There are several inexpensive, basic tracked vehicles that can be the base for your robot. Here is a picture just such a unit:
The unit can be purchased at many different online electronics outlets, such as eBay, Amazon, Banggood, and other vendors. This example uses the Wali SUV SN1100 V2 available on eBay. It, of course, comes unassembled, so let's briefly look at how to build the unit. Here is a picture of all the parts:
Here are the steps to assemble the unit:
The first step is to open up the plastic bag and look at all the parts. Here they are:
Now you'll need to put the wheels together. These fit inside the tracks. Two of them, the ones with the outer rim that is spoked, will be connected to the DC motors. But let's start with ones that don't have spikes on the outer rim. Here is a picture of one of the wheels assembled:
Half of the wheels have three holes, the other half six, although you'll only need to assemble the wheels with three. Here is the...