help with 4 wheel drive turning

[_SquiD_]

Hi there, guys.

I'm quite new to robotics and I have a Lynxmotion 4 wheel-drive platform at my disposal. The platform is​

already equipped with 4 DC motors.

Can anyone help me out with some papers / tutorials about the turning concept of such a robot​

platform? I would prefer that the left / right turn to be made without moving around to much.

Thanks in advance,

-SQD-​

 

[Sckoarn]

I too have recently got the Robotics bug. I have a Mindstorm NXT.
That platform looks very nice. If all that is there is the platform with motors, you will need more parts. Some kind of motor control boards and a processor board. Depending on the processor you pick, you may be able to use RobotC.

The lynxmotion site should have something.
Lynxmotion Robot Kits

Another resourse.
RobotShop | Robot Store | Robots | Robot Parts | Robot Kits | Robot Toys

Sckoarn

 

[_SquiD_]

@Sckoarn: I already own a control board with ATMEGA64 from Digilent: Cerebot-II. I also acquired recently some L293NE H-Bridge components and all I've needed now is the principle of how can I turn the robot.

-SQD-

 

[Sckoarn]

Ok,
I am not familure with what software you have to program your bot.
To turn or pivot on the spot, you need to make one side go forward and the other go reverse. If the Bot was a tracked vs. wheels, I think you can do the same thing in both cases. If you are using RobotC, there are functions that do this. I have only had a chance to skim the reference manual for RobotC and I can hardly wait to get into it. Currently I am using the Mindstorm Graphical programming interface, which is good for learning.

Creating a pivot routine was the first thing I tryed to do. I got it, but the task of line following did not require it, so I put that off for a while.

Links:
Lynxmotion - Software

and

**broken link removed**

The microsoft product is interesting.

Sckoarn

 

[prmurthy]

@Sckoarn: I already own a control board with ATMEGA64 from Digilent: Cerebot-II. I also acquired recently some L293NE H-Bridge components and all I've needed now is the principle of how can I turn the robot.

-SQD-

Hi,

I think it is pretty simple. In any kind of four wheel drive it is the front two wheels which are important for turning and the rear wheels are always used as power to the vehicle. Let it be a robot or a car.
The turing can be taken place in 2 forms. One angular turn and axis turn.
Angular Turn : This can be achived by make of the motor run faster than the other one ( Only front wheels used, the rear wheels will be running in symmetry and if you try to change the speeds of rear wheels the vehicle will behave odd and can topple the vehicle). Here the logic is, the slower the any one of the front wheel lesser the radius of the turn. I mean say front right wheel is running at 100 rpm and front left wheel running at 200 rpm it will take bigger radius turn towards right and vice versa.
Axis turn: This is sometime known as tank like steering. If the wheels run in opposite direction it will turn on the axis of wheels. Here you have to stop or dead slow your rear wheels. The direction will depend on which running CW and CCW. You can manuplate the direction here.

Hope this will be of helpful to you.

Thankyou

 

[natraj20]

I am not sure of 4 dc motors but i used a much simpler way to drive with 2 dc motors using the same L293 D H-bridge and the same principle might give you an idea.

In my case, the left two wheels are connected to a dc motor and the right two wheels are connected to another.
If you exite the left dc motor and turn off the power supply to the right dc motor, the motor will steer right based on its inertia.
If you exite the right dc motor and turn off the power supply to the left dc motor, the motor will steer left.
Exite both the motors in the same direction forward - the bot goes forward and exite in the opposite direction to move backwards.

You might use the same signal for your left two dc motors and another signal to control right two dc motors as in my case and the duration of the excitation and turn everything is just trial and error. Start with this and you ll end up with various ideas.

Hope this helps !!!