Radio Control with track ( overhead) power supply....

[tramcar trev]

[size=medium]So here we are again looking at the radio control setup/wiring for the track powered trams. In the top circuit we can see a diode and a huge anti flicker capacitor which is sposed to have enough current to supply the Receiver during times of intermittent contact. Now this works well in an intermittent manner, if I have surgically clean track and overhead everything is good. Introduce however the smallest bit of grunge and it dies and the receiver has to be reset.  :`(  The ESC handles signal drop outs of up to 2 seconds without problems, the receiver is far more temperamental. [/size]


[/size][size=medium]I hope the bottom circuit solves the problem. The capacitor has been rewired to provide power to the Receiver only via the Rx “power bus”. It is hopefully to be kept at a float voltage of 5V from the battery elimination circuit (BEC) in the Electronic Speed Control. It seems that the receiver is the critical link in the chain and this electricity is funny stuff , like most things prefers to take the course of least resistance and that was through the motor. I have eliminated the diode which also eliminated its inherent .7V drop. I am waiting a suitable lead to try this out. If the capacitor does not have enough capacity then a battery might be a better way of keeping the Rx “alive”. I don’t know the formula to convert uF into mAh.  The RX draws 85mA @ 5V according to the specs so how that equates to 20000uF @ 5V is anyone’s guess……[/size]

[/size][size=medium]This has to be the problem via a process of elimination, the battery powered steam tram has none of these dramas and the only thing that is different is the method of power supply... The overhead powered trams run impeccably ( meaning of course "without pec&quot on the test bench with the juice supplied via alligator clips.[/size]
[/size][size=medium]Anyone any thoughts? What have I yet again missed?[/size]

 

[tramcar trev]

Just found this. Maybe I am on the right track....


http://www.hobbyking.com/hobbyking/store/__16223__TURNIGY_Voltage_Protector.html
though my 20000uF will be much betterer.....

 

[DoctorM]

Looks like you're on the right track then Trev, just using a bit more Youf

 

[gregh]

Just found this. Maybe I am on the right track....

http://www.hobbyking.com/hobbyking/store/__16223__TURNIGY_Voltage_Protector.html
though my 20000uF will be much betterer.....

You're going to need more than the 3300uF of that thing Trev.
I just did a test on a Hobbyking V2 Rx. It takes 20mA. It stops receiving at about 3V.
Now the approximate equation for a capacitor size as it discharges is:

Change in voltage = 1/C x current x time( for voltage to fall by the amount)
C is in Farads !!!

So I grabbed my biggest C = 47000 uF. It powered the RX for about 4 secs till the RX stopped. Sticking the values of 2V change and 47000 uF gave a calculated value of 4.7 sec. Close enough for me given the cap tolerances!

So figure out how long you want to go without power and stick it in the equation, using 2V drop.

You probably need one of these:

http://www.hobbyking.com/hobbyking/store/__17098__Turnigy_Voltage_Protector_550000uf_1_4sec_.html

or Jaycar still sell the 47000uF ones I think.

 

[tramcar trev]

Yes, I am going to use 20000uf as I have a stack of them. That would allow an interruption of 2 seconds approx. The actual interruptions that are causing the problems are less than I can measure. Other measures are being taken to ensure continuity, rotating trolley wheels are out and a wire jumper from the trolley pole to the base is in. Other losses occur between the wipers and the wheels and I found that replacing the existing brushes that run on the inside of the wheels with beryllium copper wipers that run on the tread of the wheels helps scrape any crud off the wheel and provides better continuity. The test I performed on the RX was very scientific, I powered it up and dragged the + wire across the connection and that was enough to kill it. Nanosecond breaks in continuity seem to be the problem.


The 550000uF Turnigy one would be nice (right price too) but I have no where to fit it.


If the caps do not work then I'll power the Tx via a cuppla lithium button cells, [SIZE=78%]7.4V, ( 2032's and buy them in bulk from Hot$ in packs of 20 for $2) or I could fit in 3 AAA ni-mh cells that would float on the 5 V from the BEC on the ESC assuming that the 3.6V would be enough to stop the brownouts. It says in the manual that I downloaded that the Rx needs 6V and the BEC is supplying only 5, this may be half the problem but it works fine on the BEC in the battery tram.......[/SIZE]

 

[Dtsteam]

This is good stuff Trev, but if you're not careful by the time you've added capacitors and batteries you could have gone full battery, like the steam tram. Having said that, I would agree that you are trying to cover multiple tiny glitches, and on the other hand you don't want to overrun, otherwise the tram won't stop quickly enough if you de-wire.

 

[tramcar trev]

I discovered that with the current (pardon the pun) setup that the trams travel about 300mm if the pole comes off the wire. Now I would have thought that would have been enough juice to keep the Tx alive, obviously not....
Yep its multiple micro interruptions that is the problem, sort of like clicks and pops in a record....

 

[PhilP]

Could it not be the 'edges' of the very short-sharp interruptions causing RF interference, rather than brown-outs that are the problem??

Just a thought.. I would have thought if the outages are that short a small 'C' would suffice.

PhilP.

 

[tramcar trev]

Ok, I'm just about to go to my Friday Briefing, this will be a very festive occasion with all the great technological minds of the 70's to the 90's celebrating Xmas. I'll throw this into the ring without notice. Now that I have the answer it's safe to do it, you never ever ask a question if you don't know the answer.... :-X


Meanwhile I'll slip quietly into Jaycar ( following Gregh's advice) and buy a few of these, if these do not solve the problem nothing will;
http://www.jaycar.com.au/productView.asp?ID=RU6705


I know that a 1F cap will give me about 800mA for about 10 seconds so @ 20mA they should be more than adequate.... Maybe sell them to Turnigy?

 

[nicebutdim]

When I think of a 1F capacitor I think of the one I have in the shed, removed from my audio setup in the car when I ended my 'boy racer' days. It's about a foot long and the same diameter as a drain pipe. Weighs a fair bit too...

 

[tramcar trev]

I have serious problem This works brilliantly with the 1F cap plugged into the battery socket on the Rx if I test it using the power supply on the bench. I can turn the power off almost make a cup of tea, power on and all runs like a tram.
Take it out to the tramway, Tx on, trolley wheel on the wire, and zip, zilch nothing whatever happens apart from the leds and lights coming on.....


I'll have to try and suss out what is going on.... Thoughts? The tramway is powered via a 15amp 12volt switchmode power supply and a meter confirms that there is 12V. I thought it may be because the trams are laying on their sides on the test bench so I turned it up the right way connected the power, twiddled the knob and it took off.....
Its getting frustrating...

 

[Neil Robinson]

"I'll have to try and suss out what is going on.... Thoughts?"

No idea but I've an idea that may help with diagnosis.

How about making up a longish length of jumper wire with a kroc or similar clip at each end?
Clip one end to the overhead wire and the other to the trolley pole. Test run with the trolley pole down, then up and finally up with the jumper wire removed.

 

[tramcar trev]

I'll try anything Neil.... If it works with the "flying lead" (often used in full size practise to get trams out of sheds that don't have overhead in them) I'm not sure where I go from there..... Voltage drop in the overhead that the meter doesn't detect (maybe measure that under load)??
Something very strange is going on here. I asked at my friendly R/C shoppe yesterday and they said that it may be because of my "cheap" ESC that would have a linear BEC and I really should be using a UBEC... Mind you these same experts told me that there was no way I could repackage the Tx and do what I wanted to with it, when I demonstrated it to them they still didn't believe me and had to open it up to see what was inside [SIZE=78%]....[/SIZE]
[/size]
[/size]

 

[PhilP]

Anywhere you have a non-solid connection (ie. not a soldered, crimped, or clamped connection) there is the potential (no pun) to introduce noise into the system..
It would not surprise me if it was high-frequency noise, rather than power drop-out that was causing your problems.

I would try several turns of wire on a ferrite between the pole and rest of the circuitry in the tram.

 

[Tony Walsham]

Trev, You need to limit the inrush current going to the capacitor as it recharges after the break in the circuit. That inrush takes all the power away from the device it was intended for.
That would be a proper battery charge circuit. In other words, run the tram on batteries and keep the batteries charged from the overhead.
That can get so complicated, you might as well go batteries only in the first place.

 

[tramcar trev]

Ok, yep turns round a ferrite sounds good and I'll tell you why. I noted that on the more upmarket ESC's with a BEC there is exactly that on the lead to the Rx. They would not put it there for no reason.... maybe even up the track voltage and install an on-board rectifier?


I have already thought of running the Tx on batteries and that's the next step. I had given serious consideration to battery power but I have no where to hide the batteries unless I tow a trailer with frosted windows with a battery inside...


Failing batteries maybe dilithium crystals would be a more provide a pure supply? (I have to maintain my sense of humour)

 

[tramcar trev]

The mystery is solved!!!!
I checked the power supply under load and when I put a tram in first notch it just faded away. Opened it up and discovered a capacitor (fortunately an obvious fault) had split. Replaced it with a larger capacity one that was all I had available and it all runs like a tram. This explains the stop start thing. The ESC is designed to shut off at around 10.5V to protect what it thought were LI-PO batteries from over discharge, it also shuts off at 14.8V to protect itself....
So there is no need to go through the antics of soldering all the trolley wheels up etc but I will still fit the 1F caps across the Tx power bus, it does help keep things alive with dirty track.
It's so embarrassing, that should have been the first thing to check, I just put a meter across and got 13.5V...........


I'm so relieved I had salmon for dinner to celebrate!

 

[tramcar trev]

I have fitted a 1Farad (yes that is 1 Farad) super capacitor across the Receiver battery socket to prevent “brownouts”. Those of you who travel/ed by tram will recall the internal lights flickering when the tram went through an intersection. Mine do the same but it’s due to bits of non conductive matter (aka bird poop) on either the rails or the overhead wire. This capacitor keeps the Receiver and speed control “alive” during these glitches which means the tram can go on for a few ( around 7) seconds with out the need to reset the R/C setup.

[/size]All is now ready for the Watsons Bay tram to get the crowds out to South head to watch the start of the Hobart Race....
[/size]
[/size]The super capacitor is the cylindrical object with 5.5V visible.

 

[tramcar trev]

One tram was operating erratically, had me stumped....The motor kept stalling and I assumed something was binding.... WRONG the .01uF capacitor across the brushes on the motor that are needed with the keyfob controller was somehow interfering with the ESC. I had forgotten to remove it when I wired up the tram for "proper" R/C....
Yet another trap for young players....