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Thread: Spring help

  1. #1
    Associate Engineer
    Join Date
    Oct 2013

    Spring help

    New guy here. I have some questions about springs, and their application.
    My disclaimer is I am not an engineer, which will become obvious in just a minute. I am trying to design a new bass drum pedal. I have been playing drums for years, and have always wanted to make a better drum pedal. I have been sketching and designing on it for a few years now, and I need some expert advice on springs.
    The industry standard is an extension spring. My problem with that is threefold. 1) they get weak over time. It is usually noticeable inside a year. 2) the spring rate is linear(?) It starts at say 3 lbs, and increases on a curve to around 15 inside a short distance. 3) everyone uses them. Maybe they are cheap, maybe they are the best spring for this application. I dont know.
    I want to use either a composite leaf spring, a gas spring, or a torsional spring (a wrapped spring or torsion bar can be made to work). But what is best? Most of you are probably familiar with the base drum pedal. The drummers foot sits on top, and he/she pushes down, and it pushes the beater into the head. I have an idea of how I want it to look, but I am at the point I need to make sure my ideas on the spring type arent going to kill the idea. I looked up a few articles online about how to determine the properties of a spring, and it might as well have been written in martian.
    I dont have a lot of specifics honestly. But I probably would not understand a specific answer anyway. Is there an advantage to using a specific type of spring?
    Forgive my layman terminology and lack of understanding. I am an aviation mechanic, trying to design a new pedal for my business, which I am just starting up.

  2. #2
    Technical Fellow Kelly_Bramble's Avatar
    Join Date
    Feb 2011
    Bold Springs, GA
    Welcome to EE!

    Sounds like you're looking for an extension spring that lasts longer?

    First, extensions springs applied force is not linear with extension. As far as lasting I would look at the spring material or simply consider that replacing the spring at regular intervals.

    If you wan t to look at other springs types and the related calculations and equations see:

  3. #3
    Project Engineer
    Join Date
    Oct 2013
    Maybe what you want isn't a spring at all? have you considered an air filled bladder? This would have it's own problems but could offer some better flexibility to the users and could be made to mimic the same sort of feel you get with an extension spring with fewer moving parts.

  4. #4
    Lead Engineer
    Join Date
    Aug 2013
    Houston TX USA
    "The best spring for the application" is not a simple question to answer because it depends upon the spring characterisics that are most important to the performance, space requirements and cost limitations of your particular design. You need to determine a priority list of characteristics that you want your spring to achieve. For example, are you most concerned with: the lack of the constant force of the current spring or its apparent short life. I suspect that an extension spring is currently being used because it is the easiest to apply. If you are not concerned about the change in spring load with deflection or want to reduce this load change that can be achieved by using an extension spring with more coils to give lower spring rate but this will require a longer spring and more space for the spring and you may be able to achieve this using a standard catalog spring.
    . If you are most concerned about the short spring life then you need to use a spring made from a higher quality alloy spring wire with a better fatique life than currently available "off of the shelf" catalog springs and will have to be specially wound by a spring manufacturer for your application which will be more expensive but the cost per spring will be reduced as the order quantity increases so if you plan on manufacturing a number of your pedals this can still be an acceptable solution. Of course, if you want both a reduced load change and longer life then you combine both changes in your selected spring design.

    Ultimately, the best solution for your selection is to decide what qualities you want and then look in your local yellow pages for a spring manufacturer (they exist in most cities) then contact them to discuss what you need and how much it will cost.

  5. #5
    I would use torsion springs. One leg attached to the pedal the other to the base.

    For most springs you can assume the force exerted by the spring is proportional to it's displacement, F = kX... which means the applied force is linear with extension. F is the force exerted by/on the spring, x is the extension/compression of the spring, and k is the spring constant.

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