Electrical Discussion - Page 24 - RC Groups
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Jun 20, 2016, 04:14 PM
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Post#1, image 5.
If more than one ESC with BEC is used, all but one of the BECs should have its output feed (the red wire to the RX plug) disconnected.
Not too sure about the last part of the question, but both batteries need to be fully connected for them to work. A solid ground connection (conventionally the black, negative power) is vital in multi ESC setups. Any faults in this area will probably result in the thin black RX side wiring vapourizing under load followed by unwanted armful voltage appearing in other parts of the setup.
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Jul 19, 2017, 09:55 AM
lots of water; some of it thin
chum444's Avatar
Withdrawn.
Last edited by chum444; Jul 20, 2017 at 05:38 AM.
Jul 20, 2017, 12:16 AM
Which way is it blowing?
SF Sloper's Avatar
Quote:
Originally Posted by chum444
... how to connect two 7.2v batteries in series
https://traxxas.com/sites/default/fi...%20Diagram.png
Jul 20, 2017, 03:08 AM
Registered User
Quote:
Originally Posted by chum444
I searched this thread for how to connect two 7.2v batteries in series but could not find a diagram. Did I miss it? If not would appreciate a diagram of how to do it so I can double check what I've done. Any pitfalls involved with two nimh's in series? Do they discharge uniformly?

Thanks
They need to be the same capacity, charged to the same level. In series, the same current must be drawn from both, so the will discharge at the same rate. This should result in them both reaching "discharged" at the same time.
There was no drawing because the concept of "series" and "parallel" was considered such a basic concept. Add to that, the thread concept was to provide diagrams of how to plug the various model boat control and power devices together, rather than a beginners course in basic electricity.
Aug 23, 2017, 05:26 PM
Registered User
Hi mfr02,
I'm still using Futaba 6 function M Series RC that I bought new at the model shop on Deansgate, Manchester in 1977. I still have the receipt, GBP 185 for Tx, Rx, 4 waterproof servos, nicads and charger!
Futaba is good stuff.
Aug 24, 2017, 05:03 AM
Registered User
Its not really a wiring query, but.....
1977 - The channel regs for 27MHz have changed a lot since then. Futaba were probably ahead of the game back then, but in the late '90's 27MHz channel bandwidth was considerably reduced to fit more channels in. Manufacturers responded by not providing any crystals that would use them, favouring the new-ish 40MHz for the fancier stuff.
Using an old transmitter near to newer ones on adjacent channels could give problems both ways. A very few years ago that could have been a problem, but with the mass migration to 2G4, it is rare to see anybody on 27 or even 40.
Aug 26, 2017, 10:14 AM
Registered User
mfr02 is quite correct. Across the pond here, the reduced use of CB band, which shared 27mhz, has freed up the frequency significantly, not to mention the the frequency migrations already mentioned.
Aug 29, 2017, 04:23 PM
Chuck
fredspak's Avatar

2.4 GHz receiver loses power from esc


I have discovered that my 2.4 GHz FlySky receiver seems to be very sensitive to voltage drops and cuts out when the BEC-equipped esc draws current for the motor. This has been noted with a couple of different escís and motor/battery combinations. I have not had this problem using the same esc/motor/battery with my old Futaba AM receiver. The only solution I have found is to run a separate 5v battery to power the receiver (red wire for esc disconnected). I have measured the power-up current draw and both seem to be relatively low: Flysky = 25mA, Futaba = 38 mA. Question: is this a common issue with 2.4 GHz receivers or is there something else I should be looking for?
Sep 01, 2017, 03:01 AM
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Quote:
Originally Posted by fredspak
I have discovered that my 2.4 GHz FlySky receiver seems to be very sensitive to voltage drops and cuts out when the BEC-equipped esc draws current for the motor. This has been noted with a couple of different esc’s and motor/battery combinations. I have not had this problem using the same esc/motor/battery with my old Futaba AM receiver. The only solution I have found is to run a separate 5v battery to power the receiver (red wire for esc disconnected). I have measured the power-up current draw and both seem to be relatively low: Flysky = 25mA, Futaba = 38 mA. Question: is this a common issue with 2.4 GHz receivers or is there something else I should be looking for?
This might be better if posted as a separate thread with an appropriate title. You might have a better chance of it being read by someone who knows.
A BEC is normally just a voltage limiter. If its source does not offer enough voltage under load (i.e. it cannot supply the current) the BEC in turn passes on a lower voltage, which might of might not be enough. Earlier receivers were "dumb", they just processed the signal in real time with quite a lot of latitude as regards supply voltage. 2G4 receivers are really a small computer, and are quite picky about the power that they get.
Also, check the power ground line - you might be trying to power the motor through the receiver wiring.
Sep 01, 2017, 08:40 AM
Registered User

Voltage drop causes 2.4 rc to malfunction


That drop is often in first few mseconds of motor start up and is not the average current that you are measuring while the motor is running. Yes that affects voltage to the receiver which causes your problem. High power torque digital servos do this commonly. Spectrum sold a separate capacitor that plugged into a spare receiver channel to cover that temporary drop. It is real. A larger capacity battery will be less likely to drop voltage temporarily until it reaches near expenditure. A bad battery will also drop voltage quicker and cause that mishap. This is usually not as bad a deal in a boat as in a drone or helicopter model but loss of control is the same.
Jim
Sep 01, 2017, 09:06 AM
Registered User
CaptCB's Avatar
I will add, it may NOT be a voltage drop (depending on your battery), but instead, you are exceeding the amp rating of your BEC. They are designed for use in r/c cars that only have one "standard" servo. I have heavy duty servos that can draw 2+ amps under load. Add this to what the ESC and RX need, and you can easily exceed the rating, and ESC Mfgs. tend to post ratings that are MUCH higher than the actual rating.
Sep 01, 2017, 01:13 PM
Chuck
fredspak's Avatar
Thanks for replies. All helpful suggestions. I will continue troubleshooting with this in mind.


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