Let's Make Robots!


Measure water depths in lakes
Bilde.jpg881.9 KB
MarkII_LOG_microSD.zip2.73 KB
MarkII_NAV_microSD.zip5.11 KB
DELFTship_linesplan.pdf159.55 KB
Mark_II_versjon_1a_mod.zip9.02 KB

This is Mark II of the Whirligig project http://letsmakerobots.com/node/16995 code name SEA RENDERING (it’s not actually a code name, just an anagram for my name :-) )

The purpose of this robot is to have it log water depths along a predefined set of waypoints. It stores its data on memory sticks or on SD cards. The estimated runtime is about 24 hours and with a top speed of 3km/h it will travel roughly 72km. With a log entry for every 10m this would give us over 700 depth measurements   with full GPS reference.

Most of the control system has been moved from the original Whirligig to save cost and time.

The hull was designed in the free version of DELFTship http://www.delftship.net/ and built this winter. With the split mould I can produce a second hull in matter of days.

The original plan was two hulls working in pairs as a catamaran with a solar panel on top. This can still be done but two robots working independently we can cover a larger lake on shorter time.

Some images from the hull build

Adding fiberglass to one half of the mould

Mould completed

The first casting

Here are some pictures from the complete robot


Polymorph beddings for the batteries

Control system

Some electronics in the lid

The waypoints are entered using my adaptation of the Ardupilot tool. A great application that lets you interactively add waypoints to your list. This list is then copied onto the SD card and the robot is ready to run.

I run this routing 3 times and this is a GPS visualization of the log. The green markers are the waypoints.
(one of the log files are attached)

My brother (a professor at the University of Oslo) that will be using this robot, then run these 3 logs in something called  "Thin plate spline" http://en.wikipedia.org/wiki/Thin_plate_spline to see if the depths we logged made sense. And this is what he came up with.

All in all this project seems very promising.

Update 28/6-2010

After having had some problems with the VDIP1 USB interface I decided to go for the microSD shield from Sprakfun http://www.sparkfun.com/commerce/product_info.php?products_id=9802 .
Now the whole thing looks much cleaner and is probably more robust.



Update 11/7-2010

This weekend my brother and I went to the lake ‘Riskedalsvatnet’ to do a full scale test. The full waypoint routing had 337 waypoints and a total length of 18,1km.

The traveling speed of the boat is about 3km/h so the mission should have been completed in about 6 hours. As this was the first full scale test and we had some uncertainties on where the shore line actually where, we decided to split the trip into 3.
This is the first segment of the mission.

This is how the boat run

And this is an Dr.Depth rendering of the depths we got.

After all segments where completed this map was generated in Dr.Depth

A full size map in b/w is attached


UPDATE 14/7-2010

Added the Arduino sketch if anyone want to have a look.

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Hi Geir, what kind of motor and propsize do you use? 1.5A seems little to me, is it running at top speed with 3km/u? And the batteries 12ah in such a small package?

The motor I’m using is a cheap eBay motor 12V and 1000RPM.
These are not brushless racing RC motors but geared high torque motors.
It actually draws less then 1A but the other equipment also draws some current.

The propeller is a 70mm. Can’t remember the pitch or the maker, but it’s a standard RC boat propeller.
And these are the batteries http://www.biltema.no/no/Bil---MC/Elektrisk/Batteri/Blybatterier/ number 80412.
So it all adds up :-)

I took it out for a run this evening and it had an average speed of 3,3km/h with a top speed of 3,64km/h

Don't worry I trust you, I just went over this topic a few times and it makes me think about things. I ordered some solarcells from parallax to play with. With a 50 watt solar panel (2,5 kilos, waterproof) and a pile of lifepo4's you possibly have unlimited reach at no weight gain. Well, at sunny days that is.

Did you test with different props or just this one?

The propeller I’ve got is a 2 blade. I tested a 3 blade with the same size but it made no difference. According to the hull/speed calculator the maximum speed for this boat as a displacement boat is about 3km/h http://www.psychosnail.com/BoatSpeedCalculator.aspx
As we are going for distance and not speed, the current speed is perfect for this job.

The original plan was a catamaran with solar panels but as long as this boat performs as good as it does, -that’s somewhere in the future. I would like some other batteries as the boat sits a bit deep in the water, but for now, its ok.

This is an amazing project. I am also quite interested in how you created the plug for your mould?

I designed the shape of the hull using the free version of Delftship http://www.delftship.net/ (I also added my design as an attachment if you would have a look (zip file)).
Then I printed out the linespan drawing 1:1 (several copies) and glued them onto 6mm building board. Cut out the shape and had a rough shape of the hull. (attached a PDF of the linespan drawing)

After mounting the bulkheads I filled the void with building foam and cut it back.

Then several layers of plaster and sanding before I added two coats of gelcoat. More sanding and polishing before the plug was ready to be cast into a mould.

Sins the shape of the plug had steep angles I decided to go for a split mould. That is extra work but it was worth it. With this mould I can reproduce as many boats I like, and by the likes of it I might have to build a couple more.

Wow, just amazing work!

And thanks for all the details, and nice covering!!

(and thanks to rik for chillin it!)

Amazing stuff.  Great craftmanship ;D

What happened to the solar powering idea?  Maybe you could add a Li-po and some panels to replace that heavy leadacid batt.

Thanks for your kind comments ArvotroN

When the first hull was completed it was more stable then I had foreseen and then it struck me that instead of having a single catamaran, two boats working independent of each other would complete the job faster.

We could still use some more efficient batteries like LiFePO4 http://www.batteryspace.com/lifepo4battery128v20ah256wh60aratewopcm-replaceslawith10timeslongerlife.aspx or something similar but for the time being we are stuck with the lead acid ones.

Hi Geir,

have you ever looked at the M-Hulls? They use the bow wave to generate lift (pretty much as the hydroplanes do) but where the hydroplanes use a single tunnel they actually use 4. Really interesting stuff, us navy has the M80 stilleto, it's fast, can carry big loads  and has low drag. You might be able to find a better balance between powerconsumption, speed (and with that range) as you do with the sailingboat hull (which has to go slow to prevent it from getting draggy). Building one will take longer however. Take a look at the helicopter deck, nice place for a solar panel :)

There are more pics arround on the net, if you look at the hull from the bottom side it would basically be a cat with sideskirts to catch the bowwaves (the tunnels are a lot smaller towards the back of the boat increasing pressure towards the middle i guess, that's probably the tricky part if you build one yourself, the cg has to be right but also the presure rangew). As the cat's are some of the lowest drag hull designs this will even be a bit better as it returns some of the energy transfered to the waves.

My hands are itching and I smell wood the whole day...... ;)