homemade autopilot

[Dave911]

Yes, I saw that one. I think that may be the one that Jay is using.

I think I will order one of those and see how it performs.. Hook it up and drive around with it in the car... etc. See how much nearby iron affects it etc. It will be interesting to see how fast the device can be polled for data.

I found an oem that makes compasses for a few autopilot manufactures and they are just a little over $100 if ordered in quantities of 100. http://www.autonnic.com/enclosed-compass.html If you buy them from the retail sellers they are about $325-400 each. A bit of a markup!

I sent them an inquiry to see if I could buy them in lesser quantities.

Dave

[X7JAY7X]

Joakim, that is the compass I am using. The little bit I used it it seems to work great. I am polling it pretty fast but I noticed if I poll it too fast it stops responding and requires the power to be cycled for it to start working again... at least this was my experience. Dave, let me know the results of your testing. I dont have any other compass to compare it to so I would like to know how it compares to your other compass. BTW, your probably going to need a TTL <-> RS232 converter for the serial.

[Dave911]

Here is a video of sailing on Lake Erie on Sunday with the autopilot steering the course...

http://www.youtube.com/watch?v=GuVcg3vkVn8

We were out for a few hours and the autopilot did all of the steering except for leaving and returning to port.

It was really nice sailing weather. Low 60's and full sun. We only saw 3 other boats in about 3 hours. I had a hard time getting the angle right so the camera did not pickup glare off the cockpit display. It is a lot more readable than it shows in the video. My Dad, who was in the boat, could read it from the back of the cockpit where he was sitting.

Time to put everything into a proper box and clean up the wiring. The tape over the cockpit display was there since I didn't have the display screwed in place and I didn't want water spray to run into the unit.

Dave

[Tim B]

Looks good. Congratulations on getting it so far.

Tim B.

[Dave911]

Thanks.

I'm happy with the progress so far.

Once I get everything mounted into a box I will take a picture of it and put it on my website.

I ordered and received the compass board that Jay was using. Wow is that small! The board cannot cover up a Quarter dollar coin. I may try and get it talking this weekend so I can take it for a ride in my car and check it out.

The boat is in the cradle, so further water testing may have to wait until spring. April is 20 weeks away. It is going to be a long winter.

I'm already plotting out a long sailing trip for this next summer.

Having an autopilot has changed my perspective. :-)

Jay:
>>your probably going to need a TTL <-> RS232 converter for the serial.
I think the serial ports on this PLC are all 5 volts, so I should be ok. But I need to check that so I don't blow the board.
Thanks for mentioning that!


Dave

[X7JAY7X]

I think the serial ports on this PLC are all 5 volts, so I should be ok

I have never seen that. So these are serial ports that cannot be used for programming or communicating with other RS232 devices? Strange.

[Tim B]

Nothing unusual in that. The three common specs are 3.3v, 5v and RS232 (+-12v?) just use a max232 to convert signal levels.

Tim B.

[X7JAY7X]

Nothing unusual in that. The three common specs are 3.3v, 5v and RS232 (+-12v?) just use a max232 to convert signal levels.

Tim, I was referring to a PLC. RS232 is defined as the logical states being -3 to -25 and +3 to +25.


You do not need a MAX232 either. It can be done with transistors. Check out RS232 shifters. Common RS232 is +12/-12 but some laptops I heard are +5/-5.

[Dave911]

http://en.wikipedia.org/wiki/RS-232

Look down the page at voltage levels.

RS232 has gone the way of many standards - it is like the original, but not quite the same.

I've plugged into many 5 volt RS232 ports with my laptop (via a USB to RS232 converter which also probably only does +/- 5v). The original compass I have only puts out 5 volts on the RS232 port also. Actually I think that NMEA 0183 specifies a 5 volt RS232 connection.

I usually don't pay much attention to port voltages on RS232 unless something does not work.

Still I want to make sure I don't pop the compass.. I just need to check carefully so I don't blow it. Better to be safe...

Dave

[X7JAY7X]

I've plugged into many 5 volt RS232 ports with my laptop (via a USB to RS232 converter which also probably only does +/- 5v). The original compass I have only puts out 5 volts on the RS232 port also. Actually I think that NMEA 0183 specifies a 5 volt RS232 connection.

I think you guys are misunderstanding what I am saying. TTL is NOT RS232. Even if RS232 is +/-5v, TTL is 0-5v. Dave, you will need some sort of converter. You can talk 5v RS232 to 13v RS232 and vice versa. That doesn't matter. Check out http://www.sparkfun.com/tutorials/215

I usually don't pay much attention to port voltages on RS232 unless something does not work.

That is fine as long as all the devices are RS232.

[frasco]

Dave, some basic questions here.. what are you using to switch polarity on the actuator? Would this relay do the trick? http://www.ebay.com/itm/TAKAMISAWA-R...ht_1309wt_1270 And if so, should I (over)size the relay to match the actuator's max current draw? I'm planning on powering the actuator from the 12v batteries.

I also looked at H-bridges, first the L293D but again it's only rated up to 1A, would it work or would this LMD18200T (3A) be better?

[Dave911]

Jay,

Thanks for pointing this out.
http://www.robot-electronics.co.uk/htm/cmps10ser.htm

I missed that this is a TTL level serial link. Yep, I need a level shifter chip in there. I really didn't want to have to do that. But I do have some level shifter chips here that I use to adapt TTL level encoders to RS422 levels. If I use one leg of the RS422 end and ground the other, I might be able to get this board talking so I can test it. Chips are cheap, but this compass is getting more complicated.

But I already have it, so I might as well wire it up and see how it works.

Dave

[Dave911]

Frasco:

I think the actuator I have is rated at 3 amps at 12 volts at full load. I would look for some heavier relays that what you quoted. 6 amp contacts would not be too heavy. An H bridge would work, but that will not be easily serviced if the actuator motor fails and blows out the H bridge.

Dave

[X7JAY7X]

Frasco, I would go with an H-Bridge. Some have overcurrent and overtemp protection so the chance of blowing them is slim. The relay is a cheap option but I would go solid-state over a mechanical relay. There are tons out there, but to start check out what Pololu has.

[zorbas]

Hello,

I have been planing to build my own autopilot for a while now. Mostly because I think it would be fun. I have everything more or less sorted except for the drive system. Since it will be operating directly on the quadrant below deck I need to find a linear actuator that has a clutch. But I simply can't find one.. any ideas?