Gear Reduction Help for Kinetic Sculptor w/ Small Budget

[revere521]

I am a kinetic sculptor in need of some gear reduction help. I have a 2250 rpm .5 hp electric motor. i need to reduce the rpms to less than 5. the gear drive will turn a 30" plywood wheel, and it must turn slowly. the electric motor is the only one I have, so i must use it. I have a small budget, which I will use to have gears cut. I need to know gear diameter and teeth in order to create the pattern. I will attempt to upload a pdf of the gear pattern to help. any help will be greatly appreciated. also if anyone knows a gear calculator on the net with which I can calculate non-automotive gear ratio stuff, that would help too. My e-mail is revere521@hotmail.com, thanks

 

[Bystander]

"Small budget?" and, custom gear hobbing? Don't think so. Check PIC or Winifred M Berg for gears and gear boxes. The reduction you're talking, and the size of your turntable --- 1/2 horse is going to grind any gear train you get to powder in days. Find yourself a clock motor, motor from an old record player, or something a little more suitable for driving a small low speed gear train.

 

[revere521]

thanks

ok, I have already been using the .5hp motor to turn a gear set. it is quite powerfull, but i worry with a smaller motor that the almost three foot diameter plywood wheel. it needs to start on its own with no help. the mounting plate is 15" in diameter so clock gears will be too small. there is a local machine shop that has several different size gear blanks on the shelf for not too much money ($10 - $15 a piece) my budget for gears is not too small that I can't afford a solution to this problem. can anyone tell me the equations or tell me where a calculator on the net is for gear ratios? i need to be able to put in the input rpms and fill in #'s of gear teeth and tranfers (large gear to small gear on the same shaft) and get an output rpm. thanks again!

 

[Bystander]

No. of teeth on driven gear divided by no. of teeth on driving gear is the same as the ratio of no. of turns of driven shaft to number of turns of driving shaft. Same-same for shaft speeds. Not too hard? You're also multiplying the driving torque (less friction in the gear train) by the same factor. Put a 1/2 horse motor on a 2250:5 reduction, or 450:1 (you'll need 3 or 4 steps --- say 5:1, 5:1, 6:1, and 3:1), and you'll tear screws out of your mounting plate, or grind up your plywood table, or strip pinions in your first and second reduction gears if anything starts dragging.

You might investigate stores and motorized display stands --- cheap compared to dropping a sawbuck on a gear blank and then paying for the hobbing --- several times over. You'd be looking at a 25-30" 64 pitch gear if you tried to do it in a single step with a ten tooth pinion on the motor --- and there ain't too many shops can hob 4500 teeth at that pitch.

You can pick up 32, 48, and 64 pitch gears in a variety of sizes at hobby/toy stores (RC car components), and maybe some tips on how ato set up the reduction you want, if you've absolutely got to do it yourself.

 

[Cliff_J]

Simple v-belt pulley would be much more effective and by adjusting the tension you could adjust a slip point for safety - imperfect yes, but far safer than gears.

Just like you can figure ratios by dividing the teeth, you can compare the diameters of the pulleys. So if you have a 30" pulley on the plywood and a 2" pulley on the motor that's 15:1 and if you used a jackshaft with the same setup duplicated again that would be 15:1 times 15:1 or 225:1 and then if that was on a jackshaft then you'd just need one 2:1 pulley combination to get your 450:1 ratio so you get your intended 5rpm. Other combinations would work too, but this was for illustration purposes. Total of six pulleys, three belts, and two jackshafts. With luck you could find the pulleys in a salvage yard (esp industrial like air-handlers) and regular belts are pretty inexpensive and with tons of luck you could find those salvage too - for .5HP a used belt will work fine. Plus, far quieter than gears. Food for thought...

Cliff

 

[revere521]

ok, I see that I need to revise my design

The hobby gears are out, unfortunately. I am looking at 4" to 8" diameter gears (they will be exposed to view, mounted flat so that the movement of the gears becomes part of the aesthetic). would a smaller electric motor be powerfull enough to turn these gears and the 30" table. if i could find a turntable motor (i think i have one laying around) with its fastest speed at 78 rpm, that would be easier. But I have some questions.
-does a motor such as that have enough torque to turn a big piece of plywood?
and
-if i wire it directly to a 110v circuit, would that fry the motor or cause it to turn much faster? (I could create te a control circuit if someone could tell me what was involved)
thanks again for all the help!
--Doug
p.s. -- my e-mail is revere521@hotmail.com, and I have a .pdf of the gear pattern I would like to use (i have been using timing gears from automotive applications) if anyone wants to see it I could e-mail it, the smallest i could make it is 155K (too big to upload) --Doug

 

[Bystander]

Ah-sooo --- art. Gotcha. What you'll want to examine is the friction in your "displayed gear train" --- you say automotive timing gears, and --- yeah, those do drag --- 1/2 horse may not be so far out of line for your purposes. Prolly worth incorporating CliffJ's loose belt and sheave reduction between the motor and what's actually displayed.

Turntable motor turn your plywood disc? 10 or 20:1 reduction gives you 10 or 20:1 increase in torque. Try stalling a turntable with fingertip pressure --- times 10 or 20 --- is that force less or more than what it takes to spin your plywood disc? Don't use your fingertips as a means of measuring stall torque on the 1/2 horse, by the way.

 

[revere521]

i think I have found a better motor

Thank you all for this help. I know I threw the artist/aesthetic monkeywrench into this. the idea is to build this as an elaborate machine which has no specific purpose, and could be built in a much simpler manner, but is not. I know it sounds kooky, but when put alongside its sister pieces they take on the feeling of some space-clockwork-carnival. It is an attempt to re-evaluate the natural progression of technology (as if one of the developmental factors of modern design and engineering didn't happen, this is how technology would have progressed, et-cetera, et-cetera). any way, now that I have thoroughly bored everyone, I found a windshield wiper motor that I will try to use in place of the 1/2 hp motor (which has no finger stall speed, and I have the scars to prove it already). the wiper motor has a worm gear drive (rediction) and I will use a ac to dc converter to run it. it appears to turn at 100rpms, which will be much easier to reduce to 5 or so rpms. I am an artist though, so if someone could repost that equation in a telling-it-to-an-eight-year-old manner so I could use it, I would much appreciate the learning experience. thanks again for all the help -- Doug
P.S. -- I will try to post a picture of the piece when it is finished if anyone wants to see it

 

[Bystander]

Fair 'nuff --- you want to reduce from 100 to 4 or 5. That's a 25 or 20 to 1 reduction (see a pattern here? Reduction ratio times output rpm equals input rpm). Two or three reduction steps should get you enough pinions, gears, and shafts to dazzle the viewers. A pair of five to one reductions is 25:1, 2.5, 2, and 4 gives you 20:1 (product of individual reduction steps equals overall reduction, and ratio of numbers of teeth on each pinion gear-gear pairing equals the factor by which rotation speed of the driven shaft (gear) is reduced relative to the driving shaft speed (pinion gear). The shop you're working with would probably be more than happy to help you work out an artistic arrangement --- there are a lot of machinists in this world with an artistic streak in them --- just make something to be making it, rather than having to keep it functional.

 

[megashawn]

I'd try to find a motor that more closely matches your wanted output.

This site is awesome for such ventures, cause you can get stuff relatively cheap, and its pretty good products:

http://www.sciplus.com/category.cfm?subsection=18&category=172

There are several motors there which can be used. Also keep in mind you can use a lower voltage on your current motor to slow it down.