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| Both sides previous revisionPrevious revisionNext revision | Previous revisionNext revisionBoth sides next revision |
| marvin:ecp3 [2009/01/28 23:38] – deva | marvin:ecp3 [2009/01/29 00:42] – rieper |
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| === DC Motor Drives === | === DC Motor Drives === |
| {{ :marvin:motor.png |The NXT DC Motor}} | {{ :marvin:motor.png |The NXT DC Motor}} |
| The Lego Mindstorm kit comes with a set of DC Motors and therefore we shall give a short introduction to the DC motor and the DC motor controller. This will hopefully add nicely to the presentation of the H-bridge and DC servo motors given in the lesson given in week 4 of the course. Let us begin with the DC motor.((http://hyperphysics.phy-astr.gsu.edu/hbase/hframe.html))\\ | The Lego Mindstorm kit comes with a set of DC Motors and therefore we shall give a short introduction to the DC motor and the DC motor controller. This will hopefully add nicely to the presentation of the H-bridge and DC servo motors(([[http://csel.cs.colorado.edu/~bauerk/legorobots/motors.html#SECTION001210000000000000000|motors]])) given in week 4 of the course. Let us begin with the DC motor.(([[http://hyperphysics.phy-astr.gsu.edu/hbase/hframe.html|Hyper Physics]]))\\ |
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| {{ :marvin:dcmotor.png?300 |NXT DC Motor Diagram}} | {{ :marvin:dcmotor.png?300 |NXT DC Motor Diagram}} |
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| === Motor Encoder/Tacho Counter === | === Motor Encoder/Tacho Counter === |
| When designing the motors, wheels and drive train, it will almost always be important to have some sort of encoder feedback. In the LeJOS framework there are methods to get readings from the tacho counters and these sensor readings have proven to be very useful when designing a balancing robot cf. the research literature in the [[http://wiki.aasimon.org/doku.php?id=marvin:ecp0|introduction]]. In order to illustrate the concept of an encoder we use this simple set-up, which is explained in the excellent SRS Encoder article by David Anderson((http://www.seattlerobotics.org/encoder/200109/dpa.html)). Imagine a DC motor without an encoder which is illustrated in the top of the figure. If we mount a circular image with a pattern determining our resolution, we can use a simple IR transceiver to get readings back to our micro controller or signal processing unit. In the LEGO Mindstorm kit(([[http://mindstorms.lego.com/overview/]])) each motor has a built-in Rotation Sensor. This allows us to control the robot’s movements quite accurate. The Rotation Sensor measures motor rotations in degrees or full rotations [accuracy of +/- one degree]. One rotation is equal to 360 degrees, so if we set a motor to turn 180 degrees, its output shaft will make half a turn. This allows us to evaluate both the body angle and angle velocity of the balancing robot by means of simple differentiation, which is explained in one of the following sections. | When designing the motors, wheels and drive train, it will almost always be important to have some sort of encoder feedback. In the LeJOS framework there are methods to get readings from the tacho counters and these sensor readings have proven to be very useful when designing a balancing robot cf. the research literature in the [[http://wiki.aasimon.org/doku.php?id=marvin:ecp0|introduction]]. In order to illustrate the concept of an encoder we use this simple set-up, which is explained in the excellent SRS Encoder article by David Anderson(([[http://www.seattlerobotics.org/encoder/200109/dpa.html|Home-Brew Shaft Encoders]])). Imagine a DC motor without an encoder which is illustrated in the top of the figure. If we mount a circular image with a pattern determining our resolution, we can use a simple IR transceiver to get readings back to our micro controller or signal processing unit. In the LEGO Mindstorm Kit(([[http://mindstorms.lego.com/overview/|LEGO Mindstorms]])) each motor has a built-in Rotation Sensor. This allows us to control the robot’s movements quite accurate. The Rotation Sensor measures motor rotations in degrees or full rotations [accuracy of +/- one degree]. One rotation is equal to 360 degrees, so if we set a motor to turn 180 degrees, its output shaft will make half a turn. This allows us to evaluate both the body angle and angle velocity of the balancing robot by means of simple differentiation, which is explained in one of the following sections. |
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| {{ :marvin:ecoder.jpg?300 |Principle of TACHO Encoder}} | {{ :marvin:ecoder.jpg?300 |Principle of TACHO Encoder}} |
