Question on feasability of using cheap thrusters

General Discussion
1

Hi All, a real beginner here, with a limited budget. I have just completed building the CPS5 drone which taught me a lot, and now wish to build something capable of exploring the fresh-water lakes around me, which can get to 300m depth. I plan an 8 motor build resembling in some ways the Rov2-heavy. My question is: if I use the cheap 300W 20A 860KV motors which generate a 2kg thrust, will this be enough or will i be horribly under-powered ? Many thanks, Martin

2

Hi @MartinFriede -
Welcome to the forums!
Can you share more information on the motors you’re looking at? The 860KV rating is pretty high for a thruster, you generally want a lower value to have more torque (as water is ~10x denser than air!)
If the motors are standard brushless units, the bearings are likely to fail after a few dives, even in fresh water. This is because water will force itself into the metal bearings, leading to corrosion.
Generally, 300W motors should move a small ROV just fine, assuming your tether isn’t too huge / long!

3

thanks so much for the rapid reply, which tells me what i suspected and means i will probably have to break the piggy-bank. I was looking at what is proposed on Aliexpress as “Hobbyocean Underwater Thruster Combo Brushless Motor 16V 300W With 40A ESC for RC Bait Tug Boat Nest Ship Submarin ROV Robot”… at under $50 each they appear cheap, but if the metal bearings fail after a few dives then it is expensive… Is there anything suitable before we get to the $200 a piece level of the T200 ?

4

Hi @MartinFriede -
Ah, those motors are specifically for underwater use - I’ve not taken one apart so my comment on the bearings may not apply. You may want to get one, take it apart and inspect it, before purchasing the whole set you need? Sharing the internals here on the forums would likely interest many people!

5

thanks. have ordered one and will do as suggested. I suspect i will find metal bearings and any waterproofing to be suitable only for minimal depth. I had not considered (but should have) that even fresh water will degrade steel bearings especially if forced in at high pressure so efficient drying after dive difficult. I guess the adage of ‘you get what you pay for’ applies here. Will send updates as soon as received.