Wii Remote Force Calculator

Recently, I’ve been doing a fun side project.  It’s always fun when you can come up with an excuse to combine your hobbies or interests.   So I came up with the idea of using a Wii remote to calculate the force of a strike on a heavy bag.

Screenshot

I’ve had to dredge up old memories from my college physics classes, and I’m not entirely sure what I’ve got is hundred percent accurate, but I feel with proper setup it’s pretty good.  The calculation is easy enough, to get the force you just multiply the mass times the acceleration of the object.  The accelerometers in the Wii remote are accurate to about  +/- 3 Gs with about a ten percent range of error.  Not too terrible for a fifty dollar bluetooth enable accelerometer you can pick up at any store in town.  The problem is, if you try to hold it in your hand you can generate massive amounts of acceleration well above 3 Gs.  So instead,  I tied the remote onto a heavy bag.  Much more mass, means you get the same amount of force with acceleration levels well within the remotes acceptable range.

Force = mass * acceleration

Because I’m not punching any harder, the force stays the same.  The heavy bag has a lot more mass, so the acceleration has to be a lot less to equal the same force.

The thing I’m not sure of is whether I have to take into account the fact the bag is on a chain so it actually swings up in an arc.  I don’t know how much that affects the calculations, but I don’t think it would be a lot with the small amount of time range we’re talking about.

My next steps are to try and rig up some testing system to try to determine the accuracy of the measurements.  I also want to get the opinion of some physics people to get my calculations even more accurate.  It’s been a fun project so far and I’d like to get it to the point where I could bring it into the gym and have my students play around with it a little bit.

The application itself is written in C#, using WPF, MVVM, and Wiimote Lib

I’ll try to post any updates here as they develop.

5 thoughts on “Wii Remote Force Calculator

  1. Dave

    This sounds awesome. I just downloaded the library. Is it easy to get the Wiimote to make a connection with the computer?

  2. jana

    I have long thought of doing the same thing with falling bodies. Test the force for taiotoshi vs uchi mata etc.

  3. Nick Post author

    I’ve thought the same, in some ways it’s much easier because you don’t have to factor out the acceleration from gravity, because that’s part of the system from your throw. In other ways though, a heavy bag acts a lot like a rigid body mass whereas in a throw it’s a human and throwing in arcs with rotation.

    You might not be able to get accurate numbers, but you could certainly get a relative scale, where this throw generated more force than this throw, though the actual force might be in question.

  4. Paul

    Hi Nick,

    just saw your post about this nice little experiment! Could you release your app and maybe the source code? I started to playing around with a Wiimote, too. Would be a great help!

    Have a nice day!

    Best,

    Paul

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