Hi Dan Ive built a 4 wheel box with wedge at front . Drive Ive used 4 x 18v drill motors gives good speed. Speed controllers 2 x 15amp electronize. Armour 20mm nylon all round, 10mm Ti on the front and 4mm Hardox on the sides and back. As Dan says nothing is spinner proof they have not got through the armour but when they hit you, you tend to get thrown half way across the arena. So your insides need to be shocked proof. I mount my speedos useing velcro but you need to get the heavy duty type, it holds them in but gives a bit of shock proofing.