Do receivers have low voltage cutoff? Yes!

[jacobmarble]

I was flying a new T-Rex 600E yesterday with a small receiver pack (NiCd 4.8V 600mAh) and suddenly, the motor turned off. Fortunately, it was only 5 feet off the ground, so I auto'd without problem.

Afterwards, the rx pack was at 4.71 volts, so I think the receiver has a low voltage cutoff at 4.7v. I can't nail this down for sure, since the R617FS has no manual. Can anyone verify this? It was nice that I only lost the throttle channel, and not cyclic/collective.

I've since installed a CC BEC Pro, and the problem hasn't returned. Yet.

[Deet]

There is a video by another comapny that shows both their Rx and the Futaba working down to almost 3V

If you still had servos then it was not the Rx, if it goes you have nothing...

I would suspect your ESC had an issue, either that or the throttle channel of the Rx, check yopour connections first

[Jafa]

The Futaba R617FS does cut the throttle at low voltage
But it should not kick in at 4.7v - should be much lower

[jacobmarble]

Another theory here. I'm using 3x Align DS610 and a DS650, plus the GY401. The DS610s are very high torque servos, so they draw a lot of current. Could it be that the pack was substantially lower than 4.7 when the cutoff happened, and then the pack bounced back after the load was gone? I checked the voltage maybe 30 minutes after the flight, so there was certainly time for it.

[Deet]

then why did the servos keep working after the motor stopped, Its teh ESC or the Motor

[jacobmarble]

Originally Posted by Deet

then why did the servos keep working after the motor stopped, Its teh ESC or the Motor

Originally Posted by Jafa

The Futaba R617FS does cut the throttle at low voltage
But it should not kick in at 4.7v - should be much lower

What does a receiver do at LVC? I'm asking because I don't know. I can play with the receiver tomorrow. I'll plug a servo into the throttle channel and wait for the pack to die.

[Deet]

The servo will stop working before the Rx does

[DominicD]

Originally Posted by Deet

There is a video by another comapny that shows both their Rx and the Futaba working down to almost 3V

Don't even get me started on how wrong that vid is.

[Deet]

HFG, I am with you...


But i does show how low an Rx batt can go

[Jafa]

Originally Posted by jacobmarble

What does a receiver do at LVC?

When the voltage reaches a predefine (low) level, the RX will cut the throttle but continue to operate (while possible)
This will be very evident to the pilot who will need to perform and emergency auto

On the higher end RX's this can be disabled or also enabled on other channels

I don't know what the voltage trigger is, I assume it's below 4v

[jacobmarble]

I have verified that LVC did indeed kick in.

First, page 40 of the 7C-2.4 manual describes failsafe, including "Battery FailSafe" at the bottom of page 40.

When the airborne battery voltage drops below approximately 3.8V, the receiver's battery FS function moves the throttle to a predetermined position. When the battery F/S function is activated, your engine will move to idle...or a preset position. ... You may temporarily reset the Battery F/S function by moving the Throttle Stick to idle.

It goes on to describe the difference between Normal F/S and Position F/S.

Second, the rx battery that gave me troubles on Monday hasn't yet been charged, so I got it out this morning, unplugged the ESC throttle and BEC supply, and plugged in an HS-45 servo to the throttle channel and the rx pack. Before this test, the battery was sitting at 4.98V. Powered up, the voltage immediately drops to around 4.0V and continues falling fast, so I can watch the throttle (illustrated by the HS-45) behave normally for ~30sec, then go to 0%. The green light on the R617FS starts blinking red-green-red-green. A few seconds later, things get crazy as the servos start moving erratically, and the pack is showing well below 3.8V.

So, the throttle being cut was caused by low voltage cutoff. I will now change LVC from 0% to something like 65% so that it's very obvious that I need to land, and at the same time have enough to land safely. Thanks for everyone's input.

[Jafa]

Originally Posted by jacobmarble

I will now change LVC from 0% to something like 65% so that it's very obvious that I need to land, and at the same time have enough to land safely

You can't do that

In the failsafe menu, the POS setting controls where to set the servo when the RX looses contact with the TX

The RX LVC is hardwired to close the throttle at a set voltage
On the R6008FS/HS you can turn the throttle LVC off or on
On the R617FS - not sure if you can turn throttle LVC off

[jacobmarble]

Originally Posted by Jafa

You can't do that

In the failsafe menu, the POS setting controls where to set the servo when the RX looses contact with the TX

The RX LVC is hardwired to close the throttle at a set voltage
On the R6008FS/HS you can turn the throttle LVC off or on
On the R617FS - not sure if you can turn throttle LVC off

I'll quote the entire section in the manual. My previous post only quoted parts of it. Again, this is the bottom of page 40 in the 7C-2.4 manual.

Battery FailSafe (F/S): A battery low warning feature (built into the 2.4GHz receiver).
When the airborne battery voltage drops below approximately 3.8V, the receiver's battery F/S function moves the throttle to a predetermined position. When the Battery F/S function is activated, your engine will move to idle (if you haven't set a position) or to a preset position. You should immediately land. You may temporarily reset the Battery F/S by moving the Throttle Stick to idle. You will have about 30 seconds of throttle control before the battery function reactivates.

Adjustability:
- NOR FS setting for throttle results in Battery F/S going to the servo position reached by moving Throttle Stick to the bottom with Trim Lever centered;
- POS F/S setting for throttle results in Battery F/S also going to the same throttle servo position as the regular F/S.

If using a 6V (5-cell) receiver battery, it is very likely that your battery will be rapidly running out of charge before battery FailSafe takes over. It is not a good idea to count on battery FailSafe to protect your model at any time, but especially when using a 5-cell battery.

As I understand the manual, the regular failsafe throttle position = battery failsafe position.

[Jafa]

You have not understood the manual or the difference between F/S and LVC

Try reading this again

Originally Posted by Jafa

In the failsafe menu, the POS setting controls where to set the servo when the RX looses contact with the TX

The RX LVC is hardwired to close the throttle at a set voltage
On the R6008FS/HS you can turn the throttle LVC off or on
On the R617FS - not sure if you can turn throttle LVC off

When the manual refers to F/S it means the RX loosing contact with the TX
You can set a throttle servo position for that incident but not for the LVC

Why don't you set the F/S throttle setting (50%)
and then repeat your bench test with this problematic battery
You will then see that when LVC takes effect - it closes the throttle