than the standard designs - but of course it is more space-efficient than those. It's an interesting physical law that any gearbox that 'wastes' more than 50% of its power input won't work in the opposite direction - so a 49% efficient 10:1 reduction box can't be used as a 10:1 speed-up box by swapping the input and output shafts.

Hypocycloid designs generally can't be backdriven, just because of the way it's arranged. When you try and backdrive it, it'll start moving easy enough, but stop whenever the gear, the long side of the eccentric, and the direction of force line up -- in effect, self-locking. So it's not so much "power wasted" as "dead zone". The dead zone doesn't exist for the driving motor though, which doesn't give a fig which way the cam is facing.

I've accidentally made non-locking hypocycloids before though! Offsetting the teeth, like this, removes that dead zone of no-movement.

Does this mean overlapping the teeth increased the efficiency of the gearbox?

[Janet]

One of the bands who played this year broke one of our microphone clips, so I printed two thirds of your mic stand to replace it. It's like everyone here has suddenly figured out there are actual uses for the 3D printer and they all think I'm awesome. So, thanks for that!

[Corona688]

Originally Posted by Janet

One of the bands who played this year broke one of our microphone clips, so I printed two thirds of your mic stand to replace it. It's like everyone here has suddenly figured out there are actual uses for the 3D printer and they all think I'm awesome. So, thanks for that!

It's definitely one of those things which sounds insane until you happen to need it, isn't it? I wonder if it was like that when the handsaw was invented. Who would ever need to cut regular sized pieces of stuff?

[Corona688]

This is a garden-hose-to-those-annoying-threads-pressure-washers-use adaptor, so I can plug a garden hose into my boss' pressure washer to flush it out since it's plugged. It will probably need a pair of O-rings to not leak like a leaking thing.

[Corona688]

The adaptor worked, sort of. It kind of sprayed tears cartoon-like but held up a surprising amount of pressure for all that. The pump, though, I think is busted for good -- won't unclog, the clogged bit is a factory-sealed thing you can't get open without a hacksaw, and nobody makes parts for Simoniz.

[Corona688]

So, last week at work we noticed two of three sump pumps had burned out, the sump breaker blown, and the sumps themselves were really full of water. So, we have two blown pumps. But two perfectly good level switches. Can we do anything with them? Maybe.



This vaguely ominous widget is an emergency water level sensor which converts that gigantic 10-amp 120VAC float switch into a signal our computer can use. The red LED means "everything's OK". If it ever goes out that means either high water or blown breaker. Hypothetically this means I can hook it up to our monitor system and get it to send red alert emails to the boss when something bad happens.

It's built out of junk and leftover stuff from renovations: Box, outlet, level switch, two mutilated computer power cords, current sensor, light bulbs and sockets, scrap wiring. It cost us $1.00 only because we had to buy wire nuts. Estimated cost to use, $10.00 per year with these 25W bulbs, smallest we could find in what we had.

[Ensign Steve]

Originally Posted by Corona688

The red LED means "everything's OK". If it ever goes out that means either high water or blown breaker.

[Corona688]

The problem light came on this morning.

> Cron  : Pump Check Failed ; /home/mec/bin/water-check.sh
> Sent: Tue 7/19/2016 7:30 AM
> Water alarm, expected value > 2.99, got '0.00'
> Check water level and pump breaker.

Pump just needed a kick.

[thedoc]

I fixed my Weed Eater today. Several years ago my wife brought home a Weed Eater to trim up some of the weeds that are growing up around the house, since years before, Gypsy Moths killed many of the big trees that were shading out the undergrowth. My wife brought it home and after a few days was getting antsy to use it. I was inside and I heard her outside starting the Weed Eater. Then I heard it going putt - putt - putt, and sure enough when I went and looked, here she was very slowly trimming the weeds with the Weed eater idling along. I asked her if I could try it and when she gave it to me I used the trigger to rev the engine up, cutting the weeds much faster. When I looked at her she gave me a dirty look and then I showed her the trigger for the throttle, She called me a smart ass.

Yesterday I was using it to trim some weeds along the driveway, and the head stopped spinning, the engine was still running, but it wasn't turning the head. I figured it was either a broken drive cable or stripped gears, so I let it cool down and then took the head apart. It had a pair of bevel gears and they were stripped, but I could see that if I cleaned them up and shimmed them closer together they would work OK. Today i cleaned up the gears with a file and went to the hardware store and bought several washers. First I put a brass washer in that was .055" thick, but that was too much, I couldn't start the engine. I measured the original steel washer and it was .060" so I kept the brass washer and substituted a steel washer that was .050" thick, and that was enough, I was able to start the engine and the Weed eater is working again.

[SR71]

Pumpkin bumpkin!

[thedoc]

I'm fixing my roof. I have a Mansard style roof and the shingles are 2 parts. On the top the slope is shallow and there is no problem, but on the steep sides the 2nd piece is falling off when it gets hot in the summer. The problem is that the roofer thought he knew better than the Mfg. how to install shingles, and nailed them too high on the shingle to catch the 2nd piece. So that part falls off when the sun shines and the roof gets hot. The roofer was back twice and the builder was back once to fix the problem, but the shingles are still falling off, so I'm nailing them on properly my self. Sat. I did the long side where 3 shingles had come loose or fallen off, and on Sun. I did a small section where 2 shingles had come loose. I have 2 more sections to do but each section has more loose or missing shingles than the 1st 2 sections.

[Ensign Steve]

Mine's the kitty, bey's is the skull.



I wish I could take credit for the lighting, but that was totally bey's idea.

[thedoc]

One more section to do, but it will be the most difficult as I don't have a level place to set the ladder.

[thedoc]

Originally Posted by thedoc

One more section to do, but it will be the most difficult as I don't have a level place to set the ladder.

We spent a few hours clearing the weeds away so that I could find a clear place to set the ladder. Then is's put the shingles back up that are falling off.

[lisarea]

Here is what I want to do: I want to sew a sort of integrated sleep mask into a hoody, so that I could just pull the hood up over my eyes to block out light. So I figure I need to just sew some darkening fabric into the inside of the hood, but then I need some sort of flexible tape that I can use to secure it and fit it over my nose so light doesn't get in there.

What is this type of tape? I could just use some wire, I guess, like in those ribbons for gift wrapping, but if possible, I would like it to be something fairly durable and washable. I feel like this exists and I just don't know what it's called.

I promise not to go around like this in public too much. It's mostly just for "family time," you know.

[thedoc]

Originally Posted by lisarea

Here is what I want to do: I want to sew a sort of integrated sleep mask into a hoody, so that I could just pull the hood up over my eyes to block out light. So I figure I need to just sew some darkening fabric into the inside of the hood, but then I need some sort of flexible tape that I can use to secure it and fit it over my nose so light doesn't get in there.

What is this type of tape? I could just use some wire, I guess, like in those ribbons for gift wrapping, but if possible, I would like it to be something fairly durable and washable. I feel like this exists and I just don't know what it's called.

I promise not to go around like this in public too much. It's mostly just for "family time," you know.

If you sleep on your back, you can just place a folded up handkerchief over your eyes to block out the light. I do it when I take a nap in the middle of the day, and since I don't roll at all after I'm asleep, it works for me.

[thedoc]

Originally Posted by lisarea

What is this type of tape? I could just use some wire, I guess, like in those ribbons for gift wrapping, but if possible, I would like it to be something fairly durable and washable. I feel like this exists and I just don't know what it's called.

you could use the tape that models use to secure different parts of the costume so that it doesn't move and expose something it shouldn't. Look up "Dress Tape" or "Fashion Tape". Wire is more durable and permanent, the tape would be a one time use, and reapply the next time.

[ceptimus]

You could sew a sort of thin tube of fabric ( like a hem with the ends left open ) and then push a pipe cleaner through. That would let you bend it to shape to clip on your nose like those breathing masks do, but you could slide out the pipe cleaner to put the garment through the wash.

[thedoc]

Originally Posted by ceptimus

You could sew a sort of thin tube of fabric ( like a hem with the ends left open ) and then push a pipe cleaner through. That would let you bend it to shape to clip on your nose like those breathing masks do, but you could slide out the pipe cleaner to put the garment through the wash.

Isn't there a kind of plastic coated wire or a plastic with a metal core that can be shaped and washed when necessary?

[ceptimus]

I think plpe cleaners will survive being laundered okay. The problem with any sort of bendable wire though is that it will, given enough bending, eventually fracture. So I think making the wire removable/replaceable is a good idea even if you're not intending to remove it for every wash.

[lisarea]

I'm leaning toward the removable idea right now, in part because it just occurred to me that anything sturdy and stiff enough to hold it in place when I want it to would probably poke annoyingly into my back when I wasn't using it. So maybe it should be removable for other reasons.

My real main thing is that sometimes I have to take these ten hour bus trips, and it'd be nice to be able to block out light so I can sleep for part of the way. I probably would really only use it then, and the rest of the time, I could just take it out if it bugs me.

I have a whole box of ribbon cable somewhere around here that IIRC holds a form pretty well, so I might even try that. I just have to remember where I put it.

I'd hate to have to resort to something drastic like "getting a sleep mask."