how much rigidity will the

If you select a wooden base of thickness 5mm to 10mm it will be able to sustain a load of 1-2kg or even more. This will serve the purpose for competition specific bots.

Regarding motors you can definately choose a motor of lower rpm (revolution per minute) but the motor should have high torque and the wheels should be bigger in size. For more details check out this tutorial - Calculation of Torque and RPM.

Yes you can also use 'solar cells' as a power source for driving a bOt but then the bOt should be very light weight as solar cells do not provide high power.

Solar cells as a power source is a good option if you are ready to invest a handsome amount into your robot.

Solar panels deliver very less power.A typical solar panel around 5cmx6cm would deliver a power of around 250mW, which is too less to drive a decent bot.

Even with the use of some solar energy engines like Miller engine etc,the only bots that can be driven by such a power rating are the once which can be held in hand and weigh even less than 50gms

i m making a robot (my 1st). how do i connect wheels directly to the smooth output shaft of DC motors? any help will be greatly appreciated. thanks

Read our tutorial on how to couple motors and wheels. 

fellas my wheels r not straight.. the robot is dwindling..

also when both the motors r ON it doesnt go straight. it moves in some bend sort of an arc..

why dont u buy motors already coupled wid wheels if u need such a high accuracy? 

the problem of bot not moving straight is coz both the motors are not moving at the same speed..even if there is a small difference in the speed of the two motors,the bot would not go straight,rather it would move in a curved path

This is a problem that is almost impossible to remove if you are using two motors to drive your bot bcoz two motors would never move at the same speed even if they are of the same company same rating (eveything same)..

So the solution is to use a single motor ro drive the bot.For this you can either use a motor in which a shaft comes out from both the ends(or u can smhow connect another shaft to the other end of the motor)

Or,if u can get any appropriate gearbox frm some toy etc,then u can use that to control both the wheels with one motor only..u can use the gearbox of a typical jcb toycar..this way u can totally eliminate the problem of bot moving in a curved path

and if you dont want to take a little pain then u can continue with the two motors and chnage the direction of the bot every time it deviates noticably from the actual path

just use the motors with the same rpm at same voltege.. you will be able to sort this problem out...

Adi you missed the point. No two motors are exactly the same. Reckless explained this quite well. You may try pwm to vary the voltage to 1 of the motors , but that will require the Hit & Trial Method

Ya.. but i couldn't suggest to implement PWM to the person who is making his first bot...

The motors wont run at the same RPM even with same voltage then