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I have not built a robot for months and I kinda forgot a few things. Normally I always build my robots with castor wheels but now I want to build stuff that use rubber wheels but then it cant turn well.Plz give me tis on how to buld good non castor cars

there are many options open to you. you could remove the rubber for the unpowered wheels (making them more slippery, therefore better for turning), or purchase a rotacaster (google it.), build a ball caster, or simply return to you're normal, everyday caster (just curious, why can't you're project use these?). Also, if these don't work, there's always Rack & pinion steering.

Firstly, are you building a car-style robot or a tribot-style robot?
If you are building a tri-wheeled robot, there is no need for the caster to be rubber. If it is a four-wheeled robot, your problem could be lack of a differential.
(If this is too hard for you, just use two unconnected, unsynched motors for the back two wheels.

Can you post an image of your robot? A non-caster robot needs a rear differential or some other means of letting the two rear wheels turn at different rates. Without this, they don't corner very well. A quick fix is to only drive one rear wheel.

Details would help.

Some have made a good point about if its a car with steering, you need a dif in the rear if both wheels are powered, unless its for off road use, if its for off road use then a locked rear dif is much better when both wheel shave power. why? A Lego dif gives power to the wheel with the LEAST traction. So if say your rear axle has only one tire touching the ground(like going over rough terrain) the tire that is off the ground gets all the power and you are stuck with that wheel spinning. If its a straight axle locked both get power no matter what tires is on or off the ground.

If it is a skid steering( like a tank) then one thing to remember is design is important. Basic rule of thumb is W=L(width = lenght) Why? If the lenght is longer than than width it will have more friction when turning. The wider it is to lenght the easier it will turn. It should at least be equal and then widder the better.

Doc