There is a lot of friction with tank tracks. You need more motor and battery to do the same work.
Another downside is cost. A set of wheels is cheap compared to a decent set of tracks. I have not used them but Bill said the cheap ones tend to fall off.
You said so yourself: hindered turning. What do you think causes that? Friction! = lack of efficiency.
Tracks and wheels can start to balance out once you start putting your wheels on suspension though, especially once you get more than 4 wheels. Tanks tracks are simpler than a bunch of suspended wheels to simulate tank tracks- you have driveshafts, shocks, and transmissions going all over the place to power the wheels. It's still easier (and thus cheaper) to find the parts though since there are plenty of hobby grade monster trucks and zero hobby grade tanks.
TO me, the huge advantage of tracks is none of the things you just listed, but the fact that the tracks can be configured to climb very large obstacles without affecting the size of the output shaft lever arm. FOr example, you need a large wheel to climb a large obstacle, the large wheel is a large lever arm so you must gear your motor down more. Not so with tracks since a tiny tiny track driving gear with a tiny lever arm can be used to drive a humongously tall tracks that is still able to climb over large obstacles. THe losses in the gearing can make the motors unable to drive the wheels to move the robot not to mention the sheer cost of such high reduction gearboxes can outweight the cost of the tracks (keep in mind we are talking about serious climbing ability here, not your run of the mill battlebot tracked robot).
Tracks also spread the weight out more so there is less pressure on the ground. THe result is so you can traverse over softer terrain without sinking in. Probably not important unless you are the military or trying to run your robot over a bog or something.
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O.K. maybe not exactly Hobby Grade. Works great on low friction surfaces like concrete or vinyl flooring. Do a quick pirouette on carpet and one of the treads is likely to come off. As mentioned, a tank wants to climb anything it runs into.
There is one huge problem with tracks that you need to be very careful of if you are desinging them for a competition or practical use. The tracks have a tendancy to pop off of their tracks while turning on any surface that has a fairly large friction, suck as outdoors or a rubber floor. Wheels dont give is problem.
oh I didnt realize they would be so small, treads are great for the size it seems like you are going for, what is the competition (challenge) your team is competing in?
The robots in the competiton are 28"x38" and can be up to 6' Tall. They can weigh up to 150 Pounds can can draw nearly 100amps at times. These are no table top robots.