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Thread: Need information on alternatives to Harmonic Drives / Cycloidal Gear systems.

  1. #1
    Associate Engineer
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    Jul 2021
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    Need information on alternatives to Harmonic Drives / Cycloidal Gear systems.

    Hi all,

    I'm looking to find out what alternatives to the Cycloidal Drive and Strain Wave Gearing systems ( Harmonic Drives ) have been found over the past 50 years.

    I'm looking for systems that have similar reduction capabilities in a single stage ( eg, 30:1 to 600:1 ) in a small lightweight gear system, ideally one suited to an embedded motor and position sensor.

    If there is something that also does not rely on very-strong materials, so that it could be 3D printed, that would also be ideal.

    As the Harmonic Drive was first invented in the 1950's, I'm surprised that there aren't a large number of alternative solutions to it. Everything I can find says there aren't any other mechanisms that provide the same kind of function, short of multi-stage planetary systems. This doesn't seem realistic since it is so widely used in modern technology, but I can't find any indication of something better?

    Thanks in advance for anyone who can offer suggestions, directions or ideas I can follow up -

    David.

  2. #2
    Engineer
    Join Date
    Apr 2021
    Location
    Germany
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    11
    Sorry but I guess you cannot find anything with the same ratio of cycloid or harmonic gears. On the other hand, you can use hydraulic systems for reduction by employing a hydraulic pump and hydraulic motor but it doesn't be a cost-effective way. The best option is a cycloid gearbox for a high reduction ratio. If you have any problem with it let me know maybe I can help you in this regard. you can use worm gear but it has reduction ration less than a cycloid gearbox and it change the rotation direction by 90 degrees. Enable GingerCannot connect to Ginger Check your internet connection
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  3. #3
    Associate Engineer
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    Jul 2021
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    Thanks Gholambaghery - Yes, I need ratios up to and including over 300:1, though typically in the range of 50:1 to 100:1 - something small enough to fit in my hand, and without compromising strength as far as possible. Also I want balance in the gears in all axis, both dynamic and static. Cycloidal Systems just seem to have so many complicated parts and likewise Harmonic Drives. It seems strange that in 75 years, there has been little improvement over the harmonic drive, yet it's implemented so widely.

    I see a lot of cycloidal systems going into robotics devices also, so I assume that's a cost benefit over the harmonic drive technology, but it's not easy to know the cost of cycloidal systems - Do you know? ( I hear harmonic drives cost around $1000 per unit, but I have no idea about cycloidal gearboxes )

    It may be I'm chasing a dream here, and the answer is go with either a harmonic drive or cycloidal drive because there are no other solutions, but I figure asking on a forum might give me some other ideas.

    The requirements of what I'm looking for also are either lash-free or closely-controlled lash with predictable outcomes ( and very small amounts of actual lash ) - Also very very high levels of reduction from a single stage, very light weight, high performance and ideally simple.

    Thanks for the suggestion of a worm drive, and also mentioning the limitations. I hadn't actually thought of that one, but you are correct that the reduction does not seem suited to the application.

    Regards
    David

  4. #4
    Engineer
    Join Date
    Apr 2021
    Location
    Germany
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    Hi David
    The harmonic drive has less ration than cycloid gearboxes. When you step on designing and calculation you find the outer gear should be at least two cogs more than the inner gear (rotational gear). By the way, I don't think the cost of a cycloid gearbox is very high. If you design it in Solidworks and take a step file of it you can print it very easily and it doesn't charge you more than $20 or $25
    For drawing it use these formulas in the equation graph and put the "t" from 0 to 6.283
    you can draw it within 3 minutes
    X = (R*cos(t))-(Rr*cos(t+arctan(sin((1-N)*t)/((R/EN)-cos((1-N)*t)))))-(E*cos(N*t))
    Y = (-R*sin(t))+(Rr*sin(t+arctan(sin((1-N)*t)/((R/EN)-cos((1-N)*t)))))+(E*sin(N*t))


    R is the radius of the gear
    Rr is the pin radius
    E is the eccentric distance
    and N is the number of cogs (consider it one more)


    Using a 3D printer and SolidWorks it would be very cheap.
    For making a prototype of it, you can make it by hand without using any cost. for example, if using Teflon and put your drawing on it and cut the Teflon by hand or saw and rasp, you can make it at home. For mass products, you can use a CNC machine and get the G codes or M codes from SolidWorks as well.
    If you have any question for using this method let me know

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