Brushless motor

[ngkb]

I have a silly question in my head. If my brushless ESC has a reverse function, do i need a H-bridge circuit?

[KR2_Diving]

Nope!
If you are using Brushless motors, together with an ESC, then it is likely that Reverse is "included."

Now, what is more important is the type of reverse...

Some say reverse, but really mean that you can connect it to go forward, or reverse, but not both. Some allow both, but require a pause when switching direction.

Others are exactly right for ROVs! I have found that most CAR ESC's that list reverse do indeed mean the kind of reverse that is required for an ROV.

If you are still looking at this combo:

Hi, i would know how to link this ESC up with the motor.
ESC: http://www.hobbyking.com/hobbyking/stor ... verse.html
Motor: http://www.hobbyking.com/hobbyking/stor ... duct=12922

The ESC had 3 of the same coloured wire, i don't know which goes to which.
Please help, thanks.

Then you have picked a good combo!

[ngkb]

Hmm, i see. Thanks for the information! My group will be starting to build the ROV soon, hope it goes well

[martinw]

Brushless motors don't use a traditional H bridge, they are normally used on brushed motors only.

Brushless uses two FETs per phase and most brushless motors are three phase, so you need six FETs, as opposed to four in an H Bridge.

Hope this helps.

Martin

[ngkb]

Hi guys, I have got another issue now as I am using another kind of brushless motor now.

http://www.rctophobby.com/motors-esc-1/ ... de8NG2tybw

Say I am now using this, do i still need to waterproof it? I believe in standardization in brushless motor, however I just want to ask if this motor requires water proofing.

Thanks

[bikerbones1968]

ngkb that brushless motor should be just fine. As long as it is not a sensored brushless you can run it wet without waterproofing it. And to answer your previous question, if your motor happens to run in the opposite direction to your control inputs, just reverse two of the motor leads on the motor turning the wrong way and it will run in the appropriate direction.


For ROV applications KR2 is right, you will need car ESC's with reverse. Ones designed for airplanes or helicopters will not work.

[ngkb]

Yeah, I've managed to find a suitable Boat ESC with reverse! However, it seems like my motor doesn't have enough thrust for propelling my 6KG ROV. Being new to ROV, I am unsure of how to determine the thrust needed to propel 6kg of acrylic and PVC worth of material (when measured on land). By any chance, if you're to recommend what range of Kv motors i should get to run my ROV horizontally in water (intend to have 2 motors running horizontally). Currently, the Kv range I am looking at is 750kv to 950kv.

Thanks

[KR2_Diving]

Currently, the Kv range I am looking at is 750kv to 950kv.

I won't pretend to be an expert, but from my general understanding, you are on the right track!

The idea is that if you have a higher Kv rating, the prop is going to spin faster, but be less efficient, as it will generate less torque.

Think of it like the gears on a bike. Consider you are stationary. Which gear is easiest to go from a complete stop to forward movement?

Now, take that same image, and imagine that the peddles are the prop of your ROV. (Ok, here is where it is obvious I am not an expert... maybe the tire is the prop!?)

Anyway, the point is, if you are spinning the prop to fast, you are likely not getting the most efficient power out of it!

Conclusion, the lower the KV, the better...

(However, remember that this is just one part of your propulsion system. You can put a racing gearbox on a tractor, but that doesn't mean it is going to win any races! (unless you bring it to the local county fair!))

Maybe someone a bit more mechanical then I am can provide some more accurate examples!?

[martinw]

You're not really looking for an ROV to move at break neck speeds but it needs to be able to overcome the inertia of the ROV in the water so a large prop spinning at a relatively low RPM is the way to go IMHO. It also minimises the effects of cavitation.

Martin

[ngkb]

I see i see, so I am in the right track after all! Thanks both of you guys!

So now, the only thing i need to do is to get a pair of propeller of 5cm diameter or so? The propeller I have now has a 3.2 diameter. However, when i pair them up with my emax bl 2220/10, 930Kv brushless motor, the thrust seems to be relatively weak. So for now, i should get a larger diameter prop. for my motor right?