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Member postings for Chris Bott - Moderator

Here is a list of all the postings Chris Bott - Moderator has made in our forums. Click on a thread name to jump to the thread.

Thread: Build your own telemetry sensors.
26/05/2019 13:33:17
Posted by David Tayler on 26/05/2019 09:36:50:

Thanks for the project I am gradually getting my head round it. One last question is there a cheap airspeed sensor available?


I'm not sure about cheap but I think this is the sort of thing you're looking for.

26/05/2019 10:10:16

You have the Cells voltage showing the total of all cells.

To see individual ones you need to add calculated sensors.


Add a new sensor

Type: Calculated

Formula: Cell


Then chose which cell or just lowest, highest or delta.


Note: Cells will only show up when a battery balance connector is connected.

Edited By Chris Bott - Moderator on 26/05/2019 11:31:09

22/05/2019 13:02:47

Hi Michael and welcome to the forum.

Have a look at this thread where two of us have built these and used a 4258 sized 500kv motor.

We both use a 15x10 prop. Danny runs his on 5S 5000 lipo I use 6S 4500.

My ESC is an 80A unit.

(Oh by the way, in case you didn't know, using all capitals in a forum post is generally considered shouting).

Thread: Build your own telemetry sensors.
21/05/2019 22:18:56

It is confusing isn't it? That's probably the hardest thing in OpenXSensor.

Once you've worked out that V1 to 6 can use any of the analog arduino pins A0 to A8, and you have to exclude the ones that are for current measuring and for SDA/SCL when using the likes of pressure sensor, GPS etc, then you start to get to grips with it.

Then FrSky label their analog voltage parameters A1 to A4, their LiPo pack volts VFAS etc. etc...

20/05/2019 15:41:43

Mike I've confused myself again (easily done these days).

I've knocked one of these up just to measure two different receiver packs and altitude.

It's all working fine, I'm using A3 and A4 for the Rx packs with 1K to ground and 4K7 to voltage in the dividers.

Except - A3 and A4 are both reading 10x it's respective Rx pack voltage.

I have #define REFERENCE_VOLTAGE 3422 as that's what that measures.

Is there anything odd about A3 & A4 that you know about?

Hopefully it's just a silly mistake I've made.

20/05/2019 15:06:24

Ideally change it to whatever's measured on TP1

20/05/2019 12:50:21

Hi Andy well done!

Your soldering looks good and you've heeded the advice to solder direct to the ACS758. So all should be good.

Do I detect that the device is a 50B version? That's a maximum 50Amp bi-directional device.

The spec sheet says that that one has the same mV/A sensitivity as the 100U I've used, but the voltage at zero current is nominally half supply volts. This probably accounts for your current offset.

It's valid to fix this in the transmitter settings, but obviously you'll have to remember this if ever you set up another model to use it.

Checking readings against a wattmeter would be a very good thing to do, in my opinion.

20/05/2019 11:28:11

A new batch of boards has turned up.

I think we've exhausted demand, but these are here should anyone want any.


19/05/2019 20:28:29

So the max current this sensor can measure must be:


i.e roughly (3300-400)/26.4 = around 109A

The ACS758-100U has a 100A limit so that adds up.

I'd suggest that the limiting factor is in fact the quality of our soldering between wires and the ACS758.

19/05/2019 19:59:35

Indeed it is, thanks Mike I'm so glad you're watching. All of mine are 26.4. As are the settings in the RCM&E article.

In fact, the article describes all the above settings.

19/05/2019 18:49:59

For the current measurement then measure the voltage ,with a multimeter, between Gnd and TP1. Measure when no current is flowing.

Enter this figure (in millivolts) into the #define MVOLT_AT_ZERO_AMP line (config advanced section 6.5) and start with the number 26.4 40 in the #define MVOLT_PER_AMP line.

To calibrate further you could measure the voltage between Gnd and the 3v3 test point.
Enter this figure into the #define REFERENCE_VOLTAGE line (e.g. #define REFERENCE_VOLTAGE 3300).

Mikes formula above should give a more accurate current reading.

NOTE: All this calibration is only as accurate as your multimeter.

For some of mine I've measure all the resistor values and entered those in the appropriate slots in the config advanced file.

Edited to correct 40 to 26.4 - thanks Mike.

Edited By Chris Bott - Moderator on 19/05/2019 20:00:35

19/05/2019 17:55:58

Hi Andy.

One thing at a time, VFAS should be reading the full voltage of your battery.

As Mike's example above shows you need the line in config basic to be


This tells it to use the pin 6th along the list defined in the config advanced

#define PIN_VOLTAGE 0 , 1 , 2 , 6 , 8 , 7

i.e. pin A7.

It then also uses the resistor values 6th along their respective lines. i.e. 18 and 2.7. (or 18000 and 2700) if those are the resistor values you've used for R2 and R3 on the PCB.

18/05/2019 13:14:39

Ooh just noticed VFAS is showing 4.16V so we need to fix that when we have time. My guess is that that one is pointing at the wrong A pin, as well.

18/05/2019 13:11:11

Hi Andy that looks great, well done.

Just off the top of my head - it looks like you have configured Curr to work so that's good. I can't check right now but is there somewhere in either of the config files to set which pin reads current? That needs to be A3. or 3.

On the hardware side have a good check for solder whiskers that could be shorting the current chip's output or A3 input to Gnd. You could check for this with a multimeter. Or, is there a connection break between current chip and the filter resistor, or between filter resistor and A3?

I'm out for the afternoon but if the above doesn't help we can dig more deeply later. Ooh one more question. When passing current do you have the lipo connected to the wires at the top of your photo and your load (ESC/Motor) connected to the wires exiting the left of your photo?

Thread: Anyone for a Tiffie?
18/05/2019 00:00:13

Trevor I'm glad to see this progressing. Keep up the good work.

The only IT advice I can suggest is to try taking a photo with the iPad held the other way up to usual. Yes I know it rotates on the iPad screen but I've always wanted to know if doing so would help on here.


Thread: Suggestions for vintage model
17/05/2019 14:32:01

There's a few pics of my Matador on this thread page Jon.

Great relaxing fun on a Frog 150. No throttle and sometimes flown proper push button single channel.

Thread: Build your own telemetry sensors.
17/05/2019 07:18:01

Thanks Mike for the very constructive comments. I fully expected all of these points to come out in the discussion here. (Maybe not in a single post though).

As explained in the article, this has been the story of my experiments and I explained that there are many other ways to build up an OpenXSensor. The PCB was just supposed to be one example and I'm learning massively as I go there too. This forum can be so useful.

I've been taken very much by surprise by the interest, in the PCB particularly - 66 have gone out to date.

I did wonder about the ground wire to and debated with myself about whether the accuracy of voltage measurements might be affected if the reference connection relied on the black wire in the telemetry signal connection, via the Rx and the black in the throttle channel back to the ESC. Having said that my prototypes (pre PCB) didn't have that wire direct to the black power cable and they did work fine. What I hadn't done is consider that a small portion of the current between battery and ESC might flow that way. I might even try measuring that current, if I get a minute.

Thread: FrSky Neuron ESC
16/05/2019 15:13:08

That's very interesting Mike.

On the surface that appears very similar but not exactly the same as the old FrSky FUC-1 programmer for the old D8 modules and receivers which when it turned up came with FDD-Lite printed on the back.

You could then turn it into a upgrade tool for smart port devices by adding a FrSky SPC which turned 4 wires into 3 and as far as I can see only included a diode but not your pull up resistor.

Thread: Seagull 80" DH Chipmunk
15/05/2019 11:26:37

From last night.

My caption - "Beware ailien invasion force masquerading as 1940s training aircraft".


Thread: Twin ic throttle mixing
15/05/2019 08:20:34

Don't forget to set and test failsafes. I've no idea about Futaba but some other receivers have different failsafe outcomes for throttle channel to all other channels.

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