Wednesday, July 23, 2008

Half Bot, All Boat.



To me, there are few pleasures in the world better than tooling around in any variety of small, quiet boat. Last summer, I threw together version one of this boat. It was a MinnKota Endura 30 Trolling motor crudely mounted to the boat with a couple 2x4s, and connected to a group-27 lead acid battery (weighs about 40 lbs). I really enjoyed the ability to quietly cruise around the lake, lazily sip a beer, and watch the shoreline drift by.

Last winter I decided version one was successful enough that I would dare to improve it. My design constraints were to extend the boats range to about 20 miles and add a second motor to balance the thrust and push the extra battery weight. In my nerdiness, I also figured it would be prudent to drive the boat with some sort of joystick, opening up the option for autopilot in the future. Lastly, I need to walk the boat to the water (0.3 miles) on a portage cart and launch and retrieve it by hand.




In this image, I have a blow-up of one side of the motor mount. A Hitec robot servo is mounted with a sprocket from ServoCity to drive a 1/4 inch chain that turns the motor. I give great thanks to McMaster-Carr for their copious pictures and documentation that help guide me through purchasing many parts without having to send back all that many.



It's all controlled with a servo driving program for the Arduino that listens to a wii nunchuck for steering commands. One of the hardest challenges was sorting out how to cram all the driving control into the minimal tilt sensor, joystick, and two buttons offered by the nunchuck. The motor speed control is via a robowars motor driver originally designed for battle bots.

Here is a close-up of the servo mounted in the slider blocks used to tension the chain.


In July, Hannah and I put the boat to the test with a two day overnight to a nearby camping spot. The total trip was 20 miles, and the boat performed great! We used to live on a boat and took it up and down the east coast of the US. Since then, this was the first time I felt we were able to capture the magic of cruising again. I don't know of a better way to arrive in a new place than by water.

One my favorite aspects of this arrangement is the cart. The winch and heavy duty casters were late additions to the aluminum ladder back bone. The cart setup is fantastic though, allowing me to manage the boat, weighing about 220 lbs (~100 kg) single handed. In designing the power system, my greatest fear would be that the 125 lbs golf cart batteries needed to achieve the range I desired would make it near impossible to handle. The winch is certainly required, but it works well and I hope to use this cart design for pushing more boats in the future.

UPDATE:: If you are not familiar with the wii nunchuck I use to drive the boat, check out this quick entry here with a movie to see it working.

10 comments:

Robin said...

Wow. Totally awesome.

Anonymous said...

Great project! This opens up a lot of possibilities for adaptive & handicapped users as well.

Would it be possible to get a more detailed description of the build (an Instructibles posting or similar) showing how to dependably turn a heavy motor using a standard servo and similar problems faced by your fellow tinkerers?

andrea said...

You are smart. Period.

Adam said...

Me likey you smart thinky brain. Sweet post bra!

kiffAllen said...

brah... many, many thanks for your paddler/techie mod. you're proving some of us heady folk are just as "at home" with a mod life/tech life as we are in our floatable rigs. nothing better to do than mess around in boats.

from a fellow head and techable friend-

where in the world are you anyhow-

all the best...

(found you on gizmodo... way to make the bigtime)

Anonymous said...

I have been wanting to do something similar to this for so long. Not as fancy as a joystick control but steering for my endura. I second anonymous in asking for more details!

chris said...

Fantastic, yet again!

Where does your inspiration come from?

Picture the scene: you're on a river, fishing or something, and the boat keeps floating down stream. How difficult do you think it would be to use a GPS chip or something to keep the boat still relative to the bank? Quite an interesting challenge, I think.

Thanks for posting.

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Alan said...

Just wondering if you ever measured your current draw? It looks like the motor driver you used was for 50 amps, but I'm wondering if you could have gone with a smaller motor driver?

Tim Hirzel said...

Alan, Good question. Those minkotas will draw up to 30 amps each. They are rated for that, and I measured it with a "watts up" watt meter. That controller can handle I think up to 75 amps with extra heat sinks (which I added). This is all with 12v (2 6v golf carts batteries). What I didn't think to do is a trick I learned from a robot site, overvolting. You can run those 12V motors at 24V but keep the total power under control by staying below a 50% duty cycle with the controller. I think that would cut your amperage in half. I really want to do this because that controller got really hot (hot enough to cause soldier joints to break loose!) even with my little heat sink and fan. I also got a little heat in the wires and at plugs. So this is what I would recommend. I am also planning to sell the 6V cart batteries and replace them with 2 group 27 12V batteries. The T-105 equivalent golf cart batteries weigh over 125 lbs together, and this just strains the whole operation more than i like for launch and recovery. In the water, the weight is fine. Anyhow, that's my plan to solve a couple problems at once. Not to mention that it will allow for your goal too. I need to experiment with this still, and some care is required for overvolting, read more about it here: http://www.robotbooks.com/magmotor_tips.htm

and elsewhere.

-T