Wow! The BlueROV kit isn't even that expensive when you start adding up the cost of the individual parts for 6 thrusters, 6 esc, the pressure housing, etc.
Wow! The BlueROV kit isn't even that expensive when you start adding up the cost of the individual parts for 6 thrusters, 6 esc, the pressure housing, etc.
I does seem really reasonable for all you get - I was impressed.
I'm totally impressed with Blue Robotics. Their products are solid; and based on my experience with them last school year, their customer support is at Parallax levels.
The BlueROV kit is impressive for the price. I'm tempted to get one just to play around with in the local waters.
I remember an add in the back of old comic books-I believe, for a one man submarine kit. Dreamed about one for awhile.
Does anyone else see government regulation in the future, as in protecting our nateral reefs, interference with personal watercraft, law enforcement or border patrol, smuggling, spying. Another evolution in robotics something I want to get envolved with because of survivabilities.
Interesting link, macrobeak. Thanks for sharing it.
I'm curious about those yaw thrusters. A quadcopter doesn't require them, using just the torque from diagonally-opposite props to provide the yaw control. Perhaps that's not enough force to overcome water resistance?
I'm curious about those yaw thrusters. A quadcopter doesn't require them, using just the torque from diagonally-opposite props to provide the yaw control. Perhaps that's not enough force to overcome water resistance?
I think it is mostly that the are very low torque with respect to the mass of the vehicle. Not to mention that as long as it is neutrally buoyant you lose two degrees of freedom. Since it is neutrally buoyant the way it is setup would have to be different. The opposite motors would be thrusting one direction so the other pair of motors would have to counter it and thrust the other direction in order to maintain depth, but all motors would need to rotate the same direction using a pair of reversed props. Then you run into trouble when you want to ascend or descend without yawing.
Jeepers, I just discovered that this company Blue Robotics is right here in River City! Well Torrance anyway, just 10 minutes from home. I'll have to call on them whenever this dang Covid stuff blows over.
They claim that they won't foul, due to being hubless. (Imagine a propeller without a hub! [rimshot]) The hubbed Blue Robotics thrusters do foul in weeds.
The Hydromea thrusters are quite a bit more expensive, though, and run on an inconvenient 16V.
They claim that they won't foul, due to being hubless. (Imagine a propeller without a hub! [rimshot]) The hubbed Blue Robotics thrusters do foul in weeds.
The Hydromea thrusters are quite a bit more expensive, though, and run on an inconvenient 16V.
-Phil
Looks like a clever idea, particularly well suited for electric drives. Don't see any reason for it to cost much more than current electric drives though.
Based on the instructions in the manual for changing the propellers, I'm guessing there isn't one, and that the propeller floats in a strong magnetic field.
Based on the instructions in the manual for changing the propellers, I'm guessing there isn't one, and that the propeller floats in a strong magnetic field.
-Phil
I doubt it uses a magnetic bearing (or floats in the magnetic field). I think it relies on the water to keep the ring magnets from rubbing against the outer rim. They use the term "Hydro-lubricated" a lot on their website.
You can see the inside of the device at 1:42 in this video.
Apparently they use normal sensorless brushless drivers.
It looks like it's a brushless inrunner (side runner?). The coils appear to be embedded in the white plastic ring. I think it uses water as a lubricant and as a coolant. I'd be very surprised if the motor is very efficient. The tolerances used in the thruster don't look like they're anywhere near to what conventional brushless motors achieve. I think the hubless design comes with drawbacks. I don't think they can be used outside of water without overheating quickly. I personally could live with the efficiency loss if the thrusters weren't so expensive.
I think it's a very cool design, I just think you're giving up more than a bunch of money to use the design.
I'd be very surprised if the motor is very efficient.
Here's a chart from the datasheet.
(Blue = 12V, Orange = 14V, Green = 16V)
At 16V and full power the thruster is less than 8% efficient. Am I reading that right? (Edit: I wasn't) Don't brushless motors generally have pretty good efficiency? A quick search says they're normally between 70% and 90% efficient.
I think I'm wrong about it being an inrunner. The magnetic rings sandwich the coils embedded in the white plastic. I think this counts as an outrunner.
That chart lists efficiency as g/W. If that means grams of thrust per watt and we assume 23.5 amps of current at 16V, that would be 3,000g or 30N of thrust (as claimed) for 375 watts.
I am sure that is static thrust, no accounting for speed through the water - which would further reduce the amount of thrust produced.
Terrible efficiency compared to a well designed open propeller, but for niche applications it could be very useful - if it proves reliable.
They claim that they patented the design, but the rim-driven thruster concept has been around for over two decades. What they may have patented is the method of driving the ring, but why make that clear on the website?
I'd be very surprised if the motor is very efficient.
. . . .
At 16V and full power the thruster is less than 8% efficient. Am I reading that right? Don't brushless motors generally have pretty good efficiency? A quick search says they're normally between 70% and 90% efficient.
. . . .
Duane,
I think they expressing efficiency in grams of thrust / watt of motor power.
I experimented with RoV's using basic thrusters consisting of brushless motors directly coupled to propellers immersed in water without sealing.
The cost was simply a brushless motor, propeller and coupling! Less than $50!
They worked for several months providing they were sealed with oil between immersions.
I built a rig to investigate thrust characteristics and found these basic thrusters developed between 17 and 23 g/W. (with constant battery voltage, I actually measured g/A)
If I am reading their graph correctly they achieve between 10 and 18 g/W.
So yes, they are less efficient than the most basic thruster, but not excessively so.
Their claimed advantage of no fouling would make it worthwhile in water with underwater plants and debris.
My basic thruster would clog up pretty quick in those conditions!
If I am reading their graph correctly they achieve between 10 and 18 g/W.
So yes, they are less efficient than the most basic thruster, but not excessively so.
I experimented with RoV's using basic thrusters consisting of brushless motors directly coupled to propellers immersed in water without sealing.
I've heard of this approach. At first I couldn't believe something like that would work but I've seen the same claim enough times to believe it.
I haven't tried this myself yet but it's on my long list of projects I want to try.
Comments
I does seem really reasonable for all you get - I was impressed.
The BlueROV kit is impressive for the price. I'm tempted to get one just to play around with in the local waters.
-Phil
Does anyone else see government regulation in the future, as in protecting our nateral reefs, interference with personal watercraft, law enforcement or border patrol, smuggling, spying. Another evolution in robotics something I want to get envolved with because of survivabilities.
It is interesting to see underwater robots following flying robot control schemes.
http://hackaday.com/2016/05/18/subsea-rov-has-6-degrees-of-freedom-autopilot/
I'm curious about those yaw thrusters. A quadcopter doesn't require them, using just the torque from diagonally-opposite props to provide the yaw control. Perhaps that's not enough force to overcome water resistance?
-Phil
I think it is mostly that the are very low torque with respect to the mass of the vehicle. Not to mention that as long as it is neutrally buoyant you lose two degrees of freedom. Since it is neutrally buoyant the way it is setup would have to be different. The opposite motors would be thrusting one direction so the other pair of motors would have to counter it and thrust the other direction in order to maintain depth, but all motors would need to rotate the same direction using a pair of reversed props. Then you run into trouble when you want to ascend or descend without yawing.
https://www.hydromea.com/diskdrive-thruster-technology/
They claim that they won't foul, due to being hubless. (Imagine a propeller without a hub! [rimshot]) The hubbed Blue Robotics thrusters do foul in weeds.
The Hydromea thrusters are quite a bit more expensive, though, and run on an inconvenient 16V.
-Phil
Looks like a clever idea, particularly well suited for electric drives. Don't see any reason for it to cost much more than current electric drives though.
-Phil
-Phil
I doubt it uses a magnetic bearing (or floats in the magnetic field). I think it relies on the water to keep the ring magnets from rubbing against the outer rim. They use the term "Hydro-lubricated" a lot on their website.
You can see the inside of the device at 1:42 in this video.
Apparently they use normal sensorless brushless drivers.
It looks like it's a brushless inrunner (side runner?). The coils appear to be embedded in the white plastic ring. I think it uses water as a lubricant and as a coolant. I'd be very surprised if the motor is very efficient. The tolerances used in the thruster don't look like they're anywhere near to what conventional brushless motors achieve. I think the hubless design comes with drawbacks. I don't think they can be used outside of water without overheating quickly. I personally could live with the efficiency loss if the thrusters weren't so expensive.
I think it's a very cool design, I just think you're giving up more than a bunch of money to use the design.
Here's a chart from the datasheet.
(Blue = 12V, Orange = 14V, Green = 16V)
At 16V and full power the thruster is less than 8% efficient. Am I reading that right? (Edit: I wasn't) Don't brushless motors generally have pretty good efficiency? A quick search says they're normally between 70% and 90% efficient.
Here's a note from the manual.
So one part thruster, 9 parts water heater. 😈
Still, I think there are definitely applications where these thrusters would be a good choice. Just make sure you have a high capacity battery.
If they didn't cost so much, I'd likely get a couple to try.
I think I'm wrong about it being an inrunner. The magnetic rings sandwich the coils embedded in the white plastic. I think this counts as an outrunner.
I am sure that is static thrust, no accounting for speed through the water - which would further reduce the amount of thrust produced.
Terrible efficiency compared to a well designed open propeller, but for niche applications it could be very useful - if it proves reliable.
They claim that they patented the design, but the rim-driven thruster concept has been around for over two decades. What they may have patented is the method of driving the ring, but why make that clear on the website?
Duane,
I think they expressing efficiency in grams of thrust / watt of motor power.
I experimented with RoV's using basic thrusters consisting of brushless motors directly coupled to propellers immersed in water without sealing.
The cost was simply a brushless motor, propeller and coupling! Less than $50!
They worked for several months providing they were sealed with oil between immersions.
I built a rig to investigate thrust characteristics and found these basic thrusters developed between 17 and 23 g/W. (with constant battery voltage, I actually measured g/A)
If I am reading their graph correctly they achieve between 10 and 18 g/W.
So yes, they are less efficient than the most basic thruster, but not excessively so.
Their claimed advantage of no fouling would make it worthwhile in water with underwater plants and debris.
My basic thruster would clog up pretty quick in those conditions!
That makes more sense. Thanks.
I've heard of this approach. At first I couldn't believe something like that would work but I've seen the same claim enough times to believe it.
I haven't tried this myself yet but it's on my long list of projects I want to try.
https://www.instructables.com/How-to-build-a-thruster-for-a-homemade-submersible/
-Phil