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Reduction Design Using Sychronous Belts and Pulleys

06/09/2011 11:27 PM

Has anybody tried designing a multiple stage reduction gear using synchronous belts and pulleys?

I have a 1/3HP 24VDC motor turning at 2500 RPM. I need to reduce that speed to approximately 42 RPM. This would be done in approximately 4 stages.

I have not seen anything commercially available using synchronous belts so I'm considering building my own.

The benefits I see are as follows:

1) Relative high efficiency compared to a worm reduction. A single stage synchronous belt system is approximately 98% efficient making a 4 stage reduction about 92% efficient.

2) No lubrication is required for the life of the assembly.

3) Relatively no heat generated.

4) The reduction assembly would be simple to design and build.

5) Relatively unsophisticated machinery is required to make the parts.

6) The reduction assembly would be easy to repair.

The only down side I've discovered so far is the high prices for the synchronous pulleys. These pulleys are basically extruded Aluminum shapes that appear to be grossly overpriced.

Does anyone see a downside that I have not considered?

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#1

Re: Reduction design using sychronous belts and pulleys

06/09/2011 11:40 PM

How about planetary gears or cycloidal drives?

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#5
In reply to #1

Re: Reduction design using sychronous belts and pulleys

06/11/2011 10:22 PM

I did look at planetary gears but found them to be priced between $500-$700 . Perhaps I'm dreaming but I was hoping to be able to purchase both the motor with a reduction gear attached to it for under $500. I also considered stepping motors but I couldn't tolerate the system searching for a home position every time it initialized.

Thanks for your input.

Dal

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#9
In reply to #5

Re: Reduction design using synchronous belts and pulleys

06/12/2011 3:23 PM

The searching is a function of your driver and software, a stepper motor itself does not need to do that.....I probably agree that as they are a bit "notchy" at low speeds, they may not be the best choice.

I personally would go for a three phase brushless motor with full electronic speed control.

As some plane model makers build their own, extremely high power motors for the props, because powerful and small enough motors are (were?) not available to buy, you might be able to copy them an achieve a good motor relatively cheaply......but that is only a guess....

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#2

Re: Reduction Design Using Sychronous Belts and Pulleys

06/10/2011 11:45 PM

What are you using it for? Torque requirements? Need for circular motion?

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#6
In reply to #2

Re: Reduction Design Using Sychronous Belts and Pulleys

06/11/2011 10:26 PM

240 in-lbs torque at the output 6.0 in-lbs at the motor

I need a circular motion as the output drives a pinion that attaches to a rack.

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#3

Re: Reduction Design Using Synchronous Belts and Pulleys

06/11/2011 7:40 AM

Why not do it mostly electronically with some form of feedback mechanism.....you could get it exact onto 42<rpm then.

You might want to divide by 4 with pulleys first to get the torque up if needed.....a flywheel will help to stabilize things if running on the motor itself.....

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#7
In reply to #3

Re: Reduction Design Using Synchronous Belts and Pulleys

06/11/2011 10:56 PM

Hi Andy

I do require 27Nm torque at the output.

The electric motor will deliver 0.7Nm torque.

I believe that without the reduction gear I won't have enough torque.

I did want to be able to control both speed and direction of my motor. The motor is a 24VDC motor. The speed I believe can be controlled using solid state electronics employing PWM (Pulse Width Modulation) circuitry. I'm not much of an electronics guy but I do think this works. I need this feature to allow my device to accelerate and decelerate without any shock loading. Motor speed will vary between 0 and 2500RPM while the output shaft will vary between 0 and 42 RPM. Input to this electronic circuit would be a center tapped potentiometer. Turning the potentiometer one side of center would slowly accelerate the motor in one direction. Turning the potentiometer the other side of center would slowly accelerate the motor in the other direction.

Thanks for your input

Dal

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#10
In reply to #7

Re: Reduction Design Using Synchronous Belts and Pulleys

06/12/2011 3:27 PM

Your comments fit in with my general take on the subject....do use some form of feedback if you need exact RPMs. This will also stop load changes, changing speed.

Best wishes....

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#4

Re: Reduction Design Using Sychronous Belts and Pulleys

06/11/2011 7:29 PM

Electric wheel chairs use this type of synchronous belt drive only in double reduction. Bicycles are also using syncronous belt drives using a single speed or Shimano rear wheel internal hub planetary transmission. For bikes it is much smoother, very robust and cleaner. Contact ixibike.com for "plastic pulleys" and Gates Corp. for drive design help. I don't know about your application, but this should get you started.

Good Luck,

Mike

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#8
In reply to #4

Re: Reduction Design Using Sychronous Belts and Pulleys

06/11/2011 11:05 PM

Hello Mike

Some great info in your post. I'll certainly contact ixibike and Gates.

I have a lot of respect for the quality of components used on bikes. I'm quite a biker myself. I think in the last 4 years I haven't spent more than $1.95 to keep my bike going.

Regards

dal

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#11

Re: Reduction Design Using Sychronous Belts and Pulleys

06/13/2011 7:39 AM

Hi Dal,

If timing pulleys are your biggest concern then they can be made from aluminium, quite easily and cheaply on a wire edm machine. You need to provide a bar of aluminium with pre-drilled holes for your hub. the edm process could finish your hub hole diameter including a drive keyway, then cut the peripheral geared section complete in perfect concentricity.

Chose tooth configurations to suit standard drive belt drives and design/draw your pulley. If you do this, special programming would be avoided by the edm shop. Depending on gear thickness and diameter, the price should be $20-$40ea

Good luck,

Jim...

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Andy Germany (3); Dal Wagner (4); jimmymac28 (1); Mike Ellis (1); ormondotvos (1); Tornado (1)

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