Torque Increase from Speed Reduction

[AlZilla]

I've wondered how much torque increase we get from speed reducers. Is it inverse to the speed reduction?

Turns out it is. If your speed reducer provides 1:3 speed reduction, you're getting a 3:1 torque increase.

(The following assumes a start up speed of 100 rpm at the motor)

But, even though you can put a 30MM (basically 1.18 inch) pulley on your motor against a 3" hand wheel and end up with a final decrease of 1:2.5 (39 rpm) and corresponding torque increase, you're still better off throwing a 1:3 speed reducer in the middle.

Adding the typical 2"/6" speed reducer to the above gives you a speed reduction and torque increase factor of a whopping 7.58.

Most of what I've read indicates that servos want to run at or above 300 rpm for cooling. The setup imagined above with the speed reducer would be around 40 stitches per minute at a 300 rpm motor speed. (it's not only imagined, it's bolted onto my 111W153, patiently awaiting the 30MM pulley)

duck.ai provided confirmation about the torque increase. Now properly credited, here's what it had to say:

Understanding Torque and Speed in Pulley Systems

Torque and Speed Relationship

In a pulley reduction system, torque and speed have an inverse relationship. When the speed of the driven pulley decreases, the torque increases. This is due to the mechanical advantage provided by the pulley system.

How It Works

• Larger Driven Pulley: If the driven pulley is larger than the driver pulley, it will turn more slowly. This results in increased torque at the output.

• Smaller Driven Pulley: Conversely, if the driven pulley is smaller, it will turn faster but produce less torque.

Calculation of Torque

The torque available at the driven pulley can be calculated using the following principles:

• Torque Multiplication: The torque at the driven pulley is multiplied by the ratio of the diameters of the pulleys. For example, if the driven pulley is twice the diameter of the driver pulley, the torque is effectively doubled, while the speed is halved.

Practical Implications

This principle is commonly used in various applications, such as:

• Automobiles: In low gear, the engine speed is high, but the wheels turn slowly, providing more torque for acceleration.

• Conveyor Systems: Slower speeds can help manage heavy loads without slipping.

In summary, in a pulley reduction system, as speed decreases, torque increases, allowing for greater force to be applied at lower speeds.

 Sciencing aimsindustrial.com.au

So, until someone comes up with a servo offering 7X more torque than current offerings and running at a minimum 50 to 100 rpm, torque increasing speed reducers are king.

 

[friquant]

Can you post a link to the 30mm pulley you bought?
I ordered one but it arrived today and it's narrower than I expected. Only a 7mm gap for the belt, and my belts are 6.5mm wide on the inside edge, 9.5mm on the outside edge.

 

1 hour ago, AlZilla said:

Adding the typical 2"/6" speed reducer to the above gives you a speed reduction and torque increase factor of a whopping 7.58.

Once you get it set up I'm curious to hear how it is to move the handwheel manually. I've been wondering what is the optimal motor size and gear reduction that gives plenty of torque but is still easy enough to manipulate at the handwheel. I've got a 1-hp 3-phase gearmotor (4.5:1 gear reduction) on the way, it will be my first VFD setup and my first system that is geared down more than just putting a small motor pulley on it.

[AlZilla]

1 hour ago, friquant said:

Can you post a link to the 30mm pulley you bought?
I ordered one but it arrived today and it's narrower than I expected. Only a 7mm gap for the belt, and my belts are 6.5mm wide on the inside edge, 9.5mm on the outside edge.

I ordered the same one you did. I couldn't find one for a 3L belt. If it's a problem, I'll just throw a round leather belt on it. I ran that machine for several months on one.. They work fine.

I think the narrow pulleys are intended for those round rubber belts you melt together.  PU, maybe?

There are also narrower V belts.  I'll make it work.

[dikman]

Thanks Al, this has obviously been gnawing away at you for a while. 

I reckon ease of handwheeling with a speed reducer depends on the size of the handwheel. The smaller handwheel on many of the older machines might require more effort but my 4500 has a large handwheel and it can overcome the speed reducer pulleys without much trouble. I've replaced the small handwheel on older machines with a large pulley and found it much easier to handwheel.

[AlZilla]

3 hours ago, friquant said:

Once you get it set up I'm curious to hear how it is to move the handwheel manually.

i used it today with the current 65mm motor pulley and it hand wheels just fine. If it's any different with the 30MM pulley, I'll report back.

[kgg]

5 hours ago, AlZilla said:

Turns out it is. If your speed reducer provides 1:3 speed reduction, you're getting a 3:1 torque increase.

My Take:

Speed reduction is like a double edged sword. If you use a speed reducer for just reducing the machines sewing speed no harm will come to your machines internals. If you want / need the increase in torque to punch through something because of the additional available torque that a speed reducer will deliver. You run the risk of damaging / twisting internal parts that are not designed to take that load. The better option is then to invest in a different / better machine that is designed to handle that type of work.

My attitude has always been if I need to use a speed reducer for additional torque benefits I am using the wrong machine. 

kgg

[friquant]

What are y'all using to limit torque to your machines?
So far all I've got is a loose belt.

[AlZilla]

2 hours ago, kgg said:

My Take:

Speed reduction is like a double edged sword. If you use a speed reducer for just reducing the machines sewing speed no harm will come to your machines internals. If you want / need the increase in torque to punch through something because of the additional available torque that a speed reducer will deliver. You run the risk of damaging / twisting internal parts that are not designed to take that load. The better option is then to invest in a different / better machine that is designed to handle that type of work.

My attitude has always been if I need to use a speed reducer for additional torque benefits I am using the wrong machine. 

kgg

On the other-other hand, these digital servos suffer from low torque at low speeds. With enough reduction we can run the motor a little faster, where it might be a little happier and still have decent torque.

If the machine will stand up to the torque of a clutch motor at 1700 rpm to 3400 rpm, I doubt even a torque increased servo is going to damage them.

Now I need to go find out the torque put out by those old clutch motors.

EDIT: So the rated torque of the clutch is about the same as the servo (which makes sense). But the giant spinning mass of that clutch motor has got to pack a pretty healthy wallop.