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Old 04-10-2007, 05:41 PM   #1
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Default Torque and Inch Pounds

Engineers in the crowd, can you please explain "inch pounds" and better yet, help me figure out how many "inch pounds" of torque I need in a motor to run my mash rake in my mash tun. Grainger has a unit that has 50 inch pounds of torque for example.

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Old 04-10-2007, 06:04 PM   #2
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Picture a lever attached to a mounted axis and this lever is parallel to the ground. If the lever is one inch long and you tie a 1 lb weight to the end, at the moment the lever begins to fall (t=0) you will be generating 1 in-lb of torque on the axis (assuming no friction in the system).
Duh, not very clear I'm sure...

Your 50 in*lb motor is another way of saying 50/12, or 4.16 ft*lb. I would think 4 ft lb to be enough to stir a mash, even one of your 25lb batches. You could test this by attaching a torque wrench to your mash stirring apparatus and operate it at the speed you want. The reading on the torque wrench is the required torque. This would be dependent of the thickness of the mash no doubt.

Now, a motor will produce that specific TORQUE at a specific (or range of) RPM. What speed do you need your mash to be stirred at?

Depending on the speed you need to stir at vs. the torque curve of the motor, you may need to employ mechanical gearing and/or speed control via PWM or simple current control.
Sounds like a cool project!

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Old 04-10-2007, 06:06 PM   #3
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Quote:
Originally Posted by Brewpastor
Engineers in the crowd
There should be a sort of engineer group that has an autofeed.

Valid technical questions get auto-sent to their inbox haha.

I love this group of brewers.
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Old 04-10-2007, 06:08 PM   #4
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It's like, you give them an inch and they take a pound. Actually, here's the lowdown as far as I know it. One inch pound means the motor has the ability to move one pound of weight located one ince from the center of the shaft. Think of your horizontal mixing arm as a lever. Fifty inch pounds of torque can move fifty pounds if it is only located an inch away from the shaft centerline. Of course, it's proportional so it can move 25 pounds located 2 inches away or 12.5 lbs 4 inches away. I'm not smart enough to figure how much torque you'll need to stir a mash though. I suspect you can test it by getting an automotive torque wrench and testing how much it takes to turn the paddle in a typical mash.


edit... man, chill beat me.

Personally I'm skeptical that 50 inlb is enough. It really depends on the cross-sectional area of the paddle.

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Old 04-10-2007, 06:16 PM   #5
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You can attach a torque wrench to the paddle assembly and measure the required force to move the mash.

Edit: Beat By Bobbie, who was beat by Chill.

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Old 04-10-2007, 06:22 PM   #6
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My paddle is actually a rake, made from a cut up oven rack. So the blades of the rake are really only cutting trough the mash and since they are round, they do not have a huge resistence. At its furthest the edge/end of the rake is 8.5" from the center. I don't want high RPMs and the one from Grainger is rated at 1.1 rpm which should be fine in terms of cutting the mash.

Image of rake below:

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Old 04-10-2007, 06:42 PM   #7
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So the motor is 50in*lbs at 1.1 RPM? Sounds like a winner to me. Can you turn the mash rack in a stiff mash with one hand? Like between your thumb and middle/pointer fingers? If so that is for sure less than 50 in*lbs.

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Old 04-10-2007, 06:51 PM   #8
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If I remember correctly, you tend to make very stiff mashes. I think this will work, even so.

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Old 04-10-2007, 07:15 PM   #9
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If you have trouble ordering from Grainger, 6142K11 is an equivalent part number at McMaster.

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Old 04-10-2007, 07:21 PM   #10
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Ah I see. That baby already has the reduction gear attached. Makes more sense that it is 1.1RPM output now.

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