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Would adding more Gear in a series increase TORQUE?

  1. Mar 13, 2005 #1

    Would more Gearings aligned in a series on a rack mean more Torque? And also,... what gearing should I use on motor: ones that is alot bigger than the ones on the series, or ones that are a lot smaller? which ones would generate more torque(power) rather than speed? Would the rack's length have a difference in determining the torque? Here are pictures to illustrate my situation.

  2. jcsd
  3. Mar 13, 2005 #2
    Multiple gears with the same ratio aligned on the same axis will not increase the torque of your servo. You can increase the ratio by using a different gear combination i.e. use a 50 thooth driven gear and a 10 tooth drive gear 50:10 (5:1) or you can make a gear train. If you make a train don't simply cascade the gears ie: a 10 tooth driving a 50 tooth driving a 25 tooth. The net result of doing that is a 25:10 (5:2) ratio--the middle gear is called an idler gear. To make a train you'de need to have two gears on a common axil driving gears on another axil i.e. a 10 tooth driving a 50 tooth gear which shares a common axil with another 10 tooth (the second ten tooth is not in contact with the original). The second ten tooth will then drive say another 50 tooth which is used as the output axil. The second case would result in a [50*50]:[10*10] or 25:1.

    You might want to look into gear trains idler gears and gear ratios on google.

    Hope I answered your question.
    Good luck.
  4. Mar 13, 2005 #3
    Thanks for the prompt response,

    For my lack of knowledge, what is the difference between Driven Gear and Drive Gear?
  5. Mar 13, 2005 #4
    And also from the pictures do you think lifting that front part up is possible with 1 servos with correct combination?
  6. Mar 13, 2005 #5
    A drive gear is a gear attached to a motor while a driven gear is a gear attached to a load. In the gear train example, the first 10 was a drive gear and it drove a 50 thus the 50 was a driven gear. The 50 was on the same axil as the second 10. The second 10 becomes a drive gear because the torque used to turn the first ten was coupled to the axil via the 50 tooth. The 50 tooth essentially becomes a motor which turns the second 10 thus the second 10 is a drive and the second 50 is a driven.

    Do I think it's possible? Yes and no. Did you modify the servo to allow it to turn past 180 degrees? If so then you can probably get a high enough ratio to lift about anyting (we're talking small plastic parts here so the inertia is almost negligible). If you didn't modify your servo then you'll still be able to lift your device but only a little bit. Remember, a gear ratio alters a motors (or what ever your input moment is from) at the expense of motion--just like a lever.

    [edit] had drive and driven backwards in the first sentence of my response. Sorry.
    Last edited: Mar 13, 2005
  7. Mar 13, 2005 #6
    I have a "SPEED" servos that goes 360... But it looks like a motor to me... What is the difference between a servo and a motor anyway? Other than a standard servo goes 180deg while motor goes 360... Seems to me motors have more horsepower.

    Anyways, wouldn't you think those plastic pieces would break somehow? Cause with the setup i have in those pictures, the servos would just "stuck"... and sometime i can hear it try to run over those 3 gear trains.... is it just because I have wrong setup?

    EDIT: also I dun need to turn all that much. about 30deg is perfect. i just need to "tilt" or drag the "claws" up a little as needed to go over small obstacles.
    Last edited: Mar 13, 2005
  8. Mar 13, 2005 #7

    By the 50 and 10 tooth on the same axil do you mean side by side? As one rotates, the other rotate? Kind of like my 3 set series in my pictures?
  9. Mar 13, 2005 #8
    Yep, you got it.
  10. Mar 13, 2005 #9
    Well, your servo only turns 1 revolution so, if you gear it down 12:1 then you'll get your 30 degrees and increas the torque quite a bit.

    A servo is a device with a feedback circuit to let it know what angle the little output spline is at. There is a little motor, a gear train and a variable resistor inside that little black box. The motor is geared down about 100:1 if I recall and has a very limited range of rotation. A motor OTOH has an infinite rage of rotation (it can spin and spin without limit).

    You probably wont be able to lift the arm using an unmodified servo. Gear it down and see if it works.

    Good luck.
  11. Mar 13, 2005 #10
    How would the 10s touch each other though? one of each is beside 50... or did you meant one 10 face one 50, while one 50 face one 10?

    And what would you suggest I do for my case? Speed or Torque? What ratios are best for each case? Please advise, thanks.

    EDIT: I have a "SPEED" servos... though i'm not sure how to program it... it turns 360 and a little "KNOB" which I dunno what it does. Also, you think if I put another servos on the other side of the bot will help the situation?
    Last edited: Mar 13, 2005
  12. Mar 13, 2005 #11
    The tens don't touch each other, that's the point. 10 drive a 50. The 50 is butted up against another 10 not in contact with the first. The second 10 only drives another 50 in my excample so you have a 10 driving a 50 and another 10 driving a 50.

    Also, you want to increase the torque output of the servo so if you can change the gears to in crease the torque then do that first.

    [edit] adding a second servo will increase the torque applied to the shaft.
    Last edited: Mar 13, 2005
  13. Mar 13, 2005 #12
    Also, how can I check to what mass my servos capable of handling?

    I tried to use my hands to rotate the axle that connects the "tilt up" and down motion, and it is pretty hard, requires me to put on gears to be able to rotate by my hands....

    also, a 10 driving a 50? would not the 10 break because of its size compare to that of a 50?
  14. Mar 13, 2005 #13
    If you have trouble lifting your mechanism by hand then you probably wont be able to lift it with an unmodified servo. Will the 10 break? No, those little plastic gears are pretty strong.
  15. Mar 13, 2005 #14
    is there any way to verify to what level can my motor lift? and what should I be looking for speed or torque in my situation? And what can I do to accomplish it?

    BTW, here is some info: POWER SUPPLY: 4.8V Speed @ 60deg = 0.19s
    if at 6v, speed @60deg is 0.16sec

    output torque 42 oz -in
  16. Mar 13, 2005 #15
    You don't care one iota about speed. Angular velocity will not lift the arm, torque will.

    Remove the servo and add a lever arm in its place. Let the pinccer hang down and adjust the newly added lever arm so that it is horizontal. Measure from the center of the axil to the last hole of the lever arm (try using a 4 or 6 inch lego). Now, add weight until the pincer begins to rise. The length from the axil to the weighs times the weight added will be the required torque from your servo. You'll have to gear you servo to attain that torque.

    Well, I have to get some sleep. Hope your do-dad works out in the end. You might try attaching a lever arm and than attach the servo to the end of the lever via a linkage. This might give you enough mechanical andvantage (google that) to lift you pincer.
  17. Mar 13, 2005 #16
    so the best policy is to use the smallest (ie 8 teeth) drive the largest (50 teeth) in my situation right?

    And also... that 10 teeths face 40 teechs doesn't seem to work... it seems that rotation is not possible.
  18. Mar 14, 2005 #17


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    PrudensOptimus - in your situation you want the best mechanical advantage (biggest ratio) you possibly can. So yes, the smallest drive gear and largest driven gear you can find.

    Another option is a jack-shaft to act as an intermediate shaft. So the motor has a 10 tooth gear and drives a 50 tooth gear on the jack shaft. On that jack shaft is a 15 tooth gear that turns a 45 tooth gear on the final shaft. The first ratio is 5:1 and the second is 3:1 so it ends up being 15:1 which is quite a bit of mechanical advantage.

    Look at the inside of a RC servo and you see that they have multiple gears on different jackshafts to achieve their final ratio.

    Another option is to use a rack and pinion drive mechanism to lift your claw thingee.

    Also, as a side note, power is constant and is a matter of torque and speed. Using gears will alter the torque and speed but their power stays the same. So if you get more torque, you loose as much speed.

    The most likely option is you'll need more than one servo. Each servo only has so much power and can only be geared down so much because they have limited rotation.

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