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# Calculating Weight of a Mechanical Power Transmission Mechanism

10/09/2021 5:46 PM

I'm comparing different ways to transmit power - with a large rpm change - between different points in a machine, and I need a way to calculate the weight of a mechanical power transmission mechanism. I'd rather not start from scratch with dimensional analysis and so forth, and it seems to me that some approximate means must already have been worked out.

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#1

### Re: calculating weight of a mechanical power transmission mechanism

10/09/2021 8:03 PM

My way of looking at it is that first you need to determine the type of transmission you will use, then the max torque, hp and rpm required...then look for something off the shelf that would work...calculate any modifications that might be needed...est weight from available spec info....

https://www.machinemfg.com/types-of-power-transmission/

https://www.zf.com/products/en/industrial_gearboxes/home/industrial_gearboxes.html

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#2

### Re: calculating weight of a mechanical power transmission mechanism

10/09/2021 9:36 PM

It would depend a lot on the amount of power. If you have some numbers on power and ratio, I would suggest finding suitable gearboxes and looking up specs or contacting the manufacturer.

If you're looking for light weight and high reduction, a worm-gear design might be appropriate.

Maybe this will help...

22_E.Rejman, M.Rejman.pdf (mech-ing.com)

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#3

### Re: calculating weight of a mechanical power transmission mechanism

10/10/2021 4:50 AM

Right now I'm at the (very) preliminary stage where I need estimates for different types of power transmission systems. The finalists, if you like, are electric and mechanical transmission systems, and I need to choose one over the other.

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#4

### Re: calculating weight of a mechanical power transmission mechanism

10/10/2021 9:04 AM

Integrated electro-mechanical transmission systems in hybrid electric vehicles

Sorry too vague to make any judgement....

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#9

### Re: calculating weight of a mechanical power transmission mechanism

10/11/2021 2:09 AM

I guess you could call the electric option electro-mechanical, because there will be a speed reduction mechanism between the electric motor(s) and the output shaft. I'm comparing that with an entirely mechanical system.

The embarrassing thing is that I had the necessary formula (for a purely mechanical system) when I co-wrote an AIAA paper with Don Woodward in 1993. I had been flailing about trying to estimate the weight of the power train, and when Don learned of it he sketched the formula from memory. I used it, but the formula is not recorded in the paper, only the resulting estimate. Now I can't find the file of notes for my contribution to the paper, though they are probably misfiled in one of my 21 file cabinets. Don was so casual about the formula, that I figured that everybody other then me already knew it by heart.

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#10

### Re: calculating weight of a mechanical power transmission mechanism

10/11/2021 2:40 AM

I don't see how you can estimate weight without knowing the design and materials being used....I've handled enough car transmissions to know they can vary in weight quite a bit from car to car even though the engines may be similar in hp output...

..."You can expect an average transmission weight to be about 100 to 400 pounds (45 to 181 kg) or about 226 lbs (103 kg) for a standard size transmission. Generally, the lighter a transmission is, the higher the performance is, although it depends on the vehicle."...

https://www.survivaltechshop.com/transmission-weight/

Neither can you est power output by engine weight....

..."Engine size is the largest factor in weight, with most large engines like V8s weighing between 400 and 700 pounds and a smaller V6 engine weighing between 300 to 450 pounds on average. However, diesel motors can weigh more than 700 pounds. "...

https://mechanicbase.com/engine/car-engine-weight/

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#11

### Re: calculating weight of a mechanical power transmission mechanism

10/11/2021 3:08 AM
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#12

### Re: calculating weight of a mechanical power transmission mechanism

10/11/2021 4:45 AM

Clearly the real world includes factors like material and type of construction but if I remember the formula had a constant or constants to account for those factors.

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#21

### Re: calculating weight of a mechanical power transmission mechanism

11/05/2021 2:55 AM

Found my notes for the AIAA paper!

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#5

### Re: calculating weight of a mechanical power transmission mechanism

10/10/2021 5:49 PM

OK,how high is up?How low is down?How hard is hard?How hot is hot?

I need a gear.Any gear.

A wrist watch has a very high reduction ratio,very low power requirements.

A semi tractor has a large power demand.See how that works?

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#6

### Re: Calculating Weight of a Mechanical Power Transmission Mechanism

10/10/2021 5:51 PM
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#7

### Re: Calculating Weight of a Mechanical Power Transmission Mechanism

10/10/2021 11:06 PM

Friend,

Your question is so vague that I cannot give you any help. Why do you exclude other ways of power transmission such as hydraulic?

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#8

### Re: Calculating Weight of a Mechanical Power Transmission Mechanism

10/11/2021 1:44 AM

I considered hydraulics early on, but was not comfortable with the auxiliaries required to recover, store and re-use the hydraulic fluid.

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#13

### Re: Calculating Weight of a Mechanical Power Transmission Mechanism

10/11/2021 12:46 PM

Friend,

You mention recover, store and re-use, but I understand the low-pressure fluid back from the hydraulic motor needs to be returned in a closed-loop to the pump, with the presence of an accumulator or similar device in that line to absorb or cushion the pulsations that will occur in the system. Thus "recover" and "re-use" are the tubing or hoses, and "store" is a small accumulator. Are these components more of a problem than oil pans, bearings, splines, shafts, gears, seals, etc.? If there are leaks, then there is a need to replenish the fluid occasionally. In a purely mechanical system there is likewise a need to lubricate the components occasionally.

In this approach your all of the parts are relatively small, with weights easy to determine based on speed, power capacity.

--JMM

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#14

### Re: Calculating Weight of a Mechanical Power Transmission Mechanism

10/11/2021 6:01 PM
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#15

### Re: Calculating Weight of a Mechanical Power Transmission Mechanism

10/12/2021 5:14 AM

He he - must be another Don Woodward. My friend would not have been born yet.

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#17

### Re: Calculating Weight of a Mechanical Power Transmission Mechanism

10/12/2021 4:06 PM

Transmission to motor weight = 1 to 9 ratio....give or take

Single speed reduction gear

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#16

### Re: Calculating Weight of a Mechanical Power Transmission Mechanism

10/12/2021 12:59 PM

From the information given, volume x density of the imaginary material will get you as close as anything else with no specifics given.

Time to go shopping for a drive unit, COTS type.

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#18

### Re: Calculating Weight of a Mechanical Power Transmission Mechanism

10/16/2021 3:11 AM

Thank you very much for your efforts on my behalf.

I have just dug up an Air Force report comparing the weights of electrical, mechanical, hydraulic and pneumatic power transmissions. The specific application is accessory drives, but I'm confident that I can follow the same procedure for larger loads.

If anybody is interested, it is WADC-TR-53-36.

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#19

### Re: Calculating Weight of a Mechanical Power Transmission Mechanism

10/16/2021 3:09 PM

Good luck sifting any useful information out of that....

http://contrails.iit.edu/reports/2146

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#20

### Re: Calculating Weight of a Mechanical Power Transmission Mechanism

11/05/2021 2:54 AM