Help with disc

Ewan,
Even if you make the disc 20mm wide then you only increse the KE to 180j (still not a lot!!)
If you have access to cnc facilities why not have them cut you, as Christian sugested, a rim biased drum
if you could get say 70 - 80% of the mass at the rim and a width of say 75mm your KE rises to around 0.61Kj @10000 RPM BUT you are looking at around 1.9Kg in weight!! The fundermental problem here is that your dia. of 65mm is too small to allow a reasonable rim speed and therefore an acceptable KE, unless you are going to run it at silly RPM!! +/- 17500!!
If you want my advice, I think you need to have a serious think if this really how you want to go on this bot.

Sorry I dont have an MSN id. I use Yahoo IM

This is just an add-on weapon, just something active to keep the robot exciting as it will be mounted up the wedge, the disc will have very mini teeth, just the nibble the opponents underbelly. I am not looking at anything OTT, and the weight I have remaining in the bot after the fully CNCd chassis is quite small...

Fair enough Ewan, just keep it SAFE!!

Actually, most drill motors does something about 20000 RPM at their rated voltage. So with a bit of overvolting, that speed is reachable!

Has anyone thought off using friction drive for disc weapons? I have used friction drive in 2 feather weight disc weapons. The first was in Hellbringers saw using a RS-540 (next size smaller then a drill motor) with a foam wheel giving a 2:1 ratio. It was only good at hitting coke bottles (6m up in the air) but the friction drive did make a good clutch.
My next robot, The Aggressor, used a RS-775 (next size up from a drill) with a 6:1 ratio onto a 12 inch bicycle wheel. The bike wheel made an awsome fly wheel and at the last event I bent the 5mm steel teeth 30 degrees back rather then the wheel deforming. It also hit our opponent 15cm into the air in the process too.
Anyway the motors are of the high speed kind and even with the light weight saw fixed between bearings and 2:1 ratio it wouldnt have hit 4000 rpm. Thats all I wanted to say.

Daniel, a friction drive usually contains a lot of resistance. When youre dealing with drill motors, thats exactly what you dont want.

Ewan, if you want this weapon to actually do some damage, then a drum is your only option.

Just buy a 65 mm steel tube of suitable lenght and thickness, then persuade your sponsor to weld a small disc to each side. Cheap, easy and very effective!

Seeing as an output of 20,000rpm is quite possible with this type of motor (when overvolted slightly), I have recalculated, using the http://www.teamcosmos.comwww.teamcosmos.com kinetic calculator, that even a tiny disc like this has 1705j of energy stored within it (this is when you take the energy with centre milled out to a smaller thickness...

As long as most of the weight is on the outer rim, then it should work fine.

But I still think you should mount the disc on the back. As your scoop still will be your main weapon, the disc will stall then every time you push your opponent.

So it will never actually reach the kind of speed youre hoping for, unless you mount the disc on the back!

Im not complaining on your design, these are just suggestions. If you manage to get that kind of energy, then it would be sad if you didnt use it properly!

What I was trying to point out is a motor will never hit its quoted top speed once there is a load on the motor. Even with the weight of the shaft of the motor itself will put a load on it and slow it down. We had a problem in Australia (and still do) with builders quoting blades and discs spinning at 12000 - 15000 rpm and blade tips speeds over 1000 km/h from simple drill motors. Im just trying to say be reasonable with your calculations.
And the bit about the friction drive was something Ive never heard any pommys talk about. I know I dont have problems with friction because with the motor is stationary the foam rubber wheel is 1mm away from the bike wheel and with the speed of the motor itll expand to meet it.

About 63% of the qouted top speed is reasonable.