Expectations 1/8 scale hydro electric conversion

[PJBJ]

Years ago I built a dumas model of the 1/8 scale miller hydro with solid shaft. I fitted a 15 cc K&B engine and looked at it for some years (I am a builder) without getting the boat wet. Finally I decided to convert the boat to electric (on a budget) in such a way that I can change back to the K&B engine setup. I purchased the following setup: Aquastar 4084 1050 KV motor and Turnigy 180 Amp ESC with a 55mm diameter prop. The space in the fuel tank compartment is limited and I now have a Roxxy 6s 3300 Mah 25C continuous discharge rate fitted in. Burst rate for approx. 10 sec. is 50c which gives me 165 Amps. I realize that the lipo could be stronger but this is what I have. Total weight 6 kg. I do not plan to race but would like to give the boat a try on a nice day and maybe push the throttle for a couple of seconds just to see what it does. I am curious what the more experienced rc boaters will respond regarding my expectations of this setup.

[Doby]

Where to start......

Those old Dumas hulls are porky and need a lot of power to run them.

Your motor is physically to small, KV to low...about 22,000 RPM unloaded.

Lipo C rating and capacity are insufficient (assuming a 1P configuration)....burst rate is useless to try and figure out average current draw. Current draw is more based on motor kv, voltage, prop and hull type, weight, overall setup. I doubt that weak of a Lipo would even plane it and if it did, would be dead in about a minute.

ESC , while those are good ESC's in the right boat, a 1/8th scale on 6S will probably destroy it...especially with a 55mm prop(to big).

Big boats and "on a budget" are never very successful.

If you are determined to stay with those components, then keep it nitro.

[monojeff]

I know that some guys out here had great success with scorpion out runners in 1/8 scale boats.
I don't know the exact motor they used but it was not that expensive from what I remember.
Believe a record or two was set with that out runner and it didn't break the bank to make it happen.
If interested I could probably find out the motor and esc that was used.

[JimClark]

I think they were running 10s lipos also

[PJBJ]

Thanks for the info Doby. Out of the water the setup sounds great! I do not want to use the K&B so I am going to give it a try in the pond starting out slow and getting it back quick to feel the components.

If you have any suggestions on how you would proceed with this setup and getting better stuff I am looking forward to your view on this.

Thanks also monojeff and I am always interested. The motor mount I have made limits bigger motors than the one I am using now (40mm + water-cooling).

[monojeff]

Here is a link to the page that talks about the boat.
http://forums.offshoreelectrics.com/...t-Lake-Waughop

Here is the setup.
Qty-2 Gens Ace 4S 5300 packs in series driving a Scorpion HK435 800 Kv motor through a water cooled ICE 200 lite ESC.

Looks like it was 8s

[Fluid]

What are your expectations for the boat? The others have given you opionions on what you should change to make it a success. But I believe you asked what we expected to happen using what you have, not what you should change....

Chances are are very good that the boat will not plane out from a stop, especially with the solid shaft drive and unknown center of gravity. Hydros require a lot of things to be near perfect to run right...CG, total weight, prop depth and angle, prop lift, etc. Too, these boats were designed to be launched with a toss, so by all means do that. The prop size and motor Kv are fine for this size hull, but the motor size is small and efficiency will be low. 6s is low power for this boat, and while it can be made to work, the low capacity of your pack will not allow it. With luck you may get to see it plane for your "couple of seconds" with a toss launch, but not for long. The desire to see it run will demand you to hold the throttle down, which will result in a burn-down. Good luck with that.

There are many ways to get where you want but you will need different components.....the Scorpion is no longer available so you can't go the out runner route. But you don't have to.....






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[PJBJ]

Had a look at the site where a Scorpion HK435 800 Kv motor was used on 8s and a water cooled ICE 200 lite ESC. I think this is the Scorpion HK4035 800 Kv which has a power output of 4200 Watts and is still available where my Aquastar has 3100 Watts. This out runner with outside diameter of 48.9 mm is about 35% stronger and could fit in my engine compartment. Something for me to consider together with getting a 8s lipo and charger for this lipo (current charger goes to 6s and so does my ESC so have to change this too). Fluid: My expectations now are that the boat will get out of the water but it will lack runtime. With a better 6s lipo however I think I could have a nice run.

Nice pictures on your site Jim Clark!

[monojeff]

You do not need 8s batteries.
You would need 2 4s batteries
Lots of people like the T180 esc so would not be difficult to sell
You could also sell the other stuff and get some extra $ if you decide to change things.
Better to sell good newer parts then try to sell burned up stuff because the setup wasn't right.

[PJBJ]

Thanks for the input monojeff. The only thing I have not figured out apart from the approach of getting the scorpion out runner and a suitable esc is the battery. The lipo has to fit in the front where the nitro tank used to be. This means that I either have to remove the motor (with esc fitted on top) to change the lipo or work with one lipo charging it in the boat. I have no problem with this because I only want to run the boat occasionally. Using 2 4s lipo's will be difficult because I don't see how to reach the balancing pin for charging the lipo in the front of the nose. Any thoughts on this would be appreciated.

[Fluid]

If you can find a Scorpion HK4035/800 buy it, these have been out of production for well over a year. I ran one in a 10S catamaran and it performed well but these motors do not like high amps, especially since they can't be effectively water cooled. Keeping runs short helps. They run well on 8S too and will swing bigger props.

Do not be fooled by a motor's rated "power output", that is almost always misleading. The Scorpion is actually rated at 100 amps maximum, but on 8S 4200 watts is about 140 amps. For short runs it will work. The real advantage of the big outrunner over an inrunner is the greater torque of the former to spin larger, more efficient props. Your big heavy hydro will need that.

Some battery sellers can supply balance plug extensions for your 4S packs. I usually charge in the boat with no ill effects after over seven years of doing it...




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[PJBJ]

Expectations have changed and the boat will not run with the current setup.P1000354.jpg

Thanks to the recommendations from more experienced r/c boaters I decided to change the setup. Scorpion HK4035/800 is on its way and because I got a good deal on the motor I decided to break the bank on the ESC and ordered a Castle creations Hydra ICE 240 XL. Looking forward to the data logging option. Now I have to wait...

[Make-a-Wake]

I ran a Castle 2028 in my 1/8 (50") Hydro on 9s2p and got 60mph out of it, its a solid setup.

[PJBJ]

P1000370.jpg
Motor arrived. Waiting for ESC.

[SJFE]

You're not screwing around with that motor mount are ya...