Rotating weight reduction
- Thread starter Bauer112
- Start date
Quit while you are behind .......
Your lack of common sense and practical knowledge is showing..........
You did not say anything specific about weight in your first example! But lets assume a typical weight change of +15 lbs for increasing to 20" dia wheel. That 4x15 or 60 lbs increase in total weight for the wheels. Which is greater 60 or 250. In other words the inertia effects due to a slight diameter change and gear ratio change is ~four times greater than the simple weight change of the wheel. I'm making assumptions about weight and diameter changes to help you understand how one effects the other. If you felt something by adding 20" wheel it had to be the ratio change as you would not feel 60 lbs change. But maybe you can?
As far as the idiot comment, that typical behavior for a little baby when you take away his popsicle.
Cinno
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This is on the right track (punny too). A lot of engineering formulas are derived from empirical data. The best way to ensure you have the most accurate equation to establish cause & effect from changes is to minimize variables to as few as possible - ideally only the one being evaluated.
Loads of engineering mumbo jumbo out there and lots of snake oil too ... truth lies somewhere in the middle. E.g. Poo drive belt is great - carbon fibre bumper not worth the $ / weight reduction.
Perhaps a good solution to the discussion would be to consider the effect of the changes on a drag sled - reduce the variability re snow conditions.
S
SNWMBL
Well-known member
You still can't leave the diameter out of it can you.
The primary reason for the 'power loss' running 20" wheels on ur truck Has to do with sectional width. 99.999% of 20in wheels are wider than stock 16in wheels.
The low profile (to maintain similar diameter)also creates a flatter surface. The road contact surface area is probably doubled. Rolling resistance from twice as much tire contacting the road is the power killer.
GS6
The low profile (to maintain similar diameter)also creates a flatter surface. The road contact surface area is probably doubled. Rolling resistance from twice as much tire contacting the road is the power killer.
GS6
Well I give up trying to solve this problem, as you didn't describe any relevant details. wheel weight change, tire diameter change , tire weight change, wheel and tire width change, tire pressure change, air temp, air density, altitude, and how many people in the cab. Nothing.
i guess it was a trick question to bait me into making assumptions. You win.
Cinno
Tread pattern, studded or siped, air or nitrogen, chrome rims or brushed, daylight savings time or standard, regular or premium, fresh turn signal fluid.
The more I read this thread the more I realize this man is a genius.
Well this all was an interesting read.
Reducing rotational weight has a much higher impact on acceleration on a vehicle than reducing an equal static weight. That's it....period....the end. It's been proven time and again through many forms of racing, manufacturing, and any other industry/application that uses rotational motors/engines. There are a ton of articles on this in various engineering books, manuals, and technical write-ups online. Here is an excerpt from one below that ironically seems to apply very well to the discussion:
A rotating mass does not really consume or dissipate energy. A rotating mass stores energy. The rotating mass eventually either returns energy to the system in a useful way, or something converts the stored energy to some other form of unwanted energy. The conversion might be with a friction, converting to heat. The energy stored might be helpful, like the smoothing of cylinder pulses in an engine flywheel. The energy stored also might not do anything at all, or the stored energy can even be harmful, reducing acceleration or braking.
Accelerating an unnecessary rotating mass requires energy, and the acceleration process saps some of the horsepower we have available to accelerate our vehicles. Reducing available horsepower affects acceleration in a very predictable manner, and the horsepower amount needed to spin something up gives us some feel for how important a part change might be.
Four things determine the effect of rotating mass. Every one of these things is important:
Here are how these things work:
That's all I have to contribute, now I'm going to go do the exact opposite and add weight to my sled (fuel, oil) and get ready to ride it this weekend. BBRRRRRRRRAAAAAAAAPPPP
Reducing rotational weight has a much higher impact on acceleration on a vehicle than reducing an equal static weight. That's it....period....the end. It's been proven time and again through many forms of racing, manufacturing, and any other industry/application that uses rotational motors/engines. There are a ton of articles on this in various engineering books, manuals, and technical write-ups online. Here is an excerpt from one below that ironically seems to apply very well to the discussion:
A rotating mass does not really consume or dissipate energy. A rotating mass stores energy. The rotating mass eventually either returns energy to the system in a useful way, or something converts the stored energy to some other form of unwanted energy. The conversion might be with a friction, converting to heat. The energy stored might be helpful, like the smoothing of cylinder pulses in an engine flywheel. The energy stored also might not do anything at all, or the stored energy can even be harmful, reducing acceleration or braking.
Accelerating an unnecessary rotating mass requires energy, and the acceleration process saps some of the horsepower we have available to accelerate our vehicles. Reducing available horsepower affects acceleration in a very predictable manner, and the horsepower amount needed to spin something up gives us some feel for how important a part change might be.
Four things determine the effect of rotating mass. Every one of these things is important:
- How quickly and often a rotating mass speeds up or slows down. Every time it is forced to speed up or slow down, it takes or releases energy
- How heavy the rotating mass is. More weight (with no other changes) stores or releases more energy
- The rotating weight's distance outwards from the centerline. The further out, the more energy pushed in and out of a given weight
- How fast the weight spins, or the speed the weight travels in a given circle diameter. The higher the RPM, the more energy stored
Here are how these things work:
- If we push energy into the rotating mass and pull energy out several times, we move more power around than if we make a slow, smooth, change in speed. It takes much more effort to repeatedly speed and slow something in a short period of time than to gradually speed it or slow it
- The amount of weight is the least important thing! If we double the weight (with no other changes) we only double the stored energy
- Weight distance from the center line is very important, because it determines the weight's circular velocity (speed)! Stored energy goes up by the SQUARE of the radius change. If we replace a 4-inch diameter hollow driveshaft with an 8-inch diameter tube of exactly the same weight, it is not just double. It is twice the size squared, or four times the stored energy when it weighs the same!
- The faster we spin the weight, the more energy it stores. If we double RPM, we multiply stored energy four times. Again it is a square of the change, just like weight distance from centerline is a square.
- If we reduce mass from twenty pounds to ten pounds, keeping the same distance out and same peak RPM, we reduce stored energy to half the original amount. Reducing weight is a one-for-one change.
- If we cut diameter in half while keeping the same weight and RPM, stored energy will be 1/4 the original stored energy. This change is a square. Twice is a "four times" effect. 2*2=4. Four times is a sixteen time effect on stored energy. 4*4=16
- If we cut RPM in half, we would reduce stored energy to 1/4 the original amount. Once again this is a squared change. Change RPM three times, and the stored energy changes nine times. 3*3=9
That's all I have to contribute, now I'm going to go do the exact opposite and add weight to my sled (fuel, oil) and get ready to ride it this weekend. BBRRRRRRRRAAAAAAAAPPPP
A few articles about inertia
Here is some easy reading about how to size motors in applications that require extreme accelerations and how important gearing is to proper motor sizing.
The second article consolidates many of the equations necessary. Its called a "cheat sheet". The fourth page has some examples of drive train configurations that show how torque, speed, and reflected inertia (J) is calculated for those different configurations.
http://machinedesign.com/archive/new-rules-sizing-servos
https://www.servo2go.com/support/files/Smart Motion Cheat Sheet Rev3.pdf
I worked in the motion control industry for 37 years before retiring (so I could enjoy snowmobiling more). When building a machine that cost several million dollars, the powers that be, do not give you a second chance when designing the system (computers, drives, gearboxes and motors ). They want it done right the first time or your history. So you use MATH. No touchy feely stuff here and no dynos. The computers and sensors inherent to these systems can tell you everything you need to know about why you screwed up.
Here is the order I spend my money on for performance mods (not a complete list) that all make a noticeable difference :
1. Clutch kit - increases efficiency that is tuned for your application (mountain, trail, etc)
2. Motor power mods - canister, pipe, .....
3. Traction - lugs, length, pitch, ......
4. Suspension - width,shocks, coupling
5. Sled overall weight - get a polaris and just weight for the next model.
6. A lot of money see burandt sled for sale.
.
.
.
1000. Rotating mass
Cinno
Here is some easy reading about how to size motors in applications that require extreme accelerations and how important gearing is to proper motor sizing.
The second article consolidates many of the equations necessary. Its called a "cheat sheet". The fourth page has some examples of drive train configurations that show how torque, speed, and reflected inertia (J) is calculated for those different configurations.
http://machinedesign.com/archive/new-rules-sizing-servos
https://www.servo2go.com/support/files/Smart Motion Cheat Sheet Rev3.pdf
I worked in the motion control industry for 37 years before retiring (so I could enjoy snowmobiling more). When building a machine that cost several million dollars, the powers that be, do not give you a second chance when designing the system (computers, drives, gearboxes and motors ). They want it done right the first time or your history. So you use MATH. No touchy feely stuff here and no dynos. The computers and sensors inherent to these systems can tell you everything you need to know about why you screwed up.
Here is the order I spend my money on for performance mods (not a complete list) that all make a noticeable difference :
1. Clutch kit - increases efficiency that is tuned for your application (mountain, trail, etc)
2. Motor power mods - canister, pipe, .....
3. Traction - lugs, length, pitch, ......
4. Suspension - width,shocks, coupling
5. Sled overall weight - get a polaris and just weight for the next model.
6. A lot of money see burandt sled for sale.
.
.
.
1000. Rotating mass
Cinno
Computers, drives....!! Thank god you weren't involved with any bridges, sky scrapers, or planes...among other things.
Just wow........
Translation;
If you can't blind them with brilliance baffle them with bul*****.
You succeeded in discrediting yourself.........
Nothing more.........
Wheres the "brilliance" wheres the "bull****" , how did i discredit myself? Be a little more specific if you can. If you don't understand the articles then just let it go....
Cinno
As I'm only 3 years into my industrial engineering and manufacturing career coming from a previous career as a diesel performance mechanic and welder/fabricator I've played this game before. Although I agree with you in that math is the tool to take you most of the way there, you only get there 100% of the way if there are no assumptions in your model. The formulas and theories you've presented thus far have SOME merit, however, there are too many assumptions in them to make them fully applicable and correct in the real world (track slippage on the snow being a BIG one, using a set gear ratio on the tq curve vs. the variable values a CVT clutch allows us to have being another). I can't count the number of times that an incoming engineer would argue us that "this (x project) is going to work 100% because it works on paper", having it verified and approved for manufacture by several other consulting groups and overhead engineers, only to have it fail because they used assumptions and averages to make the formulas work well and didn't take into account the outlying data points that actually happen in practical application.
I don't understand your distaste for a dyno and why you would consider such a tool to be "touchy feely"....a dyno would be the perfect tool that has been, shall I say, ENGINEERED to test these theories and their practical applications. That's the exact purpose of a dyno; to be able to adjust the different variables on the same piece of equipment and test to see if what the math tells you should happen is what actually happens in real life!!! You can't just "assume" and "average" the numbers in a given formula and then expect it to work in all applications in the real world. A dyno's full application is not supposed to be to measure how much horsepower and torque one engine has in comparison to another and get bragging rights, although it's what we usually use them for. Again there are many variables from one engine to another, from one vehicle to another, from one dyno and one day to another, that make the results mostly moot in close application. Dynamometers were developed to be able to take the same engine/vehicle, change one variable...say, a snowmobile and changing out ONLY the track, and seeing what the change in the HP/Tq curves are. That's also why there are engine only dynos, transmission only dynos, and full vehicle dynos.....to get rid of the variables and see how the change effects the unit in question.....not to just use math and take an average or assumption and apply it to the whole.
You can't take electrical engineering theories that come with building and tuning drives, PLCs, motors, gearboxes with minimal variability and directly apply everything over to mechanicals. If that's how you want to build your sled, that's your choice. It's obvious most of us will be going a different route.
I don't understand your distaste for a dyno and why you would consider such a tool to be "touchy feely"....a dyno would be the perfect tool that has been, shall I say, ENGINEERED to test these theories and their practical applications. That's the exact purpose of a dyno; to be able to adjust the different variables on the same piece of equipment and test to see if what the math tells you should happen is what actually happens in real life!!! You can't just "assume" and "average" the numbers in a given formula and then expect it to work in all applications in the real world. A dyno's full application is not supposed to be to measure how much horsepower and torque one engine has in comparison to another and get bragging rights, although it's what we usually use them for. Again there are many variables from one engine to another, from one vehicle to another, from one dyno and one day to another, that make the results mostly moot in close application. Dynamometers were developed to be able to take the same engine/vehicle, change one variable...say, a snowmobile and changing out ONLY the track, and seeing what the change in the HP/Tq curves are. That's also why there are engine only dynos, transmission only dynos, and full vehicle dynos.....to get rid of the variables and see how the change effects the unit in question.....not to just use math and take an average or assumption and apply it to the whole.
You can't take electrical engineering theories that come with building and tuning drives, PLCs, motors, gearboxes with minimal variability and directly apply everything over to mechanicals. If that's how you want to build your sled, that's your choice. It's obvious most of us will be going a different route.
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This is about the only sensible post about truck wheels and resistance I've read ... Wait didn't this start out about Snowmobiles???
And a 20X6 wheel would be Awesome with a 37X9.5 You would for sure be the talk of the Mud Pit !! What would that leave room for two rows of lugs ..
I will ....YOU SOUND LIKE AN IDIOT!! QUIT WHILE YOUR STILL BEHIND !!!
Not that you yourself is an idiot but your posts have gotten a little on the Mo Ron level and usually you have good reason but man that last post looks like drunk typing !!!!" Buy a Polaris and weight on the next model" ... Does that make the least bit of sense to the original post of rotational weight reduction ??????
Well , finally someone has the moxie to take me on without calling me an idiot. 3 years huh, your just a rookie.
So did you read all of my posts? What "too many assumptions" did I make? Traction defines the limits of how much sled inertia is reflected through the drive train to the motor. It is entirely appropriate to set it at any level and use it to define the limits of the problem as it doesn't change the validity of the basic calculations. At zero traction, track weight makes a noticeable difference in track acceleration but your not moving so who cares! At 100% traction all the sled inertia is coupled and the loss of 5 lbs in swamped out by the sled weight. The traction is obviously somewhere in between but your still splitting hairs.
The touchy feely comment, in several posts, was referring to how a change, like taking away track weight, feels to some riders. They haven't a clue what really changed because all the other more important variables were not held constant, "Can't see the forest for the trees".
The "feely" issue was not referring to a dyno. You misread what I said in your haste to criticize. Why I believe a dyno is a poor choice for testing rotational inertia effects is the dyno has to be in "ramp testing mode". The motor torque is not constant or repeatable while the motor speed is changing at a rate of about 4500 rpm/sec. Changing the weight of the belt changes the load on the secondary clutch which effects the upshift rate of the clutch which further contaminates the test. So you have to lock the clutch to remove that variable. Its just not worth the dyno time. The best way is to simply calculate it. The second article (post #111), page four and six gives you all the information necessary to do it. Its NOT ELECTRICAL, its mechanical. I used those calculations in many projects. They work, if you know how to apply them. Most colleges don't teach anything about motor sizing for motion control applications and I believe most industrial engineers start out as mechanical engineers in college but can't handle the math so they switch there major.
How did that last comment feel? Welcome to my world.
Cinno
By purchasing a polaris you are getting a industry leading low inertia sled, at over 100-300 dollars per pound it's just cheaper to wait until next years sled, which is usually lighter at a very competitive price. Ditch the suitcase, add a pipe, get a track length that matches your weight, don't worry or spend money on the little things as polaris does that for you.
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