Monday, 28 November 2011

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).


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