confuzzling gear ratio definition.. wanna clear this one up?

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Posted by Anton Abaya at 1/18/2001 11:04 PM EST


Coach on team #419, Rambots, from UMass Boston / BC High and NASA, Mathsoft, Solidworks.



hehe, this is a rather stupid question that seems to confuse everyone I've asked.

When I say my robot last year drill gear ratio of 2:1, the input is 2 rotations of the motor, and an output of 1 rotation of the wheel. is this correct ?

i checked a physics book and that's how they did it. So the example above is GEARING DOWN.

From what I can tell, you would ALMOST ALWAYS want to gear down from the drill motors and would NEVER gear up because the drills are spinning really fast. What needs to be adjusted is HOW MUCH you GEAR DOWN and the ratio of that.

Am I correct in my logic? Feel free to correct me because everytime I talk to someone else, i get either the same logic, or the exact opposite.

Funny thing is I've asked perhaps 14 people and it's split in half..... wanna clear up this one once and for all Joe?

-anton

ps. i'm a cs student...why should i care? perhaps because i'm a ninny with a power tool...yeah thats it.

[archiver]

Posted by Mark Garver at 1/19/2001 9:49 AM EST


Student on team #68, Truck Town Terror, from Waterford Kettering/OSMTech Academy and General Motors Truck Group.


In Reply to: confuzzling gear ratio definition.. wanna clear this one up?
Posted by Anton Abaya on 1/18/2001 11:04 PM EST:



You are right, it would be a 2:1 ratio. And for the most part you wouldn't want to gear the drill motors up. I am guessing that you were in low gear last year and you used about 8" drive wheels? if you did this you would travel at about 6 feet per sec. (if i did the math right). If you are in low gear the speed of the output shaft is about 400 rpm. If you are in high gear the speed of the output shaft would be about 1200 rpm. I hope this helps answer your question.

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Posted by Jim Meyer at 1/19/2001 10:30 AM EST


Engineer on team #67, HOT Team, from Huron Valley Schools and GM Milford Proving Ground.


In Reply to: confuzzling gear ratio definition.. wanna clear this one up?
Posted by Anton Abaya on 1/18/2001 11:04 PM EST:



I believe the gear ratio is the # of teeth on the driven divided by the # of teeth on the driver, or the ratio of pitch diameters, driven/driver. So if the output (wheel) is spinning slower than the input (drill motor) the gear ratio is larger than one. I would assume everyone agrees with this point. Axle ratios on RWD vehicles are always greater than one, 4.10 and 3.43 are examples for GM trucks. The place where I sometimes get confused is which is a higher gear or lower gear.

When you downshift your car you actually get a higher gear ratio. When something is really "geared down" the gear ratio is infact really high. The lowest gear in your car is the one with the highest gear ratio. "Low Range" on pickup transfer cases and tractors produces even higher gear ratios.

Are all of these things wrong? I don't think so. So in conclusion it depends whether you are talking about gear ratios or just gears. My robot has really low gears = My robot has a really high gear ratio. "Low Gears" seems like more of a slang term to me but I still downshift my car (5th to 4th) when I want a higher gear ratio.

Even though I am a firm believer that there are stupid questions, I think this was a good one.

[archiver]

Posted by Anton Abaya at 1/19/2001 10:47 AM EST


Coach on team #419, Rambots, from UMass Boston / BC High and NONE AT THE MOMENT! .


In Reply to: Re: confuzzling gear ratio definition.. wanna clear this one up?
Posted by Jim Meyer on 1/19/2001 10:30 AM EST:



: I believe the gear ratio is the # of teeth on the driven divided by the # of teeth on the driver, or the ratio of pitch diameters, driven/driver. So if the output (wheel) is spinning slower than the input (drill motor) the gear ratio is larger than one. I would assume everyone agrees with this point. Axle ratios on RWD vehicles are always greater than one, 4.10 and 3.43 are examples for GM trucks. The place where I sometimes get confused is which is a higher gear or lower gear.

: When you downshift your car you actually get a higher gear ratio. When something is really "geared down" the gear ratio is infact really high. The lowest gear in your car is the one with the highest gear ratio. "Low Range" on pickup transfer cases and tractors produces even higher gear ratios.

: Are all of these things wrong? I don't think so. So in conclusion it depends whether you are talking about gear ratios or just gears. My robot has really low gears = My robot has a really high gear ratio. "Low Gears" seems like more of a slang term to me but I still downshift my car (5th to 4th) when I want a higher gear ratio.

: Even though I am a firm believer that there are stupid questions, I think this was a good one.

so for all you guys who cannot figure this one out...please by all means learn it.

that solves one problem, i wonder how we should gear these babies this year...hmmm

i think i'm just gonna order a whole range of sprockets and play around with all of them..

-anton

[archiver]

Posted by Joe Johnson at 1/19/2001 9:46 PM EST


Engineer on team #47, Chief Delphi, from Pontiac Central High School and Delphi Automotive Systems.


In Reply to: oh good... i was right.
Posted by Anton Abaya on 1/19/2001 10:47 AM EST:



The terms "gearing down" and "gearing up" are not well
defined terms the way I look at life. They are almost
always used in a context sensitive manner.

When folks speak of gearing down something or gearing
up something, they have either torque or speed in mind.
Depending on whether they are thinking one or the
other they will use the different terms to refer to the
same physical system.

The thing to remember is that when you gear down the
speed you are gearing up the torque at the same time.

Thus the confusion.

Or maybe I am all wet on this one.

Joe J.

[archiver]

Posted by Dodd Stacy at 1/20/2001 12:12 AM EST


Engineer on team #95, Lebanon Robotics Team, from Lebanon High School and CRREL/CREARE.


In Reply to: Speed Vs. Torque...
Posted by Joe Johnson on 1/19/2001 9:46 PM EST:




: Or maybe I am all wet on this one.

: Joe J.

Not until the wheel slips, my friend.

Dodd