Motor KV doesn't make sense ??

[Tim Mackey]

We're off topic here chaps

[Malcolm Fisher]

Sorry Tim,

It's easy to get carried away when asked a direct question.

I did think about a PM - honest

Malcolm,

[Glyn R]

I use a Turnigy wattmeter. This has a 130 amp rating just to be on the safe side. This with a digital rev counter tells me most of what I need to know. You can get electronic meters that will connect in circuit for EDF.

Edited By Glyn R on 18/05/2011 21:47:17

[Malcolm Fisher]

I have at last got round to buying the Neodym Wattmeter Pat suggeted.

In my ignorance I expected something which could be inserted into the circuit in the model, but it seems to be a "bench" unit and doesn't need the transmitter.

The instructions aren't as clear as this geriatric newbie to electric power needs.

Does anyone use this meter and can explain it to me in simple terms. I don't want to do anything stupid which will ruin meter or motor.

I have a recollection of seeing something about not running a brushless motor with no load. I interpret this as having no propeller. Can anyone shed light on this and say what the outcome is likely to be?

Malcolm

[Biggles' Elder Brother - Moderator]

Malcolm, I'm no electric expert but I do have this meter! If I can figure it out you've got no problem!

 

Basically it sits between the battery and the ESC. So solder what ever connectors you use on to make that possible. Also connect the ESC's throttle "servo" lead to the watt meter as well.

 

You're spot on - it doesn't need the Tx or the Rx to be present. The knob on the front acts like a throttle control.

 

Connect it all up and (restrainting the model) turn the knob. You get readings of watts and amps. Easy peasy!

 

Personally I put the prop on for the test. Aside from any questions of damage - the power, and hence the current draw, will depend heavily on what prop size you are spinning. So there isn't much point in testing without it as the readings would bear no relation to what will happen in flight! But do make sure the model is well restrained!

 

Another point that these "long term" electric types will forget to remind you of. Us IC'ers are only used to running engines outside where there is nothing else around right? But of course you can test your electric model "on the bench" in doors, no problem. BUT,...don't forget to clear away anything "light" first - or you'll blow it all over the workshop! Ask me how I know that!

 

BEB

[John Privett]

I can't say I've ever heard anything about not running a brushless with no load. All I can think of is it might make it a little hesitant to start properly with less "flywheel" effect. However running the motor with no load would be quite meaningless if you're hooking it up to a wattmeter to get some readings from it.

 

As for the wattmeter itself, plug your flight battery into the input leads (probably after soldering suitable plugs/sockets onto them!) The output leads from the meter then go to the "battery" leads on the ESC. (Again after soldering suitable plugs/sockets onto them!)

 

Now you can either plug the "throttle" lead from the ESC into your receiver and operate it using your transmitter, or plug the throttle lead into the "servo" on the Neodym unit, just beside the input leads. The throttle setting is then controlled by the knob marked "PCM" on the meter.

 

One final choice if you do the latter, set the little switch marked "PWR-SET" depending on whether you want the wattmeter to supply power to the ESC or not - if the ESC has a BEC then the answer is "not". I'll have to confess at this point that I don't know for sure which switch setting is which... I don't have the instructions to hand. Mine however has the switch in the position furthest from the servo socket and has always been used with ESCs that do have a BEC.

 

(It appears that BEB types faster than I do! )

 

Edited By John Privett on 18/06/2011 21:34:54

[Biggles' Elder Brother - Moderator]

Great minds think alike John!

 

BEB

[Malcolm Fisher]

Hi BEB and John

Thanks for your replies.

I can't remember where I saw the bit about not running the motor without load as I couldn't find it again although I think it was while I was searching for a motor. I just wondered why it could be a problem as one is recommended to do the initial setting up of electirc motors minus prop "just in case". I did learn that lesson a while ago and it cost me £10 for a new prop.

I know it would be pointless to test output in that situation.

My problem with the meter is partly the labelling.on the meter. The two small switches are both labelled PCM - SET and the instructions refer to one as PWR - SET. The instructions also refer to "up" and "down" yet the switches are on the sides and, to me, operate "fore and aft" as it were. Which switch is which, and which way is "up"?

It's good to know that I can also use the Tx to give the motor command settings as well as using the knob on the meter which, I assume, increases power as one turns it clockwise but I could be wrong.

I'm also taking my time as I need a magnifying glass to read the programming instructions for the ESC.

I also at present only have 7 cell NiMH batteries and the motor blurb suggests a 3s Lipo so am unsure if my batteries will be OK. I am prepared to wait until I can get a suitable Lipo, but don't want to discard usable power supplies. I am a Yorkshire Tyke after all.