MultiWii

Hi all

I'm starting to test fly my Hexacopter in earnest now, and I've noticed that the ESCs are getting rather hot ... almost too hot to touch after a few minutes of hovering.

Here are some specs:

4s1p 5000mAh 25C Turnigy Nano-Tech battery
6 x Turnigy Plush 25A ESCs (medium timing)
6 x Pulso U-28M motors (760kv)
6 x 11"x5.5 APC-E props (ESCs get just as hot on 10"x3.8 SlowFly props)
Flyduino running MultiWii 2.0
Hover throttle is around 35-40% with the 11x5.5 props and 40-45% with the 10x3.8 props
Hover current is 26A
3kg ready-to-fly with camera and battery
ESCs are inside a 16cm dome which covers all the avionics (the dome has cooling holes though)


I've read something about MultiWii 2.0 having a higher communication frequency for the ESCs and that this has been causing some issues with various brands of ESC? Is it possible that I have an older version of firmware on the Plush ESCs which doesn't like the higher frequency of the new MultiWii code? Is there a way to reduce the frequency of the PWM which is output by the MultiWii?

Many thanks for any advice, it's greatly appreciated


David

The high temp could be from the ESC's linear Vregs or FETS, so it would be helpful to determine which is heating up. I suggest you power up the model with motors disarmed and then see if the ESC's remain cool after a few minutes. If they start to get too hot then there is something odd going on with the BEC feature. And of course you can use your finger tips to find the hot spot source, but be careful (burns hurt!).

Excessive wire length between the battery and a ESC can cause high FET temperature (and eventual failure). The rule of thumb is to the extend motor wires, not battery wires. Your model's description seem to suggest your battery<->ESC wires are short, but go back and review the installation with a critical eye towards this issue.

If the problem continues to haunt you then it could be a ESC compatibility issue, just as you thought. But resist the temptation to play with Multiwii's ESC timing. Instead, a more gratifying solution would be to reflash the ESC's with the fancy stuff publish by guys like Simonk and others.

So here's my challenge to you. Grab one of your spare Plush 25's, confirm it has a ATMEGA (not Silabs) MCU, flash it with Simonk code, then run it on the bench and compare to the stock ESC's temperature. There is a good chance it will be cooler.

- Thomas

Hi Thomas,

Many thanks for your reply!

I've been pointed to this thread over on RCGroups where ESCs which are rated to "4S" actually get much hotter on 4S than they do on 3S:

http://www.rcgroups.com/forums/showthre ... 8&page=166

I've ordered a programming cable for my current ESCs (looked at a spare one and it has an ATMega chip on the back), but I'm starting to think re-flashing them all might not actually make all that much difference, if Buffy's experiences are anything to go by (see his post here).

Otherwise, the ESCs remain completely cool to the touch after 15 minutes of being plugged into the flight battery, my ESC power wires are about 3 inches long (maybe 4 inches if you include the copper circuit board track on the power distribution board), and the motor wires are about 18 inches long.

Thanks again!


David

That is too bad; Looks like you'll need better ESC's to solve the over-temp issue. I suppose my preferred mounting of ESC's exposed to moving air / prop wash is a good thing.

- Thomas

Could also be the ESC locations, wire length and wire gauge. What would be interesting to know as well, are the wires getting hot also.

This maybe of Interest: http://www.rcgroups.com/forums/showthread.php?t=1577876

Thomas - it would be good if I could get the ESCs out into the airflow, but I do like having them all inside for neatness! I reckon if the ESCs on the hexacopter were running as cool as those on my tricopter (albeit out in the airflow), they would be just warm when kept in an enclosed space ... The ESCs are making the characteristic Plush 'clicking' sound which I believe is a ESC -> motor timing issue, and I was hoping that re-flashing the ESCs might solve this problem as well as make the ESCs more efficient. I guess it can't harm to flash my spare one, and then flash all 6 on the hexacopter if the flashing seems to make the motor run considerably smoother. If I were to mount the ESCs by the motors, I gather I would I need to fit larger capacitors to the ESCs (with 18 inches of power wires leading to them)?

copterrichie - The ESCs sit around a central stack of avionics in the dome in the centre of the hexacopter:



The ESC power wires are about 4" long, and the motor wires about 18" long. The motor wires just as they come off the ESCs are also warm after a flight, although I imagine this might just be heat conducting up the wires from the ESCs ... the motor wires where they come out of the motor are at ambient temperature ...

Many thanks


David

You have mentioned using larger ESCs and looking at this picture, I think you would be best served with a 40 amp. You can always use more then needed. One thing that I do regardless of the ESC, cut the heat shrink off, add another piece of aluminum to help with heat dissipation, then re-heat shrink them.

copterrichie wrote:You have mentioned using larger ESCs and looking at this picture, I think you would be best served with a 40 amp. You can always use more then needed. One thing that I do regardless of the ESC, cut the heat shrink off, add another piece of aluminum to help with heat dissipation, then re-heat shrink them.

Hi Richie,

Thanks for your reply 40A does seem to be overkill when I'm only drawing 4-5A per motor ... that being said, 40A ESCs have been mentioned in the thread I linked to below as being the general size of ESCs which use 'gate driviers' which apparently allow for true higher voltage operation (4-cells and above) ...

Do you know if these would be suitable?

http://www.electriflite.co.uk/store/ind ... -p40a.html

Many thanks


David

The ESCs are making the characteristic Plush 'clicking' sound which I believe is a ESC -> motor timing issue, and I was hoping that re-flashing the ESCs might solve this problem as well as make the ESCs more efficient.

+1, I expect you will experience such improvements with the magic ESC code.

If I were to mount the ESCs by the motors, I gather I would I need to fit larger capacitors to the ESCs (with 18 inches of power wires leading to them)?

The existing caps should remain in place and additional caps are added, depending on the extended wire length. Details are nicely explained here:
http://www.rcgroups.com/forums/showthread.php?t=952523

Another possible (yet unconventional) solution would be to add a small CPU venting fan to your enclosed dome. If you can't bring the ESC's to the airflow, then bring the airflow to the ESC's. And finally, 3S packs are cheaper than 4S.

- Thomas

That ESC is rebranded and I have a few. Should work great.

I believe they are the same as this one from RCtimer: http://www.rctimer.com/index.php?gOo=go ... oductname=

Be sure the disable to internal BEC

Thanks for your input guys

I've just learned that (according to timecop on RCGroups) re-flashing will actually make the heat situation worse as the FETs will be trying to switch even faster ... he recommends this ESC which he's had great success with, and he says also feature gate drivers:

http://www.hobbyking.com/hobbyking/stor ... _UBEC.html

I would try replacing my 4S batteries with 3S, but I bought 4 of them!

I had briefly considered the fan idea, but thought it would be better to get to the source of the heating problem, rather than trying to mask it

Cheers!


David

The new ESC's are very affordable, so that is good news. Are you planning to reflash them before installation?

- Thomas

It would be interesting to see a picture of the board without the heat sink. Anyway, I believe you are headed in the right direction.

Thomas - I've just ordered 9 of these ESCs from Hobby King and plan to reflash them on arrival (hence why I've ordered 9 when I only actually need 6!). They seem to be very highly favoured in the ESC flashing thread, and I've been bouncing many emails back and forth to timecop, and between us we decided they would be a good bet for my application.

Richie - Here are some shots of the top and bottom of the Turnigy Plush 25A ESC that I was using:





Cheers


David