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Author Topic: ROV Tether  (Read 705 times)

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Offline MECH_ENGTopic starter

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ROV Tether
« on: December 23, 2012, 08:42:16 AM »
I am working with a team that is building an ROV as a senior design project.  The ROV will have 6 thrusters and two motors for a manipulator arm. The maximum steady state current draw will be less than 20 amps. Communication will be done using two twisted pairs of an ethernet line with full bridge RS 485. The other two pairs will be used to supply power to the onboard Arduino and RS 485 convertor (one pair for + and one pair for -)  with a battery pack as the source. We will be supply power for the thrusters and motors using a pair of 12 gauge wire and a heavy duty power supply as the source. The aluminum frame of the ROV will be connected to ground as well to provide a common ground between the logic circuit and motor/thruster circuit. All wires will be 50' long.

So basically the only ground connection between the power supply and battery pack will be down a 50' tether. Should the grounds as surface be connected as well? Are their any issues with grounding that I am overlooking?

I would like to make a diagram of this, any suggestions on a free program?


Offline MECH_ENGTopic starter

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Re: ROV Tether
« Reply #1 on: December 23, 2012, 09:21:13 AM »
« Last Edit: December 23, 2012, 09:23:26 AM by MECH_ENG »

Offline jwatte

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Re: ROV Tether
« Reply #2 on: December 23, 2012, 10:53:27 AM »
I would connect the grounds at the other end, although if motor controllers are on the logic side, you can't get away from connecting the grounds at the ROV end.

If you want to simulate this, look up the electrical properties of your cabling (capacitance, inductance, and resistance all are quantifiable!) and build the model in SPICE.

Offline waltr

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Re: ROV Tether
« Reply #3 on: December 23, 2012, 12:20:22 PM »
There was a thread on this exact subject within the past year. There is a long discussion on the topic of powering an ROV through the tether cable.  A quick search should find the thread.

Offline Soeren

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Re: ROV Tether
« Reply #4 on: December 23, 2012, 08:09:42 PM »
Hi,

[...] The aluminum frame of the ROV will be connected to ground as well to provide a common ground between the logic circuit and motor/thruster circuit. All wires will be 50' long.

So basically the only ground connection between the power supply and battery pack will be down a 50' tether. Should the grounds as surface be connected as well? Are their any issues with grounding that I am overlooking?
Usually, you'd connect the grounds at the end with the lowest impedance, which is at your power sources, but then they need to be isolated at the ROV, or you'd create a ground loop that could make all sorts of strange things happen to the logics.

In your particular case, I'd connect the grounds at the ROV (since they are already) and only change it if things start acting up. However... With aluminum and water, I'd add a copper wire, as aluminum oxidates extremely fast, ruining initially good connections.

In any case, only connect the grounds in one place!


I would like to make a diagram of this, any suggestions on a free program?
For simple diagram drawings (no calculations, nor any simulation), any drawing packet that you're used to will do (even Windows Paint - if you have lots of patience). AutoCAD and similar programs is shooting way over the target, unless you happen to have a lot of hours under your shirt already.
For such things, I often use Eagle CAD, but like with any other program - if you don't feel at home with them, they'lll usually take too much time to get you proper results.
Regards,
Søren

A rather fast and fairly heavy robot with quite large wheels needs what? A lot of power?
Please remember...
Engineering is based on numbers - not adjectives

 


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