Servo "Whiskey Compass"...will this work?

[JBaymore]

Steve,

Once again..... thanks for the input.  I kinda like the electromagnet idea........ IF the "quick spin" disconnect approach does not work ( Occam's Razor ...K.I.S.S. ... and so on ).

The electromagnet could be powered by one of the Phidget digital output boards and triggered by FS2Phidget reading the Whiskey Compass heading at 360 degrees.

A one minute 360 degree turn is 6 degrees per second or .16 seconds per degree.  So if your estimate of the "pickup time" of .3 seconds works out...... there is about a 2 degree "screw up" potential in there.  If the electromagnet fires off the 360 degree point for .16 seconds as the airctraft comes thru that exact point, that likely cuts the "error potential" down to about 1 degree.

Sounds like this is at least plausable either way.  I am dealing with other stuff right now.... but the first step I see in the near future is to do some experiments with an automotive compass and a bar magnet to see how it reacts.

Then get into designing the construction of the physical unit.... and then get into dealing with the servo stuff.

best,

.......................john

[SilverFox441]

Hey, no problem John...glad to be of assistance!

Of course, once you've worked out the bugs...I get to just build the final version for my pit.

This is the schematic I was thinking of when using electromagnets:

Use one Phidget output to trip the relay and it switches between the two electromagnets...very easy.

[SilverFox441]

John, if all else fails: http://bellsouthpwp.net/b/o/bobpaige/im ... ompass.JPG

[JBaymore]

So... I am a little confused about the rotation of servos.  Help me out here.  In looking at the various units most of the cheaper ones say that they rotate only about 40 to 45 degrees.  Is this correct?

So to get just about full 360 rotation (which actually will be about 359 degrees and then swing back around and pick up on the otehr side of the end point)....... I will need to geaar them up substantially.

Is this correct?  Or are there small cheap low torque servos (in the $10 to 15 range) that travel more like 180 degrees or more?

best,

................john

[SilverFox441]

What's confusing you John is a bit of mis-direction by the servo manufacturers...

You will see many servos listed at 45

[JBaymore]

If you check out: http://www.servocity.com/html/hs-322hd_ ... eluxe.html you will see that the travel is listed as

Silverfox,

Thanks!  Servocity is exactly one of the sites that I have been looking at.... and those "specs" are VERY misleading.  So if a servo says it has 180 degrees of travel in those specs.... does it go 360 degrees?  There is one that has 180... although it is quite a bit more expensive (about $30.00 if I remember correctly).

Another confusing point is that "clockwise" business on the direction or rotation.  I am assuming that refers to the "positive" direction of travel... and it will rotate BACK to center when the signal tells it to.  Am I right?

I picked up a car automotive wet compass yesterday at an autoparts store... for about $7.00.  It is a nice size to fit the pit and will mount easily in an enclosure that will hold the servo and magnet and gearing and such.

Had to buy it....... it advertises that it has "aircraft type compensators".  ;)

Now to find a good magnet and start experimenting with the "linkage" issues....... how strong a magnet, how close, how fast it can "follow" the magnet, and so on.  Have to see how to deal with that 359 degrees to 1 degree servo travel issue.

best,

....................john

[SilverFox441]

Direction of rotation (the "Clockwise" bit) refers to how the servo behaves to an PWM that is lengthening. If the PWM is shortening the servo will turn counterclockwise. It's a bit hard to figure out for the un-initiated...they get into some esoteric descriptions to provide the info:

Control System: +Pulse Width Control 1500usec Neutral

Direction: Clockwise/Pulse Traveling 1500 to 1900 usec

At 1500 usec the servo is at neutral, at 1900 usec the servo is at full clockwise and at 1100 usec the servo is at full counterclockwise.

Basically a long-winded way of saying that your assumption of servo direction behaviour is correct.

Now for 180

[JBaymore]

Hi all.

OK... did first test of the auto wet compass with a magnet.

[SilverFox441]

I can't wait to see this develop John!

I know I'll be following your lead and putting one in my 'pit if it works as good as your initial tests seem to indicate.

As for the help...why sweat that minor detail? You know I'll get full value back as soon as my 'pit designs far enough that I'm running into problems that you have already solved.

That's the whole point of a place like this Forum, help each other and help yourself in the process.

[JBaymore]

Well.......... I ordered the Phidgets single motor servo kit to get started on the next phase of this idea.  It should be here Monday or Tuesday of next week.

Have to start thinking about the fabrication of the "box" to hold the compass and the way I'll use a LED to light the thing.

Excited to FINALLY get to this idea that has been rumbling around for a LONG time.

best,

....................john

[JSpahn]

I cant wait to see how things work out on this one. This was the only analog gauge that I wanted to include in my pit. Still havent built anything yet, still planning.

[JBaymore]

Well,....as promised the Phidgets servo interface kit arrived this morning.  Soon...... will get to work on the project.

When I do, I'll change the name of this whole thread into the next in sequence of the "Cockpit Construction Part XX" pattern.

best,

.....................john

[JBaymore]

First Parts Of Whiskey Compass

Here are the first half of the parts for this part of the project:

The Phidgets servo controller (small enough for you?), the Hitek servo, and the automotove wet compass.



Soon to arrive from Servo City ......... the gears to give me the 360 degrees of rotation I need to accomplish this.

It all creeps forward.....s....l...o....w...l....y .

[BuggsK100RS]

Errrm im into my RC car racing and i do belive that if you Use a Didital servo and get the correct servo (I think futaba do a very good one) it will work in full rotation and will have the posioning information for controling the servo built in.  It should just be a relativly simple thing of pluging the servo in to the controler

[SilverFox441]

Digital servos still have the rotation limiter built into the geartrain... so no 360 degree continuous rotation for them.

The growing robotics market may see that type of servo developed... but for now we're limited to what is available and cheap.