armour

would 3mm thick mild steel hold against a spinner

No

k well the thickest i can make another bot i thinking of doing if 5mm round the sides and 2mm top and bottom

Against the top spinners ( 360 Little spinner and so on) you would need at least 4mm Hardox or Ti

Provided your armour is well mounted, I don't see a problem with 3mm steel. Yes, some spinner teeth will put holes in it but if you make sure not to mount anything expensive/important right next to the areas most likely to get hit, then most damage will be superficial and repairable.

4mm steel has taken direct hits from 360 and LS4 annd although 360 did put a hole in it it didn't break off because it's a fully welded construction and mounting armour at an angle adds thickness and helps prevent proper engagement.

It's cheap, easy to get a hold of and easy to repair. If you have the weight, it will be fine.

Take a look at Ironside - 3.5mm welded hardox - the spinners best friend lol

No sharp corners.....

i was looking into the idea of of making a round ish robot then there wouldn't be any edges

A spherical robot!

yup pritty much

I believe there was one in the First Series of Robot Wars.

It was Phycosprout. A Fibreglass ball with large 4x4 remote control car in the middle to drive it around. It went out in the second round in The Labyrinth, and as Clarkson said €œthe one that covers the least distance will be killed and eaten€, as a result they had buttered sprouts for dinner that evening. [I should not be able to remember that but hey...]

i was thinking more of a short cylinder shape tan a ball