We have shifted our thinking a bit, we were originally designing an APM plane to perform survey operations for us. This is still in the works, but we now would like to solve a different problem. After trying to tow a boat towed magnetometer and side-imaging sonar in our environment, we'd like to look into having the APM drive the survey boat. Our area has rough seas, high winds and strong currents that make staying on our survey grid lines very difficult, and it takes an extra man because the Captain cannot take his eyes off the compass and GPS track to monitor the survey instruments.
Just so there is no concern, the vessel will always be manned and we set off-course alarms and coast proximity alarms in our current equipment which would alert us immediately to any malfunction of the APM unit. In short, there won't be any safety issues and there would always be at least 2 people on the vessel, one watching data and one watching for boat traffic, obstructions and erroneous course alterations.
I understand the APM and Mission Planner pretty well, we bought the nice GPS and all the accessories we will need already. My questions comes in when it comes time to mechanically move the steering wheel of the boat (I won;t need to do throttles yet), and how to make a quick disconnect in the event we need to retake control of the vessel in a hurry, If anyone has any thoughts or insights into how to accomplish this, I'd love to hear it. I have looked at Servo City at some linear actuators that could likely pull the steering cables, but they wouldn't be easy and fast to disconnect. My thought is to have a large servo that can spin continuously in either direction (no stops or rotational limitations) and then put a small rubber wheel on the servo. Then make a clamp type system that could engage and disengage the rubber wheel to the steering wheel and turn it. Simple, cheap, and effective I think, but this is outside my experience level, which is pretty much limited to off the shelf RC aircraft, helis, cars, and boats.
Concerns with the APM mission planning system are the large dead-band in the boats steering (I assume there is probably a setting for that but I haven't seen it) and also the pitching and yawing of the vessel in rough seas, seems like I would want to have a dead band built into the correction system as well so it wasn't constantly trying to correct for GPS movement caused by the waves. I'd rather it somehow check every 5 seconds or so, average those checks, and hold the GPS line without making continual corrections if that makes sense. Not sure if there is enough fine tuning for that or not, or if I'm even thinking about it correctly.
As long as it stayed within 15-20 feet of the line it would be doing way better than us humans did. Maybe a setting where it doesn't start to correct until it is 5 or 10 feet off course or something to that effect. This is an area I haven't played with much yet, I've just been covering the basics and playing with return to home functions so far. I did have an RC boat run a mini-survey grid and return to base and it worked incredibly well with only 4 additional waypoints required at each end of the lines to make the turns. It was incredibly accurate, but of course it's a lot more responsive than a full sized boat and has virtually no dead band in the steering. The lanes for this were only 25 feet wide and it stayed within about 5 feet for the entire survey. In truth the thing was way more accurate than I ever thought it would be. If I could dial it in to stay within 5 feet in a full size vessel I would be absolutely ecstatic, and so would my captains. LOL
The end result would be like autonomously mowing your lawn. I would give it a survey grid of 20 or so straight lines, 1 mile long each, spaced 100 feet apart. The turns could be done manually, but based on tests with an RC boat the APM can handle that pretty well too. Just looking for any insight, the only thing close I've found is on Myth Busters 007 episode when the made a full sized boat RC. Nice setup, but it wasn't removable and it did not allow for normal operation of the boat when needed. Any engineers or robot builders out there with some ideas?
Thanks in advance!
Replies
Aircraft auto pilots use servos where the output shaft normally is bolted to the cables controlling the elevator and ailerons.
This output shaft is electro-magnetically connected to the gear train of the servo.
Sh!t happens, the magnetic clutch disengages, instant control back to the pilot.
http://www.mglavionics.co.za/servoacc.html
http://www.trioavionics.com/
We used the Trio Gold servos on a full size Bede 4C.......
There are several types of Autopilots for boats already in use including a couple that use stepper motors and a cog belt clamped to the spokes of the helm. These can be very cheap used/incomplete and already have a dependable means of disengagement. They are also built to last in a marine environment. Google wheel pilot or tiller pilot. I use a raymarine tiller pilot and aries wind vane on my 36' boat but I dont know if either will work for you. The aries is purely mechanical and pretty much bulletproof. The tiller pilot is for tiller steering setups only (go figure) Remember to size your auto pilot to your your boat, or in your case oversize it since it sounds like you intend to use it in foul weather.
Hope this helps, Jon
Note; Many newer otto's will connect to your chartplotter directly and require no tinkering!
Great stuff Jon, thanks so much. The Wheel Pilot is exactly what we need. I have completed testing in the RC Boat, it performs flawlessly (when I program it correctly). We were just talking today about finding me some time to go over and adapt it to the full-sized survey vessel. If the boss will give me the budget and time, I should have it working in a month or so. I will of course post my progress here, so far it has just been testing on the tiny RC boat. The poor thing barely floats with all the gear and LiPoly's in it. :-)
Thanks again Jon, that is truly the perfect solution and shouldn't be hard to control with an APM at all.
No problem! Glad to be of help!
You might look up Minnies yacht surplus, they have a ton of used bits and are very affordable! I think their website only has sails but believe me they have a lot more than that!
I cant wait to see how this works out for you, I had been tinkering with the idea for my 36 since a nice chartplotter is a pretty pricey thing.
auto steer has been around for a few years now in the Ag game, I have been playing around with the exact issue you have including the fish tow..
you need HP to tow a fish as you know :)
maybe try modifying a tractor autosteer, they are a bit exe off the shelf from leica or trimble, but should be a few oem sources you can try driving from APM.
Thanks for that Monkeynutz. that is pretty much what i had dreamed up in my head, but I didn't know it already existed. I will look into that, it should work for what we want to do. We are now surveying with a 35 foot catamaran with twin 150 outboards, it won't win any races but it very efficient in the water. Custom outriggers allow us to tow multiple instruments...plus the obvious fishing benefits. :-)
I appreciate the tip. We have been working near Cape Canaveral, FL and they don't like anything un-manned running anywhere near the launch complexes, this is why an RSV won't work for us.
Here's a pic or two of my test vehicles.
DSCN7947.JPG
20140705_215750_resized.jpg
Jason, interested in what you did for steering, I have been playing around with the idea of putting a PixHawk on a 17' whaler... Thinking a small hydraulic setup run with a position sensor and controller... Looking at the auto steer looks like it may be easier, but the former I think will be a better setup.
Very interested in your progress.
Several time I run back through tidal creeks at night via breadcrumbs from the GPS trail laid out, thinking about autopilot rather than looking at a screen would be much better...
@Jason,
Unless your are really attached to using a full size boat, you might want to consider a robotic survey vessel like this one: eTrac RSV
I am in the process of building one that is about half the size of the eTrac platform and plan to use a high quality depth finder to do shallow water survey work. The depth finder data would be sent by telemetry for on-shore analysis.
I plan to use to .60 size R/C airplane floats and a couple of outboard electric motors to provide skid steering for the platform. I plan to use either an APM2.6 or a Pixhawk with dual GPSs. The platform can carry greater than 10 lbs.
Regards,
TCIII ArduRover2 Developer