Thruster Layout Questions

[seraine]

I am in the process of designing an ROV, and I have a few questions about thruster layout. Before I begin asking questions, I think I should present my goals for thruster layout, so everyone has an idea of what I am looking for. My goals are as follows:

* 4 Degrees of Freedom (Forwards/Reverse, Left/Right, Up/Down, and Yaw). I could include Pitch and Roll, but I feel like I would never us them when operating the ROV.

* Analog Control of the Motors. I want to be able to control the speed of all motors.

* Sufficient power to operate in currents.

In order to get the four degrees of freedom, I am thinking of a layout like this. The vertical motor should give up/down, the x axis motor should give left/right, the two y axis motors should give forward/reverse and yaw. I am thinking that I could use the two y axis motors in the same way that tank drive is used on land-based robots. However, I am not sure if this will work with thrusters, rather than wheels.

In order to get analog control, I will probably use this motor with this ESC. The total cost for a ESC/motor would then come to around $30, which is why I am hoping that four will be enough. At $30 per motor/ESC, I want to use these sparingly.

The main thing I am concerned about is sufficient power. With just one vertical brushless motor, would this have enough power to lift an average ROV (probably around the size of this?

Also, I saw that some people were using this $3.50 motor. Even when paired with an ESC, these are much cheaper than my brushless/ESC combo. If they do have less power than brushless, I could always pair two motors to one ESC. Is there any real disadvantage to using this brushed motor?

I would really appreciate any advice that you guys have about this.

[scubersteve]

Well I can't tell you how it will work because I haven't got mine in the water yet, but I am using those same brushless motors and ESCs. I bought 5 of them so I could have one spare of each. (if you buy the ESCs from the USA warehouse you can save some on shipping costs, they didn't have the motors there when I ordered)
I coupled it with a 64mm edf rotor and stuffed it into a modified atrium drain and made a thruster.

thruster.jpg (174.72 KiB) Viewed 4218 times

considering that these motors are designed to turn a 12" airplane prop I figure they should have no trouble generating thrust with a 3" one. I like the long threaded shaft, it gives you options for prop mounting without having to buy an adapter.

The particular brushed motor you mentioned turns way too fast for most props. I have heard of people using cheap gear reduction motors like this...
http://www.amazon.com/dp/B00B1KZ8UU/ref ... B00B1KZ8UU

so that might be an option.
Good luck and be sure to post pics of your build.

[scubersteve]

The particular brushed motor you mentioned turns way too fast for most props. I have heard of people using cheap gear reduction motors like this...
http://www.amazon.com/dp/B00B1KZ8UU/ref ... B00B1KZ8UU

Actually I think I was thinking about that wrong. I was comparing the kv rating brushless motors use to the straight rpm rating at the specified voltage that the brushed motor uses. So I dunno...I do think that the greater torque of the gear reduction motors would be better than the direct drive ones.

[dna1990]

After working on land for a while, my robotics team is working on their first ROV. Simple direct switch control of bildge pump 550s for now.

But I am already scouting ahead for when they get ready for version 2. I am hoping for a radio/dsc approach and to use the motor/esc combo being talked about in this thread.

Please keep us updated once they get wet, am curious if they are up to the task and if the EDF fan will work. If it doesn't would the same motor/esc be effective with a more traditional (and smaller) boat prop?

[seraine]

After working on land for a while, my robotics team is working on their first ROV. Simple direct switch control of bildge pump 550s for now.

But I am already scouting ahead for when they get ready for version 2. I am hoping for a radio/dsc approach and to use the motor/esc combo being talked about in this thread.

Please keep us updated once they get wet, am curious if they are up to the task and if the EDF fan will work. If it doesn't would the same motor/esc be effective with a more traditional (and smaller) boat prop?

I am planning to use a boat prop. Is there any reason you would prefer a EDF fan?

[scubersteve]

I went with an edf because the motor I'm using is rather large in diameter and I wanted to make sure what ever prop I used would be out of its eddy.
This meant a large diameter prop but most boat props have big pitch numbers. That coupled with the 8400rpm motor speed (700 kv x 12v) I expect I would have been drawing a lot of amps.
The edf rotor has a large center hub which helps get the blades out of the shadow of the motor and doesn't have as much pitch as a comparable boat prop.

Besides it looks cool.

Now on The Guppy, I am using 12v 1000rpm gear motor that is smaller in diameter so I am going with a 1.8 inch boat prop.