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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: Who wants a Warbird Replics Hurricane?
30/09/2017 16:59:32

Anybody else building at present?

In the absence of any replies to my questions, I'll use 3.0 inch wheels.

I'm looking at the wings now. The outer panels have a slot cut lengthways in them. Is this the line to cut fully for the Ailerons, and then take the torque rods?

The plan shows ailerons a bit narrower than these slots give, but then the panels also taper a bit more than the plan shows.

Mike.

Thread: Understanding Watt Meters
28/09/2017 20:15:34

"Lower kv motors have more winds of thinner wire with greater resistance. You can't win".

You potentially win by lower losses, due to lower current, all the other wiring, the ESC and the battery. Also, if you can use a physically larger motor, then you get the extra windings without needing thinner wire. A larger motor may well be only 30 to 40gm heavier, but everything runs that much cooler, and with some aircraft you need the extra weight in the nose anyway!

Mike.

28/09/2017 15:20:09

"Multiplying the amps by the generated voltage to get the output power is surely just measuring the heat generated again, not the mechanical turning force?"

The mechanical turning force (torque) is directly proportional to the current flowing.

The generated voltage (dynamo/alternator effect) opposes the current flow. We are forcing the current against this voltage, so there is no heat generated by this, it is exactly the mechanical power. The heat is generated in the windings, and the amount is the difference between the generated voltage and you battery voltage, multiplied by the current.

A "perfect" motor would have zero resistance in the windings (and no mechanical losses!). In this case, if you apply 12V to a motor with a kv of 1000 rpm/volt, the motor will run at 12000 rpm. It will be generating 12V to oppose the applied voltage.

A "real" motor is a "perfect" motor with a resistor in series. In my examples, the motor has a resistance of 0.066667 ohms. With 30A flowing, this resistance drops 2.0 volts, so the "perfect" motor sees only 10V, so spins at 10000 rpm.

Yes, you do need to measure the motor rpm to obtain the generated voltage (called back e.m.f.).

With all motors, in one respect current is your enemy, unfortunately you need current to generate torque!
Losses due to current flowing are proportional to current squared, double the current then you get four times the losses. Where possible, it is better to use a motor with a lower kv and use more cells at a lower current.

Mike.

27/09/2017 15:44:14

A motor has a "kv" value (rpm/volt). What this specifies is the voltage the motor generates when turning. So, if you have a motor with a kv value of 1000 rpm/volt, and it is turning at 10000 rpm, then the motor generates 10 volts (acting like a dynamo).

When the motor has a voltage applied to it to make it turn, the motor still generates this voltage, which is in the opposite sense to the applied voltage. The mechanical output power, in watts, is simply the current flowing multiplied by this generated voltage.

There will also be some mechanical losses. These may be estimated by finding the current taken by the motor when it runs without a load (propellor in our case). The mechanical losses are aproximately the no load current multiplied by the generated voltage.

Here is an example, take a motor with a kv of 1000. Test it with no load (or use the manufacturers sepcification) to find the no load current. Let us assume this is 2 Amps.

Now we run the motor with a load. A wattmeter shows an input voltage of 12V and a current of 30 A giving an input power of 360 Watts. The motor is also measured to by running at 10000 rpm, so is generating a voltage of 10 volts.

Of the 30A, 2A is overcoming the mechanical losses, so 28A is left providing the output power. The output power is therefore 28A multiplied by 10V (generated voltage) or 280 Watts, at an efficiency of about 78% (280/360).

2A (no load current) times 10V (generated voltage) is 20W so this is the power loss due to mechanical losses.

Of the 360W going in to the motor, 280W is useful output power, 20W is mechanical losses leaving 60W as electrical losses. This value may also be calculated by (applied voltage-generated voltage) mutiplied by current = (12-10)*30 = 60.

Most of this is heat in the windings of the motor.

Suppose we load the motor with a larger propellor so it only spins at 9000 rpm. The wattmeter now shows 12V (what a good battery I'm using!) and 45A, so 540 watts in.

The generated voltage is now only 9V, so the output power is 387 watts ((45-2)*9), mechancial losses are 18W (2*9) and the electrical losses are 135W. The efficiency is now around 72%, but notice how much hotter the motor wil become with 135W instead of 60W of heat generated in the windings.

Mike.

Thread: Servo reverse... Be careful
24/09/2017 20:36:19

I believe the "correct" place to reverse a servo is in the OUTPUTS menu.

As you have discovered, reversing in the INPUTS menu doesn't reverse the trim.

Reversing in the mixer is OK provided you only have a single mix on the channel. With more than one mix, you would need to make sure you reverse ALL the mixes.

Reversing the servo in the OUTPUTS menu is common to all mixes and the trim. This is, in fact, the "Servo Reverse" option!

Mike.

Thread: Transmitters for DSMX indoor receiver/servo modules
24/09/2017 20:31:01

For information:

My understanding is that full power (100mW, 20dbm) DSM2 is no longer permitted to be sold in the EU as new equipment (unless the product was manufactured before the regulations cane into effect).

Any 2.4GHz equipment that transmits at a power level of 10dbm (or less) is not covered by the regultaions. If you have a Multi module, and wish to use DSM2 for indoor use only, then you may build the firmware for it (usually necessary anyway as they ship with very old firmware) with the power of DSM2 reduced by 10dbm. THis reduces the output power by a factor of 10, but will only reduce the range to about a third of full range.

Mike.

24/09/2017 15:11:31

When binding, the receiver sends back the protocol(s) it can accept, together with the number of channels, and the refresh rate (11 or 22mS). The module then stores this information.

Depending on the protocol used between the module and the radio firmware, it may also be possible for the bind information to be stored in the radio, so the module doesn't need binding when you change to another model that requires a different configuration.

An Orange module flashed with the Multi protocol will do this, provided the radio is using a relatively recent revision of ersky9x or openTx.

Mike.

23/09/2017 13:04:14

The Turnigy 9XR-PRO is only £44.21 from the Eu warehouse at present, with the iRangeX IRX4 module at £28.05 from Banggood.

Mike.

Thread: Who wants a Warbird Replics Hurricane?
23/09/2017 11:25:45

Also, any suggestions for a suitable spinner? I'm just building a motor mounting box for the electric motor I intend to use.

Mike.

Thread: Transmitters for DSMX indoor receiver/servo modules
23/09/2017 09:14:17
Posted by Geoff Sleath on 22/09/2017 21:46:29:

A club-mate has just bought an E-Flite Convergence VTOLfoamie and found it wouldn't bind to the Orange module he has in his Taranis and had to buy a new transmitter to use it. He got a DX6e which binds and flies it OK.

I ported the Multi (4-in-1) code to run on the Orange DSM modules. If the module is flashed with this, then it is very likely to then work with the Convergence. Many "bind'n'fly" models don't work with the Orange module as supplied but then are fine when the module is flashed with the Multi code.

Details on how to flash the module are on this thread: **LINK**.

Mike.

21/09/2017 23:12:51

You might consider a Tx that supports a (JR style) module, then get one of the "4-in-1" modules that supports many protocols as well as DSM2 and DSMX.

Suitable, low cost, transmitters include the Turnigy 9XR-PRO and the FrSky QX7. You also then get the power of the open source firmware available, should you need it later.

You don't need to learn all about the open source firmware, when you create a model it starts as a simple, 4-channel setup ready to use.

Mike.

Thread: low voltage lipo battery
21/09/2017 12:59:53

Hmmm.

"this circuit will automatically cutoff once the pack drops to 2.95v per cell ensuring the battery will not be damaged if you accidentally leave your transmitter switched on"

So if you accidently run the battery low while flying, the battery protects itself, while turning the Tx off so the 'plane crashes!

I won't be using this sort of battery! I'd rather the battery got damaged than I lost a complete 'plane!

Mike.

Thread: 2 position flaps
18/09/2017 19:26:26
Posted by Andy48 on 18/09/2017 16:51:14:

See "Getting Started" section page 22, where an example of a switch is being used. This is easier than programming a curve, . . .

I'd disagree that putting three mixer lines in is "easier" than a single mix with a single curve.

Mike.

18/09/2017 16:18:37

Several ways of doing this. A quick way is to assign the 3-pos switch as the mix source, then create a 3 point curve and set the required flap positions using that.

It should also be possible to use the mix settings for weight, offset and expo to get the required positions, but this is less obvious when trying to set up.

Mike.

Thread: FrSky Taranis - user chat
18/09/2017 09:45:57
Posted by trebor on 17/09/2017 22:21:40:

I'm pretty sure I did the final bind with throttle in down position. Has to be related to the failsafe as I have had warnings when getting too close to the model with the transmitter.

I'm not sure where you got this from, I've never known FrSky receivers use this method to set the failsafe.

Normally you either set the controls as required and press the F/S button on the Rx, or, for 'X' receivers, you have the option of setting the failsafe on the Tx.

Mike.

Thread: Who wants a Warbird Replics Hurricane?
16/09/2017 19:58:06

I'm also now looking at the undercarriage (retracts).

First, measuring the plan, it looks to show 3.5 inch wheels, but the vac. formed wheel wells look to only take 3.0 inch wheels. So which is correct 3.5 inch or 3.0 inch?

The next question is are retracts and oleos going to be available?

I have a pair of Hobbyking electric retracts I could use, but I still need some oleos anyway.

Mike.

Thread: 2013 Taranis
12/09/2017 12:38:37

No, both open source firmware (openTx and ersky9x) have full support for editing models on the radio, you don't actually need a PC at all, except for flashing new firmware. Even then, the bootloader allows for flashing from a file on the SD card.

When trying to flash the Rx, make sure you are using the Smart Port and not the SBUS port. I find the "best" way for connecting the Rx is to only connect ground and SPort signal, and power the Rx from a separate battery connected by a switch. Get to the "finding device" stage, then switch the Rx on.

Mike.

11/09/2017 23:08:14

V1.1.02 is the original FrSky version of openTx, and it doesn't include the bootloader.

The only way to update the firmware is to connect the radio to a PC using USB (with the radio off), then use a DFU program to flash new firmware. I don't think there is a DFU available for the MAC unfortunately.

If you can get either openTx or ersky9x flashed once, you should then have the bootloader that will make things easier.

Mike.

Thread: EASA consultation extended
10/09/2017 18:58:26

I was interested to see (as I understand it) they reckon there are 1.5 million model aircraft flyers in Europe, i.e. those who fly "traditional" style models.

Mike.

10/09/2017 15:41:32

I've just had a look through some of these 2 documents. There seem to be several options being proposed, some of which are (mostly) reasonable. I notice several specific references to "model aircraft" indicating existing model flying is recognised as something that might not be impacted to much.

However, as far as I can see, all options seem to propose a height limit that varies from 30m (for "toys" up to around 150m, although either 120m (or 30m below 120m) is the most common height limit.

Personally, I find 120m (400 feet) restricting. I enjoy flying electric thermal gliders. From launch, I'm at 400 feet within around 15 seconds. What I do notice (both while flying and from examining telemetry log files) is that I seldom find any useable thermal activity below 400 feet, mostly it seems to start at 500 to 600 feet. Last time I flew I did catch a thermal at around 700 feet and spent several minutes in a dive (with flaps deflected up), to keep under 850 to 900 feet it was so strong. Once I cleared it, I dropped to 300 feet where I did find some weak lift that took me up to 350 feet, but nothing really useful. So I conclude that a height limit of 120m (400 feet) will mean no more thermal soaring!

Mike.

Edit: I've made a comment to this effect, although I've now been waiting for a few minutes for it to be accepted!

Edited By Mike Blandford on 10/09/2017 16:12:04

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