Drive system

In order to drive the tank and power a computer, we need 1 or more batteries that can last a decent period of time.

The first thing that comes to mind is a car battery, but after some research I learned that car batteries are not suitable as they are designed for high amp, short term power to start an engine and would not last very long at all and also these batteries do not like being discharged completely and can become damaged quite easily like this.

We need long lasting energy to power a laptop and the other components onboard and it seems a "VRLA" (or Valve-Regulated Lead-Acid) battery is the most suitable type.
These are the batteries used in electric wheel chairs, garage doors, alarm systems, etc. and prices can vary quite a bit, but there seems to be some affordable varieties on eBay.

Our dad being a very resourceful person managed to find an old lead acid battery in the garage and so we will use this as our first attempt and upgrade if we need to.

We purchased some 12V 15RPM geared motors from eBay and Rob built a little platform that we could use to test out our new equipment.
He made up some little brackets for the motors and found some old plastic wheels, which he used some metal to put a flat side in the hole so it would be keyed like the motors axle.
There is a single caster at one side, the 2 mounted motors on the other, the lead acid battery on top and some terminals to connect all the wires together.

As these motors are geared for torque, not speed, it was moving quite slow, but that will change a little when we get appropriate sized wheels, etc.

This made us think that because we are going for pulling power, not speed, we should test out the load carrying capacity of the rig.
We loaded up an additional full size car battery and it moved all that effortlessly.
After that we loading up more and more until we got to a point where rig stopped moving, but only because the motors were ripping through the plastic wheels.

This made us pretty confident that these 12v motors would be strong enough for any equipment we want to load up, as long as the motors are strongly coupled to the wheels (or in our case, the tracks).

Research

So I went to watch my girlfriend's dad have a rally drive experience, it was really cool.

When out of nowhere I hear a rumbling noise as I turn around what do I see?

That's right!
A TANK!!!!

So needless to say, I went and further examined it for my knowledge of how a real army tank is made, this tank had been to Vietnam and has now been retired.

I took a bunch of photos, especially of the track system as this is one of the parts we think we will have to custom build from scratch.

Proof of Track Idea

Rob got a chain! He went down to the tip yesterday morning and because we only want the chain (not the whole bike) he managed to get one for free! The plan is to use a segment of this chain as a test piece to prove the idea.

Rob ground the ends off the axles and we used a center-punch and hammer to pop them out, completely disassembling the segment of chain.

We reassembled the chain by replacing axles with long nails and placing (over-sized) spacers between the chains.
Obviously these spacers are way too big, but just to give the feel of what it could potentially look like.

Looks tough!!
If we can get some long mild steel axle (instead of nails) from a steel shop and cut it down to size, and find some sort of spacers (steel or even plastic should be ok) that will be all we will need to build the tracks as we planned.

The fall-back plan can always be similar to that instructable which doesn't involve disassembling the chain at all and just drive it from a roller-blade wheel or something, but we think this was would be cooler :)

To make the tank look real-ish, the ratios have to be proportional.
The length of the chains and the width of the spacers is going to depend of the overall size of the tank. This means we have to work out what else the tank is going to house (air compressor, etc.) and help from Google Images will be useful!

ThinkTank - Part I

Yesterday Rob and I had our first brainstorming session for The Tank.

After getting some inspiration from the Internet we started planning out the features for our first iteration, which basically included:

• Proper (dual drive) tank tracks
• Pan & Tilt turret
• Pneumatic cannon
• 2 web cams (turret and tank)
• Wifi control

First point of discussion was the tank tracks.. which I had no idea how we were going to do that, then Rob found this instructable:
http://www.instructables.com/id/How-to-make-custom-and-strong-tank-tracks-for-very/

Which looks tough!
The only thing is we cant actually drive the chain with those bolts in the way (they use a roller blade wheel). What we really need is about 3 chains joined side-by-side. That way we could have the half-pipes (used as track from the tutorial) connected to the 2 outer chains, leaving the middle chain free to be connected to the driving gear.

The hard part is getting the 3 chains attached to each other, which Rob thinks we can actually disassemble the chain and replace each individual axle with a longer one, with spacers between the chain, forming quite a thick track... except its a massive job!
We would need to drill out each axle, replace it with a bigger one, then bash the ends to keep it riveted in working order.

We then found that we can get full working push bikes from the tip, with good chains on them for $5 each (but then we have to pay to bring them back to the tip). So thats the first thing we will have to try.

We briefly discussed how the cannon will work and a mechanism idea for rotating the turret, then how the Netduino will fit in the picture.

Ended up getting Anthony over as our Netduino consultant, and discussed how we can get motor speed control by using "Pulse Width Modulation" with the digital outputs of the Netduino and a BJT (transistor). Also got his help to set up a development environment on my machine, so I can play around :)

Pretty good first day of planning, with a few jokes thrown in (such as running the tank with a motorbike engine and flame-throwers.. which wont be happening, lol)