Also to add; try avoiding using bolts for teeth if you can. As mentioned in other posts, they're likely to shear/not be very effective. However, if you're working on a tight budget, they are a cheap option to begin with.

Running two Speed 900s on an Electronize is possible but I wouldn't recommend it with anything less than an Electronize 30A model with external relays (40A capability). The stall current of a Speed 900 at 12V is 54A, for two that is 108A. Nominal current is 8A (16A for two) so under normal running conditions the controller would be fine but you would have to cut the power to the motor at the first sign of stalling to avoid damage to the controller. Another option, if you don't mind having no variable control, is to just use a couple of microswitches (or a single, two-way, one) and a servo to control it. Not the best but certainly another inexpensive option that will do the job.

Just to give you an idea of drum material; Drumroll uses a length of stainless steel tubing that is 3mm thick. I would say this is the minimum you'd want (maybe 2.5mm) if you want a tough weapon. I got tubing for both my first drum and new drum from http://www.metalsdirectuk.com. They don't have any of the stuff I use on there at the moment (it tends to come and go) but they can do cutting for you. The material I got for my new drum was 670mm long, so I got them to cut it into two lengths of 255mm and the excess piece of 160mm, so I have a spare 255mm bit if I want to get another Drumroll-sized drum made and a 160mm bit for making a more compact, slightly lighter drum (and possibly a new robot to go with it :twisted: )

Having just checked on their website, they've got some 2.5mm thick, 76.2mm diameter piece of tubing for £34.00. If you got that cut into, say, three 250mm bits it would give you some spare tube material if you need to remake a drum, or have one as back-up. It would also be easier to package up and send to you.

Speaking of which, I didn't get your actuator sent off on Wednesday but it did go out yesterday so should be with you before you leave the Isle of Wight