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ROV

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MECH_ENG:
Input voltage will be <18V and the maximum current draw at steady state should be around 20 amps (likely an overestimate). The stall current of the thrusters is 11.7 amps and the steady state current at maximum thrust is 4 amps, only two thrusters will be allowed to start at the same time.

Also, a power supply powered by a generator will be used for the power source and the ROV will be controlled with analog inputs from the surface.

Thanks for the responses, any more advice is appreciated.

Soeren:
Hi,


--- Quote from: MECH_ENG on November 19, 2012, 06:06:31 AM ---Also, a power supply powered by a generator will be used for the power source and the ROV will be controlled with analog inputs from the surface.

--- End quote ---
If you can find room for it, caps 0f 10'000F on each thruster (right on the power terminals and assuming the power is controlled locally) would be my immediate response, but you could start with smaller caps, as it's hard to know beforehand, how much is needed - it will depend on how the thrusters behave.

This is something that can be done when you have the tether connected and the thruster in water (even a small barrel or a bath tub will do).

MECH_ENG:
I now plan to use this motor driver: http://www.pololu.com/catalog/product/756

It comes with a 100 uf capacitor which, correct me if I'm wrong (likely as I'm a Mechanical Engineer and this electronics stuff is new to me lol), is designed to handle current spikes when the motors start,  would you still suggest adding 10k uf capacitors across the terminals?

Soeren:
Hi,


--- Quote from: MECH_ENG on November 19, 2012, 02:12:57 PM ---It comes with a 100 uf capacitor which, correct me if I'm wrong [...], is designed to handle current spikes when the motors start, 

--- End quote ---

I'm more concerned with power surges than spikes from the motor, which the motorcontroller should be made to handle.

You feed power through 50' of an (to me) unknown gauge of wire. This will have a certain resistance, resulting in voltage dips at the receiving end, hence the need for buffer caps, connected right at the supply side of the controllers.



--- Quote from: MECH_ENG on November 19, 2012, 02:12:57 PM ---would you still suggest adding 10k uf capacitors across the terminals?

--- End quote ---

Perhaps you can make do with a little less - it all depends on how your system plays.
Put a 'scope on the input side of a controller and let it rip (in
--- Quote from: MECH_ENG on November 19, 2012, 02:12:57 PM ---I now plan to use this motor driver: http://www.pololu.com/catalog/product/756

It comes with a 100 uf capacitor which, correct me if I'm wrong (likely as I'm a Mechanical Engineer and this electronics stuff is new to me lol), is designed to handle current spikes when the motors start,  would you still suggest adding 10k uf capacitors across the terminals?

--- End quote ---
water to get the proper load), then you'll see the voltage drop you have to deal with.
The formula to use is C = A*s/V
Where:
C = capacitance in Farad
A = current in ampere
s = period of the dip in secconds
V = the voltage drop you'll allow
Note, this is the formula for how the capacitance behave when charged once and then loaded with the current*time/drop, but since the voltage will probably not drop to zero due to the supply, you won't need quite as much capacitance as the formula will show.

The heavier the gauge, the less capacitance is needed, assuming a good supply.

MECH_ENG:
Thank you for the replies, greatly appreciated!

One more question however, since I'm using analog control with 50' of ethernet line, what would be the best way to provide 5 volts to the potentiometers? Should I provide the 5 V from a source at the surface or from the 5 V pin on the Arduino aboard the ROV via a strand on the ethernet line?

Again thank you!

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