twin screw brushless/lipo set up now has wierd problem please help!

[pmdevlin]

Hi all,

really don't know if I am in the right place, but help needed before I go wildly spending money on the wrong things. Ok, its not one of your fast type racing boats, but the "normal" rc boat sites will not understand what I have. Its a 4 foot ply built scale model of a 1950's Vosper Crashtender (Fireboat), please don't lose interest at this point, its pretty special, it runs direct drive (propshafts go straight into the motors) 800kv twin motors, each motor has a turnigy 60amp reversing esc, and runs off 2 x 2 cell 5000mah lipo. DX6i tx, with eagle tree data logging and propshop 3 blade 50mm cleavers its good for 23mph, lame compared to your boats, but its well over scale speed, and is great fun.

So here is the story, its been running ballistic, last time out, I use a low voltage setting of 3.2v per cell on the esc's, and always run with each pack having its own voltage alarm, so no chance of over discharge. Shafts are oil lubed, everything runs nice and smooth, the shafts have 4 bearings, plus the motor bearing, so you get a picture of what we have. I really look after it!

Took it out to sail, with balanced packs, and right away I get a low volt alarm and a slow boat, with one of the escs shutting down. Back to base I charge and balance all packs, everything is fine. I check the settings on the esc's (by the beeps, real pain!) and triple check all is ok, back out to the lake, after a very short run it happens again, the problem is by the time the boat is in the batts have recovered and I don't know which has gone down, infact they have recovered pretty much to full charge going by the digital displays on the voltage alarms, The eagle tree is saying I had a very high amp draw, surprisingly not at peak speed, but quite low speed. Nothing tight or fouling. I had borrowed 2 4 cell 3000 mah packs so fitted them, knowing there is nothing wrong with these, same problem, almost like something is sucking the juice momentarily from the packs, causing the low voltage protection to kick in, again when the boat is back in the cells are showing almost fully charged.

Back home, I charge my packs, and discharge under load on a twin motor rc plane, they kick in to 3.2v within 20 seconds of each other, so I am thinking its not the batteries, although they are a no name brand, nothing special. Back to lake, I throttle real slow, and find as soon as I hit max throttle same problem, one or both of the esc's goes into low voltage shutdown. I check throttle range, all is ok, and decide to replae one of each of the 2 cell lipos with some 3 cell 5000mah packs, so now 5 cells per motor, everything seems to run fine, boat is fast.

SO..... (Are you still here!) its a real big job to change the motors, as the whole set up is very specific, the boat has only run a few times, so its not old. I could try another pair of esc's, I don't think its the batts, as I tried two other 4 cell sets that I know are good, and it was the same propb. When I put an extra cell in per motor, it appeared to be ok, but I am worried I just over volted through the actual problem, I really need a logical step by step diagnosis, I am in danger of running all over the place and cant afford to just buy things blindly, qalso work commitments mean I don't get a lot of time to keep testing things.

Any ideas!! (couple of pics so you can see the offending setup!)

Thanks

[lenny]

Hi,
First very nice boat and I want to see some video's of it running some time.
It sound like the esc cell count setting is not set wright.
Do you have the program card for the esc ?
What is the esc cell count set for normally ?
Also what is the low volt setting set at ?
And they are 120a turnigy esc's right ?

[properchopper]

First off, that boat is really beautiful ! Nice Job Given that you're using those ESC's know that it is fairly common for these ESCs (at least the 180A version) to go into premature LVC even when it's not called for. It acts as if the LVC circuit is monitoring momentary voltage downspikes (which are not unusual) instead of average voltage. To see if a wonky ( yup, I watch Top Gear on BBC) LVC is causing your problem, set the LVC to "disabled" and give it a try.

[Doug Smock]

Beautiful boat sir!

[pmdevlin]

cheers guys,

embarrassed to say, they are 60amp turnigy reversing boat water cooled esc's. Good advice regarding the lvc, its set at 3.2v, strange that it could be both at the same time? its a real conundrum, so here is what I have done today. When it started cutting to low power (visible when running) after only 1 min or so I get one of the 4 batt alarms going off, now I am on reduced power I get the boat in within 20 seconds, but now the batts have recovered, I have to disconnect the power to reset the low voltage shut down on the esc's, the boat is real hard to hold when flat out, but it all seems ok, when its released, the thing goes into low power again! so I cant see what is going on. If I continue to run on 4 cells per motor it keeps happening, at max stick, 2/3rd its fine, but who wants to run at 2/3rd's after all this work with the propshaft straight onto the motors etc etc !! ha ha !!

When running on 5 cells per motor its fine, I made a note of counting the beeps for cell number recognition, and it counted 4 when on 4 cells, I tried it on 3 and 5 every time both esc's count cells right, they are set on auto cell number recognition. Don't have a programme card, so its the real messy beep beep beep programming! Data logging with eagle tree was on board, nothing unusual, other than at the start on 1 session, there was a big amp spike, but at max speed was only 38amps, so quite low as the esc's are 60amps

Just had two of the 2 cell 5000mah packs on the charger, and they are no where near discharged, 3.8v per cell, so something is sucking the juice with a spike, as its happens all the time, that gets rid of prop fouling on lake garbage etc . I cant bench run for long as the shafts have water lubricated glacier bearings and will overheat, but on the bench test no problems, no tight spots, no slippage etc, its got to be esc or motors,

keep the ideas coming please!

[pmdevlin]

Lenny, what is that boat in your avatar? looks similar to my Fairey Huntsman 28

Video of the fireboat, on last run, quality is pants sorry, santa has now brought a HD camcorder, but you get the idea of what its like, now its on counter rotating cleavers so the porpoising has gone, pity about the lack of speed now.........................

leave the picture small, stay watching for the onboard cameras, if it was like this when I put it away, whats gone wrong!

[lenny]

Try setting the lv to off and also set the cell count to what ever s cell you are trying,
But do not use the auto cell count.
As for bench testing try running with out the flex shafts connected to the motors,
And check the temps on the motors and esc's if it kick to slow running.


No video.

This video contains content from BMG_Rights_Management, UMG, Warner Chappell, Sony ATV Publishing, UMPG Publishing and EMI Music Publishing, one or more of whom have blocked it in your country on copyright grounds.

[pmdevlin]

I will try your suggestion about the esc settings lenny thanks. Check out the motor mount pics there are no flexi shafts or couplings etc as the propshafts go into the motor. The motor shafts are removed! That's why it will be so difficult to try other motors. Let's hope the esc changes to settings works!

[lenny]

Ok and good luck,
And I still want to see that boat running.

The boat in my avatar is a Mark Chris Craft Constellation,
It is still in the box it came in.
I picked it up about 25 years ago at a salvation army thrift store.
http://www.uncle-als-toys.com/shop-d....html?c=5&p=47
http://www.lindberg-models.com/water_model70814.html

[pmdevlin]

Hi lenny,

did the link above not work?

try this, quality is pretty rubbish though!

http://www.youtube.com/watch?v=Ci6HHCZVQ0c

[pmdevlin]

last night I decided to strip it all down again, on one motor, there is a very occasional "clicking" sound as I turn the can by hand, does not happen all the time, and its not going tight all the bearings are fine, I wonder if the can is running out of true, and its catching very slightly between a magnet and the windings causing the amp spike?, which might cause the sudden drop in voltage, resulting in the lvc........

I am going to reset the esc's disable the lvc as suggested, and lock in the cell count instead of relying on the auto feature, I hope its not a motor, its guess work at the minute,

[lenny]

Hey Fastvee had a problem something like your in this build,
And I think it ended up being a bad motor that took out one of his esc to.
https://forums.offshoreelectrics.com/...e-style-build)

The only thing is both of your motors are going into low speed,
So I still think it is the esc's settings.
Those esc need to break in some time by running them on different setting sometimes,
To get them not to be so sensitive with low volt and auto cell count.
I have read this on hear in a thread about that problem and fix by just changing the setting a few times.


Video still will not play for me,
I went to your you tube and did see the lights on it.
Looks like some cool stuff your into.
Hear is something you may like,
I have the boat now and just need to put in back together.
Peter is the builder and check out some of his work in the link.
http://www.youtube.com/watch?feature...&v=3KTv0BP9ZhM

[pmdevlin]

Hi lenny, thanks for the info, I just read that link, similar problems.

the video has music, I thin k its getting blocked where you are,

Paul

[pmdevlin]

well as work is stopping me water testing, I have stripped all the drive lines down, replaced a couple of noisy bearings, and closely inspected the motors for any signs of damage, they look perfect. I have a pair of castle creations barracuda esc's that have not been used for ages, so might programme them and try them, this will eliminate esc's, but first will knock out the lvc and auto cell detection on my current esc's. Weather permitting, and wife giving me a pass out, hopefully will be this weekend

[lenny]

Also if you get a test run in check the temps on all your connectors,
I would put 5.5 bullet on the whole setup and be done.
Those banana plugs can be bad news on most setups just like the deans to.

[pmdevlin]

interesting Lenny, thanks, I use deans on pretty much everything thinking they were tight connectors and could handle the amps, I take it I am wrong, I do have 5.5mm on my huntsman 28. Just programmed out the lvc and auto cell count, and checked programming on a pair of old cc barracudas as a back up, so hopefully will sort this out, pity link didn't work, the video has two mini cameras on board, and the shoreside camcorder

Paul

[NativePaul]

Thanks for the memories Pmdevlin, my dad had a similar Vosper MTB that looks to be about this size that he powered with a pair of Irvine .40s back in the day.

It sounds like driveline binding or motor issue to me, as nice and neat as the long motor/propshaft combo is, you are bound to get some water up the shaft into the front motor bearing which could easily have rusted the bearings in storage, with the motors in situ the cogging of the motors wont let you tell if there is any binding properly. Regular use will stop deep pits of rust forming and will make the bearings last longer, drying and oiling the bearings after each day of use is the answer but is unfortunately not very practical. Hopefully the new motor bearings will get you going again for quite a while.

Check the drivelines for binding again now you have the motors out.

How big was the amp spike at the start of the run, circa 75A or more? Was that a full throttle holeshot and was it the only hole shot you did? A full throttle holeshot is always the biggest amp draw a boat will see, a prop has its highest load when spinning full speed at a standstill and unloads as the water speed nears the pitch speed, I typically see around double the ampage in the holeshot than I see at top speed.

The Video works for me, but I am in Great Britain too.

[pmdevlin]

Hi Paul

I have stripped it all down, and was surprised to see how much gunk had travelled up the tubes, after only a few runs. One motor had a slightly tight front bearing, so its all lubed up and free now. The amp spike was approx. 60a, boast usually peaks at 40a ay biggest speed, this was at a low speed. I don't punch the throttle, feed gently. Drivelines are very free, so hopefully the bearing clean up and replacement, and the esc changes will give me some positive results at the weekend, weather permitting!

[siberianhusky]

What does the Eagletree say the voltage is doing? That will tell you a lot about what is going on. You should be able to see what the voltage is at when the escs shut off as well as how well the batteries are holding their voltage under load.
One thing I noticed is you said batteries were at 3.8v/c, showing that voltage at rest means the packs are very close to 20% remaining capacity which for all intents and purposes means they ARE discharged for a lipo.
On all my 5000mah packs if I show 3.7V/cell at rest it takes about 4000mah to bring them back to full charge. Voltage under load is much lower.
The more I think about this the more it looks like batteries, you'd be drawing a lot more amperage than you are if you are going from a fully charged pack to 3.8V in a minute or less, that 3.8 resting voltage also tells me the esc isn't cutting anything off early, sounds like it's working properly to me and cutting the voltage at 3.2.
How many MAH is it taking to charge the packs? If you are getting a full charge and dumping the packs to LVC in 1 minute it has to be the batteries. Otherwise you are drawing somewhere in the vicinity of 240 amps!
@ 60 amps steady draw with a 5000mah pack you would see about 4 minutes of runtime or 1 amp per minute usage. My ballpark theory for determining runtime based on amp draw.