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Old Jul 24, 2013, 04:23 PM
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Sydney Australia
Joined Jul 2008
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Question
Suitable radio

I have just completed two submarines.The Dumas Akula and converted the Revell 1/72 Type VII.Up to now I have been operating them in my local pond on the aircraft band of 36 mhz. This was done due to the fact that I could not find a three channel radio on 27mhz. I finally found two suitable radios on 27mhz removed from a couple of ready to run sail boats.
I have opened up the Akula and replaced the 36 mhz receiver with the 27 mhz.However since doing that the speed controller worked ok but then became intermittent with failure of both the motor and BEC output and has now completely failed.
My question is, after that long drawn out explanation,can there be a compatibility problem with some older receivers and the newer speed controllers or could it be just coincidence that the speed controller failed ?
I have some knowledge in electronics but cannot understand why this happened and don't want to go swimming again to rescue my sub( it's winter down here).
Any advice would be greatly appreciated.
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Old Jul 24, 2013, 05:47 PM
Submarines, etc.
tsenecal's Avatar
Arvada, Colorado
Joined May 2005
1,595 Posts
without knowing anything about the receiver or the speed controller, i can only guess that there is no direct correlation between the replacement of one and the death of the other. however, weirder things have happened. check and make sure the voltage/amperage from the BEC is/was compatible with the 27mhz receiver, maybe it was drawing too many amps and overloaded the BEC. if that was the case, use of an external battery for the receiver would fix that for the next speed controller.
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Old Jul 24, 2013, 05:58 PM
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Mesa Falcon Fld, Arizona, United States
Joined Sep 2004
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Something that might have happened is that the BEC (usually a Low Drop Out Regulator) just gave up because it was getting too hot being in the space constrained WTC. I would do a quick check to see if you were getting any voltage out of the positive and negative leads that are running to the RX. This should confirm that the BEC has gone bad. If there is no voltage, then it is the BEC.
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Old Jul 25, 2013, 05:34 AM
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Sydney Australia
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Quote:
Originally Posted by tsenecal View Post
without knowing anything about the receiver or the speed controller, i can only guess that there is no direct correlation between the replacement of one and the death of the other. however, weirder things have happened. check and make sure the voltage/amperage from the BEC is/was compatible with the 27mhz receiver, maybe it was drawing too many amps and overloaded the BEC. if that was the case, use of an external battery for the receiver would fix that for the next speed controller.
As I said before the radio is one that was removed from a ready to run 1 metre Chinese sail boat.The speed controller was purchased from a Hong Kong model shop.I have included some photos of the radio and speed controller.The original receiver used before the change to the 27mhz receiver was a Hitec.
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Old Jul 25, 2013, 09:47 AM
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United States, NV, Las Vegas
Joined Aug 2011
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So, if you put it back like you originally had it, does it work again?
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Old Jul 26, 2013, 12:38 AM
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Sydney Australia
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Originally Posted by tchalfant View Post
So, if you put it back like you originally had it, does it work again?
Tried that but the speed controller has failed completely.I am just beginning to think this was just purely a coincidence that this happened.
I was also wondering if poor spark suppression on the motor could have something to do with the ESC failure?How close do you have to match motor and ESC?Is it only current draw or is there something in either the motor or ESC that you have to be carefull of?
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Old Jul 26, 2013, 05:51 AM
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Mesa Falcon Fld, Arizona, United States
Joined Sep 2004
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I am not sure that you have been able to rule out, at least with what you have shared with us that the speed controller is dead. On a typical speed controller, there really is two sections. The first section is the actual part that is intended for control of the motor. This contains the necessary logic and power section for this function. The other section contains the BEC or battery eliminator circuit. This section usually provides power to the logic section of the speed controller section, but also provides power to drive all the logic and motors of the servos attached. This section is a small LDO. If these things get too hot, they will fail. Most of the time they are already on the edge of their cooling rating (for that matter so is the rest of the motor power section) as the vendors of these components think that there will be some airflow over these parts. In our subs, there is no airflow, and the internal temps can get rather warm in a WTC. I would bet that these two conditions conspired to kill the LDO on your speed controller.

If it were me, I would go poking around to figure out if this was true, and then order a replacement part and repair the device, but I have the tools to do this. As I described above, it should be pretty easy to determine if the LDO has gone out. First plug in a battery to the speed controller. Then probe with a multimeter the pos and neg wires that would plug into the RX to see if you have any voltage coming out. If there is no voltage, then you are pretty assured that the LDO has died. It might also be worth probing the battery inputs to see that one of the battery wires is not internally broken.
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Old Jul 26, 2013, 04:50 PM
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Originally Posted by Aeroengineer1 View Post
I am not sure that you have been able to rule out, at least with what you have shared with us that the speed controller is dead. On a typical speed controller, there really is two sections. The first section is the actual part that is intended for control of the motor. This contains the necessary logic and power section for this function. The other section contains the BEC or battery eliminator circuit. This section usually provides power to the logic section of the speed controller section, but also provides power to drive all the logic and motors of the servos attached. This section is a small LDO. If these things get too hot, they will fail. Most of the time they are already on the edge of their cooling rating (for that matter so is the rest of the motor power section) as the vendors of these components think that there will be some airflow over these parts. In our subs, there is no airflow, and the internal temps can get rather warm in a WTC. I would bet that these two conditions conspired to kill the LDO on your speed controller.

If it were me, I would go poking around to figure out if this was true, and then order a replacement part and repair the device, but I have the tools to do this. As I described above, it should be pretty easy to determine if the LDO has gone out. First plug in a battery to the speed controller. Then probe with a multimeter the pos and neg wires that would plug into the RX to see if you have any voltage coming out. If there is no voltage, then you are pretty assured that the LDO has died. It might also be worth probing the battery inputs to see that one of the battery wires is not internally broken.
Thanks for that info. What I have done is ordered a replacement speed controller specifically designed for 540-550 brushed motors and a new motor.
I have a little electronics knowledge but not enough to start poking around this.The ESC consists of two boards joined with a plug on one end. One looks like the power section and the other the driver section.Access is very limited and for the sake of $25 for a replacement ESC it's probably not worth wasting time on it.
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Old Jul 26, 2013, 08:51 PM
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Bloomington, IL
Joined Apr 2004
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My only hesitation with 27 MHz systems is that they are the ones found in the really cheap RC toys. As such, they will probably be made with "disposable grade" components. I would expect them to fail sooner than a Hitec made-for-RC system.

The decoded signals coming out of the receiver should be the same, regardless of the frequency of the RC link.

And as mentioned above, the BEC may be at fault too. Good quality BECs cost more to build. Even an LDO linear regulator will have a typical efficiency of 40%, and may be as low as 15%. Which means that in a good case scenario, you will have to dispose of 60% of the power as heat. That will become a big problem in the WTC. In the best case, the BEC will simply do a clean thermal shut down. In the worst case, it will let the blue smoke out.
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Old Aug 03, 2013, 04:01 AM
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Sydney Australia
Joined Jul 2008
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I replaced the motor and speed controller and tried using the 27 mhz receiver with not much success. The receiver had very little range under water. The original 36 mhz Hitec receiver has been refitted and initial tests are very promising.
Thanks everybody for the advice that was provided.
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