Hello all,
My name is Alexandru, and i'm working on my underwater drone can you help me please with formulas from calculate dc motors ? I want use 2 turbo jet for propulsion and 2 more propeller motor for up-down moves, and i need to know what propeller must to be used, what power/rpm/torque of motor. I search a lot of internet but i didn't get a usefull information.
I hope you can help me . Have a good day, and i will come back with CAD and more information when i get it !
There is a big difference between props regarding the amount of power they draw in relation to the amount of thrust they generate. Shrouds also can improve the amount of thrust to. Seems to me that most people use the Wet Finger Estimate. Maybe take a look at some of the commercial available ROV's to get an idea. Also on this forum and youtube you can find information about people who did some testing with different props.
I was going to type a short reply but it turned into more of a primer on Do's and Dont's...lol.
Three blades on the prop work better than two.
Props with symmetrical blades work better than boat prop style because boat props are designed to be most efficient going forwards, while ROV's run their thrusters both ways to move in the water.
Get motors with a high torque rating. Water is thick and hard to move, so torque is more important than speed. I use 190kv brushless motors but my ROV is huge.
Boat ESC's work well and are usually rated for higher amps. Offroad truck ESC's work well also. Remember some esc's are for brushed motors, others for brushless.
Brushed motors have...brushes...lol, which don't work well in water, unless sealed. Brushless motors have a fixed stator with a ring of magnets driven outside that, and so are almost purpose-built for submersion.
Salt water causes corrosion way worse than fresh water, so bearings must be replaced with ceramic ones, and stator windings could use a coating of epoxy resin fiberglass thinned with denatured alcohol. Use this same coating for other electronics exposed to salt water.
LED's with exposed circuitry can be coated with epoxy to waterproof them.
Keep LED's as far away from your camera as possible. Definitely not inside the camera dome...lol. Water contains dead stuff and other particulate matter, which reflects light back into the camera and blinds you. Like trying to shine a bright light through a snowstorm. Keeping the light source off to the sides will minimize this effect.
Servos can be submerged if they are filled with mineral oil, which is non-conductive. Water won't get in if the space is already filled with something besides air.
ROV should be slightly positively buoyant, so it floats up slowly if left alone. This necessitates running your vertical thrusters more, but stirs up bottom silt less. Buoyancy can be adjusted by putting more or fewer washers in lower tubes of ROV.
I prefer having batteries on my ROV rather than running power down the tether. Any real current draw will require thick wire which makes the tether thicker and stiffer, not to mention heavier. Also any electronics on the ROV share that power and goosing the motors will draw amps, so without onboard batteries the electronics will 'brown out'.
Most beginner ROV's are lightweight small things and are plagued by 'tether drag' which means the tether is constantly dragging on the ROV and it never points where you want. I compensated by having onboard batteries, a really heavy ROV, but that made tether drag a non-issue. My first ROV was the size of a large refrigerator, but i have a truck.
Video can be a cheap FPV microcam feeding signal up two wires. Use video baluns for clear video. I got more complicated and used a security-system DVR on the ROV to send 8 camera views up my tether via eKL ethernet over coax extenders.
Most cameras are fixed, but i like being able to look right and left so i put my cam on a pan/tilt gimbal. Plus i used a Panasonic SDR T55 camcorder, originally $300 US but used on ebay $40. It has 78x optical zoom for close-ups.
Going down and looking around is fun for awhile, but eventually you'll want to pick up all those dropped iPhones you'll see. Don't buy the Newton Gripper from BlueRobotics. Trust me. Hack a manipulator together from Servocity and Robotshop or ebay parts. My original one looked like the one used by EV Nautilus, but mine was electric and so was less jerky and easier to use than their $6 million-dollar version. A drunk monkey armed with a $2 Harbor Freight grab-arm could do a better job.
Thank you a lot guys, you`re awesome . I need must calculate dimensions, power, diameter and a lot of stuff like this for motor so i need mathematical equation who can provide me information. I need to calculate force can propeller provide me, angle of prop,torque can prop provide me to dimension my motors to be sure my ROV can move safety =)) .
Thank you again for your advice and excuse me for my bad english and inconvenience:) Cheers and have a good day
can you help me please with formulas from calculate dc motors ? I want use 2 turbo jet for propulsion and 2 more propeller motor for up-down moves, and i need to know what propeller must to be used, what power/rpm/torque of motor. I search a lot of internet but i didn't get a usefull information.
. Have a good day, and i will come back with CAD and more information when i get it !