Over sized Thrusters

[gargoile]

Hello all, I'm trying to make a thruster big enough to push me around in my belly boat ( a inflatable boat i'm half submerged in the water). Normal propulsion is my feet with flippers on. So a trolling motor is big and bulky requires descent sized batteries. I'm my research I have run into you ROV smart guys. My knowledge of DC motors is limited but i'm not completely ignorant. For a motor I'm thinking a 2000+ gph bilge pump. I went to a hobby store and the RC boat props were very small, the replacement trolling motor props were a little big. I will be looking around the internet for something that might work. Will be trying to put a shroud around the prop, probably out of PVC. Power supply will be a 12v deep cycle +- 50Ahr battery. Then mounted under a kick board type flotation device. Something like a DPD (Diver Propulsion Device), but it will not be submerged more than a foot or so and will just be in fresh water. Any suggestions would be much appreciated. MY fishing forums just laugh at the idea and say go buy a boat but, I like me a good project. Thanks

[hobbydude]

Local shops sometimes stock in Summer
http://m.ebay.com/itm/261950449040

[gargoile]

Local shops sometimes stock in Summer
http://m.ebay.com/itm/261950449040

Yeah I've seen these thrusters and they are pretty close to what I'm going for the reviews of the product aren't very good. If there are modifications that can be made to make it more reliable i'd be open to that. Like i said I like a project and if I could get to a similar end product from scratch i would feel more self fulfilled.


I did find this prop.

http://www.ebay.com/itm/PROPELLER-4-str ... 3641.l6368.

for $10...... do you think a 2000gph bilge pump would be enough power?

[TigerShark]

Bilge pump motor will be too weak for that. I suggest a Bluerobotics T200 or a seascooter modified for your needs.

[rossrov]

Hello gargoile. Nice props in that ebay store. 4" diameter and the pitch and shape of the blades would possibly be too much load on a small motor though. I've wanted to make a similar boat-thruster as an alternative to a trolling motor, using something with specs like this: http://hobbyking.com/hobbyking/store/__ ... y_DYS.html . The "KV" of the motor needs to be low for direct-drive (no gearbox) water use. Add a suitable ESC, and what is called a servo tester to create the control signal for the ESC. A large sturdy model aircraft prop can be trimmed down in diameter to create a water prop if you cannot find a good "conventional" prop. You could make a cheap and effective thruster using this approach. Some ROVers immerse and run these motors in fresh water just as they are (no sealing). Personally I would be using some sort of housing to get more mileage out of the motor. Have fun!

[gargoile]

Bilge pump motor will be too weak for that. I suggest a Bluerobotics T200 or a seascooter modified for your needs.

T200 looks real nice, the T100 (maybe two) look nice. The price is on the high side of the budget. I think they are plan B and save up. Thanks for the link.

[gargoile]

Hello gargoile. Nice props in that ebay store. 4" diameter and the pitch and shape of the blades would possibly be too much load on a small motor though. I've wanted to make a similar boat-thruster as an alternative to a trolling motor, using something with specs like this: http://hobbyking.com/hobbyking/store/__ ... y_DYS.html . The "KV" of the motor needs to be low for direct-drive (no gearbox) water use. Add a suitable ESC, and what is called a servo tester to create the control signal for the ESC. A large sturdy model aircraft prop can be trimmed down in diameter to create a water prop if you cannot find a good "conventional" prop. You could make a cheap and effective thruster using this approach. Some ROVers immerse and run these motors in fresh water just as they are (no sealing). Personally I would be using some sort of housing to get more mileage out of the motor. Have fun!

Thanks for the reply. have of couple of questions the RC world is new for me so some of them might be basic bear with me.
Would the the hobbyking motor you referenced be enough power to push the ebay prop?
"KV number need to be low" what is low?
KV as I under stand it is Volts to revolutions the hobbyking motor is 360KV every volt applied the motor spin 360 times.
Is a 12v deep cycle battery something like http://www.batterysharks.com/Power-Sour ... oCPA3w_wcB going to work with the ESC and the brushless motor?
I know I need the ECS for the brushless motor is there just a basic ESC i will only need a throttle channel?
Can the ECS be controlled with just a manual dial rheostat style switch to control power or does it need to be remote controled?

New prop I found R1460 4 Blade Propeller 95mm on this link http://www.cornwallmodelboats.co.uk/aca ... llers.html

Again thanks to all the responses I appreciate the help.

[rossrov]

Easiest way to determine what prop is the most suitable is to buy a couple and try. They will all work, just have to find the one that gets the most power out of the motor without overloading it. 100mm diameter may be a bit big for some props but that depends on the pitch etc. Get one with as low a pitch as possible, if the choice is available.

Motor linked to is more powerful than most ROVers use. Think in terms of horsepower. 800 watts is equivalent to roughly 1 horsepower. Losses come into the equation but you get the idea.

360KV is low for this sort of motor

Motors and ESCs are typically voltage rated in "S". 3S and above should be fine for 12 volt

If you are going to buy a lead-acid battery get a "deep cycle" type. Consider using a LiPo battery, though for LiPo you need a suitable charger

Heaps of ESCs around that would work. If you want reverse get a car type. Make sure the power rating is up to that required by the motor

The ESC needs a PWM signal to run. This can come from the RC receiver or the servo tester. Servos and ESCs need the same PWM signal input type. Just buy a servo tester and maybe replace the standard control knob with your own waterproof potentiometer (pot is like a rheostat kind of)

I do not recommend any particular retailer but all the gear described (except the pot) is available from HobbyKing, so do your homework there.

Will be good to see some results and photos of your project