First Ever Robot Build: Invertible Featherweight Vertical Disc Spinner

[overkill]

Sorry for the thread hijack but I've got a 650W pillar drill and it struggles even drilling a 6mm hole in mild steel, the motor itself does not stall but the belts slip even in it's lowest gear ratio. Any ideas why this is happening? Should I replace the belts with slightly smaller ones?

The belts that come with cheap bench drills are usually complete crap. Try replacing the belts with cogged versions as they have more grip. You can usually get cogged belts at engineering or auto spares stores, or on line. There should be a short tensioning lever somewhere of the drill head; adding a length of pipe to the lever lets you get much higher tension on the belts.

[overkill]

ha 720 would get nowhere near 10mm of bite unless it was moving forward at a rediculous speed *waits for smart arsed comment from mouldy*

Brave man! 720 would need to be travelling at 18KPH to get a 10mm bite depth with a two tooth drum spinning at 15,000 RPM.

[typhoon_driver]

I always do the sum for a robot moving forward at 1m/s as it's most indicative of what a robot will likely be doing before a collision

[overkill]

I noticed at the last Nats event that Mouldy usually likes to drive 720 quite a bit faster than 1 m/s so the maximum bite depth is going to be deeper than the 2.22mm he would get at that low speed.

[typhoon_driver]

Sure you get big hits now and again, but the majority are slow speed. It's an interesting problem. I did consider a while ago having an axe with the head being a disc or a mechanism acting on CO2 to shove the disc forward quickly but building it strong enough would be a night mare

[overkill]

I agree that most contacts are lower speed than they should be, its why I gave up the idea of super high RPM weapons. There is little point in owning bragging rights to the fastest weapon if it doesn't deliver wins all the time.

Getting back to the Matt's questions, the minimum practical size for a disk is a grey area. You need the disk to project a fair way out of the bot's frame in order to be affective, so a small disk needs to have a very compact bearing so that the disk's axle is as near as possible to the edge of the frame. As a disk gets smaller, it needs to get thicker to maintain its weight and kinetic energy - eventually it starts looking more like a drum than a disk. I would say that for an effective disk, the minimum diameter is a bit under 200 mm.

[Niels - Team K.a.L.M.]

I'd say that the only true sweet spot concerning spinning weapons should be KE and Bite.
The amount of energy and the abilty to pass it on into it's target.

It will always be diametre vs width vs teeth vs speed in varying measures but it will always boil down to that.

[TheNeonMatt]

Thanks, I will try to make the disc as big as possible but at the moment I think it is going to become a trade off between disc size, height of the bot, and whether it is invertible because I would like to keep the bot within a 45 degree angle.

[TheNeonMatt]

For a basic drill drive, the BotBitz 30 A speedo is more than good enough.

If my drill motor is 12V and 550W it means it is just under 46A, does that mean I need a different speed controller?

[harry hills]

What kind of drill motor do you have that is 550w? Most of the drill motor/550 size 12v-18v motors barely touch 100w.

[typhoon_driver]

Dewalt motors can easily be around that high. What did the drill motor come from?

I would recommend the t85a controllers

[Eventorizon]

Thanks, I will try to make the disc as big as possible but at the moment I think it is going to become a trade off between disc size, height of the bot, and whether it is invertible because I would like to keep the bot within a 45 degree angle.

If the disc is to large it will have a high RMI and take forever to spin up. My first machine had a 200mm disc with the same weapon drive as anoter machine with a 300mm disc. Mine was up to full speed in less than a second. The other took 4-5 seconds to reach top speed. However the other machine hit harder and did more damage due to its higher tip speed and mass.

[typhoon_driver]

For the ultimate expression of that take a look at how long it took a 5hp chainsaw engine to get typhoon 2 up to 1000rpm. A good 30 seconds or so

It's a balancing act and the best part it, you will never be right because every battle is different.

[Niels - Team K.a.L.M.]

As pointed out before, KE and bite is everything..

Just because I'm not versed in the actual sweet spot. What kind of KE should a spinner have in 1 or 2 seconds?

[typhoon_driver]

With a feather anything over 1kj will start doing damage