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Rc surveillance boat

#1

Ok, im building a boat with these motors:
www2.towerhobbies.com/cgi-bin/wt … LXJ767&P=N
this H-bridge:
hobbyengineering.com/H1918.html
This battery:
lynxmotion.com/Product.aspx? … egoryID=48
and these propellers:
www2.towerhobbies.com/cgi-bin/wt … XMNN0&P=ML
I will be making the rudder out of lexan mounted on a SES ‘C’ bracket and controlled by a servo. The body will also be made of lexan which will be sealed around the seems with culking to make it water proof. I will be using clear lexan to try and camoflage the robot in the water as well as to enable me to use the cockpit to store the lights (blue cathode lights):
crazypc.com/products/8247B.html and some mini wireless cameras:
superdroidrobots.com/shop/it … itemid=187

Now the big question is…what do you all think??? Any suggestions will be greatly appreciated especially if you know alot about this topic.

thx.

#2

Looks cool. If you want to camoflage the robot/boat with the water… making it have brighr blue glowy lights will help a lot. I agree.

#3

yep. I have six sets of them…so I realized I should use them :smiley:

#4

Ok so here is a pic of the rudder assembly I will be custome making from aluminum or Lexan or both. I have a question though. I realized that the rudder wont just be pivotting with the “C” bracket but also moving side to side (kinda). I just want to know if this will work.

freewebs.com/thespyproject/r … sembly.bmp

thx.

#5

Won’t work I think. There will be too much water going in. The servos might get damaged or other electronics will get damaged.

#6

thats what I was thinking…though the servo wont be under water and it will be boxed off from other electronics…I think it may work…??

#7

Ok…so as robodude666 tolde me offline, I should use an “L” SES bracket. That way water will not enter from a bottom slit. Water can only enter now through the top if it is splashed up. It is a much better idea though…

heres the new pic:
freewebs.com/thespyproject/r … sembly.bmp

#8

Incidentally, the 805BB servo is water tight.
It’s overly large and won’t fit into an ASB-04 (which probably won’t matter, since you don’t need to link it to other brackets).
It’s servo horns also do not match the SES mounting holes (which won’t matter, since they’re plastic and you can drill them to fit, as I have done).

About the motor/propeller:
In high school, I built a simple submarine out of Gerber jars and two tiny DC motors.
The biggest problem I had was keeping the water from coming into the hole which the propeller shaft was exiting.

A combination of hot glue and plastic tubing closely fitted over the shaft worked well enough to get the grade.
Even that wouldn’t have been waterproof enough to last very long.

When designing your boat, I’d suggest keeping the drive shaft long and angling it into the water at a 45 (or so) degree angle.
That way, the hole that the shaft comes out of in your boat’s body can be much higher than the water level.

Most motors won’t much mind being submerged in water (this is how many break motors in).
However, I wouldn’t subject any of the other electronics (especially the batteries!) to such conditions.

#9

yes, i am planning to have the motors angled down towards the water. The servo rudder will not use an SES bracket, but a custome made L bracket I will create. I just tested a prototype with small dc motors and realized that they shouldn’t get wet when the motor died after being submerged. will water get into the motors if I only expose the shaft and propellers throught a tight fitting whole??

#10

If there is any space at all, water will somehow get into the space. Sort of the rule of water… And life. If it is possible to happen, it will happen.

#11

hmmmm…I am wondering if the motor will work well if the whole is tight. can the water go into the motor where the shaft connects??

#12

Probably not. If you make the hole too tight the motor wont spin as fast and you will lose some speed. If the hole is a bit smaller than the shaft or exact size, the motor might spin instead of the shaft. If the motor is not mounted well then it will break the mount and start spinning which will wrap the wires around it which will cause the wires to break if they are not soldered on right.

#13

Ok, I have decided to discontinue the project until I have more information on RC boats…thx.

#14

So you’ve grabbed an unmounted, motor by the output shaft while it was turned on, too?
:stuck_out_tongue:

#15

Naw, don’t discontinue it. Just give it a try. I remember I sticked one of those small tiny motors underwater and nothing happened to it. I suggest asking around at rcgroups.com/ Its a BIG community for RC stuff. Planes, boats, cars, .etc

#16

no, but I also found out that you shouldn’t run a small DC toy motor at 7.2 volts, unless of course you want blue smoke :smiley:

#17

well, i dont think it is plausible to build a sort of ROV with lexan and boat motors…Water is too powerful… :cry:

#18

Hobby Lobby has a lot of boat drive stuff for people building their own model boats so if you want to find a solution they might be a good place to check out.

Alternatively, if your goal is to make a glass bottomed boat so you can have a camera view underwater, perhaps an airboat model might be an easier approach? That gets you on the water, gets you a big flat clear surface under the water, and allows you to power and steer using cheap air plane parts. You could use the SES brackets to facilitate mounting the servos to the hull to save a lot of creative cutting and alignment.

#19

Thats exactly what I was thinking but wasnt sure if it would work. thx.

#20

I don’t know if you are talking about an ROV in a general sense or a submersible one. If you are talking submersible it will depend on how deep you want to go. If you are thinking shallow and your prop RPMs are low then O-rings between the shaft and the housing, along with some lubricant like petroleum jelly, would keep the water at bay nicely because the pressure differential is low. Remember positive pressure is your friend and your seals will start to leak when there is a pressure differential across them. If you want to go deep then you probably need a way to pressurize the inside of your ROV as you get deeper. How much you need depends on the size of your ROV.

Here is a thought though… small brushless motors don’t have brushes… by definition… so if you coat the windings with varnish and use sealing heat shrink on the connections there is nothing to short out. Here is another consideration… the reason there are holes in the bells of small cd-rom style motors is for cooling but if you are submerged you have a built in liquid cooling system. The design of these motors also lends itself to lower rpm and high torque applications. I have NO idea how practical this is in reality but it seems like if you wanted to do a little research and experimentation you might be able to design a power “pod” that could propel a submersible ROV, and the only seal you need worry about is where the wires enter the hull.

You might also find this to be interesting reading. :stuck_out_tongue:
rollette.com/rovrev2