Re: how much equipment needed for robot arm control?

by adafruit_support_bill on Tue Jan 08, 2013 8:13 pm

I don't think you can get the reset button to work the way you describe. But a push-on/push-off power switch should work: https://www.adafruit.com/products/482

The 6xAA battery holder will give you 9v: http://www.adafruit.com/products/248
I don't know of any examples or tutorials for exactly what you are trying to do with a robot arm. But I'm sure there are some related projects out there.
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Re: how much equipment needed for robot arm control?

by kgraf on Thu Jan 10, 2013 12:30 am

1. the 5.5mm/2.1mm Plug fits the mega ac/dc adapter plug? It looks perfect. Should I get the 8xAA,
I ultimately have to drive 4 sensors and 5 motors.

2. How do I connect another gyro to I2C? pins 20 and 21 are the only ones that say SDA SCL. I understand I2C can identify about 112 different devices. I have to add two more gyros and a FSR and drive 5 motors.
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Re: how much equipment needed for robot arm control?

by adafruit_support_bill on Thu Jan 10, 2013 6:04 am

1. the 5.5mm/2.1mm Plug fits the mega ac/dc adapter plug? It looks perfect.

Yes, it fits.
Should I get the 8xAA, I ultimately have to drive 4 sensors and 5 motors.

I don't like running Arduinos on 12v. It tends to make the on-board voltage regulator run pretty hot - especially if you have additional circuitry attached. I would recommend a separate power supply for just the motors. This will keep the motor noise from feeding back into the Mega and causing problems.

2. How do I connect another gyro to I2C? pins 20 and 21 are the only ones that say SDA SCL.

The L3GD20 does not have a way to change the I2C address. But if you wire it for SPI, you can address multiple gyros. You can share the SAO, SDA and SCL lines, then use a different CS (Chip Select) pin for each gyro.
http://learn.adafruit.com/adafruit-trip ... and-wiring
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Re: how much equipment needed for robot arm control?

by kgraf on Thu Jan 10, 2013 10:43 am

1. I bought 2 6xAA 9V holders one for the mega and one for a 5V miniboard from futurelec that appears to have 10 5V output pins. Does ada have any thing equivalent to the miniboard power supply?

2.
Code: Select all | TOGGLE FULL SIZE
// By default, uses I2C
//Adafruit_L3GD20 gyro;
// Alternately, you can use SPI, but you have to define the pins
#define GYRO_CS 4 // labeled CS
#define GYRO_DO 5 // labeled SA0
#define GYRO_DI 6  // labeled SDA
#define GYRO_CLK 7 // labeled SCL
Adafruit_L3GD20 gyro(GYRO_CS, GYRO_DO, GYRO_DI, GYRO_CLK);


Does this mean connect CS on the gyro board to pin 4 on the mega? SA0 to pin 5 on the mega? etc.? there is only pins 2-13 available for SPI connectivity?

3. How many gyros can I connect to the mega? 1 thru I2C and 2 or 3 in SPI?
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Re: how much equipment needed for robot arm control?

by adafruit_support_bill on Thu Jan 10, 2013 11:32 am

Does ada have any thing equivalent to the miniboard power supply?

These aren't mounted on a board like the Futurelec product, but the output is the same: 5v@1A and they are very compact.
https://www.adafruit.com/products/1065

Does this mean connect CS on the gyro board to pin 4 on the mega? SA0 to pin 5 on the mega? etc.? there is only pins 2-13 available for SPI connectivity?

The Library uses Software SPI, so you should be able to use any pin on the MEGA that supports pin-change interrupts (pins 0-23).

3. How many gyros can I connect to the mega? 1 thru I2C and 2 or 3 in SPI?

You can connect one via i2c and the others with SPI, or connect all of them via SPI.

The limit on SPI is how many pins you have available. You will need a separate CS pin for each gyro.
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Re: how much equipment needed for robot arm control?

by kgraf on Tue Jan 15, 2013 12:11 am

I received my 6xAA power supplies. Does it matter whether the red and black wires are soldered on the outer sleeve and central hub of the 5.5mmx2.1mm plug in any specific connection? red center or black center?

How good a quality camera (approx. cost) is needed to take a picture of a circuit that will be usable online?
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Re: how much equipment needed for robot arm control?

by adafruit_support_bill on Tue Jan 15, 2013 6:05 am

red center or black center?

The red (positive) should go to the center pin. Black (negative) to the outer sleeve.

How good a quality camera (approx. cost) is needed to take a picture of a circuit that will be usable online?

You don't need such an expensive camera. Most cell-phone cameras these days can take a pretty decent photo in the right conditions. The most important thing is to have enough light. Near a window or even outside will give you much better light than yo will get from a desk-lamp.

I would avoid web-cams though. They tend to be too low in resolution.
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Re: how much equipment needed for robot arm control?

by kgraf on Tue Jan 22, 2013 12:48 am

The 6xAA battery pack works great. I have two motors rotating (arm linkages of an OWI edge arm) successfully from the gyro data thru the mega into a toshiba dual motor driver driving the dc motors.

1.
Then I integrated the z rotation angle to compute the absolute angle. The idea is that the gyroscope produces a delta angle (call it θ):

θ = ∫0t θt dt


the gyro is giving readings in degrees/second. What time interval is being used to make
the data? Is there a constant clock (SCL?) time value? If I turn the gyro 10 degrees in one second
it gives a reading of 10. If I turn the gyro 10 degrees in 1 ms it gives a reading of 10,000. How do I determine the time of the rotation to integrate?

I believe our project requirements permit using the gyro (sensors) breakout boards. However,
we have to make our own power supply boards, motor driver boards, and microcontroller (eagle and send to pcb printer) boards.

2. Do you sell the individual driver chips like DRV8833 (need to drive 6 motors) or only the breakout boards? Any surface mount soldering suggestions? Do you sell individual chips like atmels or power regulators?
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Re: how much equipment needed for robot arm control?

by adafruit_support_bill on Tue Jan 22, 2013 6:40 am

The gyro is reporting the instantaneous rotation rate. To minimize the effects of noise, while still keeping the arm responsive, I would keep my sample window to about 100-200ms and average as many readings as you can take over that time.

We do not carry the DRV8833 chips. We do have some Atmel chips, including Atmega328s and some DC/DC converters that are pin-compatible with 7805 regulators. There are some tutorials on surface mount techniques in our Learning System.

http://learn.adafruit.com/smt-manufacturing
http://learn.adafruit.com/adafruit-guid ... face-mount
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Re: how much equipment needed for robot arm control?

by kgraf on Wed Jan 23, 2013 12:43 am

sample window to about 100-200ms and average as many readings as you can take over that time.

do you mean milliseconds or microseconds?
At what rate is the mega sampling the gyro data? Is there a base clock rate thru the scl?
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Re: how much equipment needed for robot arm control?

by adafruit_support_bill on Wed Jan 23, 2013 6:59 am

do you mean milliseconds or microseconds?

Milliseconds.
At what rate is the mega sampling the gyro data? Is there a base clock rate thru the scl?

The sample rate is (mostly) up to you. It does one sample (X, Y and Z axis) every time you call "gyro.read();". It takes at least 10 milliseconds per read, so the upper limit on the sample rate is somewhat less than 100Hz.
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Re: how much equipment needed for robot arm control?

by kgraf on Tue Jan 29, 2013 12:25 pm

our project team just bought a lynx al5d-ns metal (h/w only) arm with medium wrist upgrade.
we need 5 more servos to move a payload of a full soda can (13 oz). do you sell any
servos you recommend for this arm?
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Re: how much equipment needed for robot arm control?

by adafruit_support_bill on Tue Jan 29, 2013 12:42 pm

The Lynxmotion arms are pretty nice. You will want a high-torque metal-gear servo - especially at the base. As you have probably discovered already, the motor at the base needs a lot of torque to lift a fully extended arm. I think the Lynx arm comes with counterbalancing springs to help counter the weight of the arm itself. If not, rubber tubing works well for that application.
https://www.adafruit.com/products/1142
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Re: how much equipment needed for robot arm control?

by kgraf on Thu Jan 31, 2013 1:09 pm

we are currently considering analog versus digital servos. the digitals seem
to cost more. do you have any recommendation of analog vs. digital?
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Re: how much equipment needed for robot arm control?

by adafruit_support_bill on Thu Jan 31, 2013 2:59 pm

Digital servos can be more precise, but they do cost a lot more and I don't know of any Arduino libraries to drive them.

Analog servos are simple to drive from an Arduino, and the libraries are well supported.
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