Pico Mos 33 with brushed motor
|Stephen Belshaw||19/11/2018 10:59:37|
|106 forum posts|
I am trying to get my old Twin Star airborne after a very long lay off. I have swapped out the old NiCad for a new 2S Li-Po battery. All connected to a GWS micro receiver (I am running this on Futaba 35MGhz gear), all the other three channels work fine apart from throttle which leads me to think the ESC may be at fault.
It's receiving power and shows two red lights, when I open the throttle one red light goes out but the motors do not spin. The ESC is not beeping either, which I believe it should do on start up?
|John Rudd||19/11/2018 11:32:51|
|96 forum posts|
The beep noise comes from the motor, not the speedo....does the motor work in isolation? Ie does it run with a supply connected to it...( Safety first....take the prop off until you get it all working..)
|Denis Watkins||19/11/2018 13:50:29|
|4327 forum posts|
early Brushed ESC were not set up for Lipo, and may work, but is hit and miss
Edited By Denis Watkins on 19/11/2018 13:56:30
|Stephen Belshaw||19/11/2018 14:25:15|
|106 forum posts|
John, thank you for prompting me to look at the motors - it turned out to be a dodgy connection on both of the motors. Although they appeared fine on an earlier visual inspection, the spade connectors had worked loose causing the loss of voltage, I had therefore assumed wrongly that the problem lay with the ESC.
All is up and running now on the Twin Star for the first time in many years and it seems the old technology ESC is "happy" with the Li-Po battery.
|Stephen Belshaw||19/11/2018 14:40:04|
|106 forum posts|
Interesting article, so whilst the LiPo will run my brushed motors through the Pico Mos 33 it will destroy itself in the process due to the ESC not being able to adapt the cut-off voltage to suit a LiPo.
Does that mean all my efforts are in vain? Should I ditch the ESC?? Such a shame as the thought of resurrecting my "vintage" TwinStar without replacing averything bar the airframe was very appealing. I intended to use this as my return to flying plane and fly it in to the ground as a route to regaining my flying skills.
|Peter Beeney||19/11/2018 15:30:24|
|1587 forum posts|
I’m not sure you have to worry too much, Stephen, I flew a Twinstar with the brushed motors on a 2S lipo for a long time without any problems at all.
As it happens the gentleman in the linked article is actually talking about a 3S lipo, and the ESC cut-off is related to the battery TLC anyway, rather than the ESC, i.e. it cuts off the power supply at a predetermined level to protect the battery; perhaps it’s better title would be a voltage cut-off point; in your case about 6.5 volts if you can adjust it. In my case I just let it run until it began to sag a bit and then land.
In my opinion the worst thing that can happen is the power might be cut off a bit early, resulting in a shortish flight time. I don’t think you will do any damage. If it fails to recognise the battery voltage at all the performance will eventually start to fail but at least that will give you an indication of the flight time.
|Simon Chaddock||19/11/2018 16:26:53|
5685 forum posts
The issue of LVC will depend on how many cells the brushed ESC thinks it connected too.
Some had auto 'cell detect' some had to be 'programmed'. How many cells in its original NiCd battery?
A fully charged 2s LiPo will be showing close to 8.4 volts.
If the ESC has auto detect it would likely assume 7 Nixx cells and set the Low Voltage Cutoff (LVC) to about 7 volts.
As Peter suggests this is just a bit 'early' for a 2s LiPo but quite safe.
If the ESC was a programmed type and was set for an original battery of 8 cells (9.6V) then the LVC will be too high for a 2 s LiPo cutting power at about 8V which would mean only about 30% of its capacity has been used.
The LVC for Nixx batteries was really more to maintain power to the radio before the battery ran flat so was not that critical unlike LiPo where maintaining a minimum voltage is vital to avoid permanently damaging its cells.
|Stephen Belshaw||19/11/2018 16:32:17|
|106 forum posts|
Thanks for the reassurance Peter, that's very good news - I can cope with shortened flight times as I need the landing practice!
That's one model sorted then. Moving on to my next resurrection, a Cherry ii, this ran on a 10 cell Nicad powering a Speed 700 and I've swapped this for a 3S LiPo controlled by a Graupner "Mini Switch 40". Can I assume the same scenario with this set-up or do I need to worry anew?!
My third project is an unflown partially built Graupner Match, this has a Speed 600BB (I think) running thorugh a Jeti JES 350 ECO, originally intended to be powered by 7 cell Nicad. I intend to use a 2S Lipo and queried the suitability of the ESC with Jeti and received the following reply: "Thanks for your enquiry, the JES 350 Eco was designed to work with 6 to12 Ni-XX which is 7.2 to 14.4 volts so should be fine on a 2 or 3 cell Lipo"
|Peter Beeney||19/11/2018 17:31:54|
|1587 forum posts|
Yes Stephen, I’d think the Cherry II would be ok, I suspect the 10 cell nicad LVC point would be about 10 volts perhaps, you might like to consider cutting the the 3S lipo power at a slightly higher point, do a bit of experimenting and then stay within the flight time limits.
I’ve never been very fussed about LVC points anyway, I have a long time flying mate that generally flown small fast foamies for many years time now and he’s always gone right to the limit all the time without any particular problems.
If you start doing some serious flying you may find those brushed motors soon start becoming a bit tired, at that point have a go at upgrading to brushless. You will like the improvement!
|Stephen Belshaw||19/11/2018 18:39:26|
|106 forum posts|
Thanks once again Peter, yes I will upgrade to brushless at some point but probably when I get a new airframe (or two). My intention was to get as much out of what I've got whilst getting to grips with flying again and of course not worrying too much about the risk to my models which long ago paid for themselves.
My background is slope soaring but sadly I don't have the hills around where I live, but I do miss the simplicity of it compared to electric flight!
4383 forum posts
Stephen, I think a lot, possibly the majority, of pre-lipo friendly ESCs had the LVC (PCO) set only in order to ensure a sufficient voltage level for the BEC to operate (5 - 6V) regardless of how many cells were being used. Remember unlike lipos, nickel batteries can be run down to very low voltage levels without suffering any permanent damage.
Here's a link to Ripmax info on the JES 350 ECO.
PCO - Power Cut Off system - gives a safety margin during the flight. As the
Whilst it's not definitive I would take that to mean that it could go down to around 5 - 6v before cutting off. Also there's no mention of the LVC/PCO being varied according to the number of cells.
I've been using a pre lipo Model Motors (Makers of AXI) 40 brushless ESC with 3s lipo in my RelaxE thermal glider for around 10 years without any problems. Most flights have been 30 - 40 secs of power followed by glide repeated up to another 4 or 5 times, depending on my boredom threshold on the day. I've already checked from previous sessions that the battery won't have run down to a damaging level with this usage pattern. About a year ago I fitted a telemetry voltage sensor set to trigger an audible alarm in the Tx if the voltage drops to 9.6V - so far the alarm hasn't been triggered.
Re your Twinstar; even if the LVC is 5 - 6v this is not likely to cause lasting damage to a 2s lipo if only reached occasionaly. However IMO it would be prudent to time the first few flights then check the voltage & adjust the length of normal flight time accordingly.
|Geoff S||20/11/2018 00:37:46|
|3585 forum posts|
I don't worry too much about the LVC (low voltage cutoff) level on my LiPo brushless models. I don't think I've ever got anywhere near triggering it. I time all my flights and know when to land with at least 15 to 20% remaining so, if you start out with relatively short flights and check energy consumption, there isn't any danger of damaging a LiPo.
Last Thursday I took my Wot 4 which flies with a 4S 4AH LiPo up to the field with 5 batteries. My flights were up to 10 minutes and the worst case was 22%. I aerobatics but practice throttle control.
Don't worry and fly your TwinJet. You've reminded me that I have one up in the loft. I should get it out
Edited By Geoff Sleath on 20/11/2018 00:38:18
|Dave Cooper 3||20/11/2018 08:56:10|
|65 forum posts|
I think the worst-case scenario is late cut-off of the BEC. This happened to myself and a friend when we built the HobbyKing Phoenix 1600 electric glider (this is our club's chosen one-make competition machine).
The motor is a modern brushless with a programmable ESC and a 2s LiPo. His model crashed (fortunately without too much damage) when he ran out of radio contact and he immediately phoned me to check mine. The motor and ESC are supplied with the kit. I tested mine on the bench and had a max.of two or three control movements just as the motor was running down. None of the other kits had this problem and came from an earlier shipping 'batch'.
After some more bench testing, HobbyKing supplied a replacement ESC...the first job was to 'calibrate' the ESC to the motor, the second was to set the prop brake (using their instructions). Next, I took a LiPo that was down to about 50% capacity and timed a 'dummy' last flight until I was satisfied that I had enough range and control movement to safely land the glider.
The moral of the story, IMHO, is to know the limitations of each model /installation and use planned flight duration times if there is any doubt...Happy flying everyone !
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