Homebuilt ROVs Forum

Thats a very low RPM!! i think you'd struggle to find props large enough to make your ROV be of any use! what size of props were you planning on using?

I am planning on using 50mm diameter propellers.

Low RPM motors are probably not a good choice.... A 50 mm prop is not going to produce enough thrust at 4-600rpm to move your ROV very fast if at all. (that's like idle speed for that size prop.) You would need a much bigger prop at such a low RPM.

Is there a particular reason you want to use such a low RPM motor?

-Steve

Hello Steve,

The main reason that I wanted to use a significantly low RPM brushed motors for my ROV, is so I can get a greater torque, and the brushed motors that I have chosen have low current on load. The motors that I am looking at, are one of these types :http://www.ebay.com/itm/For-ASLONG-JGA2 ... ug&vxp=mtr . They may not be identical to that one, but similar.

What would be the right RPM for a dc motor on an ROV, that will make the ROV movement appropriate ?

Hello Vik. A bigger and slower turning prop will potentially offer more efficiency than the smaller higher-revving props that are usually used, but they are impractical due to their size, need for a gearbox, torque effect (making control difficult), and cost on a small ROV. Hence the common usage of bilge pump and brushless model aircraft motors with suitably sized props. If you are building a big ROV or AUV then there would be need for bigger props and slower motors, but then you would need a more powerful motor than the one in your link. I cannot advise re RPMs, but some good reporting is to be found here: viewtopic.php?f=3&t=1268

Thank You, for the reply. I have now convinced myself to use higher RPM motors , and the motors to be brushless motors. I seem to be confused on one thing. What kv , should I aim for when choosing a brushless motor? The voltage that I will be working with is 12. My ROV design, is pretty compact. 50cm long, 30cm wide and 30cm high. These are rough estimates. Also will 50mm propellers be OK! Or should I go with 40mm ?

So will this motor be something thatnI should be looking for ? http://hobbyking.com/hobbyking/store/__ ... Motor.html

The big issue with brushless is that for our intended use they can be TOO fast

Any "Kv" rating of less than 1000 should be ok, though the lower the better, the lower the KV rating = torque and speed.

I'm using these http://www.hobbyking.com/hobbyking/stor ... ff=1517460 on my next ROV with prop adaptors

I tried many combinations of motor and props.
The best combination that works for me was a 500kv motor with a Graupner 65mm prop and 4s lipo.
At 100% power (forward) draws 7.47a - 2.2 kgs thrust

Thank You guys for the replies, I will not be considering motors that have kv less than 1000. I have one question. Is there any equations that I can use to determine information about the chosen motor and the chosen propeller. This way I can calculate a lot of things about the ROV, and its movements and so on.