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AR620 Power up issue

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Charles Aldous 115/08/2019 16:15:57
15 forum posts
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Here is a strange one which essentially seems a difference in the way the new AR620 powers up when compared to say an AR8000 or other earlier Spektrum rx's when using a safety switch.

I have an Emcotec safety switch in line between the lipo and the esc and the switch's remote plug, when removed, makes the esc live. The esc is connected to the rx by the signal wire only.

I power the rx via a Castle Creations BEC which is connected to the input wires of the safety switch. When the lipo (TX on) is connected the rx powers up but the esc only becomes live once the safety switch plug is removed.

This works on older rx's but not the newer AR620. When the AR620 is used with my set-up and the lipo connected, the rx does not power up until the safety switch plug is removed and the esc receives power. When the safety plug is replaced, the rx stays powered up and the esc isloated as it should work.

The AR620 works normally without the safety switch in the circuit.

So it seems that the AR620 (which takes it's power from the separate BEC and should get that as soon as the lipo is connected) will not power up until the esc (signal wire only to the rx) receives power once the safety switch is open, yet once this done the rx works as normal and stays live when the safety switch is subsequently on or off. When the lipo is disconnected and re-connected the issue repeats.

I have tested the above with different esc's and rx's, with the safety switch in and out of the circuit and the AR620 always works as above.

If anyone can explain this and if there is another way to make it work as the older rx's I would be very grateful.

Edited By Charles Aldous 1 on 15/08/2019 16:22:19

Steve J15/08/2019 17:16:34
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1372 forum posts
41 photos

It sounds like that with the Emcotec off the signal line is being held either high or low and this is preventing the 620 from booting up. The only thing that I can think of that might solve your problem is using an opto ESC.

Steve

Cuban815/08/2019 17:17:35
2641 forum posts
13 photos

Just checking.....

1 Does the 620 work as it should when just powered from the separate CC BEC and Lipo?

2 Does it work correctly when powered from the Lipo/ ESC BEC but without the safety switch?

3 Does it work correctly when all connected up but without the RX connection to the ESC?

If the BEC is powered from the input of the safety switch i.e. in parallel with it - can't see how the BEC's Lipo supply would be affected.

Something funny going on here.............bit like one of those IQ test questionswinklaugh

Any chance of a photo of the wiring? Gotta be something simple.

 

Edited By Cuban8 on 15/08/2019 17:33:04

Charles Aldous 115/08/2019 20:45:53
15 forum posts
1 photos

Hi Steve,

It sounds like that with the Emcotec off the signal line is being held either high or low and this is preventing the 620 from booting up. The only thing that I can think of that might solve your problem is using an opto ESC.

I'm no electrician, but what you say maybe is what is happening?

Hi Cuban,

1 Does the 620 work as it should when just powered from the separate CC BEC and Lipo?

Yes

2 Does it work correctly when powered from the Lipo/ ESC BEC but without the safety switch?

No, Not with the esc (signal wire only) connected

3 Does it work correctly when all connected up but without the RX connection to the ESC?

Yes

If the BEC is powered from the input of the safety switch i.e. in parallel with it - can't see how the BEC's Lipo supply would be affected.

It is strange and other Spektrun rx's work fine with this set up. With the rx connected to the esc, add power and nothing. Power up the rx, then plug in the esc then all good. So if the esc is connected to the rx when power is applied only to the rx the esc does not arm. When the safety switch is opened the esc arms and can be dis-armed and re-armed using the safety switch

Charles Aldous 115/08/2019 21:15:56
15 forum posts
1 photos

Hi Cuban, wiring diag below

I can work around this issue just by opening the safety switch, which allows the esc to arm and power up the rx, then close the switch for safety. Just don't understand why the esc prevents the AR620 from powering up until it sees power, when other spektrum rx's don't have this issue? 

20190815_210219.jpg

Edited By Charles Aldous 1 on 15/08/2019 21:32:49

Steve J15/08/2019 21:48:14
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1372 forum posts
41 photos
Posted by Charles Aldous 1 on 15/08/2019 20:45:53:

It is strange and other Spektrun rx's work fine with this set up.

The 620 and other recently released Spektrum receivers use a different processor to the older ones (Cypress discontinued the processor that Spektrum were using).

I would be tempted to see what happens with the positive connection between the Emcotec and ESC disconnected.

Steve

PS It may be worth having a browse through the AR410/620 topic over on RCG.

Edited By Steve J on 15/08/2019 21:56:15

Charles Aldous 115/08/2019 22:09:24
15 forum posts
1 photos

Thanks Steve. Disconnecting as you mention above made no difference, rx still only powers up when switch opened. I double checked that tha bec is live to rx when lipo connected1

I'll take a look at the link.

Charles Aldous 116/08/2019 00:17:45
15 forum posts
1 photos

Hi Andy,

Thanks for link. Take a look at reports 608/9 using the link you posted. I am assembling a Sebart Angel 50 which is pretty simiilar to the Mythos.

Regards Charles

Cuban816/08/2019 07:27:13
2641 forum posts
13 photos

Diagram is exactly as I expected & looks fine. Where you say 'signal wire only' presumably you mean the +ve ESC BEC supply is disconnected, leaving you with two conductors in the plug i.e signal and 0V into the throttle port (from which the RX would usually get its power from a BEC/ESC). Common ground running through the components, so shouldn't matter.

Have you tried removing the external BEC supply from the RX's battery port and supplying the RX via a spare servo port instead? These are normally all part of a single 'bus' common to all the servo connectors at the side of the RX, but there's something strange about the 620.

 

 

Edited By Cuban8 on 16/08/2019 07:40:33

Steve J16/08/2019 09:35:07
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1372 forum posts
41 photos
Posted by Cuban8 on 16/08/2019 07:27:13:

Where you say 'signal wire only' presumably you mean the +ve ESC BEC supply is disconnected, leaving you with two conductors in the plug i.e signal and 0V into the throttle port

Generally you don't need the ground wire between the receiver and ESC if you are using a UBEC. In fact, leaving the ground connected gives you a nasty fault path.

I have models wired in a similar way to Charles' sketch although I have a pair of bullets where he has the Emcotec. These bullets only get disconnected when I am messing about with the model in the workshop.

Steve

Nigel R16/08/2019 10:24:04
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2985 forum posts
471 photos

Emcotec is a solid state switch. I don't know whether it switches ground or positive or both. I'm presuming it is FET based as most such things are. There will be capacitance and high resistance across the switched connections when the switch is disengaged (i.e. ESC off). This may, depending on the ESC, produce an undesirable voltage level to be presented to the throttle signal connection. The 620 (and other same generation RXs) may well be verifying the voltage on each pin during powerup before it starts up in order to protect the RX circuitry, before it starts normal operation.

I would try removing the fancy dandy solid state switch from the equation, for the purpose of sanity checking several scenarios:

That is,

1

Lipo -> BEC -> RX

throttle signal wire only, connected to ESC

absolutely no other connection to ESC.

 

2

Lipo -> BEC -> RX

Lipo negative -> ESC

throttle signal wire only, connected to ESC

 

3

Lipo -> BEC -> RX

Lipo positive -> ESC

throttle signal wire only connected to ESC

 

 

Edited By Nigel R on 16/08/2019 10:25:39

Charles Aldous 116/08/2019 12:13:42
15 forum posts
1 photos
Posted by Cuban8 on 16/08/2019 07:27:13:

Diagram is exactly as I expected & looks fine. Where you say 'signal wire only' presumably you mean the +ve ESC BEC supply is disconnected, leaving you with two conductors in the plug i.e signal and 0V into the throttle port (from which the RX would usually get its power from a BEC/ESC). Common ground running through the components, so shouldn't matter.

Have you tried removing the external BEC supply from the RX's battery port and supplying the RX via a spare servo port instead? These are normally all part of a single 'bus' common to all the servo connectors at the side of the RX, but there's something strange about the 620.

Thanks.

Signal wire only, otherwise esc arms, by-passing safety switch....this set-up works fine with older type spktm rx's.

Have tried sparate pack to supply rx and esc arms normally.

Edited By Cuban8 on 16/08/2019 07:40:33

Charles Aldous 116/08/2019 12:37:12
15 forum posts
1 photos
Posted by Nigel R on 16/08/2019 10:24:04:

Emcotec is a solid state switch. I don't know whether it switches ground or positive or both. I'm presuming it is FET based as most such things are. There will be capacitance and high resistance across the switched connections when the switch is disengaged (i.e. ESC off). This may, depending on the ESC, produce an undesirable voltage level to be presented to the throttle signal connection. The 620 (and other same generation RXs) may well be verifying the voltage on each pin during powerup before it starts up in order to protect the RX circuitry, before it starts normal operation.

I would try removing the fancy dandy solid state switch from the equation, for the purpose of sanity checking several scenarios:

That is,

1

Lipo -> BEC -> RX

throttle signal wire only, connected to ESC

absolutely no other connection to ESC.

2

Lipo -> BEC -> RX

Lipo negative -> ESC

throttle signal wire only, connected to ESC

3

Lipo -> BEC -> RX

Lipo positive -> ESC

throttle signal wire only connected to ESC

Edited By Nigel R on 16/08/2019 10:25:39

Thanks NIgel and I think you are on to something regarding the capacitance etc.

I am not overly electrically savvy but the set-up I use works flawlessly except with this new AR620. The AR620 works fine with the safety switch once the esc has has been powered up by releasing the switch and then can be isolated again with the switch. I have tried most or all of the permutations you kindly suggest but will re-visit later. See link below for tech specs etc of switch

http://wiki-en.hacker-motor.com/index.php/SPS_SafetyPowerSwitch

Nigel R16/08/2019 13:35:42
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2985 forum posts
471 photos

Charles

reading the page you link, something immediately jumps out:

"Therefor the minus pole can be bypassed with an external power resistor."

and the caution at the end of the page:

"CAUTION: There must not be an electrical connection between the drive battery's minus pole and the receiver respectively the receiver current supply! When using some telemetry sensors this ground connection is made by the sensor respectively by its electronic. So the receiver can be damaged. When using such products the usage of the SPS SafetyPowerSwitch is not possible"

This is almost where you are at, I think.

These two statements on the information page, imply to me that only the negative connection is switched. No particular issue there.

However. This would infer that the positive connection from lipo to ESC is permanently in place and that part or all of the ESC could be at the positive voltage of the lipo. If the BEC ground output seen by the RX is markedly lower, and if the RX is checking that the signal terminal is within 0V to 5V (i.e. inside its own supply voltage), that check would fail under this circumstance. This is not a great place to be, electrically.

I would try using this negative bypass resistor. A 10W 470ohm resistor is not expensive.

Edited By Nigel R on 16/08/2019 13:39:04

Edited By Nigel R on 16/08/2019 13:48:38

Charles Aldous 117/08/2019 13:19:17
15 forum posts
1 photos
Posted by Nigel R on 16/08/2019 13:35:42:

Charles

reading the page you link, something immediately jumps out:

"Therefor the minus pole can be bypassed with an external power resistor."

and the caution at the end of the page:

"CAUTION: There must not be an electrical connection between the drive battery's minus pole and the receiver respectively the receiver current supply! When using some telemetry sensors this ground connection is made by the sensor respectively by its electronic. So the receiver can be damaged. When using such products the usage of the SPS SafetyPowerSwitch is not possible"

This is almost where you are at, I think.

These two statements on the information page, imply to me that only the negative connection is switched. No particular issue there.

However. This would infer that the positive connection from lipo to ESC is permanently in place and that part or all of the ESC could be at the positive voltage of the lipo. If the BEC ground output seen by the RX is markedly lower, and if the RX is checking that the signal terminal is within 0V to 5V (i.e. inside its own supply voltage), that check would fail under this circumstance. This is not a great place to be, electrically.

I would try using this negative bypass resistor. A 10W 470ohm resistor is not expensive.

Edited By Nigel R on 16/08/2019 13:39:04

Edited By Nigel R on 16/08/2019 13:48:38

Hi Nigel,

Many thanks for this latest post which sounds the likely diagnosis. I'll check this out further when back home end of next week. Would you have a link to a suitable resistor please and how I should connect it?

Much thanks to the other contributors on this thread and I'll advise outcome in due course.

Regards Charles

Steve J17/08/2019 13:43:34
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1372 forum posts
41 photos
Posted by Nigel R on 16/08/2019 13:35:42:

A 10W 470ohm resistor is not expensive.

10W seems excessive. If you stick 470 ohms across a 6S LiPo you are only looking at 1.5W.

Charles stated earlier that removing the connection between the SPS and ESC didn't solve the problem.

This topic has made me have a look at this device from Emcotec and I must say that that I really don't see the point in using one. Program a kill switch on your transmitter and mechanically stop the prop from rotating while you are putting the battery in and taking it out.

Steve

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