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Member postings for Mike Blandford

Here is a list of all the postings Mike Blandford has made in our forums. Click on a thread name to jump to the thread.

Thread: Lipo charging
13/09/2018 22:09:57
Posted by Dave Hess on 13/09/2018 13:45:57:
I can't see any inductors to smooth the PWM. I can't see a reason to do that anyway because charging lipos doesn't need a smooth voltage. The inductor at the other end of the PCB looks like it's part of the buck converter circuit to raise the 12V high enough to charge a 6S battery - probably something like 25V.

The chargers I have use the inductor in both buck and boost modes, converting the supply voltage to that required to charge the battery. They operate using the charge current to regulate the output voltage that is controlled by the PWM mark-space ratio. The PWM frequency used is sufficiently high that the inductor, with the associated output capacitor, produces quite a constant voltage/current, in the same way any switch mode power supply works.


Thread: What gauge wire
09/09/2018 22:13:12

A bit difficult to see exactly what those waveforms are showing, and they don't look much like the ones I got on my digital storage 'scope, where I could capture and "freeze" them.

The ESC outputs are square wave voltage, and the non-driven wire shows a sinusoidal feedback voltage. The current is likely to be reasonably constant as the inductance of the motor tries to keep the current flowing, and the parasitic diodes in the MOSFETs provide a current path.


09/09/2018 17:29:01

The motor, as you have said, includes inductance, in the same way a switch mode power supply uses an inductor. When operating a switch mode power supply in step down mode, the current in the output may be higher than the current in the input, the power in each is the same (except for losses). The same can happen with a brushless motor.

I've just put my 'scope on the wires to a motor. The pwm frequency remained fixed. The outputs to the motor followed a sequence of 6 "phases".

"A" at supply voltage, "B" pulsing low, "C" not driven.
"A" at supply voltage, "B" not driven, "C" pulsing low
"A" not driven, "B" at supply voltage, "C" pulsing low
"A" pulsing low, "B" at supply voltage, "C" not driven
"A" pulsing low, "B" not driven, "C" at supply voltage
"A" not driven, "B" pulsing low,, "C" at supply voltage

On the wire that is not driven, you can see a sine wave, which is the induced voltage in the undriven winding.

(OK, a sample of size 1)

This is as I described.

BTW Kirchoff;s law is for a "node" not a circuit.


09/09/2018 14:40:32
Posted by Focae on 09/09/2018 10:05:14:

Mike, the output current can never exceed input current. A certain gentleman named Kirchoff determined that in one of his Electrical Laws. ‘The sum of the output currents must equal the input current’. You will also never have the same current in two legs of the motor wiring. Outrunner motors are essentially three phase ac motors. The rotating field is created my rapidly switching dc to the legs in turn. The voltage and therefore current in these legs will never be instantly at the dc voltage because the motor windings, being inductors will cause the voltage to rise relatively slowly creating a sinusoidal wave in each leg. Because the windings are 120 degrees apart, you never have all of the current in one leg being opposed by an equal and opposite current in another and you can never have all of the current flowing in one leg. Also consider this, how thick are the wires that form the winding? They are essentially just a continuation of the wires that connect them to the esc. If you did have all off the current flowing in one leg for longer than the ‘average’ switched time, the smoke escapes, usually at the winding because it is thinner than its supply wires.

"the output current can never exceed input current" No, but there are capacitors on the ESC input that provide the "extra" current for the current pulses.

"Outrunner motors are essentially three phase ac motors" No, they are DC motors with electronic commutation.

The ESC connects one of the three motor wires to the positive supply, a second to the negative supply and reads the induced voltage on the third wire to time the commutation.

Yes, the inductance will limit the current rise, but actually sufficiently slowly that the current is essentially constant.

"you never have all of the current in one leg being opposed by an equal and opposite current in another" Yes you do as it is a DC motor, I just described how the commutation is done.

"how thick are the wires that form the winding?" About the same thickness as the wires from the ESC. You may look at the windings and see quite thin enammelled wires, but, for ease of winding and to get more copper in place, the windings are made of multiple, parallel thin wires.


Thread: Horus X10S with Spektrum receivers
09/09/2018 10:09:23

The "patch" is actually to flash the multiprotocol firmware to the module. I created the changes to the multiprotocol firmware so it compiles and runs on the Orange module.

Instructions are available here: **LINK**

The power output may be adjusted in the multiprotocol firmware, the default is +4dbm from the RF chip, then amplified by power amplifier. The RF chip may be set to 0dbm if required.

With the bootloader on the module, you are ablue to then flashit using a FTDI type device, and on sme transmitters you may flash directly from the Tx using a file on the SD card. At present the X10(S) is not one of those as I've not got one so haven't ported ersky9x to it. On transmitters that do run ersky9x, I have added a feature to the Tx bootloader that lets you run an "app". If you are running openTx, you may replace the bootloader with the one from ersky9x, then you get this feature. One of the "apps" available is the one to flash the multiprotocol module.


Thread: What gauge wire
09/09/2018 00:19:22
Posted by Focae on 08/09/2018 09:41:05:

The output wiring from the ESC to the motor does not have to be the same wire size as the input wiring from the battery. The input wires have the continuous current.....the output wires have a switched load so the current is less. . . .

I'm not sure I agree with this!

Suppose that at full throttle you have 30A in the input wiring.
Now you have 3 wires going to the motor, let us call then A, B and C.
For a third of the time you have 30A going out on A and in on B, the next third of the time you have 30A out on B and in on C and the last third of the time you have 30A out on C and in on A.

Yes, the average current in each wire is less, but the current, when it does flow is the same as in the input wiring.

Now suppose you reduce the throttle to have only 15A in the input wiring. The ESC has done this by only driving the output for part of the time. I think you will find you actually have 30A out on A and 30A in on B, but for only half of the first third of the time, and similarly for the other 2 thirds of the time. So the output wires are actually carrying more current than the input wires!


Thread: Horus X10S with Spektrum receivers
08/09/2018 20:13:03

The openTx team are NOT supporting this Tx. The firmware on it has been forked from openTx 2.2, then has a few small changes applied to it. The hardware is a (cut down) copy of the FrSky QX7, with the rotary encoder replaced by buttons, so is running a near copy of the QX7 firmware. The firmware will have been compiled with whatever options Jumper have chosen, you don't get to choose as you do when downloading "official" openTx.

Basically, it seems, Jumper are simply copying the QX7 and the multi-protocol project, both of which support open source firmware. The T12 doesn't add anything that existing radios don't already do.

From a post of mine on RCGroups:

"The patch to openTx is very simplistic, and doesn't have all the conditional compilation needed for the T12 to become another supported Tx. Much more would need to be done, including adding support in Companion, for proper support.
They have basically cloned the FrSky QX7 CPU connections, but left out the rotary encoder and "mapped" four navigation buttons onto the encoder code. This has the unfortunate effect that the "up" button moves up through menus, but then decrements values. There is also no acceleration of changing values, so large changes take a long time. It really needs the buttons handling in the same way as those of the 9X/9XR/9XR-PRO.
I have a T12, supplied for me to port ersky9x to it. I note the following:
1. It is physically quite small, I don't find it comfortable to use (pinching the sticks, not thumbs).
2. There is no momentary switch.
3. The pots on the sides have a lot of movement from end to end, you need several "goes" to move them fully.
4. No SD card was included.
5. The battery bay is sized for 4, AA cells, any LiPo/LiFe battery needs to be quite small to fit. No battery is included. I'm currently using a 2S 1000mAh LiPo, which just fits.
6. On my Tx the audio output is very "tinny". I tried playing some "background" music and it was quite unpleasant! This may be specific to my Tx of course.
7. The display is quite small about 4.8cm diagonal compared with 7.4cm of the QX7. The backlight is not very even.
8. I found the stick spring tension very low, and the throttle friction very weak. I did open the case and use provided adjustments to increase these, but I still find them weak.

The 4-in-1 module included uses the USB port with a USB-to-serial chip inside. This means the USB bootloader doesn't work. The module also has the incorrect chip for the serial inversion (00 instead of 86). This means it only works with inverted serial, and the "Flash from Tx" method has to use inverted serial."

The firmware is likely to be confusing as it includes support for things that are not present, e.g. settings for an internal RF module and haptic.

I do have ersky9x ported to this radio, and will be supporting it, but, as I did with the Turnigy 9XR-PRO, support for the FrSky 'X' receivers and SPort telemetry is disabled unless Jumper reach an agreement with FrSky that these may be included.

From another post of mine on RCGroups:

"A general comment regarding the multi-protocol module. Transmitters use a "unique ID" that is used when binding. Manufacturers produce their own transmitters so that this is unique to each Tx.
The multi module, in most cases, uses a randomly generated ID, so you don't have any guarantee that your Tx doesn't share the same ID as another Tx, either from a manufacturer or another multi module.
DSM protocol is different as it uses a unique value from the actual RF chip, so is guaranteed unique."


Edited By Mike Blandford on 08/09/2018 20:17:31

Thread: Hello
02/09/2018 13:59:07
Posted by Bob Cotsford on 02/09/2018 13:12:05:

Mike, doesn't LBT only affect D16 protocol use?

Yes, but as I said, you may find you cannot select the D8 protocol, particularly on an internal module in a FrSky transmitter.


02/09/2018 13:09:36
Posted by john stones 1 on 02/09/2018 12:22:39:

XJT..can support can support V+D rx's If flashed with non EU firmware, is it this problem ?

I think that is incorrect. The XJT supports 'D' and V-II" receivers whether it has EU LBT firmware or international firmware, I just double checked by binding a LBT XJT to a D8R-II.

Where there may be a confusion is on FrSky transmitters running openTx (and possibly FrOS), if the Tx itself (not the module) has EU firmware, then the 'D' option is not available for selection in the menus.


02/09/2018 12:22:24

You need to link the channel 1 and 2 outputs of the Rx, then power it on. I think the LEDs should not be flashing at this stage.
With the module on the Tx with SW1 on and SW2 off, power on while holding the bind button pressed. The red led should be flashing and the module beeping.
The bind to the Rx should then take place, and the Rx LED(s) should then flash to indicate this has happened.

Now power both Tx and Rx off, then back on, you should then have control.


Thread: See if you can help me with this
30/08/2018 11:45:58

Posted by David Davis on 30/08/2018 07:19:57:. . . I started to dismantle the motor but found that I could only undo one of the grub screws. Whatever I did, including dressing the end of of an Allen key to ensure a better fit, just resulted in the tool turning round in the grub screw without moving it. . . .

For now, you shouldn't need to undo the grub screws. At the "other" end of the motor you should see a circlip. Just remove this, then the whole "bell" and shaft should slide out. Because the magnets are very strong, you will need to pull quite hard. Be careful when replacing the bell and shaft, the magnets pull everything together very firmly, make sure fingers etc. cannot be trapped.


29/08/2018 18:52:38

I disagree regarding to using the motor power rating. You should use the motor CURRENT rating as the limit. Regardless of the voltage, the heat generated in the motor is current squared times the winding resistance. Exceed the current rating and the motor will overheat.
Note also that many motors show a "headline" current limit, but closer inspection reveals this is limited in duration (often 10 or 60 seconds). Look for the continuous current rating.


28/08/2018 19:01:31

An electric motor is driven by the current, not the voltage. A larger prop needs more current then a smaller one at the same RPM.

Giving a motor a voltage specification is a bit arbitrary, it is the current that really matters, in particular the maximum current. If you are using a 3S battery, and are at the maximum allowed current, then going to a 4S battery requires you to fit a smaller prop to keep the current at that value, however, since power is voltage times current, you will have more power.

When a motor rotates, it acts as a generator (its called an alternator in your car!). Specifically, if say the kv of a motor is 900, then it means if it rotates at 900 RPM, it generates 1 volt. This happens even if the cause of the motor rotating is a battery. So, if you apply 10 volts to this motor, it will rotate at 9000 RPM (with no load). In practice there are some losses so the motor will rotate a bit slower. If you put a load on (fit a prop), the motor will then run slower.


Thread: Please Help Me Out With The Arithmetic On This One Gentlemen!
22/08/2018 18:47:04

The limiter, according to the rules I just read, is set for 1750W-mins, so that 40 second power was running at around 2.6kW. On 10 cells, this is 75A, and less than 1Ah. I note that F5B people mention they are sometimes running at 100C discharge rate, and using pre-heated batteries (to reduce internal resistance).


21/08/2018 12:47:10

I tried to find some data on the specified motor, but it has been supersceded by a PO-3547-800. That motor is specified as having a maximum current of 29A continuous (36A peak for 10 seconds).

The original question described a flight of 2 minutes cruising followed by 4 minutes of full power, after which the battery (2200 mAh) was "flat".

Such a battery could (theoretically) provide 2.2A for 60 minutes, which is only 33A for 4 minutes, so I reckon the motor is only taking around 25 to 28A (at full throttle), which would be appropriate for the specification of the replacement available. The Ammeter the OP shows could, at least, give an indication if this is what is happening in practice.

Personally, I doubt the motor is really an 800W motor, other purple power motors of the same size, but different winds, have ratings of 710W and 580W. I would also suspect these ratings are at the peak current specified, so are only for 10 seconds anyway.

My take is the OP needs full power for 5 minutes, and, perhaps 4 minutes at "cruising" power. I'd estimate cruising power would be around 10A (from my telemetry log files where I have flight pack voltage and current logged).

4minutes at 10A is 40 Amp-minutes. 5 minutes at 25A is 125 Amp-minutes, a total of 165 Amp-minutes. 265/60 gives 2.75 Ah so a battery of 2800 mAh should be OK, I'd use 3000 or 3300mAh as the higher capacity may well have a lower internal resistance, so providing a higher voltage (and hence higher current) at full throttle.

I would also recommend checking what the maximum current rating of the motor actually is.


Thread: Power Safe for any receiver
19/08/2018 13:19:03

Try these (should be available with different number of connections) **LINK**

Preci-Dip part 801-87-036-10-001101 is a 36 way version where you may "snap off" however many connectors you need. Clearly, these may be available from elsewhere (found them at Digikey as well as Farnell).

I measured the (square) pins on a FrSky Rx (X8R) as 0.6mm (digital caliper), and the pdf file for these shows 0.635 as the square pin size that fits. For round pins it shows 0.7mm to 0.9mm. 0.635mm square is 0.898mm across the diagonal, so I reckon a 0.5mm square pin (diagonal 0.7mm) would also fit, so should be fine for 0.6mm.


Edited By Mike Blandford on 19/08/2018 13:19:35

Thread: Stabilisation
18/08/2018 19:57:16
Posted by Robin Mosedale 1 on 18/08/2018 18:21:12:

This confused me Mike until I realised that they only work with FRSKY tx's.

See the opening post

Posted by Mike Blandford on 18/08/2018 14:38:08:

For FrSky, the S6R and S8R stabilising receivers are only a couple of pounds more than the X6R and X8R. You may configure them with the stabilising function turned off, so I reckon you might as well always get them.

They may be configured from the Tx (assuming you are using ersky9x or openTx).


It was aimed more at BEB!


18/08/2018 14:38:08

For FrSky, the S6R and S8R stabilising receivers are only a couple of pounds more than the X6R and X8R. You may configure them with the stabilising function turned off, so I reckon you might as well always get them.

They may be configured from the Tx (assuming you are using ersky9x or openTx).


Thread: Finding records of WWII service men.
17/08/2018 12:39:19

Definitely look into getting his service record. My wife got those of both her parents and I got my fathers record. It will probably cost £30.

They can make interesting reading, although sometimes the writing is difficult to read and you need to look up acronyms!


Thread: Power Safe for any receiver
17/08/2018 12:28:06

Very nice and a good idea.

A thought on Rx brownouts. You could use a schottky diode feeding the power to the Rx, then include a (large value?) capacitor on the Rx side to keep supplying power to the Rx if the power rail does dip.

As always, adding this makes everything larger and more complicated, but may be useful if you are concerned about brownouts.


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