Devo 10 nasty failure: solved HTH

On the Walkera DEVO 10 Devention WK-DEVO10

the shafts of the AUX4 and AUX5 pots are electrically connected to their wipers.

Since the endpoints of the pots are connected to GND and V+ (3.3 volts), twisting one to max and the other to min sets up the possibility of shorting V+ to GND. Twisting either above min means there is a potential between that shaft and any GND. At max, again a possibility of a short to any available ground.

Since the Devo 10 enclosure is plastic this is not (usually) a problem. Never mind how it did become my problem, but it took me a longer than I want to admit to suss out.

I do not know if this is the design of the potentiometer or a failure mode. In either case it is not like any potentiometer or failure I have ever seen, hence not anything I was looking for and was quite surprised to finally find it out.

I present it here in case it can help or prevent problems that any of you might experience, weird and capricious and intermittent, the kind that can reduce confidence and make one reluctant to use the Devo 10 to control 100s of grams of quadcopter going 10s of meters per second.

I also ask those who are more familiar with these fora to suggest any other place I might stick this that might help someone poking around desperately.

I posted this identical message on rcgroups on the H8 Mini Acro firmware thread, just because that's where I've been hanging.

There is some good news, in a way: convinced my Devo 10 had become possessed, I ordered a Devo 12e and a 4in1 as a replacement for my now > 2 year old bruised battered and well worn Devo 10. Now I guess the 12e will be a spare or a gift one day.

crash7X

FDR wrote: …

I'm still interested in knowing how did you managed to short the housing to ground.

Longer story then:

The shafts of the AUX4 and AUX5 pots are electrically connected to the wipers.

The shafts are not insulated from the mounting nuts.

The pots are each on a small aluminum dial plate which carries the name and range graphics on a decal of some kind.

So.

When I drilled a hole through the dial plate and the plastic case in order to mount an SMA connector for yet another radio for my deviation I introduced the possibility of a short circuit.

I say introduced because for some great number of months the problem never was. A problem. Evidently the decal on the dial plate afforded sufficient insulation.

The first time I saw the problem was when I was calibrating the transmitter joysticks and pots. Curiously, if I turned AUX5 up slowly to maximum there was no problem. But if I turned it up rapidly the transmitter powered itself off.

I will spare you many frustrating tests and not tell you how many times I opened and closed the case before figuring it out. I lost count.

After a while, turning up AUX5 no matter the rate would cause the short circuit. By this time I suppose I had worn out the decal insulation.

You can see my solution, which was to cut a small strip into the dial plate separating the pot from the SMA connector.

My Devo 10 is an older model, the dial plates are quite large. I see now that the aluminum plates are quite smaller and wouldn't have caused my problem. I think they are still probably "active", I bet cranking AUX4 up and AUX5 down one could measure 3.3 volts if he was to scratch a bit through the decal.

I did also get to know more than needed about the power supply of the Devo 10. Oddly the massive ON/OFF switch is really a "soft" switch, I believe I saw a schematic of it on this website. In any case, I can tell you it survives many short circuitings of the 3.3 supply rail to ground…

crash7X

You can do a test without "going in".

Remove the knobs and crank the pots to opposite extremes and look for any voltage from one shaft to another. This would demonstrate the connection or lack thereof between shaft and wiper.

I cannot imagine that they rely on the decal insulation, so the pots must be different in that way OR mounted with an insulating collar of some type.

Surely if they were Devo 10 style many users would have run into real problems - just tightening the mounting nuts would scratch through the decal and allow the aluminum to conduct sooner or later.

I'm just glad I discovered this in the lab and not in the air.

As I said, I'll have my own Devo 12E and have my own look!

BTW as a sanity check I looked at every potentiometer I have in my parts drawers. Plastic shafts or no connection to metal shafts, except in the case of trimpots where it is obvious that the wiper is connected to, say, the screwdriver slot used for adjustment. One more reason to have a plastic tweaker.

c7

The postman delivered my 12E this day. Also in the same delivery was a 4in1 module I had ordered at the time of panic when I thought my Devo 10 had become unreliable.

I let the package warm up, it was -10 C here this day. Then I got out the 12E, put in a set of AAs and did this test:

Using any two of the AUX pots, crank one to max and the other to min. Then measure the voltage between their knobs' respective grub screws.

There is the 3.3 nominal V+ present, so these pots are the same as the Devo 10, that is the shaft and mounting bolt are electrically connected to the wiper.

It seems that the 12E dial plates are entirely plastic, so I don't think this will be a problem. Nevertheless, it is something to know just in case. In particular if you have the knobs off.

I may sell or give away the 12E before or after I install the 4in1. Or just use it and demote my good old Devo 10 to spare status. I may in that case have to do something about its blinding whiteness - I am sure in my grubby grippers it will look pretty sad fairly quickly.

crash7X

Discovered this when i installed an nrf24lo1 module and had to drill out a hole.

When i connected everything back up radio worked as normal until i moved the aux knob i had moved and the tx crashed display went blank. Quickly found the issue.

Remove the metal strip. Problem solved

Just wanted to chyme in that I sort or went through the same situation when I fried a surface component on my Devo 7e. In a fit of panic I immediately ordered a Devo 10 with 4in1(to avoid the complicated task of trying to mod a 7e all over again..)
Now my new Devo 10 is in the mail and After picking through forums a whole bunch I ordered the part I hopefully need to fix the 7e..
I don't know if I regret the purchase of the 10 yet or not, I guess if the 7e does not get revived I will be happy with the purchase, otherwise I guess I'll have 2 deviation controllers with 4in1 modules. Guess it will be time to add some more models to my collection!
Cheers!

I may sell or give away the 12E before or after I install the 4in1. Or just use it and demote my good old Devo 10 to spare status. I may in that case have to do something about its blinding whiteness - I am sure in my grubby grippers it will look pretty sad fairly quickly.

crash7X

Hey, crash, are you still thinking about selling it? If so, I'm interested! Sent you a PM about it.

I am hanging on to the 12E for now. I looked over at ucdrone.com and they have it for $99 but (or and!) that includes a receiver.

It was once possible to unselect the receiver and get just the transmitter, $85. I wrote to ask why they no longer do that or if it was some switch or page I was missing.

c7

Alright, thanks!