I have a question ??

[Gene Gold]

I have a Dumas 36" Chris Craft. That has a Dumas Motor (10,000 rpm) and the Battery is a 1500.. I would like to increase the speed.. Should I go to a larger motor or Increase the size of the battery.. I am using a 30amp Futaba controller.. Thanks for any Ideas, Gene Gold E-Mail address is genegold@pacbell.net

[freq]

Gene,

You should be able to increase the speed of your boat with changes to battery, motor, or prop. This is best achieved with a delicate balance of the three.

Adding a cell to the battery will probably yield the most notable difference in speed. It has its risks, however. The motor is sure to run hotter, and may not last long, depending on how hot it actually gets. If speed is what you're after, burning up your original motor is a great way to rationalize the purchase of a more beefy motor, which can make a big difference.

Another inexpensive option is getting a bigger prop. With a larger diameter or higher-pitch prop, speed can increase, but you are sure to draw more current from your battery, through your ESC and motor.

Experimentation is the best cure, as there is no sure-fire formula for success. Example...

I wanted more speed on my Kyosho BlueStreak. Over time, I went from a 6-cell battery to a 7-cell battery and got a much bigger prop. Though my ESC was fine (a beefy Tekin car model), this toasted my factory water-cooled can motor in a jiffy. :eek: I eventually settled on a more reasonable prop and got a modestly beefy 19-turn car motor, and happiness ensues.

I'm not sure how important scale looks are for your situation, but most of the Dumas props I've seen have been 4-bladers. A 2-bladed prop from Octura should be more efficient, but may require a prop-shaft adapter, and may disturb the scale-like appearance of your boat.

Your 30-amp ESC may be a limiting factor of how much juice you can push through your gear without burning it up.

Again, experimentation is in order. Keep pluggin' away 'till you find the right combination. Good luck!

-chris

[Gene Gold]

Great Info.. I think I work backward and start with the Prop. I also thought about going to a 1700 Battery.. The Speed controller has a forward and reverse, so will I need an ESC also?? If that is the case How would you hook-up the ESC and controller. Would you Hook the ESC to the receiver in the Throttle slot and the speed controller into either rudder or elevatorm slot?? Thanks again. A big Help Gene

[freq]

Didn't mean to confuse you...

ESC stands for Electronic Speed Control. Looks like you've got a speed controller already, but I'm not sure if it's electronic or mechanical. You should get the same performance either way, but a mechanical one uses a servo that switches different resistors in the circuit (they typically look like springs in this case). The resistors are effective in limiting the current to the motor, but waste energy from your battery in the form of heat. To over-simplify, an ESC uses transistors to switch the current on and off rapidly, varying pulse width depending on your throttle position, effectively limiting the amount of electrons delivered to the motor without wasting any. Thus, an electronic speed control is more efficient as far as conserving energy and allowing the longest run-time, if you're running partial throttle at all.

I think a new prop is a great (and usually inexpensive) way to start. You may be able to get a prop that fits your shaft directly, or may need an adapter. Octura has a great selection of props and adapters.

As I stated earlier, beware that larger props draw more power. After a run, carefully feel your motor, ESC, and battery with your hand, to see if they're too hot.

In terms of battery, switching from a 1500mAh battery to a 1700mAh battery will not likely make much of a speed difference. The 1700 has a greater capacity, in terms of milli-amp-hours, and will give you a longer run-time in the water, but it probably won't give you much more speed, though it will be able to deliver a bit more current, should your motor draw it.

I'm guessing that you're using a 6-cell (7.2 volt) battery. If so, switching to a 7-cell (8.4 volt) battery is sure to increase your speed, as it will run the motor at a higher voltage (and RPM). Since you'd likely be running your motor (and ESC) a bit out of spec, you will probably shorten it's life a bit, and may be running the risk of burning it out sooner than expected. Again, this is a case of checking the temperature after a run to see if you could fry an egg on it. This is, of course, a pretty relative method and not very scientific without an ammeter, thermometer, and specs on the motor.

I've found that trial and error is the best way to get the most fun out of your toys in this hobby. Playing is only half of it. Experimentation is the other. Yep, you'll kill a part or two in the process, but that's always an excuse to upgrade. ;)

Good luck and have fun.

-chris

[Gene Gold]

I may have a few more qestions.. Later.. I will ponder over what we have talked about and let you know how things are going.. Thanks much, GeneG:)