texas_hippie

I'm nearing completion of the Dumas American Enterprise. I'm going with two of the Graupner mini jet drives, powered by the Speed 500 motors (two, of course). I'd like to know (since they'll both need to run at the same speed all the time, and forward only), if it is possible to control them both with just one ESC? If anyone has any experience with this, I'd love to hear your opinions.
Possibly recommend an ESC that would be sufficient as far as handling the required amps, ect. I'm not looking for speed here, just a scale like motion at full throttle, and the maneuvering when coming alongside the dock to moor. Of course, cheaper is better if it can be done so. Thanks in advance, I'm new here, and after reading the scale forum for the last few hours, I must say I'm genuinely impressed with the knowledge of the members here!

Pusar

My Feedback: (1)

Not cheap but a real powerhouse and you will be happy. Buy the fan that cools it also. Any pictures?

Marty

http://www.teamnovak.com/products/es...yxr/index.html

ernest2

hippie, how big is the american enterprise? and how heavy is it? im a bit worried that the mini jet drives might not be enough. i am currently working on a semi-scale patrol boat 1meter long x 16cm wide, and using 2 mini-jets from graupner, with 2 tamiya sport tuned motors. i tested it in a tub using an astroflight 212d esc and the esc barely got warm. i then tested it using a tamiya adspec (the adspec is designed to be used only with one sport tuned motor) it got warm a bit, but not really hot. both test using 7.2volts. hope this helps somehow.
ernest

LtDoc

texas_hippie,
The simple answer is to do a stall test on one of those motors. Whatever max current draw is, double it, and that's the max current rating the ESC should have to handle two motors. More than what's needed is better than less than what's needed. Not exactly the cheapest, maybe, but best in the long run.
- 'Doc

texas_hippie

Dayum! That bad boy ought to do the job! By the way, I just added some pics to the gallery under my profile. Thanks, Marty!

texas_hippie

So basically Lt, I just need to hook a meter in line, apply power to the motor, and stop the shaft for a reading? The esc should be purchased to handle twice that amperage, correct?

texas_hippie

Ernest, boat is about 52 inches, and nearest as I can calculate, should weight in at about 12lbs, with everything installed. I figure I'll add one of Graupners larger jet drives without the reverse buckets added for pure thrust if I need to. This third jet will be an on/off switched motor that'll run at full throttle settings only, when max cruising speed is needed. It'll of course have a larger outlet, just as the real vessel used.

Dude631

Man, thats a great looking model !

ernest2

texas hippie, just be sure to leave the necessary space for that future turbo jet in-between the mini-jets can't wait to see your boat runs.

LtDoc

texas_hippie,
That's about it. There are a couple of things to remember about doing stall tests though. They need to be done quickly. Holding the motor stalled for any length of time isn't exactly good. And the other thing to remember is if the motor isn't a real 'wimp' to start with, you won't want to hold it in your hands while doing the test... that DO smart, keep bandaids handy - lol.
- 'Doc

texas_hippie

Ernest, what type of drives/motors are powering that patrol boat in your gallery?

ernest2

the pt-15 have a small brushless motor on the mini-jet drive (20mmx40mm inrunner), and i must say that it runs ok with 8AA cells. sub-c or even 2/3a cells will be even better. the motor and esc are hk/china stuff from ebay.

Ghost in the shell

texas, running two 500's off a single esc, I dont think that will give you much trouble as long as your esc is beefy enough, for such application I'd be tempted to try Proboat/overlander "Tornado50" or if you are using thrust reverse buckets for reverse thrust, an aircraft type esc

texas_hippie

Problem solved...I went with a "Y" cord, and two esc's from the throttle channel. I got 30amp esc's for less than $10 apeice. Only trouble now is that at very low speeds, one motor starts turning before the other, possibly drag induced by some misalignment of the starboard drive, however, I can't seem to correct it mechanically by adjustment. I wonder if there is a potentiometer in those tiny esc's that can be tweaked? It's absolutely imperative that both motors provide identical thrust.

hansvonpensch

I have 2 boats with duel motors and the left one will starts first on both, both motors turn out, I was told that the timing on a motor that turns counter clock wise is set up to run before one that turns clockwise.

texas_hippie

Now I'm really confused, as both my motors turn in the same direction. I'm using them on Graupner mini-jet drives, which I purchased for manuevering at slow speeds reasons. It really makes it hard to squeeze into a tight dock, when the motors won't rev at equal speeds! I'm thinking one of the drives has a bit more drag than the other, but can't physically feel it, or see where the binding might be. The impellor may be rubbing the housing, and maybe it will "wear in" with use, and the problem solve itself. I only have about three minutes run time on the drives, as I was testing the boat for ballasting purposes.
Hippie>>>>sends
P.S. Thanks for the info

texas_hippie

First "in the water" test today...absolutely no need for the third jet drive! Those mini-jet drives with the Graupner Speed 500 motors are powerful! What a delightful surprise, as I was worried they wouldn't push the boat at all.

mfr02

Apart from the possibility of one jet drive being stiffer than the other thus allowing one to start rotating easier than the other, there is also the possibility of slight differences between the motors and the responses of the ESCs. Try substituting, swap the ESC/motor combinations over and note if the problem stays where it is or moves, then do the same with the motor/jet drives. You need to know which bit the problem is coming from before you can start to cure it.

DavidMC

My Feedback: (6)

Hi Texas Hippie.

I just bought an American Enterprise kit of ebay and am thinking of doing jet drive. Do you have any photos of your setup? How fast does it go?

Thanks,
Dave

texas_hippie

I used two of the Graupner mini jet drives, and two Graupner speed 500 motors, purchased from Hobby Lobby. I finally got her in the water last Sunday, after a ten month build. I used every method I could think of to build the boat as light as possible, fearing the drives wouldn't be powerful enough to move the boat at scale speed. I was pleasantly surprised to find that she moved as fast as she did! Way faster than scale speed, I'm using the Spektrum DX 6 radio, that is computer programable, so I'll set the throttle throws down to keep the boat a bit slower. I need to warn you to go ahead and purchase the drives and motors, and install them in the transom as soon as you assemble the transom, and the two aftmost bottom hull plates. Don't wait untill the hull is completely finished as I did. This made installation a real pain! The transom is also too thick for the flanges on the drive if you assemble them as per the plans. The optimum set up, would be to cut out the inner transom (its made of two thick pieces of balsa, sandwhiched together), enough so the inboard flange has plenty of room, to butt up against the outer most transom piece. This will allow the flanges to seat properly against eachother. Also critical, is the fact that the transom has to be EXACTLY at 90degrees from the keel, and the bottom hull plates where the intakes mount. Mine was a few degrees past 90, and it required alot of filling and sanding to make things right. Here's two pics of the drives as they were roughed in. If you need more, feel free to e-mail me at [email protected]
Also, I have pics of the real vessel as she looks today for detailing purposes. There may still be a few pics on the gallery in my profile.
Fair winds, and following seas......
Hippie>>>>>>>sends