Gear ratio

Discussion in 'Off-Topic' started by Dritech, May 1, 2014.

  1. Dritech

    Thread Starter Well-Known Member

    Sep 21, 2011
    756
    5
    Hi all,

    Since this is an electronics forum, I decided to post this thread in this section. So, here is my problem. I have a motor connected to a drive gear marked M1 Z30 08-918. A driven gear (M1 Z40 08-512) is connected to the drive gear.
    Now I need to calculate the number of teeth for a third gear which will be connected to the drive gear (M1 Z30 08-918). I want this new gear to turn 2.5 times with every single turn (360degrees) the driven gear (M1 Z40 08-512) makes.

    Can someone please guide me on how to calculate this?

    Thanks in advance.
     
  2. Wendy

    Moderator

    Mar 24, 2008
    20,765
    2,536
    Count the number of teeth. It is what determines the turn ratio, assuming they mesh properly.
     
  3. Dritech

    Thread Starter Well-Known Member

    Sep 21, 2011
    756
    5
    Hi,

    So that mean I need to use a gear with 12 tooth ?
    Also, what shell I look for to find a gear which mash with the drive gear?
     
  4. MaxHeadRoom

    Expert

    Jul 18, 2013
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    The ratio is in directly proportionately to the gear teeth ratio.
    In other words if you have a 12 tooth gear and you want the driven gear to go 2.5 times faster then it would be 12x2.5 = 30 teeth (gear up).
    Keep in mind that the resultant torque is directly proportional to the ratio, so if you geared up by 2.5 the torque would be reduced by 2.5.
    Gear down and it would be increased by 2.5.
    Max.
     
    Dritech likes this.
  5. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    Er, won't 30 teeth gear it down?
     
  6. bertus

    Administrator

    Apr 5, 2008
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  7. MaxHeadRoom

    Expert

    Jul 18, 2013
    10,520
    2,369
    Correct, I had it backwards.
    Momentary lapse.;)
    The torque ratio is correct.
    Max.
     
    Last edited: May 1, 2014
  8. shortbus

    AAC Fanatic!

    Sep 30, 2009
    4,006
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    But in a three gear train, the first and last gear are all that matters for the ratio. The second/middle gear is just along for the ride, an idler. And it does make the first and third turn the same direction.
     
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  9. inwo

    Well-Known Member

    Nov 7, 2013
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    :eek: I never thought of that!

    Works for more gears too.:confused:
     
  10. MaxHeadRoom

    Expert

    Jul 18, 2013
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    The difference comes when the intermediate shaft carries two gears of different sizes for compact reduction/increase.
    Max.
     
  11. Brownout

    Well-Known Member

    Jan 10, 2012
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    Since gears which mesh have the same pitch, and number of teeth are directly proportional to pitch and gear diameter, then you can use diameter ratios to calculate gear ratios. Hence, the gear you want will have a diameter of 1/2.5 = .4 of the driving one.
     
  12. atferrari

    AAC Fanatic!

    Jan 6, 2004
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    I learnt it the hard way! Assembled two equal gears at the ends with a different one in between. I was surprised to see that I was getting the same speed which was NOT what I wanted! :mad:

    Had I do the maths...

    At least, now I know. :( :p
     
  13. MaxHeadRoom

    Expert

    Jul 18, 2013
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    There are four diametric circles used in gears, the most common is the pitch diameter or Diametric Pitch.
    Not all gears are rotary, as in a rack and pinion where the diametric pitch of the pinion is used to calculate the travel per revolution.
    Max.
     
  14. shortbus

    AAC Fanatic!

    Sep 30, 2009
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    Yes, as long as they aren't 'compounded'. By that I mean two different gears physically linked together on a single shaft. On a simple train of gears only the first and last have to do with ratio. An even number of gears will reverse rotation. An odd number of gears will keep the same rotation.
     
  15. Dritech

    Thread Starter Well-Known Member

    Sep 21, 2011
    756
    5
    Hi,
    Thanks for the replies. Does 8 tooth 0.8 module gears exist please?
     
    Last edited: May 3, 2014
  16. MaxHeadRoom

    Expert

    Jul 18, 2013
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    There are two main differences in practice when matching gears is the pressure angle, those being either 20° or 14.5°, if 0.8 module are 20°?
    Try SDP/SI Spindle drive products or Misumi.
    Max.
     
  17. Dritech

    Thread Starter Well-Known Member

    Sep 21, 2011
    756
    5
    To be honest I don't know the angle, but on the gear I have it say 0.8.

    I found a 0.8 module 8 tooth gear on this site:

    http://www.smallparts.com.au/store/item/gs080080400b0300brn/gearsspurmodule08/

    Is this a mistake or does such gears exist? I'm asking because this the the only 0.8module gear I managed to find with 8 tooth.
     
  18. MaxHeadRoom

    Expert

    Jul 18, 2013
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    I believe it will be 20° for module 0.8.
    Try these, I have used their miniature gears before www.wmberg.com.
    Not sure if they have metric gears however.
    Is there any chance of changing the gears you have for a more common size?
    Max.
     
  19. markdem

    Member

    Jul 31, 2013
    73
    38
    Here is a great program I use when working with gears.. Might help someone.
    Download the demo and you can still use it for calculations. The demo will not allow printing or output to gcode or .stl.
    http://www.gearotic.com/

    Have Fun
     
  20. MrChips

    Moderator

    Oct 2, 2009
    12,435
    3,360
    In electronics terms, think of the middle gear as a unity-gain inverting amplifier.
     
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