What VEX accesory should I buy?

I only have 20 dollars and im thinking either the advanced gear kit, the differential gears, linear slide or something else.

well linear slides are way better when you have the rack and pinion kit that comes with adv. gears. and differential gears are included with the adv. gear kit so it looks to me like adv gears is your best bet.

To me, the differencials only have two real useful applications and neither of them are that great in a robot. You can use them in a car style robot so that the rear wheels don’t have to skid on their surface during a turn and you can make a dual differential drive system.

The second is really cool, but I just finished one and it takes a lot of planning and layout of gears and I think it sucks down a lot of power while also introducing a number of small failure points. Oh, the neat thing about a dual differential drive system is that it goes straight mechanically rather than via sensors or human interference. That alone makes it quite awesome.

But it is soo mesmerizing to watch.

You can get some of the gears separately (I got the advanced gear kit pretty much only for the diffs, then later ordered a couple more diffs).

I wish I had some linear sliders, but DinerKid is right that they are much more useful with rack gears (which I think you can order separately too).

Honestly, I think if I only had $20 to spend, I’d hang on to my cash. Wait until you have $50-$100 and then keep an eye on Craigslist (or ebay) in your area for a really good deal on Vex stuff.

With patience, you might score yourself someone’s full Vex set plus accessories for that price range. Having tons of parts is far, far more fun and useful than just a couple of special purpose parts, imho.

I’ve never been building something and said “crap, now I’m stuck because I don’t have any differencials / rack gears / linear sliders ]” but I have run out of metal plates, those plastic bushings, even some screws and a few other parts. You can work around the lack of a differential (in a robot that small, who cares if the wheels have to skid a little). When you run out of metal, you are just stuck.

The claw so far has been my favorite part. We’ve done a ton of cool robots with it. Advanced gear kit is a good second choice. For five dollars more you can get the VEX 6" Wheel Legs.

One of our most popular ‘demo’ bots is a modified 4 wheel drive square bot with the Wheel Legs and claw on a custom wrist unit.

But I spend a ton of money on shaft collars, bearing blocks and locking bars, and the swerve drive kits. If you spend the money for the rack/pinion gears, spend the money for the bracket.

The advanced gear kit is fun to play with. Some parts of it have little use in the competition, but to play around with it is a blast. You can get very creative with designs for recreational robots.