Slow, torque-ey motors

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Re: Slow, torque-ey motors

#21  Postby Adco » Apr 12, 2016 7:45 pm

Servo motors are more complicated but you can get them complete with controllers. They don't generally have low ratio gearing. They are similar to radio control motors. They move fast.

A simple geared DC motor would be the best best. Get a 12VDC geared motor that is overrated for your needs and give it 3-5VDC only. Will turn reliably and slowly. If it is still too fast, cascade another gearbox onto it. Choose a motor that can lift say 3-4kg at 12VDC and then it will be able to lift 1 kg at 3-5VDC easily. It will have great torque and constant speed. If you engineer the whole set up well enough, you won't have to worry about it. And, you don't need too much electronics knowledge either.
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Re: Slow, torque-ey motors

#22  Postby ScholasticSpastic » Apr 12, 2016 7:47 pm

I'll look into that. I'm also looking at clockwork as a possible solution. If I can find a mainspring that would store sufficient energy to chug along for about a week and make the armature out of brass, that would be very steampunk, don't you think? :D
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Re: Slow, torque-ey motors

#23  Postby Adco » Apr 12, 2016 7:51 pm

ScholasticSpastic wrote:I'll look into that. I'm also looking at clockwork as a possible solution. If I can find a mainspring that would store sufficient energy to chug along for about a week and make the armature out of brass, that would be very steampunk, don't you think? :D
Very.

Ideally, a wall clock module would be perfect. they run off one 1.5V battery, last for a year and the hour hand section is slow turning. Problem is they have no torque. Pity they don't make giant ones.
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Re: Slow, torque-ey motors

#24  Postby ScholasticSpastic » Apr 12, 2016 7:57 pm

Adco wrote: Problem is they have no torque.

This is probably the problem I'd run into with wound-spring clockwork, too. :(
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Re: Slow, torque-ey motors

#25  Postby Adco » Apr 12, 2016 8:24 pm

Ultimately, only you know what you need. My 2 cents is based on limited experience with geared motors.

Whatever you do, engineer is well. Make it look steam punked because that means you took care and it therefore has a better chance of working. Overkill the power specs on both the motor size and the power supply size. If you need a 12V 1A PSU, get a 12V 2A PSU. etc. That way, you can turn it on and walk away with a worry. Oh, and house it properly. Make or buy an enclosure to keep out dust, insects etc.
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Re: Slow, torque-ey motors

#26  Postby ScholasticSpastic » Apr 12, 2016 8:26 pm

I've just found a local electric motor dealer and fired off my question. If their response is useful, expect a fun movie in this thread by 2017. Sorry I can't make it go faster, but I'm a biologist, and biology keeps its own schedule.

The armature will not be visible in the movie. So I'll need to take a picture when it's done. I'm quite sold on the brass idea. And not just because brass is a relatively soft metal and that makes it easier to work with.
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Re: Slow, torque-ey motors

#27  Postby Adco » Apr 12, 2016 8:31 pm

Well, good luck. Look forward to the movie.
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Re: Slow, torque-ey motors

#28  Postby ScholasticSpastic » Apr 12, 2016 8:42 pm

With any luck, you will observe a minimum time compression of 43,800x. :D
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Re: Slow, torque-ey motors

#29  Postby GrahamH » Apr 12, 2016 9:29 pm

What is the smallest incremental movement you require, beside too small to see?
You could use an escapement mechanism where you turn on the motor for long enough to complete one step of the escapement (ratchet) and move the load one smallest step. Then the motor is off for as long as you like. Motion is as slow as you like. The smallest step uses full motor power for best torque.

If you can use a counterbalance (e.g. a mass on a cord that runs over a pulley) then you can greatly reduce the torque required since most of the static load will be balanced out. If the counter balance is a bit heavier than the load then it can provide all the force to move the load and your motor only has to tip the escapement ratchet enough to let the weight drop one increment. Look at a typical clockwork balance wheel escapement and think about just rocking the ratchet with a motor (or a pendulum, or a balance wheel or a solenoid...)
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Re: Slow, torque-ey motors

#30  Postby chairman bill » Apr 12, 2016 10:52 pm

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Re: Slow, torque-ey motors

#31  Postby Macdoc » Apr 12, 2016 11:59 pm

Electrics have max torque at zero speed so the trick is smooth control at low rpm or as pointed out a gear box which adds cost.
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Re: Slow, torque-ey motors

#32  Postby tolman » Apr 13, 2016 1:09 am

ScholasticSpastic wrote:
laklak wrote:A bucket full of water, over a pulley, with a small hole in the bottom.

I actually thought about this. It's too fast. (Not joking!)

If you wanted *really* slow, and you weren't looking at moving the weight too far or having predictable speed, one non-motor solution would be to have an overweight counterbalance for the 1kg weight, with the counterbalance weight resting inside a liquid-filled tube somewhat wider than the counterbalance weight. Bulky, but it would have some nice properties.
As long as the excess weight of the counterbalance was less than the buoyancy it would feel if fully submerged, it would float at a fixed depth in the liquid, so slow removal of the liquid would slowly lower the counterbalance.
If you wanted glacial slowness, you could wait for natural evaporation, or speed that up with heat or fan-assistance,,but some miniscule leakage arrangement much more subtle than 'hole in bottom of bucket' should be possible to engineer.
While there's the issue of distance (the counterbalance has to be able to sink as far as the weight is lifted) one advantage of a drained-buoyancy system is that the lift rate depends not only on the leakage rate, but on the cross-sectional area of the draining system - for a given leak rate, a 'broader' system drains slower.
I guess a spherical counterweight would be the least likely to jam even in a tube not much wider than it was.

Speed wouldn't be constant in a simple system, but there might be ways to compensate for that to some extent.
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Re: Slow, torque-ey motors

#33  Postby GrahamH » Apr 13, 2016 10:28 am

Macdoc wrote:Electrics have max torque at zero speed so the trick is smooth control at low rpm or as pointed out a gear box which adds cost.


True, if max current is flowing, but not true if current is moderated to achieve a low speed.
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Re: Slow, torque-ey motors

#34  Postby Scot Dutchy » Apr 13, 2016 10:48 am

GrahamH wrote:
Macdoc wrote:Electrics have max torque at zero speed so the trick is smooth control at low rpm or as pointed out a gear box which adds cost.


True, if max current is flowing, but not true if current is moderated to achieve a low speed.


That is where thyristors come in.

http://innovaenterprises.co.in/thyristors.html

Thyristors are also used in motor speed controls, light dimmers, pressure-control systems, and liquid-level regulators.
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Re: Slow, torque-ey motors

#35  Postby Cito di Pense » Apr 13, 2016 10:52 am

Scot Dutchy wrote:
That is where thyristors come in.


Have one off at thyristor somewhere else.
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Re: Slow, torque-ey motors

#36  Postby Adco » Apr 13, 2016 11:04 am

Scot Dutchy wrote:
GrahamH wrote:
Macdoc wrote:Electrics have max torque at zero speed so the trick is smooth control at low rpm or as pointed out a gear box which adds cost.


True, if max current is flowing, but not true if current is moderated to achieve a low speed.


That is where thyristors come in.

http://innovaenterprises.co.in/thyristors.html

Thyristors are also used in motor speed controls, light dimmers, pressure-control systems, and liquid-level regulators.
A thyristor is an on/off switch basically. It is used mainly in AC applications where the voltage would swing through 0V thus switching the device off. When a thyristor is used in DC applications, it becomes an on switch. Once the gate is triggered, it stays on until voltage is removed from the circuit. A GTO thyristor can be turned off via the gate but it is still only a switch. It would be difficult to use a thyristor in a DC motor application to control speed. You would only have no speed or full speed.

Basically, a thyristor turns on when triggered via the gate and turns off when power is removed.
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Re: Slow, torque-ey motors

#37  Postby ScholasticSpastic » Apr 13, 2016 3:40 pm

So... When a thyristor is used in AC applications can it serve to moderate motor speeds? Because the local electric motor supplier I've just corresponded with recommended a 1rpm AC gearmotor and if I can take it lower than 1rpm without using a bunch of gears that might be nice. Alternatively, I don't mind assembling a bunch of gears. Could be fun once I figure out how to couple to the motor's shaft. It would probably be best to combine some sort of motor throttling with additional gears to take me to the speeds I want.
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Re: Slow, torque-ey motors

#38  Postby GrahamH » Apr 13, 2016 4:05 pm

If you go for an ublanaced arrangement, where the motor shaft supports the load (no counterweight) you should use gearing that will not 'overhaul' if the motor power is off. A worm gear is a good option here because it will not overhaul and provides high gear ratios.

Ignore the thyristor thing. Get a motor speed control module to suit whatever motor you get.
Watch out for low speed motors. That 1rpm motor may be an induction motor who's speed is set by the mains ac frequency. It could be tricky to control the speed electronically. You could just turn it on for a few seconds every now an then. WIth the right gearing you would not notice the small steps.
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Re: Slow, torque-ey motors

#39  Postby Onyx8 » Apr 13, 2016 6:20 pm

ScholasticSpastic wrote:
laklak wrote:A bucket full of water, over a pulley, with a small hole in the bottom.

I actually thought about this. It's too fast. (Not joking!)


Duct tape a hairdryer to the top of the bucket. What could possibly go wrong?
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Re: Slow, torque-ey motors

#40  Postby ScholasticSpastic » Apr 13, 2016 7:00 pm

Onyx8 wrote:
Duct tape a hairdryer to the top of the bucket. What could possibly go wrong?

:lol:
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