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Old 07-07-2023, 05:40 PM
 
23,589 posts, read 70,358,767 times
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Agree with #1

Look into the history of time prior to clocks, it is fun. What I found enlightening was that in the very first days of mechanical timekeeping, industry and businesses cheated and kept employees working longer than was agreed upon. The town clock with its bells was in response to that.

As for the whole numbers -
If you want a .5, you make a gear with twice as many teeth. Every other one is a .5
If you want a .333, you make a gear with three times as many teeth.

To get back on topic, you can estimate the number of work hours left in a horse by looking at its teeth. The more worn down, the fewer remaining hours on the clock.
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Old 07-12-2023, 12:52 PM
 
Location: SCW, AZ
8,301 posts, read 13,434,842 times
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Very interesting points/info.

This still makes me wonder if as a society we are just too stuck in the old ways, taking comfort or being lazy instead of looking to improve the standards to make things more efficient?
While I like the "don't fix it if it ain't broken" motto, I always look to improve things that could be easier and/or quicker, especially if they don't fully sit well with my logic (because, mainly, I am lazy).

Then again, I never see any technical historical data about what certain common standards or inventions people tried to improve/upgrade and failed. That would probably make a good show.
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Old 07-12-2023, 02:52 PM
 
2,020 posts, read 1,310,772 times
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Quote:
Originally Posted by RobertFisher View Post
I need to mount a small motor on a piece of 2x4 wood. I want to know whether the wood can sustain the force generated by the motor.

I found these:

1 horsepower = 746 Watts = 746 Joules/Second

1 Joule = 1 Newton of force displacing 1 kg mass 1 meter

Does this mean 1 Joule = 1 Newton?

Is it possible to express the force in pounds that we are more familiar with? Because wood strength is described in pounds. An 8' 2x4 can probably sustain 200 lbs before it breaks.
The number you want to look for in boating is "thrust". That's the force that pushes the boat forward.
The motor's propeller pushes the water backwards, and the reaction to that force pushes the motor forward. The motor is tied to the boat, so the reaction to the motor pushing against the boat is what pushes the boat forward.

The Internet says that the thrust is somewhere between 20 and 100 pounds per horsepower, so a 2.5 hp motor would apply between 50 and 250 pounds of force to the 2x4. Thanks Internet for a vague answer.

You can find better numbers for your engine if you search for the model and the word "thrust".

Something to know that complicates things in your design is the the typical propeller on an outboard is about 2 feet below the transom, so the force it applies tries to cause a rotation that pulls the top of the mount backwards off the boat. Also, unless you're going slow, hitting a sandbar or log will be the greatest force your mount will experience.

Here are some discussion threads.
https://www.boatdesign.net/threads/h...to-1-hp.24964/
https://www.boatdesign.net/threads/o...-thrust.44894/

There's no fixed number for you.
Just like with cars with the same horsepower, there is a trade-off between top speed, acceleration, and gearing. In boats the tradeoff is between towing force, acceleration, top speed, and propeller size and pitch. So two identical boats with identical engines can have different thrust and top speeds depending on propellor design.
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Old 09-03-2023, 03:52 PM
 
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horse power is an energy measure. Force is not. I could create a force of 1000 ft# with a 50 cent motor and a AA battery if I had a million dollar transmission.
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Old 09-03-2023, 08:04 PM
 
Location: Sunnybrook Farm
4,506 posts, read 2,651,635 times
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Quote:
Originally Posted by fatkatie View Post
horse power is an energy measure. Force is not. I could create a force of 1000 ft# with a 50 cent motor and a AA battery if I had a million dollar transmission.
Well, kind of but not really. Power is the rate of doing work, strictly defined as time rate of change in energy. When you further break it down there are many ways to have a time rate of change in energy, for example constant force X constant velocity, voltage X current, etc.

Furthermore foot-lb is a measure of torque or energy or work not a unit of force.

I think one of the most useful tools I learned in four years of college was dimensional analysis. You might miss a constant but for comparisons, not absolute values, and for identifying equivalencies, it's been essential to me.
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Old 10-20-2023, 03:59 PM
 
966 posts, read 514,798 times
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Too many variables. WAY too many variables. HP is just a single term, it always works w/ RPM, torque, etc. Maybe the HP is low at one RPM. Maybe its high at another RPM but torque there is low. On and on and on. Best thing to do is design something and see what happens. R&D. Or better yet, use a proven design that can be scaled up or down.
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Old 03-06-2024, 08:39 PM
 
1,859 posts, read 837,121 times
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force is measured not calculated


Hp is how fast you hit the wall
torque is how far you move the wall
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Old 03-07-2024, 08:05 AM
 
Location: Sunnybrook Farm
4,506 posts, read 2,651,635 times
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Quote:
Originally Posted by b29510 View Post
force is measured not calculated


Hp is how fast you hit the wall
torque is how far you move the wall

Dear sir or madam, I believe you are under a misapprehension as to the meanings of the terms "force", "power", and "torque".

Sincerely,

rabbit33
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