Spinner Energy

[stinger]

Elsewhere on the FRA site, you may have seen that Im working with James Baker on some guidelines for Spinning Weapons. We have a neat way of assessing the Kinetic Energy in your designs which shows how fast we would let you run. We only need to make a crude assessment of Style (mass distribution) + measured figs for actual Mass & Dia.

Now, at present the FRA are NOT sanctioning use of spinners except under controlled conditions in Class 2 arenas. James and I want to set sensible rules that will allow more spinners, albiet with a limit on permissible rpm.

We suggest that you start designing them with alternative drive systems - one geared down for live events, and another geared up for serious combat. You never know, the reduced spin-up time with a low ratio might even be an advantage ! Please note, that we do not anticipate permitting electronic speed limiters (but would allow reduced voltage).

We need to collect as much data as possible to decide where we should set the level for different arenas. For example we believe the most aggressive spinner is up at around 38KJ, with the most well know in the region of 16KJ, and Feathers peaking at 5-6KJ.

We have some experience of 6KJ in Jonnos arena, and want to collect as much additional info as poss to help establish challanging, but manageable poower limits.

Please post details here, or if you dont want to go public, then send them direct to me or James.

We would like to see Basic Dimensions of the spinning element plus its Mass and anticipated RPM. If you have a calculation for KE - then please post that as well.

Thanks,
Kevin S

[storm]

Vortex - 3Kg
4500rpm
Diameter 200mm - almost all mass at the edge of rim - it only has 2 spokes on the disk.

No idea what energy that translates into, but hope the figures are of some use.

Ed
http://www.stormrobot.comhttp://www.stormrobot.com

[robotwars]

Strip - Feather weight - 3.5Kg disc
3500rpm
Diameter 500mm - mass equally distributed apart from two 0.25kg teeth on outer edge.

Jonno
http://www.roamingrobots.co.ukwww.roamingrobots.co.uk
http://www.ukinnovations.co.ukwww.ukinnovations.co.uk

[ewan]

Big Daddy- Featherweight- (revised disc from my profile pic) 2kg Bar at 3000rpm, 500mm dia, vertical
with 0.8kg mallets at the end of each side.

[big_nipper]

Looking at Strip and votex I think those figures sound wrong but what to I know. I dont know how to work it out either, but I do know that 90% of the mass of vortexs disc is on the rim and strips is evenly distrbuted. Going off the size of the discs i would say if the speeds are true they are very even in power. I wouldnt say that its 2.5 times the power of vortex.

Prove me wrong.

[geoff]

Roger,
Yes you are right in princable but we are dealing with rotating mass not mass traveling in a straight line!
There are questions involving moments of inertia to contend with as well as angular velocity.
I also confess to be a bit rusty but as I remember it the kinetic energy of a rotating mass is somthing like..


Kinetic energy = ½ moment of inertia X angular velocity squared

or E = 1/2Iw^2


I hope this helps, although as I said its been a long time since I really had a use for maths like that so dont take it as gospel!

Geoff,
Team Scorpion.

[geoff]

Been giving this a little more thought, The calculation of angular velocity is relatively simple. But the problem I can see in trying to calculate KE in a rotating weapon is going to be determining the moment of inertia. It will totally depend on the construction of the weapon . How mass is distributed through the disc will have a serious effect on the value. I think (and I may be wrong) but the only way to arrive at an accurate value will be to calculate it for every component of the disc and add it all together to arrive at a total value. Which is fine if you could weigh all the component parts separately, this would also mean having to calculate their velocity which of course is relitive to their radius from the center but how you calculate that once the disk is built, I have no idea!
Maybe some one who understands this better than I may have a solution. I would love to know what the answer is!