help with Digital Compass Modules

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1

hello ,

I’m trying to make my own Digital Compass Modules as shown here

https://www.youtube.com/watch?v=sBKHdt0OdPg

I have done almost everything , my problem is in the part that make the servo rotate

I don’t know how to make the servo rotate according to the HMC883L

can you help me with this ? show me the part of the code for the servo ?

Thanks,

2

Code ? For what platform, PIC, Arduino, ???

You might want to read this …

http://arduino.cc/en/reference/servo

But be aware most hobby servos advertise a 0 - 180 degree range and actually do a little less. You can get wider range servos but I doubt they will do a full 0 - 360 degrees.

3

code for Arduino

I have read the page - and it didn’t help

my servo is 720 degrees (for sure) , but for start I want to see it work like post in the youtube channel

4

Aaah I forgot about sailwinch type servos. If yours (a link might be nice as we here can’t read minds) is a typical analog servo, then it works like a typical 0-180 servo. Except that a 180 degree command will get you 720 degrees. And a 90 deg command gets you 360 degrees. So all you need to do is use the standard library as shown on that page and map the 0-360 degrees of compass angle into the 0-90 degrees of servo command. To restate the obvious, the servo command is the compass reading/4.

If your servo uses an extended pulse width to get the 0-720 degrees of motion, then the same logic as above applies and you can command pulsewidths, in usec, instead of degrees.

See if you can follow the example here.

http://arduino.cc/en/Tutorial/Knob

http://en.wikipedia.org/wiki/Servo_%28r … Connection

http://www.servocity.com/html/how_do_servos_work_.html

5

this is the servo I have

http://www.ebay.com/itm/121173284235?ss … 1439.l2649

I have read all the information in wiki and servocity - I get the theory. but when I try to use it , I get loss

even when I tell the servo to move to 22 - it make 2 circles.

I don’t know what I’m doing wrong

is there no why I can see the code that was used in the youtube? - just to see the part of the servo ?

thanks ,

6

even when I tell the servo to move to 22 - it make 2 circles.

Let's see if that makes sense. First off let's see what servo you have. The link says ...

Sail Winch Servo 55g metal gears 10.63kg torque 6 Turns travel

So it’s not a 720 deg servo, it’s a 6*360 = 2160 deg. A 22 deg command is 22/180 = 12.22% of a normal servos full range. 12.22% of 2160 deg is 264 deg, not even one turn. But then again each degree of command is 12 deg of rotation (ideally), and this servo might us a wider pulsewidth (than normal) for it’s turns.

So your command is about correct, certainly not 2 turns of command. Given the reviews I read over at HobbyKing for the 4 turn version of this servo (SW5513), it may well be that yours is broken. It seems to have quite a high failure rate.

http://www.hobbyking.com/hobbyking/stor … g_0_9.html

7

so from what you are saying - (just to see I understand )

if I tell him:

servo.write(13) - it need to do 1 full turn ?

also - is there any way to be sure it doesn’t working well?

some test code that show the store that it doesn’t work correct?

Thanks,

8

david1234:
servo.write(13) - it need to do 1 full turn ?

I don't understand what you mean by the above. Are you trying to say you did a test and that when you commanded 13 deg you got 1 full turn ?

is there any way to be sure it doesn’t working well?

I would use the .writeMicroseconds() command and determine both the smallest command the servo will accept and then the largest. Then write a program that goes from the smallest time to the largest in steps of 100 usec and note the rotation at each command. It should be a nice linear relationship and show ~ 6 turns (if you bought a 6T servo). If it doesn't then it's broken.

BTW what it supplying the (? 5v ?) power to the servo ? I hope it’s not the Arduino regulator. It’s not powerful enough for this type servo.

9

I’m using en external power supply (5V 1A )

I’m trying to to do as you told me

but I did:

Servo .writeMicroseconds(n)

n=1000 - did 3.5 turn CW

n=1100 - did 2 turn CW

n=0 - did 5 turn CCW

no logic …

10

Hmmm … OK let me think about that. Perhaps you should make a list of position vs command for n = 700 to 2300 in steps of 100 usecs.

What Arduino do you have ? And what have you selected as the target/board type in the Arduino IDE ?

11

I have mange to find that

writeMicroseconds(n)

n=550 → some kind of 0 position

n=630–> going ~180 degrees

n=690–> going ~360 degrees

I’m using Arduino Ethernet (without POE)

12

Sounds like it’s a lot more than a 6 turn winch. Continue to find out what usec commands get you 1 turn, 2 turns, 3 turns … etc up to a pulsewidth of 2500 usecs. Send that data to the vendor and tell him it’s not working like a 6T winch should.

Ideally a 2T winch is all you need. That way you’re guaranteed to get a full 360 degrees of rotation and it’ll have better resolution than a servo w/more turns.