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Giant Wimshurst Machine - could use some guidance

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Dr. Slack

Thu May 29 2014, 09:52PM

Registered Member #72 Joined: Thu Feb 09 2006, 08:29AM
Location: UK St. Albans
Posts: 1659

wrote ...
I place a spacer of soft material between the disks and bosses, to allow adjustments on the verticality of the disks with the pressure of the screws.

Interesting... I may try that method. What is "softer" material to you? HDPE/PVC, wood, or much softer like foam or cardboard?

Maybe something like rubber sheet, or perhaps a rubber tap washer at each screw, but don't have it too stiff and crack the acrylic torquing it down. Be careful that an adjustment like that may become un-adjusted with time and vibration, so you might want to think about using 'nylok' nuts, or assembling with thread-locker.

Can I just say Awesome that I'm most impressed with your progress. It's good to see someone putting their nuts on the line and getting on and building something, maybe I'm just a little bit jealous. Keep calm and crack on.

AwesomeMatt

Fri May 30 2014, 12:59AM

Registered Member #4454 Joined: Sun Feb 26 2012, 12:47AM
Location: Western Canada
Posts: 74

wrote ...
Be careful that an adjustment like that may become un-adjusted with time and vibration, so you might want to think about using 'nylok' nuts, or assembling with thread-locker.

Not my problem for a while, it's a prototype that's being discarded.

Discarded... to me. Then I'll fix it up a bit better I hope, with help, and time.

wrote ...
It's good to see someone putting their nuts on the line and getting on and building something, maybe I'm just a little bit jealous.

Well, it makes it easy to work on projects when someone else is buying the materials. That's what prevents me from doing most of mine. Not the cost really, just, that the cost is a barrier to curiosity because if it doesn't work then I wasted money.

It also helps that their main shop guy quit and the other is overworked with the backlog and most of the rest of the build staff is out on vacation, so, I'm in demand :p

...

I'm making the charge collecting combs right now. I'm going with the wire comb style.

I do not understand this part of the machine, other than "it picks up charge." I don't get how.

Anyway, I took some 12g wire and wrapped it around a pipe once then straight pointed towards the disc. The bar is about 6" long and there are 5 such wires on each side of each comb. Then I soldered it all.

Will that work? Should I have more combs? I see some designs with like, an actual metal comb, dozens of wires. Others use serrated-cut foils. Should I have thinner wire? Should the wire tips be sharp, flat, or rounded?

I don't really get what does what and why it does that, so it's hard to solve it with intuition.

2030

I will trim them to length later, obviously.

Eleccentric

Fri May 30 2014, 08:37PM

Registered Member #33460 Joined: Tue Aug 27 2013, 06:23PM
Location: Seattle
Posts: 46

Those charge collectors should work OK. I expect you will see leakage off the back sides where the wire wraps around, though. It would probably be better if you drilled holes into the pipe, inserted straight lengths of copper wire, and soldered around the hole. That way the sharp points are all on the inner side, facing the disks, where you want them. Don't change it for now, though. This should get you going.

The wire tips should be sharp. The wedge shape left by the wire cutters is sharp enough.

You know how we've made a big deal about large diameter conductors and smooth curves for your high voltage carriers? This is the one place where the reverse is desired. A sharp point will bleed off charge, whether it is actually attached to the charged object or placed near it, so long as there is a potential difference between the sharp point and the object from/to which charge is moving. The sharp point creates a high gradient in the electric field, triggering ionic conduction through the air.

A series of needles or finer wire might work better, but if you decide to remake this part later, you'll probably get the best results either from shielded serrated foil like in Homemade Lightning or else a pair of soft carbon anti-static brushes. It would be minor improvement in output, I expect, unless these charge collectors end up bleeding off a lot of charge. You will be able to see whether this occurs by examining the machine with dark-adjusted eyes.

I have no doubt that you'll be making sparks with this thing early next week. Your determination shows, you've got a solid basic design in progress, and you're not afraid to be honest about what you do and don't know. That last part alone puts you head and shoulders above most people.

teravolt

Fri May 30 2014, 09:24PM

Registered Member #195 Joined: Fri Feb 17 2006, 08:27PM
Location: Berkeley, ca.
Posts: 1111

copper mesh, screen works good to

AwesomeMatt

Sat May 31 2014, 06:36AM

Registered Member #4454 Joined: Sun Feb 26 2012, 12:47AM
Location: Western Canada
Posts: 74

wrote ...
The sharp point creates a high gradient in the electric field, triggering ionic conduction through the air.

So, the comb vacuums up arcs and I should see them in the air? Or is it invisible, like static itself?

I only actually saw a Wimshurst for a couple minutes a few weeks ago before I started asking all these questions, and it had brushes so there wouldn't've been any arcs to observe.

...

Progress:

- Assenbled but didn't solder the combs and conductor structure.

- Assembled and soldered one neutralizer frame (needs brushes).

- Cut PVC handles for electrodes.

- Cut 1" copper bar electrodes.

- Reamed 2" of handle, free-hand, with a 1" drillbit so it would accomodate 1" copper pipe from the electrode.

- Jammed one handled together, it appears to work.

- Drilled out 2x 2" holes in 2x4 surface to mount the PVC supports.

- 2" was too loose, so I wrapped it with green masking tape and yellow duct tape as a cylindrical shim so it would be nice and snug.

- Drilled out both PVC pillar supports for output electrodes (pivot pillars) using NOT the 1" drill bit (shattered PVC and spat chips) but the 1" hole saw. Hurray for practice pieces.

- Drilled 21 mounting holes in each new piece of 1/2" plexi. (1) 3/4" axle. (4) 1/4" holes to mount to the pulley. (8) 7/32" inner holes to mount to the big discs, (8) 7/32" outer holes to mount to the big discs.

- Cut out the new 1/2" plexi shoulders.

- Drilled 21 mounting holes in each of the big wheels. (1) enlarged the axle hole from 1/2" to 3/4" (0.761 on the shopbot for whatever reason, took some experimenting). (4) 1/4" holes for pulley mounting, (8) 1/4" inner holes, (8) 1/4" outer holes. These were different than the sizes on the small discs because these are through-holes and the small discs get threads tapped. Between the 4 discs, it was 5.5 hours on the Shopbot with help. A couple near-disasters had us thankful we used test cuts first.

- Tapped 32 holes. Stopped about half way through to power tap them, since plexi is soft.

- Threw in 4 (metal, button head) screws per side to mount the disc pairs to the pulley.

- Threw in 16 (nylon, mix of button head and tapered since no place had enough) screws per side to hold the discs to each other.

- Drilled out a second set of large pulleys to 1/2". I think I will go with the 1-loop drive belt thing that Finn suggested (

<-- link), because I didn't have to make an understructure (like the one Antonio linked).

- Mounted it up and gave it a whirl.

2031

... Hot damn. First disc was almost perfectly balanced, straight up and down, spun like a charm.
... Whoops. Disc #2 looks like a drunk on a unicycle. More tweaking needed.

Some people in the shop stopped by to oooh and ahhh.

- Tried and discarded using bungees as drive belts. Nylon is super slippery and they were too thin anyway. A couple alternatives to go buy tomorrow.

- Drew up a "To do" list and a shopping list. But of course, got to the reno store at 9:02, closed at 9. Went to a different one, crap for stock. More shopping tomorrow morning.

... I bought some realllllly thin threaded rod that I think I can use to hold the globes together and to the shaft. That was one of the remaining unknown assemblies, hopefully it works out. Also picked up some nylon hardware (all they had, again) so I'm not using 2.5" screws when I need 3/4".

Somewhat optimistic again. Seeing the discs together and holding up under very light rotation was a big motivator.

Also, found out a typical budget for a single exhibit like this, is $40,000-$80,000 from a fabrication shop (i.E. Not me, unless I get a solid bid in and figure out some insurance issues and partner up with someone who does better metalwork than I). So, I feel a little less bad about wasting $200 worth of acrylic the other day. I figured, $12-18k, not 3x that amount.

RAJEEV TUTEJA

Sat May 31 2014, 11:29AM

Registered Member #46265 Joined: Sun May 11 2014, 06:01PM
Location: AMBALA CANTT, INDIA
Posts: 9

dear AwesomeMatt

we are making almost the same machine except that yours is 48" and mine is 36".
for the belt i have a suggestion if you like.
i bought some mixed nylon polypropylene and what not endless belt stuff from a sewing machines dealer which can be cut to whatever length you want and then just heat up the ends and join them.
and believe me even if you are a WWF champion you won't be able to split apart that joint and they are available in different thicknesses. And another plus point of the belt is if you cross them for the other disk the problem that many face of belt dust is almost eliminated (WELL UPTO 90% IN MY CASE At LEAST)
hope this helps
regards and best wishes
p.s. want photos i can post them if you like or a video ?

ohh i forgot to tell you that the belt is meant for motorised sewing machines which are set on a table with electric motor and a foot switch to contorl its speed
rajeev tuteja

Eleccentric

Sat May 31 2014, 07:10PM

Registered Member #33460 Joined: Tue Aug 27 2013, 06:23PM
Location: Seattle
Posts: 46

Looks like you'll need double pulleys or dual-groove pulleys for Finn's suggested belt drive.

wrote ...
So, the comb vacuums up arcs and I should see them in the air? Or is it invisible, like static itself?

It will be visible, but only in deep darkness with dark-adjusted eyes. Not arcs, but soft corona discharge. I differentiate between arcs, sparks, and corona. A spark is what the output of this machine creates - bright, sharp, a single defined path. An arc is a continuous discharge that will wave and ripple with convection. Corona discharge is a lower current phenomenon, soft and diffuse, typically covering a volume of space and can often be touched without harm to your skin. It also can be called a non-thermal or non-equilibrium plasma.

AwesomeMatt

Sun Jun 01 2014, 08:55AM

Registered Member #4454 Joined: Sun Feb 26 2012, 12:47AM
Location: Western Canada
Posts: 74

This post is useless without pics. But, too busy. Just pasting my log for the day's work.

Progress:

- Fastenal closed. Industrial supply place closed. Ability Medical, was open, closed at 2pm. Auto Parts source had no oring cord, bought washer fluid hose instead for drive belt. Hopefully works, nothing else is open until Monday. Also bought superglue and 1 min epoxy to join hose.
- Rona: caps for 2" support post PVC, 3/4" nylon screws, rubber washers, 1/2" PVC, T-nuts (for Homemade Lightning ball joining suggestion).
- Yesterday's threaded rod far too small, holes in globes are bigger than I thought. Need to shop for larger tomorrow, brought globe home with me.
- Drilled out electrode handle PVC, cut 1" copper to fit, cut copper nipple to joint pieces. Electrode bars are done.
- Cut & straightened wire for combs, new design.
- Took down & disassembled disc assembly. Discovered chipped acrylic. Designed semi-squishy/compressible gasket (bubblefoam), cut and applied.

- Peeled backing from half of discs.
- Reassembled wheel #1 using proper nylon screws. Wheel #1 still spins great! Looks great! Hurray!
- Reassembled wheel #2. Wheel #2 still wobbles like a drunk, even worse than before.
- Disassembled wheel #2, tweaked bolt tightness to compensate for wobble.
- Reassembled wheel #2. No effect.
- Disassembled wheel #2. Problem might be with bushing seat. Disassembled pulley using 20 ton press, reset bushing in pulley extra deep. Set bushing in acrylic.
- Reassemble wheel #2. Wobble is okay except for 1/4 of rotation, has a 3/8" wobble. Attempted adjusting, no effect. Wobble is 3/4 fine, 1/4 to outside, so, probably useable as-is. Wheel is centered well.
- Designed, measured, cut, sanded template for sectors. Template was 2" wide, 2" aluminum tape is actually 1 3/4" wide not 2". Super. Re-engineer all the measurements, now will have 50 sectors per disc (even 100 total), measured, cut sanded new template.
- Carefully traced out 120 sectors on aluminum tape (extras for ones that get ruined while peeling backing).
- Very slowly and carefully cut out 120 sectors of aluminum tape. Everything smooth, no jagged edges. Did not think sectors would take 8 hours from start to finish, and they're not even peeled or applied yet.

Didn't get an answer for whether the machine needs to be done beginning of Monday or end, but was told the person working on the proposal would not be there Monday, so... Tuesday morning it is?

Eleccentric

Sun Jun 01 2014, 06:40PM

Registered Member #33460 Joined: Tue Aug 27 2013, 06:23PM
Location: Seattle
Posts: 46

If you need to ease the time crunch, you can apply a fraction of the sectors and still have a functional machine. Leave out every other or every two sectors, making sure that they line up from one disc to the other. The charging current will be lower, but the voltage should be nearly the same; you'll get sparks the same length, but less frequently for the same number of disc turns.

The wobble sounds negligible - one disc width's worth has not been a problem for the machines I've built, though none have been nearly this large.

When assembling the belt, I suggest that you find a short length of rubber tube that fits snugly inside the hose. Lube it with 90-99% rubbing alcohol and shove as much into one end of the hose as you can, then trim the exposed end to a similar length, lube it similarly, apply your glue of choice, and shove on the other end of the hose. The alcohol will evaporate and the rubber should friction-bind, adding significant strength to the joint. Slicing the hose at an angle for the butt-joint is also a good idea, so the glue has a larger surface area to work on. This is not unlike the gluing method shown in Homemade Lightning for Van de Graaff belts.

If the glue doesn't hold, and if the hose you are using is fiber-reinforced, you could stitch the joint together with nylon thread, as well. I believe I've seen this done on old leather belts for treadle-powered sewing machines.

Assemble the neutralizers before the high voltage collectors and discharge arms. The machine will charge and you will be able to draw sparks off the areas where the collector combs will sit when finished.

Newton Brawn

Mon Jun 02 2014, 05:23AM

Registered Member #3343 Joined: Thu Oct 21 2010, 04:06PM
Location: Toronto
Posts: 311

Hi Rajeev,

How do you assemble de acrilic disk with the wood pulley?

Are you going to use bolts, steel bolts?

The distance of a bolt to the center of the shaft in disk A may have a different distance of a bolt to the center of the shaft in disk B in order to avoid the bolts crash.

If you have videos, I will happy to watch.

AwesomeMatt

The wobble is something annoying.

The first idea I have was assemble a secong bushing in each pulley, assemble the shaft/pulley in a lathe. Then the lathe can face the surface that is in contact with the acrilic disk..

Othewise, a 0.5 mm thick chim applied between the disk and pulley may correct the wobbling. A 40mm long masking tape can solve the problem .

Regards

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