# Help with Flywheel calculations

#### Gozza

I am designing a kayak training machine as a final year project. Basically, the design consists of a frame supporting a weighted flywheel that provides the resistance. The flywheel is mounted on a shaft through bearing units in the frame and opposite direction sprag clutches are mounted onto pulleys and attached to the shaft. This enables drive motion to be applied to the flywheel with a freerunning motion in the reverse direction. Attached to these pulleys is a rope that runs to the paddle at one end, and a bungee cord at the other that will re-right the drive motion of the kayak stroke.

1. Essentially the problem is, how big a flywheel will I need to produce a force of 40N with each stroke. This is based upon a situation where stroke rate will be around the 82 strokes per minute area.

I am pretty clueless at what data is needed to solve the problem. I can find out more data if neccesary to solve it. If anyone could help me I would be greatly appreciative.

Thanks,

Gozza

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#### jambaugh

Gold Member
I can't quite visualize your setup but...
There are more variables involved than just the flywheel size. In particular there is an issue of how much mechanical advantage you get in connecting the paddle stroke to the flywheel.

A more important issue is that in addition to the flywheel you will need a braking system to dissipate the energy the stroke puts into the flywheel. Imagine the first stroke spins the flywheel up to speed, then if it is free-spinning, the second stroke will have much less resistance and so too subsequent strokes until the flywheel gets up to a speed where the user can't stroke fast enough to keep up with the flywheel. (The kayak has almost zero drag in the water.)

What you need is a brake or or drag fan capable of dissipating the energy stored in the flywheel with each stroke. You will probably want to allow variation both in the drag and in the flywheel resistance. You can then a.) adjust to get optimum and b.) allow adjustements for various users abilities.

You'll want to figure the appropriate momentum mass and velocity of a typical kayak and try to equate these with the flywheel's angular momentum and speed.

Then you'll want to match the braking system to the typical drag on a kayak figuring how much energy per stroke is used to maintain typical speed and equate that to how much energy the braking system dissipates.

Be sure as well that if you are using a brake there is a means of dissipating the heat it generates.

#### Gozza

Ok, I've got a braking system that is similar to that used on indoor spinning bikes. The brakes are made of a synthetic wool that dissipates heat excellently whilst under constant friction. The design is conceptual, so the actual amount of braking needed for each resistance variation does not need working out, due to conceptual testing being able to be completed to work this out.

The problem I am having is that I cannot figure out the calculations I would need to work out flywheel size.

The force at paddle tips could reach to 350N maximum probably. Based on an average of 82 strokes per minute, with constant braking is there a way to calculate the flywheel weight that could give a potential force range of say 20N to 200N etc subject to different levels of braking

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