u/Deep-Today5715

Hi, for my next DIY ROV, I am trying to design bi-directional ducted thruster propellers (which would have equal thrust forward and backward), and I've been using OpenProp and it's recent reimplementation PythonProp to iterate over various designs to try and find the most efficient one within my constrains.

I need some help / guidance with this.

My constrains are:

Thruster hub => 32mm in diameter to fit small BLDC motors.

Duct diameter <= 70mm (it's a very small ROV)

Motors - I can choose from 950kv A2212 (proven choice in the past) or 350kv F2838. Not many other motors in between.

I wrote an OpenProp script that keeps the torque (Q) of the motor constant to give prop designs a fair comparison, assuming I would be running motors at or near their maximum torque capacity. From datasheets, I calculated it to be ~0.1 Nm@10000 RPM for A2212, and 0.2 Nm@3000 RPM for F2838.

First, disregarding these two motors, for a baseline, at 0.15 Nm torque I swept through the RPM range from 3000 to 10000, noting efficiency and thrust:

Q	Z	RPM	D	T	EFFY
0.150	2	3000	0.070	18.782	0.398
0.150	2	4000	0.070	23.532	0.374
0.150	2	5000	0.070	27.520	0.351
0.150	2	6000	0.070	31.060	0.329
0.150	2	7000	0.070	33.844	0.308
0.150	2	8000	0.070	36.113	0.288
0.150	2	9000	0.070	38.042	0.268
0.150	2	10000	0.070	38.960	0.248
0.150	3	3000	0.070	18.669	0.396
0.150	3	4000	0.070	23.189	0.368
0.150	3	5000	0.070	26.788	0.342
0.150	3	6000	0.070	29.925	0.316
0.150	3	7000	0.070	31.907	0.291
0.150	3	8000	0.070	33.286	0.265
0.150	3	9000	0.070	33.804	0.239
0.150	3	10000	0.070	33.361	0.213

As you can see, efficiency clearly drops with higher RPM, suggesting I should stick with low kv motors. Difference between 2 and 3 blade props is minor. This holds true for all D values. I also played around with various blade chord scaling factors, but surprisingly, even making blade 2x larger doesn't seem to affect numbers much.

So, sticking with 0.2Nm@3000RPM, all I'm left to play with is prop diameter and blade count:

Q	Z	RPM	D	T	EFFY
0.200	2	3000	0.070	22.869	0.363
0.200	2	3000	0.065	20.900	0.333
0.200	3	3000	0.070	22.827	0.363
0.200	3	3000	0.065	20.991	0.334
0.200	3	3000	0.060	18.559	0.296

And from here it is obvious that larger diameter is better, both for thrust and efficiency. Blade count is once again (surprisingly) inconsequential.

I also checked hub diameter influence on the results, and it's clear that smaller hub always wins, so I'm skipping that table.

So, with my "best" design, Dhub=32mm, Z=2, D=70mm, I get 22.86 N of thrust (which is enough), but only 36.3% efficiency, which is terrible.

This was all done using this blade chord profile:

https://preview.redd.it/hx73bfk0lq0h1.png?width=901&format=png&auto=webp&s=24f3d7fdfb5510a55f34d816180027ff0786b78e

And section profile used parabolic meanline and elliptical shape. After exporting the section curves to 3D, they look like this:

https://preview.redd.it/f8q745i7lq0h1.png?width=1443&format=png&auto=webp&s=65e920b7e04496899e5d61831b9da29cb4517461

Also confirmed by 2D blade image from OpenProp:

https://preview.redd.it/il1ywi5ilq0h1.png?width=1247&format=png&auto=webp&s=8692333ab357c3ca3c7ecdea94ef9809cd6e9692

Now, I don't know much about propellers, but something tells me that such a small radius of curvature at the tip of the blade (black section) is really bad. No way the flow can be expected to follow such a tight curve without detachment.

But the only way I can find to solve this is either increasing blade count (helps a little), increasing prop diameter (which I can't do due to my constrains), or decreasing torque/thrust (which won't utilize my motor to the max).

Can anyone experienced with propeller design help out a newbie? Is there something I'm doing wrong here, or is this the best I can expect with my constrains? Is there any way I can achieve higher efficiency without losing thrust or increasing prop diameter? And how do I get rid of that "hook" at the tip of the blade?

I would really appreciate any comments. This is my 3rd attempt at getting help with prop design over various subreddits, and no one seems to be answering :(

Hi, I am a hobbyist, designing an underwater drone (ROV). It's my 4th ROV, and the goal this time is efficiency. It will have 4 ducted horizontal thrusters in 45° configuration, and 4 vertical thrusters. All thrusters need to operate with very similar performance when running forward and backward. Because of the motors I chose and other design constrains, I need to design my own propellers, which will then be printed from polycarbonate, sanded smooth and sealed with a thin coat of epoxy for a smooth surface.

I don't know the first thing about propeller design, and I'm not expecting to make the most efficient prop in the world, but I want to do a reasonable job without going down the rabbit hole, because I understand that prop design is a very complex subject. Up until now I just copied other prop designs without any consideration to the motors I was using, and that didn't work too well - either the thrusters were too powerful at the slowest speed the motors could go at without stalling, or overpowering the motors before reaching any significant thrust.

Requirements and constrains:

-Motors: 350kv BLDC F2838 motors running on 3S power, no load RPM is 3950. Maximum power is 83 W, power draw is 7.5 A as per datasheet.

-Duct internal diameter can be anywhere from 55mm to 70mm, length from 54mm to 72mm. Hub diameter is 32mm minimum. Propeller diameter restricted by duct diameter with 0.5mm clearance.

-Minimum motor speed should provide low enough thrust to have fine maneuvering control, because BLDCs stall when run too slow. I don't yet know what "low enough thrust" is in Newtons, I am still trying to figure that out based on ROV inertia and CFD resistance data.

-Thrusters should be sufficiently powerful to allow the ROV to reach 1.5m/s in any horizontal direction to do station-keeping in underwater currents. I can figure this out with CFD sims if I know thruster thrust or water flow rate.

Goals:

-Figure out the best duct length and diameter, propeller blade shape and count, propeller pitch and other parameters to maximize efficiency with these motors.

-With a candidate design, build a RPM / thrust / torque / motor power draw / efficiency dependency graph.

-Use the graph together with CFD sims to validate whether the lowest possible thrust of the thrusters is in the required range for fine control before stalling the motors, and the high power settings don't overpower the motors before achieving maximum possible thrust and efficiency.

Questions:

1. Is it possible to fulfill these goals on paper / prop design software / CFD software with the data I have? Most prop calculations I found require to know the vessel speed, but I can only figure it out after I know the thrust or water flow speed the thrusters will provide, so I can run CFD on the entire ROV model and figure out the speed/resistance dependency. Seems like a chicken and egg problem But I expect that speed to be approximately 0.5-2 m/s, most of the time offset at 45° to the thruster facing direction.
2. Is it possible to figure out how much the propeller will load the motor, and how much power it will draw at any given RPM, if the motor datasheet doesn't provide any performance data?
3. What workflow should I follow to get in the ballpark for the design of these props and their ducts, and then optimize them?

Notes:

* I have access to Solidworks CAD and Flow Simulation (CFD), I also downloaded OpenProp, but it requires lots of input data that I don't have (thrust, ship velocity, etc.), and I am not sure how to relate the results to my goals.

* I would very much like to avoid having to do live tests. I did build a test rig for testing props in a water bucket a while ago using a load cell, but such a setup is just not good enough to get any usable data, and I don't have the facilities to make anything better.

Would appreciate any suggestions and guidance. Sorry for a noobish question, but I am trying to learn.

Hi, I am a hobbyist, designing an underwater drone (ROV). It's my 4th ROV, and the goal this time is efficiency. It will have 4 ducted horizontal thrusters in 45° configuration, and 4 vertical thrusters. All thrusters need to operate with very similar performance when running forward and backward. Because of the motors I chose and other design constrains, I need to design my own propellers, which will then be printed from polycarbonate, sanded smooth and sealed with a thin coat of epoxy for a smooth surface.

I don't know the first thing about propeller design, and I'm not expecting to make the most efficient prop in the world, but I want to do a reasonable job without going down the rabbit hole, because I understand that prop design is a very complex subject. Up until now I just copied other prop designs without any consideration to the motors I was using, and that didn't work too well - either the thrusters were too powerful at the slowest speed the motors could go at without stalling, or overpowering the motors before reaching any significant thrust.

Requirements and constrains:

-Motors: 350kv BLDC F2838 motors running on 3S power, no load RPM is 3950. Maximum power is 83 W, power draw is 7.5 A as per datasheet.

-Duct internal diameter can be anywhere from 55mm to 70mm, length from 54mm to 72mm. Hub diameter is 32mm minimum. Propeller diameter restricted by duct diameter with 0.5mm clearance.

-Minimum motor speed should provide low enough thrust to have fine maneuvering control, because BLDCs stall when run too slow. I don't yet know what "low enough thrust" is in Newtons, I am still trying to figure that out based on ROV inertia and CFD resistance data.

-Thrusters should be sufficiently powerful to allow the ROV to reach 1.5m/s in any horizontal direction to do station-keeping in underwater currents. I can figure this out with CFD sims if I know thruster thrust or water flow rate.

Goals:

-Figure out the best duct length and diameter, propeller blade shape and count, propeller pitch and other parameters to maximize efficiency with these motors.

-With a candidate design, build a RPM / thrust / torque / motor power draw / efficiency dependency graph.

-Use the graph together with CFD sims to validate whether the lowest possible thrust of the thrusters is in the required range for fine control before stalling the motors, and the high power settings don't overpower the motors before achieving maximum possible thrust and efficiency.

Questions:

1. Is it possible to fulfill these goals on paper / prop design software / CFD software with the data I have? Most prop calculations I found require to know the vessel speed, but I can only figure it out after I know the thrust or water flow speed the thrusters will provide, so I can run CFD on the entire ROV model and figure out the speed/resistance dependency. Seems like a chicken and egg problem But I expect that speed to be approximately 0.5-2 m/s, most of the time offset at 45° to the thruster facing direction.

2. Is it possible to figure out how much the propeller will load the motor, and how much power it will draw at any given RPM, if the motor datasheet doesn't provide any performance data?

3. What workflow should I follow to get in the ballpark for the design of these props and their ducts, and then optimize them?

Notes:

* I have access to Solidworks CAD and Flow Simulation (CFD), I also downloaded OpenProp, but it requires lots of input data that I don't have (thrust, ship velocity, etc.), and I am not sure how to relate the results to my goals.

* I would very much like to avoid having to do live tests. I did build a test rig for testing props in a water bucket a while ago using a load cell, but such a setup is just not good enough to get any usable data, and I don't have the facilities to make anything better.

Would appreciate any suggestions and guidance. Sorry for a noobish question, but I am trying to learn.

Hi, I am building an underwater drone (ROV), with ESP32 P4 Nano as it's MC, which will use Ethernet connection via a PLC or fiber optic module pair (to extend range) to connect to a topside laptop via a long cable. ESP32 will stream video and telemetry to the laptop while receiving control signals to control the drone.

The goal is to have a low-latency live stream (<150ms) with good enough quality to record some nice underwater videos, because there is no space for a secondary camera. I'm not expecting GoPro equivalent here, 720p will be fine.

The ROV will operate in totally dark environment (500m depth), but will have several powerful directional LEDs to illuminate it's surroundings. Nevertheless, these are difficult conditions for camera and compression - low visibility, not many points to focus on, lots of debris in the water that make it murky.

I would prefer this camera to have a FOV of ~150°, 120° is bare minimum. Software-controlled manual focus would be amazing, because I imagine auto focus would have lots of issues. Most important factor is how well can the camera handle these visually difficult conditions.

Can anyone recommend any compatible camera that would work best? So far I figured out it has to be a MIPI CSI 2-lane, with 15 pin connector, but I'm not sure what models are compatible and best for my use case. I know that the officially sold camera with this ESP is RPI Camera (B), which is OV5647 5MP, but I'm hoping there is something better that's compatible. Maybe IMX219, IMX290, IMX477, or something else..?

Any suggestions?

My workflows often call for reusing sketches in multiple features and fine-tuning sketch/feature order, and the "normal" view mode (where sketches get absorbed by features) does more harm than good.

I much prefer working with the Flat Tree View mode.

However, in that mode, I cannot organize features into folders, any pre-created folders becomes invisible, and I can't create new ones. And when my parts have dozens or hundreds of features, this becomes an issue of it's own. That forces me to constantly switch between the normal mode and Flat Tree View mode. I have a keyboard shortcut for that, but still, it is annoying as heck.

Can anyone suggest a way to overcome this software limitation? Some registry tweak, add-in or macro perhaps?

Hi, I am building a tiny low-cost underwater drone (ROV), and due to viscosity of water, I am searching for low KV BLDC motors that can operate submerged in seawater. Ceramic bearings would be best, but I can make do with regular bearings by oil-filling them in a vacuum chamber or just replacing when they corrode.

Ideal size would be similar to A2212 (27mm diameter), but the only affordable option I found is F2838 350kv motors. These are 28.4 x 48.4mm, but unfortunately quite expensive - 19€ per motor (link).

Can anyone suggest any other similar motors at a similar size and KV rating?

Hi, long story short, I am building a DIY ROV (underwater drone), and it needs a clear dome for it's camera. The dome has to be very strong, because the ROV is going to dive to 500m depth, so typical CCTV camera domes won't work, they are too weak The dome needs to be at least 5m thick, preferably 8-10mm. There are specialized domes like this, but they are usually too big and too expensive, I need one that is small and easy+cheap to make. So I thought of casting it from epoxy. The idea is to make this project open-source, so that anyone can build it, so I'm trying to make this process super simple.

Problem is making the molds. I tried 3D printing them, but the layer lines require sanding, then sealing with epoxy to get a smooth surface, and then polishing. Any surface irregularity will result in visual distortions when camera looks through the dome. It is extremely difficult and time-consuming to make these molds good enough.

So I had another idea - to buy a 80mm and 60mm domes from Aliexpress (link), nest them inside one another, drill some holes in the smaller one for epoxy to flow through, and use a 3D printed guide to keep everything aligned and vertical during the pour. All 3 mold pieces would be sacrificial. I could also scuff up the "bad" side of the Ali domes and epoxy on some hooks / ropes to make separation easier afterwards. The pieces would be held in place by friction or a few tiny drops of superglue. Of course all parts would be coated in release spray.

Here are the screenshots from CAD of how I'm envisioning it. Inner Ali dome is brown, outer Ali dome is green, 3D printed holder is yellow, my final dome is white:

Molds separated:

https://preview.redd.it/joe7oppy14yg1.png?width=993&format=png&auto=webp&s=e10716461fa6c2c62c5cd419ade8b66aa74a17a8

Molds separated cross section:

https://preview.redd.it/2indode024yg1.png?width=915&format=png&auto=webp&s=5ed003b495790c7b67385feb0dcc6abb49abded0

Molds nested:

https://preview.redd.it/vqqod0l124yg1.png?width=1450&format=png&auto=webp&s=5cb8edfcda7ef501683f9a24e27506a12570733e

Molds nested cross section:

https://preview.redd.it/0wfellp224yg1.png?width=1522&format=png&auto=webp&s=de6066c824c398c4d1d32c0281c4df0532844fe3

Initial cast:

https://preview.redd.it/hy4uudp324yg1.png?width=1607&format=png&auto=webp&s=b4c21acf98732bb0422c6613d935e6c7d8beb4c4

After cleanup:

https://preview.redd.it/7uwek2e524yg1.png?width=1555&format=png&auto=webp&s=af8e19bf94e4ad9ab0bd48b519174945e25f48eb

Can anyone with more experience in casting (I've only done it 4 times, and just for decorative parts) comment on this, would this work?

I am building an underwater drone (ROV) with internal 18650 3S battery pack with this BMS module from Ali (3S, 60A Balance version). The charge pins will be connected to wires going outside the ROV for charging the battery so that I don't have to open the waterproof housing every time. However, due to the charge port being exposed to water, it would be required to install a plug before launching the ROV, and the operator might forget. If the connector is exposed to water, it will essentially short the BMS charge pins.

Question is, are these BMS modules protected from such an event? Is it safe, or do I need to install diodes or something to protect it?

Hi, for my next 500m depth ROV I am searching for an underwater barometer. Up until now, I have been using MS5837-30BA, which is a tiny 30 bar sensor often sold on a breakout board with I2C interface for ~$15 or so on Ali and other websites (link for reference). I found it to be extremely accurate, repeatable and reliable.

However, it is only suitable for 30 bar, and I need 50 now. I did some research, and found that Blue Robotics uses the same sensor for their low-depth ROVs, and for anything from 300m to 1000m they use Keller PA-4LD, packaged and rebranded as Bar100XT. But that sensor is a whopping $380 from their website, and original Keller is nowhere to be found for sale.

The only affordable option I found are these generic oil pressure tranducers, like this one (1000psi / 70 bar version), but they are very large and heavy, and I doubt it would be easy to remove their steel housing, they are probably epoxied permanently there.

Can anyone from DIY ROV scene suggest any more compact depth sensors capable of 50 bar at a similar price point? I know I could use a gas pressure sensor with an air pocket or a bladder, I did some experiments with that back in the day and found that the final accuracy is quite terrible in the end, plus it's a lot of effort to build.