Need some motor suggestions

[S.]

For part of my final year project I need to build a test rig, for this I need to turn a shaft at between 0-20Hz (0-1200rpm in other words). I am not so fussed about the output speed, if it'll only do . The shaft will be turning a 2.5" eccentric that's pushing a ~120kg (suspended) mass up and down. So what I need is a motor (and possibly gearing) of some kind that will allow the output speeds I want, with enough torque to be pushing that weight around without slowing down/speeding up during the cycle too significantly. If need be I can reduce the eccentricity to maybe 2" but I'd rather not.

So far the ideas I have are:
1. Old chainsaw motor. These put out about 5hp or so, and rev to about 9500rpm, so would need to be geared down significantly. I have access to these so they cost me nothing, but on the other hand they have SFA power low down (they're 2 strokes designed only for running at full throttle really) and like all petrol motors they don't run at 0rpm. They do however have centrifugal clutches so it might be possible to make something work, but given that I need to be able to test down as low as 60rpm, I think it'd be very difficult to gear it down enough (would need about a 20:1 gear ratio, maybe using some bodged up bike gears).
2. Car starter motor. Pretty torquey, easy to run off a battery, but again needs gearing down quite a bit. Easy to get hold of too.
3. 4wd winch or something along those lines - anyone know what the motors in these are like? They must be geared down like crazy to work with winches, and they might also be worm gears as well? These are harder to come by (for cheap anyway).

Any comments on the above or other suggestions are most welcome.

[del]

Chainsaw motor or maybe a 4stroke lawnmower engine, with worm gears would be my best bet? depends how much you have access to I guess.

[bowzaa]

Considered something like a ride on lawnmower motor?
Might rev a bit high for you though steve, i'm not sure, but are readily available in slightly larger hp ratings than a chainsaw if needed.
I'm guessing the motors out of like industrial fans and the like again would probably rev too fast, but might work, depending on the gearing?

[S.]

It needs to be something I can get my hands on fairly easily/cheaply (via car wreckers or ebay or the trading post or something). I think a chainsaw engine would be reasonably powerful (5hp is quite a bit, and being a suspended mass that it's moving, high frequencies won't be THAT great an additional load on the suspension. I just don't think the lower-speed control is that good, because I need to be able to keep it at a constant speed at fairly low output speeds. Chainsaw throttles are quite sensitive and are not easy to modulate.

[Angry Atheist]

So you want to turn a shaft at near zero rpm?

The only way you are going to achieve that is by using a stepper motor. Try using a gas-anything and you'll find that it either stalls or you'll have to use a fluid clutch to prevent the gas motor from stopping. Unless you know what you are trying to achieve with regards to viscousity (sp), vane size, low speed power (near idle) of the gas motor liquid clutch, the best option... the easy calculatable option would be to use an electric motor.

Where to find a large torque stepper motor?

ans: ever had a play around with a later model washing machine?

...and before you say "portability" (if it IS a requirement), the way to make such device work is to use a gas motor to run an alternator (and possibly deepcyle wetcell), which feeds into a step-up transformer which outputs a (hopefully) clean sine wave. Most put out a dirty square wave so some of these transformers are not suitable to large induction forces. The more $ the better.

The wires which typically feed a washing machine stepper motor are around 0.6mm diameter (~22 ga). Typically a few amps - totally within the specs for a lowish power tranformer. The added bonus is that you can look at the control board and (cough) sort of copy (cough) it.

Go here (http://www.jaycar.com) and on the left browse box select "Inverters"

The list should give you a general idea.

EDIT: Jaycar needs Javascript enabled, otherwise you'll get zero results.

[BM Epic]

4wd winch would be good,but very expensive,unless you could get your hands on one at a 4wd wreckers,control of revs and modulation would be great,but getting one will be costly! It would handle 120kg's without a whimper!

[S.]

So you want to turn a shaft at near zero rpm?

The only way you are going to achieve that is by using a stepper motor. Try using a gas-anything and you'll find that it either stalls or you'll have to use a fluid clutch to prevent the gas motor from stopping. Unless you know what you are trying to achieve with regards to viscousity (sp), vane size, low speed power (near idle) of the gas motor liquid clutch, the best option... the easy calculatable option would be to use an electric motor.

Where to find a large torque stepper motor?

ans: ever had a play around with a later model washing machine?

...and before you say "portability" (if it IS a requirement), the way to make such device work is to use a gas motor to run an alternator (and possibly deepcyle wetcell), which feeds into a step-up transformer which outputs a (hopefully) clean sine wave. Most put out a dirty square wave so some of these transformers are not suitable to large induction forces. The more $ the better.

The wires which typically feed a washing machine stepper motor are around 0.6mm diameter (~22 ga). Typically a few amps - totally within the specs for a lowish power tranformer. The added bonus is that you can look at the control board and (cough) sort of copy (cough) it.

Go here (http://www.jaycar.com) and on the left browse box select "Inverters"

The list should give you a general idea.

EDIT: Jaycar needs Javascript enabled, otherwise you'll get zero results.

Yeah need to get it down to around 60rpm (1Hz) which is extremely slow, but also up to around 20Hz (1200rpm). Gearing something down to 60rpm would require a ridiculous level of gearing really (probably in the region of 1:50). Cheers for the suggestion. Portability isn't an issue provided I don't need a forklift or anything to move the thing, if I can lift it myself it's fine. How much torque do those things put out? Do they tend to have gearing built into them (since washing machines aren't exactly the fastest-spinning things on earth)? I've never played around with one... I do know a guy who works on industrial laundry equipment for a living though, I'll get stuck into him. I also have absolutely fark all knowledge of electrical controls and stuff, most of the stuff you're saying is going straight over my head (deep cycle wet cells?). Since portability isn't too much of an issue (it's for a test bench thing, doesn't need to be moved whilst testing) I was hoping to just use 240V power for it...

[Angry Atheist]

Yeah need to get it down to around 60rpm (1Hz) which is extremely slow, but also up to around 20Hz (1200rpm). Gearing something down to 60rpm would require a ridiculous level of gearing really (probably in the region of 1:50). Cheers for the suggestion. Portability isn't an issue provided I don't need a forklift or anything to move the thing, if I can lift it myself it's fine. How much torque do those things put out? Do they tend to have gearing built into them (since washing machines aren't exactly the fastest-spinning things on earth)? I've never played around with one... I do know a guy who works on industrial laundry equipment for a living though, I'll get stuck into him. I also have absolutely fark all knowledge of electrical controls and stuff, most of the stuff you're saying is going straight over my head (deep cycle wet cells?). Since portability isn't too much of an issue (it's for a test bench thing, doesn't need to be moved whilst testing) I was hoping to just use 240V power for it...

That laundry guy... if he sticks his fingers in them, he'll know a hell of alot more than me.

The old washer is the front one ie: MW512 ....I think :
http://i296.photobucket.com/albums/mm199/AngryAsshole/Motors-6kgfront.jpg
This is the stepper motor
http://i296.photobucket.com/albums/mm199/AngryAsshole/Motors-Diameter.jpg
What is looks like:
http://i296.photobucket.com/albums/mm199/AngryAsshole/Motors-StepperMotor.jpg
Close up of the poles showing thin wires
http://i296.photobucket.com/albums/mm199/AngryAsshole/Motors-StepperPoles.jpg

The washer is a six kilo rated which fills with water and agitates. I don't know how much water it uses, but I guess around 70L. If it can turn a tub with ~75kg with ease, then if you were to have a direct drive shaft to the cam, the motor would be at its absolute rating. (As you should know, over engineer roughly +50%). Introduce a 3-1 gear ratio and you'll keep the motor under its "safe 100%" rating.
Also the max speed it spins it 1000rpm. Remember the +50%!

And finally deep cycle wet cells are:

deep cycle = typically a secondary battery that can be discharged to 85% of its rating repeated over many dis/charge cycles.

wet cell = generic name for lead acid

deep cycle wet cell = typically a marine/solar power specific lead acid battery rating somewhere around 400AH, and physically big.

A little one (http://springers.com.au/Products.aspx?ProductID=188)

Now, the choice is yours.

EDIT: the cam I talk about is what you talk about when you say eccentricity???

[Angry Atheist]

4wd winch would be good

Exactly what i thought about...

until you want near zero rpm with power applied.

ADDition to above:

If using a non-stepping type of motor you'll find that a motor with no load wants to run at a certain speed. At that certain speed the motor is using the least amount of power to run = optimal!!. As soon as you apply a load to it it will still want to run at its optimal rpm, it will suck more power until is running at optimal again. If you load down a motor soo much that is starts drawing extreme amounts of current then two things happen....

and both involve alot of smoke!

A requirement of near 0 rpm is not possible with these types of electric motors unless a slipper clutch is used.

The problem being slipping = friction, friction = heat and wear, both = $$ and maintenance.

+1 for pimping the stepper motor.

[S.]

Righto, cheers for that, will definitely look into it. Thanks heaps for your help.

[Incontinent]

How 'bout something like this?
92cc of supercharged goodness.
Spins out to 12,000 rpm
Weight 25kg (so it is portable)
Wonder if Weber can make a gearbox to suit?


http://www.weberprecision.com/weberprecision1015010.jpg

[Matt H]

Ahaha that's awesome - it a V8! :D

[Incontinent]

Ahaha that's awesome - it a V8! :D

Yes and it works !!!!
Claimed as the worlds smallest V8 engine.
It's creator doesn't give output rating for it, probably couldn't find an engine dyno small enough for it.

[Angry Atheist]

You got to have a look at for miniature V8 on youtube.

Some of them even sound phat.

Hint: have a tissue closeby to catch your drooling.