Need some advice.

[Emerald]

Hey im making a HW bot. I plan on having two rotating blades/disks. I plan on powering both using a single motor with a one way bearings to allow one to rotate when the other is stopped. Need some advice


How powerful should the motor I use be? (suggestions will help a lot )
How heavy should I make them?
does the size of the disk make much difference or is it just the weight?

thanks for any help

[maddox10]

I see some problems in that plan. One way bearings ain't as strong as normal bearings.

On disk power. To bring it in non engineer terms. Mass*speed=hitting power.

The faster and heavier the nastier. But for every joule that is stored in the disk, you need to put it in.

And that brings us to the motors you can use. And that's totaly depending on your budget and skillset.

Cheapest powerhouses, but inefficient-need more battery- are old fasioned car starter motors , or as they are called, series wound motors. Needs some work, especialy if you want to reverse them with a remote.

Then we get to the Bosch 750 or modern, available surrogates. Movimotor, Iskra or the Chinese knock offs (search MY1020 on aliexpress or Ebay). But the 750w-1Kw motors don't cut the cheese anymore. Feathers use more powerfull motors for disks.

Next, industrial pancake motors. The Etec or LEM as examples. BIG pockets needed, and I myself ain't convinced those are the right way to go.

To end up with the high end Brushless motors that find their origines in the BIG RC models. From the reasonable priced Hobbyking stuff, to the really hidiously expensive stuff from famous brands like Plettenberg, LHR and so on.

[john_frizell]

Size and weight of a disc both make a difference to the amount of energy it stores, as does speed. Here is a useful calculator: http://www.botlanta.org/converters/d.../flywheel.html

Spinning discs are VERY dangerous. I would suggest not building a spinner unless:

1. You have a safe place to test it. [I tested my first one in an empty barn while sheltering behind a 12 inch brick wall.]
2. You are confident of the strength of your mount. If a disc breaks free of its mount it can go a long way and even a modest one can be lethal.

[overkill]

Here is a more accurate (but somewhat more complicated) kinetic energy calculator: http://www.teamcosmos.com/ke/ke.shtml. In the KE energy equation energy goes up with the square of the speed, so its most efficient to keep the mass relatively low and increase speed to get more energy. You can also get more energy for the same weight by moving the weight out to the edge of the disk, which is why most disks have a heavy rim and spokes.

What motor you use depends on your budget and how destructive you want the bot to be. Historically, bots with an Etek (now replaced by Montenergy motors) have always been the most destructive.