# CD/DVD Drives Test

By Abdou Fares

CD/DVD Drives testing:

Equipment:

1)      HP CD ROM Drive Model GCR-8483B

2)      Micrometer.

3)      Multimeter.

4)      Soldering Iron.

5)      Fish Scale.

7)      Arduino Uno board.

8)      Random weights.

Procedure for calculating the resolution of the CD Drive Stepper motor:

In order to measure the resolution of the CD/DVD drive stepper motor, a digital micrometer was used.  The distance along the screw was measured. Figure 1 below shows the total length of the screw using a micrometer, which turned out to be 51.56 mm.

Figure1: Total length of the screw.

Third, the number of steps/ revolution of the stepper motor without the effect of the screw was looked up on the web. The part number was found on the back of the stepper motor which is 15RF073K. Looking at the specifications for this stepper motor, the following information was found and shown in table 1.

 Step angle 18 degrees Holding torque 25g.cm  = 0.0024 N.m Rated Current 0.24 A Drive Model Bipolar

Table 1: Summary of the 15RF- 073K series specification.

From the table above, the step angle is 18 degrees which corresponds to 20 steps/revolution. Now that all the information needed is available, the resolution of the stepper motor could be calculated as shown below:

Resolution = (Distance between adjacent threads) / (N Steps/rev) = (4.29mm/rev) / (20 steps/rev) = 0.214 mm/step.

Which is 3 times better the resolution required which is 0.68mm/step.

Testing the Holding Torque and Change of Current

In order to determine the change the current drawn by the CD/DVD drive stepper motor at different weights the following test was performed.

First, as seen from Figure 1, the CD/DVD drive has four terminals.  In order to determine the connectivity between any two of these terminals to one coil, a multimeter was used. The multimeter was set on the buzzing mode. Then the positive and ground terminals of the multimeter were used to touch two stepper motor terminals at a time as shown if Figure 2.  The terminals that has connectivity will set a buzzing sound on the multimeter.

Figure 2: Testing for connection.

Second, after determining the connections properly, jumper wire were soldered onto each terminal of the stepper motor and then  were connected to the correct pins on the adafruit motor shield that goes on top of ARDUINO Uno as shown in Figure 3 below:

Figure3: Connection between CD Drive stepper motor and the adafruit motor shield.

Fourth, the stepper test code from the Adafruit Library was used to run the stepper motor. The code that was used is shown below:

The CD ROM drive was attached upside down to the table in order to test different weights values. A fish scale was used to measure the weight.  Figure 4 shows a better picture of the procedure described:

Figure4: Attaching loads to the CD ROM drive.

Fifth, in order to determine the current drawn by the CD ROM drive at different loads, a multimeter was connected in series to the Adafruit board. The results are shown table 2 below:

 Mass of load(g) Current drawn(A) 0.2 0.27 0.5 0.27 0.9 0.27 1 0.27

Table2: Current drawn by the stepper motor at different loads.

From the results in table 2, the CD/DVD stepper motor reached its rated current.  The results show that the CD/DVD drive stepper motor cannot hold a lot of mass. This explains the small holding torque in table 1.

In conclusion, besides the high resolution that CD drives stepper motor has, they have a small holding torque.

MakerBot, CupCake CNC 3D printer.

The Cupcake CNC 3D printer uses NEMA 17 stepper motors to drive the XYZ axis. The NEMA 17 stepper motor has the following specifications shown in table 3 below:

 Step angle 1.8 degrees Holding torque 0.28 N.m Rated current 0.84 A

Table 3: Specification of the NEMA 17 stepper motor.

As seen from the table above, the holding torque of the NEMA 17 Stepper motor is 100 times better than the CD/DVD drivers.

References :

CD/DVD drive stepper motor datasheet: http://www.moatech.com/eng/prod_stepping_10.html

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