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# Using a Rotary Potentiometer to Detect the Position of a Robotic Arm

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Introduction

Using a Rotary Potentiometer to Detect the Position of a Robotic Arm Plan: A rotary variable resistor would be set up as shown mechanically and electronically: Various different fixed resistors would be tried, with several readings taken for each. I suggest 9 readings should be taken, every twenty degrees starting at 20 for each resistor. That way, a full range of angles can be tried along the whole movement of the arm. Once the results have been obtained, then graphs can be plotted to calibrate the sensor, and from these graphs the most suitable resistor can be chosen for the sensor involved. Initial experiments show that all readings will be in the range of 0 to 5 volts. Results: Voltage across sensor (V) Resistor Used in Potential Divider (ohms) Degrees 100 220 470 1000 2200 4700 10000 0 0.00 0.00 0.00 0.00 0.00 0.00 0.00 20 0.35 0.17 0.08 0.04 0.02 0.01 0.00 40 3.14 2.32 1.48 0.86 0.44 0.21 0.11 60 3.98 3.45 2.68 1.84 1.07 0.57 0.29 80 4.23 3.82 3.17 2.36 1.50 0.84 0.44 100 4.42 4.10 3.60 2.87 1.96 1.17 0.64 120 4.46 4.22 3.78 3.13 2.24 1.39 0.79 140 4.51 4.29 3.99 3.31 2.45 1.59 0.92 160 ...read more.

Middle

For example, the 100-ohm resistor has 12 readings less than 0.5 volts apart. This results in a low SD, even though the spread is less even). I have also divided the standard deviation by the range to allow for comparison between resistors of different ranges, and quantitative comparison. A larger graph that better depicts these readings is in the appendix. Again, the higher the SD/Range ratio the better for a generalist arm. However, I believe that range should also be maximized, and as such I believe the 2.2k? is the most effective in this role (see below). Linear variation is most desirable for this use in a non-specialist arm. This is beneficial, in a typical arm, because a large and even difference in voltage is present wherever the arm in its arc. A more specialized arm, for example in a car factory, might need great accuracy in a certain position, such as near the car, and less accuracy in others, like storage position, and well above the car. This arm would require a large spread of potential difference over certain angles, and smaller spread of potential difference over others. ...read more.

Conclusion

Its accuracy and range would be extremely good, however. Response time of the system was around 1 second. It was this poor due to the voltmeter used. The sensor itself had a very low response time. If linked into a different voltmeter, or logic circuitry, the response time would no longer be a problem, as the voltmeter that causes the delay has been removed entirely. In addition, there was no drift of the readings, as long as the arm was bound well enough to the sensor, and the extreme repeatability (near zero random variation) of the sensor means it would be very reliable as the position indicator for a robotic arm. I will end on the limitations to this project. It cannot consider the effects of time and age on the sensor, its reliability under adverse conditions such as varying temperature, vibration, shock, and water resistance. It did not compare the advantages of other rotary potentiometers over this one, either. Appendix: 1. 3.14-0.35 = 2.79 2.79*100 = 279 (as the voltmeter used was accurate to 0.01 volts) 279/20 = 13.95 1/13.95 � one fourteenth 2. 180*13.95 = 2511 ?/2511 = 0.001251132 0.001251132 * 1000 * 1 � one millimetre at 1 metre ...read more.

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