RC controlled electric motor boat!

Heyy guys.. I need help on this one. I need to build an Rc controlled electric boat with the following specifications:
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Machine specifications

Dimension and Fabrication

Maximum length of the boat: 20 inches.
Maximum width of the boat: 7 inches.
The boat has to be controlled by a wireless remote control mechanism throughout the competition.
The boat must not be made from Lego parts, or any ready-made assembly kits.
Remote control systems from toys might be used. Remote control systems available in the market may also be used.
Balsa wood or fibre glass or any other light in weight but strong material can be used for the construction.
Motor specifications

The boat must have an onboard power supply to provide power to any mechanism requiring electric power.
Only dc motor should be used for the power supply.
The maximum allowed speed of an electric motor is 7000 r.p.m.(i.e. Participants can also use dc motor of 5000 r.p.m or any other dc motor lower in speed than 7000 r.p.m).
The electric voltage provided to the motor should not be more than 7.2V.
Speed controller should be used so as to control the the speed of the dc motor.

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Pls help me out with the design and construction of such a boat! Thank you.

Regards,
Sagar

 

What is the objective of the boat? Is it to be a speed boat, a tug boat, a fishing boat, etc. If speed is the object then weight will be critical. A 7.2 volt battery pack is too heavy for a 20 inch boat unless you use very expensive Li-ion batteries. Even with those batteries the 20 inch boat is too small to be a good choice. You have two choices for motors. The conventional brush type motor, which is very cheap to buy or the Brushless type which costs quite a lot more but it has definite power advantages. The brushless type requires a speed controller that is designed for use with brushless motors. The brushless controller also costs more than a conventional controller. If you are limited to 7000 RPM ( how, will the RPM be measured and by whom?) If you use a motor with brushes the RPM is dependant on the number of turns of wire in the armature at a specific voltage. Since your voltage is specified at no more than 7.2, you will want to use a motor with more than 20 turns of armature wire.

Beause your model is small, too small, you might contemplate using lower voltage to limit weight. The motor can be configured to optimize output to suit the selected voltage. Batteries are available in several sizes. The usual size for boats is size C. Thats a big battery and each of them has a potential output of 1.2 volts. You can also use AAA size batteries that have the ame individual voltage. Smaller batteries obviously have less capacity. A small battery pack will run the motor for only a very short period of time as the motor draws quite a lot of amperage.

 

@messabout
Firstly, thanks so much for your assistance.
Yes.. it is speed boat. I would like to know about the construction plans for such a boat. The design, materials used and the structure. And also, what do i do about the radio control?

Thanks again. )

 

The cheapest way will be to buy something like this:
http://cgi.ebay.com.au/Radio-Remote...d_Vehicles?hash=item27ae8c98d7#ht_4276wt_1053
and use the parts in your own boat modeled on something like the plastic one included.

If you want to get the cheapest components then go to here:
http://www.hobbycity.com/hobbycity/...ucts.asp?idCategory=82&curPage=2&v=&sortlist=
Also you do not need DC motors to run off DC power supply. Most of the electric motors used in models these days are 3-phase PMSM. They use little DC-AC controllers like this:
http://www.hobbycity.com/hobbycity/...6&Product_Name=Hobbyking_SS_Series_15-18A_ESC

Rick W