500 motor-Where to find?

[wayne frey]

I just went web surfing for a dumas/pittman 500 motor.

Hobby Lobby shows the same part number for 2 different dumas 500 motors. One would not suit our purposes. The other, low draw-long duration would. But on contacting them they said it is the same.

So.. have the brushless motors taken over? I want the best 500 ball bearing brushed motor I can get. Not a 540. Not another. Looking for the old fashion, knuckle draggin, 500 dumas/pittman, graphner BB low draw 500 motor for my project.
After saying all that, how does one know which brushless counterparts are the equivalent models of a 500 in case this motor can no longer be had?
Any sources you guys know of ?

[wayne frey]

Does the brushless motor not

Does the brushless motor not require gear reduction? Sounds like a good forum discussion point. And has anyone gone to the trouble of matching the brushless motors as a replacement thrust wise, etc, to the old 400, 500 motors, for us who have seen/driven (and can relate to) these motors and want to replace them with a "best match brushless". An gear reduction. I was looking at in the high 3s tied to a 500 BB motor. If you went brushless, turning about a 2 1/5 prop, wouldn't gear reduction be good on a brushless too, or are there properties of the brushless I dont know.
To be honest, I know they cost more (not a big deal), they are electronicly "quieter,right?).
Big Dave,you have tried em, pitch in here.
What are the other advantages?

[fgroza]

Wayne,
Brushless fall into two catagories-inrunner

Wayne,
Brushless fall into two catagories-inrunner and outrunner. Inrunner tend to be high speed some requiring gearboxes. Outrunners tend to go direct drive as they have a large amount of torque for their size. Most flyers use outrunners for this reason-small motor turns a big prop and most are very easy on the amps. The difference in the motors is this- inrunners have the magnets on the rotor whereas outrunners have the magnets on the rotating bell or the outside of the motor and the winding is stationary and the magnets rotate around the winding. Eflite has some good motors as does Himax and AXI. I'm sure others will chime in here with other suggestions but to replace a 500 size motor with a brushless one will suprise you at the actual size of the motor. I would guess a 450 size Eflite outrunner might fit the bill for you. Much depends on prop size and battery weather lipo or NIMH . Most used lipo type are either 2 cell or 3 cell- 7.4v or 11.1v.
Hope this isn't too confusing.
Frank

[wayne frey]

I am still trying to

I am still trying to wrap my head around it, yes.
Outrunners-torque. So that would be the design of choice, sounds like. Still not sure on a few things. No gear reduction needed? No loss of run time? And slow throttle?
E Hobbies shows the motor. But they define size by size/weight of the plane. No specs.
Need some guys with hands on stick time to jump in here.
BTW, Lipos would be the batteries.

I am suprized there are no dumas/pittman 500 BB low draws out there!

[Guest]

The two main things that

The two main things that determine how much torque a motor generates are the stator diameter and the amount of turns in the armatures winding. More turns, lower RPM, more torque. The more turns, the greater the resistance, so motors wound for toque are typically a little less efficient than motors with low winding counts.

This might be a cause for concern, and lead one to believe that a low wind motor with a gearbox is the answer. Not necessarily the case- gearboxes make noise and generate heat, which is all wasted power. Any efficiency gains are lost in friction.

Outrunners produce torque because the outside can rotates instead of the armature. This gives a longer lever and hence a greater moment of torque.

They also use rare earth magnets and are not constrained by a commutator, this gives improved torque and a reduction in motor size and weight.

Unfortunately there aren't many ready made brushless motors on the market ideally suited to our boats.

The Robbe Roxxy range is worth a look at.

[wayne frey]

Ok, to outrunner motors are

Ok, to outrunner motors are high-torque by design. No gear drive needed.
Exccellent. Would still like to hear from some hands on drivers of brushless boats out there for their reccomendations and pitfalls that come from experiance. Would like to hear about run times too.
But something tells me this is going to be like leds to incandecent bulbs, isn't it?

[Guest]

Cogging is much less of

Cogging is much less of an issue than it used to be with sensorless controllers, and it does depend on how well the motor is made e.g. how well the magnets spaced etc.

I think outrunners can be cooled okay. Mount them on a metal endcap, or a copper plate that extends into the wet stuff, that should keep things nice and cool.

I've never found outrunners to be noisy. The ones I run in aeroplanes are silent.

Having said all this, a high quality Pittmam, Portescap, Maxon or Buhler DC motor will be very efficient indeed and should last a lifetime in a model. They're easy to control with a wide range of inexpensive ESC's, run extremely well at low speed due to multi-pole commutators, torquey and cheap if purchased surplus on ebay or at radio fairs etc.

[skip asay]

Wayne - go back to

Wayne - go back to your original thought. Pitman motors are a great choice. They're certainly torquey enough, they're quiet running and also quiet electronically. While I use caps across the board, I have run these motors without any noise suppression with no problems. These motors are also very long lasting. I installed a used Pitman in my Type XXIII 29 years ago and it's still humming right along. And it only draws 1 amp while driving a 2 3/4" prop!

Skip Asay

[hakkikt]

How is the situation with

How is the situation with the power rating?
If I have decided that a certain brushed motor is the right one for my boat (power-wise), should I choose a brushless motor that is as close as possible to that rating? Or is it an effect of the higher torque that a motor with a lower rating can be used?

[fgroza]

Wayne,
I have a couple of

Wayne,
I have a couple of 6v pittman motors but I think they are oilite bushed, not BB. They look like the ones they sell today for around $70. I had them in a Lindberg Sport Fisherman and just took them out to replace with faster motors. Email me at fgroza@msn.com if you are interested in one.

[wayne frey]

Thank you for the offer,

Thank you for the offer, but I just ordered up something for the boat.