Pedal Boat Design

They make these things called speed reducers, some of which are merely worm gear drives. You can get extremely dramatic speed reductions in a small, lightweight package.

Don't have time to select one now...gotta get my kids to school.

 

This place has a good range of geared motors. You need to be looking at up to 200rpm so the boat will do a speed in the same regime as the full scale.
http://www.robotmarketplace.com/products/motors_geared.html
You do not need much power. 10W should be ample.

I have purchased good RC stuff from here also:
http://www.hobbycity.com/hobbycity/...ucts.asp?idCategory=82&curPage=2&v=&sortlist=

Rick

 

I am not seeing anything geared that is also brushless for use with a speed controller. When you say 10w output Rick i have no idea how to figure that out or convert it to the torque and RPM that is usually all you get for a motor description.

A setup like this one:
http://www.robotmarketplace.com/products/AB-70093.html
would work best for outputting the power to both wheels and being mountable in the boat, though they do not give size information. Also the motor is not brushless so I have no idea how you would control speed. Or if it's even close to big enough.

They have a nice inexpensive waterproof controller but it doesn't say whether it is brushless only and is not listed in their brushless section...though I don't know how it couldn't be.
http://www.robotmarketplace.com/products/0-PRB2314.html

Also Rick, 200 RPM is quite a bit for parts this small. 1/8" thick followers running in ABS tracks with the loading planted right on little 1/16" pins. To put it in perspective, it's a bit like a plastic clock, but home made...and running at 156 kph, (98 mph for us Yanks). If it does handle 200RPM, it won't for long.

Boy have R/C prices fallen through the floor in the past 15 or so years since I messed with it.

G

 

The little double shaft motor is rated at 1A at 3V input power. This is 3W input and at 70% efficiency is about 2W output. They say it can run to 8V so 8W input, maybe 5W output. It would probably do something but with no margin for error.

You would prefer to see a motor that is comfortably rated at 10W output. I have not done a model of your little hull to determine its drag yet so my estimates are not precise.

The linked controller is rated at 40A and 12V. So 480W. It is way bigger than needed.

Control for brushed motors is much simpler than brushless and shoul;d be cheaper but most of the motors are made for airplanes and brushless dominate so volume dictates the price and availability. For the boat it does not matter. You want to find the motor with gearing to best suit.

I think all the brushless motors on the hobbycity site have output power nominated. Fitting gearing is a nuisance. It is best if you can get a geared drive to suit.

You will find 200rpm on a 2.something diameter wheel to be very slow. If the little wheel gets hung up then you can bet the bigger wheel will experience the same problem.

Rick W.

 

BG
This motor is in the right sort of range although it does not have a through output shaft:
http://www.robotmarketplace.com/products/0-BPK27.html

This controller would be suitable:
http://www.hobbycity.com/hobbycity/...oduct=6468&Product_Name=Eagle_30A_BRUSHED_ESC

I have one of these transmitters and it works fine:
http://www.hobbycity.com/hobbycity/...ct_Name=WFLY_6Ch_Flight_System__(Mode1__40mhz)

They also have inexpensive servos for the rudder.

Rick

 

You might find something here:

http://www.robotobjects.com/Default.asp

or here:

http://www.hobbyengineering.com/

 

OK...feel like my eyes are about to start bleeding lol.

Looks like Rick's brushed ESC here is the best bet. No idea about the plugs as they don't show them and there is no link to a manual I could find. It also lists BEC but then says nothing about it nor does anyone mention it in the comments so I am not sure if I need to get that additionally.

Was thinking these batteries and this charger though again who knows if the plugs will match up. Feels a bit of wasted money as I don't see myself as a recreational R/C boater but we may end up testing other items so maybe not. Be nice if I could throw a couple of 9V batteries on it though =) As I understand it, the charger works off of the cars battery. All the Lipo battery horror stories have ma a little worried but I can keep an eye on them. How long do you guys think I will get for run times? The batteries seem to have enough capacity for about a 30 minute run.

This motor was also about half the one you were looking at Rick. I know your away from home and were rushed. The specs seem similar so if you think it will do I can save a few bucks there. Will likely add a toothed belt gear to the motor and one to the shaft. Cut a motor mount from acrylic as it has no provisions for same. Not sure where I will mount the thing yet as it will likely throw the balance of the boat off and be out there eagerly waiting to get wet. Will figure out something though.

 

Curtis--

Thanks for taking the time to hunt those up. I didn't find anything in the size range Rick suggested though. I keep looking at the pictures of your CAT model getting a bath as motivation...maybe next time get a hottie bikini model in there so my Wife will stop teasing me about my "Industrial Strength Pedal Boat ****" habit =).

 

If you get the low cost RC transmitter it will come complete with Receiver. This is a tiny unit that has no internal supply. It picks up power from the motor controller. The little servos I got use the power from this source. The receiver accepts the ESC plug and the servo plug. The motor is only two wire and you solder or crimp controller output. Likewise with the battery and the ESC input. Nothing very complicated. The motor will reverse by reversing the wires.

The motor you nominated looks good. (I am back home now.)

30 minutes running is heaps of time. You do not need this long realistically for just testing.

I simply use rechargeable AA cells. The fit inside 20mm electric conduit and I have a couple of chargers for camera batteries and other things that I set them into. Unless you want to make a model plane later you should not need to buy expensive lithium batteries. The boat will need to weigh around 15kg to be true to scale so you will need to find weight somewhere. Human engines have quite low power to weight ratio and that is what you are modelling.

I gave my last radio control unit away about 2 years ago with a sailing boat I made and it was cluttering the garage. However I recently purchased a new unit as it is the best way to test things. I am amazed at the value for money with this stuff. It all comes out of China and shows the efficiency of their economy - along with the low expectations of the current generation. They can pay premium prices for all their inputs and still manage to convert them to outstanding products at far cheaper prices than any other economy.

Rick

 

I have a box full of servos and a few radios knocking around in the garage already so we're golden there. Would I just build a battery pack with 10-12 AA cells then? Standard rechargeable AA are about an ounce so that would give us some ballast.

30 minutes was mostly a guess as that motor lists something like 700mAh as it's nominal draw. Rechargeable AA's are 1.2v and something like 1250mAh capacity so 10 cells hits right at 12v and SHOULD run the motor at nominal and the R/X for an hour I think. As you said, that's plenty. I can use the spares for my Digi Cam so theres no waste.

Sounds like a plan.

Efficiency is nice, but no OSHA, unions, government oversight etc don't hurt either =) I have wrestled my conscience many times over this topic. We have begun working with a few companies in China and it is common for them to send video of production of the tooling at various stages as some sort of reassurance. I see people working sand blasters without even a dust mask let alone a respirator, and you know they are using common beach sand. Simple things too like workers around welding and other molten metals wearing flip flops. If you convince yourself that not doing business with China somehow is the moral high ground then those workers in flip flops and their families go hungry. The lady that we deal with and I had a long conversation about it and she was pretty blunt. People there in her factory are better treated then most factories, but she says it's nowhere the "codling" workers in the US or EU get. She says nobody ever complains because they are simply thrilled to have work and proud to provide. She also assures me that no children are working in any of her facilities, if for no other reason then there are way too many adults without work. I live in a country where life on the dole is preferable to the "indignity" of a menial job. Entitlement is all relative.

 

BG
10 cells will give you 12V under load. Most these days are over 2000mAh. So you will get better than 1 hour at the estimated power level. When I get the inclination I will model the proposed hull and see how it goes.

By the way I am not overly exited by the slenderness of the hull. I think something wider would be better. This will be an odd beast to mount because it will settle so much. It will make a bit of difference to stability as the centre of buoyancy will be a little lower and the overall width to outriggers is slightly less than it would be if the main hull was wider. It is not at all critical for the model or testing of the wheels but probably something for review after the scale testing.

This will be a big model although I was wrong with the previous weight estimate. It will be around 5kg not 15kg. I was thinking about drag rather than mass. But 5kg is still heavy so I think you will be looking for added weight rather than pruning it.

Rick

 

HAHAHA! Hey, I didn't think of that . . . too bad I don't have photoshop or something like it, I'd replace those rolls of quarters in the pics with something more . . . aesthetic.

 

Hahaha - Industrial Strength Pedal Boat. There IS something addictive about 'em.

I bet she can't wait to try it out.

 

Rick--

I worry about the boat being unstable as well, and I know I must seem overly fixated on getting the boat deeper into the water, but really it's only a practical consideration.

The attached image is roughly to scale and shows a wider 8" hull with it's shallower draft. Intentional beaching is going to be tricky. In our bay accidental beaching happens all the time. The water is reasonably clear but the bottom color is so uniform that depth changes are almost impossible to gauge with the eye and at certain times of the day the glare makes this even worse. Keep in mind we will hardly ever see water more then 3 feet deep and 2 feet or less is MUCH more like it.

It's also natural to run out a ways then travel parallel to shore.

What happens when a beaching occurs where the approach is at an angle to the the hulls direction of travel and one outward tip catches first? It seems to me the mass of the boat will want to swing around and the distance between that hang point and it's inner down strut is going to increase. Theres not a lot of area for a joint where the down strut meets the cross strut and with the cross strut being 48" or more long there IS going to be flex.

BEST case is it spreads .5" and all three foils have their pins pop out and your lame till you can reassemble. If the hulls the deepest point it's more likely it beaches first.

Keep in mind I started all this with a CAT as the goal, and the rotating hydrofoil propellers really would be better suited to that platform IMHO as it has some unique weaknesses.

 

Sounds like you need a "bottom finder." Remember the old "curb feelers" they used to put on cars for parallel parking? Maybe something like that . . .

. . . yeah, I know -- it's a drag. Just an idea, though.