### Author Topic: hi!!!  (Read 1530 times)

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#### abh34

• Jr. Member
• Posts: 21
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##### hi!!!
« on: July 31, 2009, 04:24:44 AM »
hi
i am abh34
i am new here

i am very passionate abt robotics but the prob is that i know nothng of t

i was going thru the gear tutorial and have a couple of questions

firstly,
if i have 2 sprocket gears (90% efficiency) one of radius 4cm and other of 1 cm
they are connected
suppose i rotate the bigger gear at 50 rpm, so since the gear ratio is 4:1 then the smaller gear shud rotate at 200rpm
but the gears have 90% efficiency
so will the smaller gear have rpm of 90% of 200= 180

i just wanna ask that am i right in saying that the small gear will rotate at 180 rpm???

also ,
i have read sumwhr in tutorial that the greater the radius of wheel  the less the torque.
but isnt torque= force x radius

then how??

thnx

#### wil.hamilton

• Robot Overlord
• Posts: 207
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• rtfm
##### Re: hi!!!
« Reply #1 on: July 31, 2009, 05:59:38 AM »
it takes more torque to spin a larger wheel.  It would be more accurate to say a larger wheel has less "push", or ability to move the robot.  you can figure this out using the same formula you posted:  force = torque/radius

as for the gear efficiency, is that efficiency listed for a motor? or for the gears, i've never seen efficiency listed like that for gears, but i have for motors,  for motors it has do do with how well it converts electrical power into mechanical power and can be used to figure out how long your motor(s) will run on a given battery supply
use the google.  it's your friend.

#### abh34

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##### Re: hi!!!
« Reply #2 on: July 31, 2009, 12:38:01 PM »
sorry i got the gear name wrong
it is spur gears
heres the gear tutorial

http://www.societyofrobots.com/mechanics_gears.shtml#spurgears

if u scroll down the section to spur gears u'll see its written that it has 90% efficiency
if u sum up the gear ratio and the efficincy

is the result which i come up to correct???

#### wil.hamilton

• Robot Overlord
• Posts: 207
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• rtfm
##### Re: hi!!!
« Reply #3 on: July 31, 2009, 12:52:13 PM »
http://www.societyofrobots.com/downloads/gearology.pdf

if you read page 82 it talks about how to do calculations with efficiency.  after a quick read, it appears that efficiency plays a greater role in the output torque rather than output speed.
i'd recommend an in depth read because i may be wrong
use the google.  it's your friend.

#### abh34

• Jr. Member
• Posts: 21
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##### Re: hi!!!
« Reply #4 on: August 01, 2009, 05:09:41 AM »
read it

thnx
i asked that questioon bcoz when u have 2 connected gears of unnequal radius
the smaller one is always gonna rotate faster then the bigger one

i just wanted to know if u can calcluate the smaller gear speed given u have the bigger ones speed
i guess the way to learn it is by doing it
thnx

#### Admin

• Administrator
• Supreme Robot
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##### Re: hi!!!
« Reply #5 on: August 03, 2009, 12:50:12 PM »
Quote
if you read page 82 it talks about how to do calculations with efficiency.  after a quick read, it appears that efficiency plays a greater role in the output torque rather than output speed.
i'd recommend an in depth read because i may be wrong
Basically as torque resistance goes up, motor speed goes down. Both output torque and output speed are equally lost due to the efficiency loss.

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