I am building a Hobby-weight robot and my weapon of choice is a spinning disk at the front.

As regards the disk I was thinking of buying commercial (grinder-type) disks and change type of disk depending on the "enemy's" chassis construction material. So for instance I would have an aluminum cutting disk if the enemy's chassis is made of aluminum and so on.

First question is therefore; do such disks do the job in practise (or break, fail to cut?)

Secondly, should I use a brushed or brush-less motor for the disk? I actually have ESCs for both but sort of feel a brushed motor will give me more torque while a brush-less motor might give me more speed. So which is more important speed or torque?

I do know - from my uncle who uses metal lathes - that machines that cut metal usually spin at a slower speed (drills, cutting wheels etc)- indeed he likes to say that metal working machines are safer than wood-working ones partially for this reason.

But I am a newbie and really would like to have an effective weapon if possible and breaking or not-cutting disks do not make such a weapon!

Also is it normal practise to use one battery for everything (drive and weapon) or have two separate batteries?

  • $\begingroup$ This is as much a question about machining as it is about robotics. Steel can be cut with abrasive saws (like angle grinders), but aluminum not so much -- it melts and sticks to the abrasive surface, which makes the cutting less effective. Many times, you can cut aluminum successfully using a saw blade designed for wood. $\endgroup$ – Ian Oct 15 '14 at 14:58
  • $\begingroup$ The commercial disk I bought is intended to cut aluminium, but the best thing I can do is trial it on a bit of scrap aluminium I have handy; I also have wood type ones which look much more menacing due to the larger teeth but may be less effective. I will run some speed experiments this weekend with different motors and will also try to cut through aluminium. If push comes to shove I will have a disk made out of cast iron or mild steel for me but I still have the problem of the motor. Maybe I should just buy an in-runner brushless for a r/c car or heli and use that.. $\endgroup$ – Galahad II Oct 15 '14 at 20:38
  • $\begingroup$ I abandoned the disk and went for a drum with spikes. The "drum" is a printer rod (made of bright mild steel (BMS)and is 1.5 cm in diameter). Along the length I drilled out and threaded 9 x 5 mm holes and inserted spikes (cut from a 5 mm diameter BMS threaded rod). Locknuts on both ends completed the job. The drum fits into ball-bearings set in alum blocks. The motor is an standard brushless one and is connected to the drum/rod using 2 pulleys and an O ring for slippage / avoid high stall currents. It is also assigned to a variable channel on the r/c so that I can freely adjust the speed. $\endgroup$ – Galahad II Jan 16 '15 at 12:01

Well grinding machines in general use really high cutting speeds, so a very high revolution speed. At a metal lathe it is pretty easy to get the force of your tool onto the workpiece. In a robo-fight it's actually not that easy, so i suggest very high speed. More like an angle grinder

  • $\begingroup$ Ah yes that makes sense. So speed is the thing then. $\endgroup$ – Galahad II Oct 15 '14 at 20:34

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