The following is Instructions for assembling the first generation robot arm that I am developing for the Eyebeam Atelier AiR program as part of an animatronic self-portrait. This arm has 4 degrees-of-freedom (DOF) from the wrist to the shoulder, runs at less than 20 W and is about 12 ounces. I am currently working on V2 with limit and home switches for each DOF, a single DOF hand and adding another 2 DOF to the shoulder. Motor control units for the arm are also currently being developed. You can check out the progress of the arm by clicking here or go to robot clothes dot com
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Signing UpStep 1: Motors and Encoders
I decided I would try to find separate shaft encoders and motors and try to make an assembly (or a couple varieties of assemblies) that would couple them via gear pairs or pulleys. We tried out a number of different motors and finally decided we would use a few gearmotors from solarbotics. We chose the solarbotics motors because they had a range of reductions, sizes, shaft output orientation and were overall very light, very cheap and very available. We are using the encoders to provide closed loop feedback for precision and obstacle sensing.
The GM3 224:1 gearmotor and the GM14 Sanyo 297.1:1 gearmotors have seen the most action so far in our arm assembly. The GM3 (and the GM2, GM8 and GM9) are all similar, use the RM3 DC brushed servo motor and have plastic gears and housing. They all also have an output D-through- shaft that can couple to an encoder shaft. The regular output shaft is also easy to couple to and the motor is pretty easy to mount with two built-in mounting through-holes. They are capable of 50 in*oz of torque, with a kludge clutch rated at 60 in*oz and a weight of 1.31ounces. They cost ~ $6.00 each.
The GM14 is smaller, lighter and has metal gears. This is a very small motor, small enough to universally make people say ?cute? when they see it. It produces ~40 in*oz of torque and weighs .29 ounces. The output shaft has a flatted side, so it is easy to mount to, though there isn?t much shaft axially in general. Not particularly easy to mount but it does have some mounting holes and can be mounted by putting the whole motor in a rectangular recess. They cost ~ $25.00.
Both motors run on ~5VDC and draw current in the range of 100 ma to 600 ma.
I choose the U.S. Digital S4 miniature optical shaft encoder as the proprioceptive feedback device. This encoder is cheap, small, very accurate, comes in a number of resolutions, is easy to mount and can be purchased with a gear bearing shaft so the encoder can handle a substantial radial load. They cost ~ $45.00.
The GM3 224:1 gearmotor and the GM14 Sanyo 297.1:1 gearmotors have seen the most action so far in our arm assembly. The GM3 (and the GM2, GM8 and GM9) are all similar, use the RM3 DC brushed servo motor and have plastic gears and housing. They all also have an output D-through- shaft that can couple to an encoder shaft. The regular output shaft is also easy to couple to and the motor is pretty easy to mount with two built-in mounting through-holes. They are capable of 50 in*oz of torque, with a kludge clutch rated at 60 in*oz and a weight of 1.31ounces. They cost ~ $6.00 each.
The GM14 is smaller, lighter and has metal gears. This is a very small motor, small enough to universally make people say ?cute? when they see it. It produces ~40 in*oz of torque and weighs .29 ounces. The output shaft has a flatted side, so it is easy to mount to, though there isn?t much shaft axially in general. Not particularly easy to mount but it does have some mounting holes and can be mounted by putting the whole motor in a rectangular recess. They cost ~ $25.00.
Both motors run on ~5VDC and draw current in the range of 100 ma to 600 ma.
I choose the U.S. Digital S4 miniature optical shaft encoder as the proprioceptive feedback device. This encoder is cheap, small, very accurate, comes in a number of resolutions, is easy to mount and can be purchased with a gear bearing shaft so the encoder can handle a substantial radial load. They cost ~ $45.00.
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Here are the 7 pins in DC motor controller:-
Pin No. Pin Functionality
1 GND Ground
2 IN-1 Logic input for the motor direction.
3 Diagnostic 1
(DG-1) Output pin with logic 1 output in normal operation. Represents side of the internal
H bridge corresponding to IN-1. Pin is pulled to logic low by the motor driver in
case of over temperature or overload due to short circuit.
4 PWM Used to apply Pulse Width Modulation to control motor velocity
5 Diagnostic 2
(DG-2) Output pin with logic 1 output in normal operation. Represents side of the internal
H bridge corresponding to IN-2. Pin is pulled to logic low by the motor driver in
case of over temperature or overload due to short circuit.
6 IN-2 Logic input for the motor direction.
7 CS* Current Sense output to measure the current flowing through the driver