Model Boat Mayhem

Please login or register.

Login with username, password and session length.
Pages: [1]   Go Down

Author Topic: RPM, and acronyms  (Read 2693 times)

Black Shoe

  • Guest
RPM, and acronyms
« on: August 13, 2010, 06:58:40 pm »

 Firstly, I've searched and read a host of posts trying to understand the acronym "BEC". Seems everyone but me knows what it is. What is/are "BEC"?  :embarrassed:

Secondly, being very new to the RC world, I know so little about it, I don't even know how to ask the questions yet.  {:-{ I did a search, and may have even read an answer, but didn't recognize it.

I am running a tug with a DX6I, to an MR200 Marine Receiver. From there to a Proboat ESC, (I do know what that means  :-) ), then to a M.A.C.K. Products 12V 5 Amp motor attached to a 4:1 gearbox final drive. Everything works very well together with the exception of the very low shaft RPM range. I have a few mm of throttle stick travel with 0 shaft RPM. When I get to a certain point the RPM jumps from 0 to about 1/3. from there, the RPM increase is smooth and predictable, but there is no finesse, the tug throws out a wave, squats, and is underway. I would gladly give up top-end RPM in order to have some dead-slow turns in the beginning.
Another curious problem is, I need to pull the throttle stick down for forward, and up for reverse. In conjunction with this, I get more turns in reverse than in forward.
As I mentioned above, this RC world is very new to me, and I'm reluctant to change anything for fear of "smoking" a piece of equipment out of ignorance.

My thanks for any advice!

Regards

Tim
Logged

BarryM

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 1,701
  • Location: West Lothian
Re: RPM, and acronyms
« Reply #1 on: August 13, 2010, 07:12:55 pm »

Tim,

'Battery Eliminating Circuit' - a gizmo removing the need for a separate Rx battery and permitting the supply to be taken off the power battery.

Barry M
Logged

Shipmate60

  • Global Moderator
  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 5,800
  • You bark - I will bite!!!
  • Location: Fareham
Re: RPM, and acronyms
« Reply #2 on: August 13, 2010, 10:33:21 pm »

Tim,
It sounds like the Speed Controller is working in reverse.
You will need to change the servo reverse for the throttle channel (usually channel 3 aileron).
Then reverse the motor connections.
I think this speed controller only supplies 50% power in astern and you have this as ahead.

Bob
Logged
Officially a GOG.

Black Shoe

  • Guest
Re: RPM, and acronyms
« Reply #3 on: August 14, 2010, 12:12:08 am »

Tim,
It sounds like the Speed Controller is working in reverse.
You will need to change the servo reverse for the throttle channel (usually channel 3 aileron).
Then reverse the motor connections.
I think this speed controller only supplies 50% power in astern and you have this as ahead.

Bob

Thank you Bob. Is this something that will be addressed in the radio manual? (I won't have access to it for a couple more days.) You're correct about the 50% in reverse. Even at that, the RPM is way too high, even at 50%. When I change things around, will this give me realistic acceleration?


Tim,

'Battery Eliminating Circuit' - a gizmo removing the need for a separate Rx battery and permitting the supply to be taken off the power battery.

Barry M

Thank you Barry! Now I know I have a BEC!

Thanks guys,

Regards,

Tim
Logged

Shipmate60

  • Global Moderator
  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 5,800
  • You bark - I will bite!!!
  • Location: Fareham
Re: RPM, and acronyms
« Reply #4 on: August 14, 2010, 02:39:14 pm »

You could always drop the operating voltage to 6 or 7.2 volts and try that.
OR
Go for a much smaller prop.
Or a larger drop gearbox 1:6 or 1:8
If it was mine I would try the voltage reduction first.

Bob
Logged
Officially a GOG.

malcolmfrary

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 6,027
  • Location: Blackpool, Lancs, UK
Re: RPM, and acronyms
« Reply #5 on: August 14, 2010, 02:45:15 pm »

Quote
When I change things around, will this give me realistic acceleration?
Probably not.  The Proboat ESC has been noted as having very little low speed control, cutting in suddenly at about 25% throttle.  The workround is probably to blip the throttle for low speed, the real cure is an ESC intended for fine control.  Reducing the voltage to give a realistic top speed will certainly help.
Quote
Then reverse the motor connections.
Not really, just reversing the one or the other will get the response agreeing with the stick movement, reversing both will give full forward revs, but leave the reversed response.  In all probability, reversing the switch will be actually "unreversing".
Logged
"With the right tool, you can break anything" - Garfield

FullLeatherJacket

  • Guest
Re: RPM, and acronyms
« Reply #6 on: August 14, 2010, 02:49:13 pm »

Servo reversing is usuallly done via a small slide switch on the Tx. The manual will explain this - it's very simple.
Ref the slow speed control, these particular speed controllers are not designed for slow speeds - they are essentially car speed controllers with the word "Boat" added, and are intended primarily for racing boats where top speed is more important. Yiou may be able to program in some exponential throw on this channel via the Tx, but I'd not spend much time trying. Better buy a proper marine ESC which can deliver good slow speed control (and full speed in both forward and reverse) and save the Proboat for later.
As Bob says, if the top speed is too high then reduce the supply voltage.
More about BEC here:
http://www.action-electronics.co.uk/pdfs/BEC.pdf
FLJ
Logged

Black Shoe

  • Guest
Re: RPM, and acronyms
« Reply #7 on: August 14, 2010, 09:41:50 pm »

Thanks again guys. I wish I knew then what I know now.......seems like that could apply to several facets of my life! :-) Any way, when I acquired this boat I just went to a local shop and said "...here's what I've got, what do I need?". They fixed me up with what I've got, but it was all in good faith, I don't think for a minute that they were just loading me up with parts. Had I known about the ESC's and the benefits of external BEC's I'd have gone that way, I just didn't know enough to ask the correct questions.
Thank you for the link FLJ, is there a place that has these type of schematics with an index (search function) that I can access and study?

Regards,

Tim
Logged

Shipmate60

  • Global Moderator
  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 5,800
  • You bark - I will bite!!!
  • Location: Fareham
Re: RPM, and acronyms
« Reply #8 on: August 14, 2010, 09:44:30 pm »

Tim,
What tug is it?
The probability of someone on here building and running the same or similar size/weight is very good.
They could then tell you how their set up works.

Bob
Logged
Officially a GOG.

Black Shoe

  • Guest
Re: RPM, and acronyms
« Reply #9 on: August 17, 2010, 10:52:37 pm »

Hi Bob,
Sorry about the delay in replying, but it's "tourist season" up here this time of year, and friends and family are always dropping in for a few days. Love to see them come for a visit, but LOVE to see them leave too, if you know what I mean. O0

My tug is a 26 lb modified "Amsterdam", single screw, stock rudder.
I anticipate a bow thruster, and Kort nozzle before next season rolls around. As I mentioned before, my biggest concern is being able to attain a very low shaft RPM.

Thank you,

Tim
Logged

CGAux26

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 655
  • Location: Deep in the heart of TEXAS (Tomball)
Re: RPM, and acronyms
« Reply #10 on: August 17, 2010, 11:14:49 pm »

Misery loves company.  I too have a Proboat ESC, in my Springer, and it does have that deadband of about 2 or 3 clicks on the Spektrum DX6 throttle, at which point the motor comes on at too much speed.  This happens in forward and reverse.  I am working on getting a proper ESC that will give me proper low speed turns.
Logged
Pages: [1]   Go Up
 

Page created in 0.087 seconds with 21 queries.