i just found out how to make it work :D , when u have the power tool equiped hold shift and scroll and it will go through the upgrades you put on the tool go through the uprades till u get the plasma cannon and then hold right click to fire ;D. i dont blame you it was hard to find out
Shift and scroll never worked for me. The tool select never showed up. However, I was just showing my husband one of my creations and hit some combination of buttons (in the Q,~,Tab area), and the tool select showed up and my cannon works now. Unfortunately, I have no idea what buttons I pushed. Shift+scroll still doesn't work for me, though. I just have all the tools available for use without having to select anything.
This is a better version of what i previosly wrote, so here: when you installed the plasma cannon moudle, press esc and press these: options>controls>cycle tool backward/forward>press them then edit it to what i recommend: ctrl, there should be two ctrl on your keyborard then press esc, press ctrl (or what ever key you binded your cycle tool backward/forward) then you should see the picture of the plasma cannon, that means you equiped it! Hold left-click, you should see this big ball-thingy, when it gets as big as it can get, let go of left-click and you shot your big ball-thingy!!! There you go! You got the plasma cannon installed!