2013 Mass Build - general chat thread

[Phil Winks]

Mike I believe those chargers are pretty solid and reliable.

1/3rd C is a very low charge rate even for an old lipo which had a recommended charge rate of 1C

check the max charge rate of your packs and try to achieve at least 50% of this.

The ext temp sensor is more use when charging NiMh btys as the sensor is magnetic and NiMh btys need to be kept cool while charging and so if charging at high rates to as the car boys term it develop punch, its a good idea to watch the bty temp closely

Mind you it wouldn't hurt to have the charger monitor a lipo's temp so if the worst was to happen it could terminate the charge process before disaster hits. what temp you would set as a max is prob around 35 to 40 degrees C though others will know more about this setting

Phil

[Mike Hardy]

Thanks Guys, I hope I am still posting in the right place! The questions are linked to my Tucano, I am getting ready to run up my motor so I can check direction of rotation then I can fit the motor and fit the top deck

Once charged how long can i leave the packs in this state? If I am not using them for say a week is that OK or do I have to discharge to the storage voltage?

Another Question: To run up the motor can I just plug the ESC Rx lead into my servo tester and adjust the speed with the pot. Or do I have to connect to the Rx and run up via the Tx (pain) I have an Aurora 9 which I have yet to commission.

These questions may be basic to you guys, but they are not to me and maybe others on this forum so please bear with me.

Mike.

[Chris Bott - Moderator]

They might be basic questions mike but all of your thinking is spot on.

I leave packs full for weeks, it's very hard to predict when I might need them. To drop them to storage volts I have to envisage not using them for months.

Yes the servo tester will work fine. It does of course need power it's self, but this is conveniently supplied by the ESC's BEC. Just beware that you really want it to be set to minimum when you power it up, check this with no prop of course.

[Mike Hardy]

Hi all, I want to lengthen my ESC main battery wires by about 50mm is this acceptable? Using a 3S 3600 pack with XT60 connectors puts the connector pair right up against the fuselage inside wall making it difficult to part the connector. The extra 50mm would make it much easier to handle and part. It is not possible to move the ESC in order to gain extra pack lead length'

Mike.

[Chris Bott - Moderator]

50mm will be absolutely fine Mike

[Mike Hardy]

Thanks Chris, I have another question: My motor is SK3 3542 1185kV The prop adaptor shaft dia is 0.236" (5.9mm) my alum spinner back plate hole dia 1/4 unf, I take it hole dia 0.250" (6.3mm) giving 0.4mm slack which can be enough to 'throw out' the spinner on the prop adaptor shaft. Can I add tape to the shaft to make up the difference. Or is there an adaptor washer available?

Mike.

[Phil Winks]

Posted by Mike Hardy on 10/07/2013 16:49:02:

Hi all, I want to lengthen my ESC main battery wires by about 50mm is this acceptable?

Mike.

Mike I concur with BEB here lengthening the ESC to bty wires is far preferable to lengthening the ESC to motor wires, they're the noisy ones electronically speaking. and while modern 2.4Ghz sets are less prone to interference than the older 35Mhz sets I believe its still prudent to keep these wires as short as possible

edit

As for the spinner back plate I think you should be looking to replace the adaptor washer with one that fits a s snug as possible though they may be difficult to find if you have acces to a lathe or a friend who has then its a simple task to turn out a bespoke one or 2 incase of the inevitable dropped one

 

Phil

Edited By Phil Winks on 10/07/2013 17:43:13

[Chris Bott - Moderator]

BEB? has he answered too?

Phil, the conventional wisdom is that generally it's better to lengthen the ESC to motor wires than the Batt to ESC ones. The reason given is that the increased inductance of long wires can cause high voltage spikes when the high speed switching occurs. This in turn can be too much for the capacitors at the input of the ESC.

However, the 50mm in Mikes case is insignificant.

[Danny Fenton]

John Ranson fits capacitors every few inches on the long battery leads in his 100" Hornet I believe. Here is a neat solution by Castle Creations.

There seems to be supporters of both solutions, lengtheneing the esc - motor wires, and battery - esc wires. On the latter, the ripple seems to be the killer.

Cheers

Danny

[Phil Winks]

Posted by Chris Bott - Moderator on 10/07/2013 18:01:16:

BEB? has he answered too?

Phil, the conventional wisdom is that generally it's better to lengthen the ESC to motor wires than the Batt to ESC ones. The reason given is that the increased inductance of long wires can cause high voltage spikes when the high speed switching occurs. This in turn can be too much for the capacitors at the input of the ESC.

However, the 50mm in Mikes case is insignificant.

1 st need to visit spec savers Chris sorry fella my opinion on the motor to ESC wires is based on what I remember when having glitch problems with a model back when I was running a futaba 6ex 35Mhz set and I was advised that shorting the motor to esc wires could be a possible cure it certainly worked then if I remember correctly the original wires were only about 60mm and taking the ESC to within 30mm of the motor made a huge difference obviously this required that I had to extend the esc to bty wires and I was advised beck then that this was ok and unlikely to cause an issue but as in this case it was only a short extension

Phil

[Ian Newton]

Chris / Phil, I do beg to differ in general principle, but I have done a lot of research on this subject as I am building a 72" wingspan Lancaster with of course 4 wing mounted electric motors. To do this I will need to extend either the three leads between the esc and motor or the 2 battery to esc leads. The recommendations from the perspective of the esc is to lengthen the 3 leads (which can, within reason, be lengthend as much as you like), but this is not always possible/desirable. If you lengthen the 2 battery leads then you do risk damage to the esc, and the manufacturers do not recommend this. The likelyhood of damaging the esc is dependant upon a number of factors. However, If your esc is capable of supporting 1 or more cells than you are using (e.g. the esc can support up to 4s LiPo and you are using a 3s) then that gives some margin to extend the battery leads without to much worry, as long as it is only a couple of inches. Damage may not be immediate but could have an accumulative effect. Basically it can damage the capacitors across the battery leads at the esc and at some point in the future these may fail. If you are near to the limit or wish to make a significant increase in the battery lead length then further capacitors (at the esc) can be added in parallel with those already mounted on the esc. The electrical characteristics of these capacitors is quite important i.e. you can't use any old capacitor. I do have lots of links and further info if you really want more but it gets quite heavy! (I am an electrical engineer - as opposed to an electronic engineer- but some of the theory in some of the items does make hard reading). It is quite likely that you will get away with this mod, certainly in the shorter term but if you are running close to the current and particularly voltage limit of the esc you may experience either immediate or, more likely, early failure. I know in the past I have lengthened the battery leads with no apparent problem but in one case (used on a 6s LiPo running at the esc max voltage rating) I did suffer an immediate failure which at the time I put down to a faulty esc but I now believe I pushed it too far!

Perhaps this is a suitable subject for an article in RCM&E?

[Phil Winks]

Posted by Ian Newton on 10/07/2013 18:47:21:

Perhaps this is a suitable subject for an article in RCM&E?

I agree Ian some sort of definitive article would help here.

Looking at what you've said seems to support my approach of ALWAYS using an over rated esc I tend to run my esc's at app 60 to 80% of their capacity (though there have been exceptions) and have always looked for one that can handle a good bit more voltage never (till now actually realising exactly why) hence an esc that can handle 6s lipo's in my 3s powered tucano a habit another member of this forum convinced me was a good idea some years ago now his reason's become very clear

Phil

[Chris Bott - Moderator]

Try this thread on another forum chaps. Lot's of discussion here.

Or this one

Also a simple google search such as "extend ESC" brings up all sorts of info.

Edited By Chris Bott - Moderator on 10/07/2013 20:42:31

[Ian Newton]

Chris. Yes, that is one of the many useful articles that I also found. Much is easy to understand but some of the articles were between designers of esc's and electronics engineers were very technical (and quite heated in some cases!!)

Edited By Ian Newton on 10/07/2013 21:56:41

[Ian Newton]

We will have to be careful not ot hijack this thread but here is some more info I picked up

Rule of thumb
If you have to lengthen the battery wires, add extra electrolytic capacitors in parallel with ESC, never in series with ESC. As a rule of thumb, for every 4inch/10cm extra length/distance between battery and ESC, add an 220uF extra capacitance near the controller (electrolytic condensators, voltage the same as the capacitors already installed, low ESR type) (Ludwich Retzbach, German e-flight author&editor, the 'R' in LRK).
Better to use several smaller caps (in parallel) instead of one biggie. Smaller caps can shed more heat and total inductance will be lower (inductance per cap is lower and those inductances are paralled to boot ).

**LINK**

www.rcgroups.com/forums/showthread.php?t=1095329

There is a huge amount of conflicting discussion but my earlier posting appears to be the best and most accurate guidance. One point to consider though. Inserting a wattmeter between the battery and esc lengthens these wires by quite a few inches! There are many postings saying you should not use a wattmeter when pushing the current and or voltage limits of the esc. Use a clip on current sensor instead and a voltmeter across the battery leads, mutiply the results to get the watts.

Another point made often is adding 1" between battery and esc is lengthening the total wire length by 2".  Most articles/postings/calculations are talking about this total length!

 

 

Edited By Ian Newton on 10/07/2013 22:37:22

[Chris Bott - Moderator]

I would have thought that a good wattmeter would include some decent low ESR capacitors for just the reason stated?

[Ian Newton]

Chris, quite possibly they do -I've never dismantled mine! - but again (as per the castle creations link that Danny posted) the guidance is to place these capacitors as close as possible to the esc - not halfway down the leads.

[Nigel Hawes]

This discussion reminds me of a test we did in the early days of brushless ESCs (sensorless, not Hall sensor of course) regarding ESC to motor lead length.

We were all in the dark back then and opinion contrasted greatly, so we connected a motor to its ESC using block connectors on the end of a 100-metre roll of 1.5mm twin and earth lighting circuit wire! Some said the ESC would blow in no time, others said the coiled-up nature of the roll of wire would be seen by the ESC as extra windings and ruin its ability to sense the feedback pulse!

In practise the motor started and ran normally, and despite several ground runs we couldn't get the ESC to become any warmer than normal - so for anyone with any doubts, the ESC to motor wire length makes no difference whatsoever.

As long as your model is less than 100 metres long anyway!

Edited By Nigel Hawes on 11/07/2013 06:26:44

[Mike Hardy]

Hi Chaps, All very interesting but as you can see there is no room for any additional capacitors!!

Nose hatch - fit or no fit - which have you guys chosen!! No hatch then the motor is burred for all time!! A hatch is needed to help target the screwdriver for removal of mounting screws. and disconnect the ESC from the motor, both parts can then be removed.

Returning to my earlier post re aluminium washers for the spinner back plate - what I need is a washer - 0.370" o/d 0.236" i/d and 0.175" thick. I have no machining facilities so I need the services of a kind master builder who has a Myford or Boxford lathe to make a couple of these. Of course I will pay for time and materials.

Any volunteers please. (mods - am I OK to ask on this forum)

Mike.

Edited By Mike Hardy on 11/07/2013 09:59:12

[WolstonFlyer]

Hi Mike

I would personally just make up a short extension lead with XT60 on each end. I am using twin 2200mAh batteries so have an extra bit of cable for the LiPo parallel connector lead and I am not worried about the extra 50mm of wire and connections.

[Mike Hardy]

Good point Wolston, Just worried about the volt loss across the extra connectors especially when pulling 40A or more at take-off.

Mike.

[Biggles' Elder Brother - Moderator]

No problem Mike - just do it. The connectors are gold plated contact loses are very low.

Regarding the top hatch - personally I didn't bother. But I must admit to some trepidation with that - had there been problems with the motor/ESC I'd have had to cut a hatch to get at it. But all has gone well so far and I've had a couple of dozen flights with her - failure in these systems tends to follow the classic "bathtub curve" ie failures either occur almost immediately or life expectancy is good. Fingers crossed!

One precaution I did take was to massively overspec the ESC. I have no additional cooling so I was concerned about overheating. The ESC I'm using is (I think) an 70A job and peak current is just 40A - this probably helps a little to cope without cooling.

On the washer question - I'm not sure I quite understand. Are you saying you need a bit more "stand off", effectively a spacer, so the spinner is gapped correctly from the front of the nose?

BEB

PS No probs in asking for help!

[Mike Hardy]

Thanks BEB, The alum spinner I am using is made for a 1/4" motor shaft, my motor shaft is 5.9mm (6mm) dia. So I need a replacement for the small washer shown in the photo but with a 6mm hole for the motor shaft. If I use the existing washer then the spinner can run out of true and liable to vibrate at speed.

Mike.

[Mike Hardy]

Just been in touch with RC World who supplied the spinner and would-you-believe they have a lathe and are going to make some washers for me at a nominal cost!! And introduce a range of washers or inserts to convert their spinners to 6mm shaft as an option.

Panic over.

Mike.

[Biggles' Elder Brother - Moderator]

Good news!

BEB