JSchneider

Here is my question....

I just completed a repower of my Dumas Donzi. Until this week, she was powered by 2 - 540 sized motors with a 2:1 gear reduction, powered by 2 - 7.2v batteries. It was a bit sluggish on the water so I installed 2 - Johnson HC970 motors with the same batteries (minus the gear reduction). The question I have is....would 2 - 7.2v batteries be considered a 14.4v system, or would it still only be running on 7.2v's? If I were to go to a 12v battery, would I see any increase in power?

Also, how could I increase run time? At full power, with this set up it only seems to run 10-15 minutes at most? What could I do to increase this? I've heard of large boats running for 4 hours at a time, is this possible?

Thanks.

Kmot

My Feedback: (24)

Depends on whether you wire the battery packs in series or in parallel. You would do better to wire in series for the 14V as long as your esc can handle it. Here is a video of a Donzi with the high rpm versions of those Johnson motors:

http://media.putfile.com/Dumas-Donzi-at-Hansen-Dam

JSchneider

Thank you for the input. Is there a difference between the HC970 motors and the motor's you are using? Also, what voltage are you running your boat at? What kind of run time do you get with your set up?

Thanks again.

Pusar

My Feedback: (1)

If you really want to complicate things....

JSchneider

Will the HC970's push the boat up onto plane? I haven't had it out on open water yet. Last night I ran it in a small pool and at full power the boat had a lot of pull. It sounded like 2 turbo diesels. I am just looking for a realistic scale speed for the boat.

Kmot

My Feedback: (24)

There are two versions of the big Johnson 970 motors. One is a low rpm, torque motor. The other is a high rpm speed motor. The video is of my friends boat. He is running 14.4V and using a Novak Super Duty esc. The boat gets up on plane easily and has a top speed close to 20 mph measured with a GPS. He usually gets around 15 minutes using the NiMh cell battery packs he has in there. Here is a pic of the high rpm versions of the Johnson 970 motors:

JSchneider

Where can you purchase the high rpm version? Maybe I will just purchase 2 of those and keep the boat on the 14.4v system instead of converting to 24v.

Kmot

My Feedback: (24)

They are hard to find now. I have a pair of them brand new I can sell you for $40 shipped. Otherwise, just look around on ebay or surplus stores to try to find some.

But don't buy these:

http://cgi.ebay.com/PAIR-2-NEW-JOHNS...QQcmdZViewItem

Those are the low rpm versions.

This is the high rpm version:

http://www.enigmaindustries.com/Johnson_Mini-EV.htm

JSchneider

This may be a stupid question, but do these motors run in reverse as well? Today I had a chance to test out the Johnson HC970's that I purchased for the Donzi. Unfortunatly, I was disappointed with their performance. When I tested them earlier in the week, the reverse worked, but would not work today. Could it be that I burned something up in the speed control?

Thanks.

Kmot

My Feedback: (24)

All electric motors will reverse. So it sounds like your esc has a problem.

JSchneider

Ok, I have two of the mini EV's arriving tomorrow. Do they come with the capacitors preinstalled? I think this is why the boat was cutting out so bad yesterday, because I have no capacitors on the motors I am currently running.

Kmot

My Feedback: (24)

No. You should also solder cooling tubes on them and run a water cooling coil around the motor as well.

Who still has the Mini-EV for sale?

JSchneider

I found them here...

http://www.robotmarketplace.com/mark...otorsmisc.html

JSchneider

One more question...What speed control are you using in this boat? I know nothing about speed controls and would like to install one that will not burn out with this set up. The current speed control I am using is a 14.4volt from a Traxas Villan I had, but I think something burned out as reverse no longer works.

Kmot

My Feedback: (24)

That's interesting. Robot Marketplace had been out of stock for the past year or so. Must have found another case of them somewhere.

Reverse can be disabled by programming on the Traxxas EVX speed control. Do a check of your programming to be sure you did not accidentally disable it. The esc being used by the Donzi in the above video is a Novak Super Duty. The Traxxas EVX is made by Novak, in case you didn't know.

JSchneider

Great, so the speed control I have should work with those motors. I'll check the programing. Thanks.

JSchneider

My old speed control is fried. So, here is what I did...I bought 2 novak super duty speed controls and a Robbe F14 twin stick controller. This should give me the option to control each motor independently. Do you see any issues with running 2 -7.2 volt batteries to each speed control and motor? It sounds like the speed controls are built for that, but will the motors handle it? They are rated up to 18 volts. The boat will then be powered by 4 - 7.2 volt batteries total which I hope give longer run times. Let me know if you think this set up will work. If not, the boat is going back on the shelf and it will be a display model only.

Kmot

My Feedback: (24)

I routinely run two 7.2V packs wired in series (14.4V) to one of these motors in an 11 lb. 36" long boat. But I have added water cooling to the motor. In any case, it handles that voltage easily. You should not have any problems running 14V to these motors. Your run time will depend heavily on the mAh rating of the batteries. It sounds like money is not an issue for you, so you should think about getting the new 4500 or larger mAh battery packs.

I have read that when running two esc's that each have BEC capability, it is very important to disable the BEC on one of the esc's. You should get more info on that by doing a search or asking a new question about that in the forum.

JSchneider

Are you able to disable the BEC on the novak super duty speed control? How do you do that?

Kmot

My Feedback: (24)

u163665

20mph, eh? Nah - - it doesn't go that fast, but one could wish. On low batteries, we once clocked the boat at 12.5mph. Not bad for a 30lb+ beast running on batteries!

I would advise against using two Novak Superduty ESC's for your Donzi - for simplicity alone. Getting both ESC's to deliver the same amount of power to each motor would pose a serious challenge in my humble opinion. The boat operates very reliably (and easily) with just one ESC (thus one channel) for smooth acceleration.

Also - I am using 8.4v (7 cell) batteries in series to deliver 16.8V total power. The earlier picture KMOT posted was an old picture taken about a year ago. I have changed so much since then. For one, no more silly SLA batteries! In addition, I have added silicone water cooling jackets to the motors - which do a fantastic job keeping the motors cool and boosting performance (much better 2nd and 3rd runs).

Lastly, if you do go with the Novak SuperDuty ESC, make darned sure you install the aux fan. It gets quite hot inside your boat and your ESC will quit on you if it is not cooled.

Kmot

My Feedback: (24)

It's about time you got into this thread Matt!!

Kmot

My Feedback: (24)

And I thought the GPS speed was 19.5 mph?

JSchneider

Ok, I have one more question. I received all of the parts and installed them successfully in the boat. The Mini EV motors pack one heck of a punch, I was imperssed. The problem I am having is that when I put the boat into reverse, it runs very fast, its almost like it goes into full reverse power. Does anyone have any ideas why this could be happening? I tried re calibrating the speed controls with the transmitter without any luck.

u163665

That sounds very familiar. Although the SuperNovak speed control is a good one - it certainly is not perfect. Although it has a "boat mode" where it allows 25% power for reverse, I have the same problem. The SuperNovak is really designed for cars, and therefore has a "brake mode", so when you reverse the first time from forward, you will likely have no reverse response. The second time you reverse, BOOM - there it goes!

I deal with it by being very light on the stick and just giving 1 second reverse holds - - anything other than that will likely be too much!