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Author Topic: Robbe U47 Electronics etc  (Read 2640 times)

rnli12

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Robbe U47 Electronics etc
« on: December 20, 2014, 07:59:09 AM »

Hi,
A few questions as it has been a while since I built and sold my last sub, can anyone recommend a better set up with Speed contoller, gyro and battery configuration for the U47 other than the Robbe recommendations.
I am also considering going to static dive rather than dynamic but avoiding significant cost if possible.
Any thoughts or links anywhere appreciated, many thanks.
Rich
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Rich

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Re: Robbe U47 Electronics etc
« Reply #1 on: December 20, 2014, 11:04:28 AM »

Microgryo's ESC and leveller/pitch controller. Batteries wise you could use a pair of Life po4 batteries or 2s lipo. Some people use NiMH batteries, I'm less of a fan of those, but each to their own.

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Re: Robbe U47 Electronics etc
« Reply #2 on: December 20, 2014, 11:57:12 AM »

Regarding static conversion. Most modellers using this kit have gone down the route of fitting an Engel piston tank. A 500ml or 750ml tank can be used, the larger tank giving a closer to scale surfaced waterline if that is important to you, but the bigger tank is a bit of a squeeze.

These tanks aren't exactly cheap if purchased new, they do come up second hand from time to time.

If you have a lathe, you could have a crack at making your own piston tank, this is much cheaper than a commercial unit, but as I say it is dependent on you having the right equipment and knowledge.

An alternative to piston tanks is to consider either an air pump or water pump based system. These can be put together relatively cheaply and only require basic tools, as the most of the parts are prefabricated.

Sadly there haven't been many published examples of systems for the U47 other than the Piston tank conversion, but it's still just a sub, so you can borrow a lot from other conversions.

rnli12

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Re: Robbe U47 Electronics etc
« Reply #3 on: December 20, 2014, 06:41:55 PM »

Many thanks for your response Suculture, was thinking of of the water/air pump option with bladder tanks.
Guess I will see what I can find on these on the net.
Regards,
Rich
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Re: Robbe U47 Electronics etc
« Reply #4 on: December 20, 2014, 08:20:26 PM »

If you decide to go with a water pump, then it's worth remembering that pretty much without exception, they're built to run at 12 volts. They will run on lower voltages, but they tend to be painfully slow, and as the U47 needs a fairly sizeable tank, diving could be an exceptionally tardy business.

So you will probably want to consider an exchange of drive motors and moving up to a 12 volt system.

Air pumps tend to be a bit more flexible, voltage wise, and air pumps tend to  shift a lot of volume rapidly. The snag with air is that it tends to be a bit less controllable than pumping water.

If you're experimentally minded, you could consider using a two stage system with a smaller trim tank built inside a larger one. The large tank could be evacuated quickly with an air pump and the smaller tank controlled by a water pump. This apes fullsize boats, and will give you very fine control over the boats buoyancy.

The downside is it's likely to be a bit more expensive, and it adds a slight amount of complication.

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Re: Robbe U47 Electronics etc
« Reply #5 on: December 21, 2014, 08:21:59 AM »

Thanks again to you, any recommendations for motors? is it a good idea to go brushless with esc to match?
The Life po4 are 9.9v is that correct, I dont mind the experimental bit but in the long term, i lke the idea of the trim tanks and water pump are there any good links.
Regards,
Rich
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Rich

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Re: Robbe U47 Electronics etc
« Reply #6 on: December 21, 2014, 10:15:38 AM »

Rich, if you go down the Engel tank route, give me a shout...


Rich
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Rich

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Re: Robbe U47 Electronics etc
« Reply #7 on: December 21, 2014, 11:31:34 AM »

Lifep04 batteries have cell voltages of 3.2-3.3 volt per cell, so it all depends on how many cells you have in a pack. e.g. 4-cells would give you 12.8-13.2 volts.

Brushless motors are smaller than brushed counterparts and a bit more efficient. However their low speed running is inferior to brushed motors and you will likely need to fashion some mounts to fit them in.

Brushless motors and controllers are available cheaply from Hobbyking.

Good links for hybrid systems. There's not much published on them. A good choice for the water pump is a peristaltic model, as they don't need check valves. The slower pumping speed isn't an inconvenience for a trim tank, as most of the time you'll be filling and emptying the main tank.

I'm not sure what the overall displacement of the a U47 is, but will take a guess at about 7-8 litres, which will mean your trim tank should be sized at about 100ml. That will give you the 1% you need to adjust for different water densities, plus a few grams more to create some downthrust for static diving.

Ebay is good source for cheap peristaltic pumps e.g.

http://www.ebay.co.uk/itm/NEW-DC-12V-Dosing-Pump-Peristaltic-dosing-Head-For-Aquarium-Lab-Analytical-Water-/311134007908?pt=UK_Pet_Supplies_Fish&hash=item4871083264

For your main ballast system, you have a choice to make, do you want an aspirated system, or a recirculating one. Both come with pros and cons.

An aspirated system takes up less space, but you need to be surfaced to empty the tank. A recirculating system will allow you to empty the tank when submerged, however you will have to consider where you are going to store the compressed air when you fill the tank.

Either of these approaches can be taken with air pumps or water pumps.
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