ESC Calibration

[john vlna]

I fly electrics with both timers and U/Tronics controllers. Sometimes an ESC which has been used with U/Tronics will not work with my timers. The first time this happened I just assumed it was an esc malfunction, but when it happened several times I realized there was something else going on. I found that the U/Tronics was setting the throttle range outside the limits of the timers. For example my U/Tronics will put out a .860 msec pulse on low throttle. The timer puts out a 1.013 msec pulse. The esc thinks the throttle is not in the low position and won’t start. Of course the esc doesn’t know that the timer is at idle. For some reason a new esc doesn’t have a problem, but once set with the U/Tronics it has too be recalibrated for the timers.
I found a neat tool which makes this process easy. It is the GWS MT-1. HK sells them for $20.
http://www.hobbyking.com/hobbyking/store/__4573__GWS_Servo_Tester_MT_1_w_Manual_Auto_select.html
 
You can measure the output pulse of a timer, U/Tronics, or RC Transmitter with the MT-1. Once the timer output is measured the MT-1 can be used to set the throttle range so the esc will function properly. The only thing I needed to set the timer up was a special cable I had to make that supplies power and connects to the GWS box and timer.

[Tim Wescott]

So are you using the box to adjust the timer, the ESC, or Clancy's U/Tronics controller?

What ESC brand are you using?

The "standard" servo pulse width range is 1ms to 2ms.  I put "standard" in quotes because it's not written in stone, it's just what everyone does, and there are some deviations.  Servos are much more tolerant of extra-large ranges (they just move more than 90 degrees) than ESCs (which have microprocessors in them, and therefore display anal-retentive tendencies).

I'm not surprised that a better ESC would recalibrate -- the designer doesn't want it to start up unexpectedly, but he does want it to idle nicely.  So as soon as you use the U/Tronics box, the ESC says "ah ha!  I'm being used with some weirdo system with non-standard pulse widths -- I'll just memorize that!!".

If it were me, what I would do going forward is to calibrate all my U/Tronics controllers so the throttle pulse width never gets below 1ms.  This requires that you either  mechanically limit the range of your throttle pot, or that you put an "idle" trim pot in series with your throttle pot to electronically limit the minimum pulse width.  This is going to affect the maximum (high-throttle) pulse width, and I honestly don't know what the ESC is going to make of that, what sort of ranges Clancy's controllers deliver, and so whether its worth while to also put in a trim pot to adjust the high-throttle end.

The schematic below is based on an astonishingly whole lot of guesswork on my part (and I hope Clancy sees this post, in case I'm handing out misinformation).  But it appears that his controller just sends out a pulse width that's proportional to the total pot resistance, plus a bit.  If so then the schematic below should let you adjust both end points.  The idle adjustment will be mostly independent of the full throttle, but the full throttle will pretty much track the idle -- so you'd want to set idle, set full throttle, then repeat once or twice to get everything dead on.

Code: [Select]

  White wire
       o----------o----o------.
                  |    |      |
                  |    |      |
                  |    |      |
                 .-.   |      |
            10K  | |<--'      |
    main control | |          |
                 '-'          |
                  |          .-.      100K
                  |          | |<--.  full-throttle trim
                  |          | |   |
                  |          '-'   |
                 .-.          |    |
     1K (or 5K)  | |<--.      o----'
     idle trim   | |   |      |
                 '-'   |      |
                  |    |      |
                  |    |      |
                  '----o------o----------o
                                 Channel Control Wire
(created by AACircuit v1.28.6 beta 04/19/05 www.tech-chat.de)


[john vlna]

I use the GWS box to set the esc. In RC it is common to range set the throttle.  Plug it the transmitter, go to high throttle, connect power, the esc beeps twice(OR WHATEVER FOR THAT ESC), go to low and the esc and transmitter are matched. The U/Tronics works exactly the same way.
The problem is that if the esc has been set outside of the timers low throttle range by either aRC or u/tronics unit, it won't recognize low throttle and it won't start.

The timers do put out a nominal 1msec pulse, but the U/Tronics can set a low down to .8msec which is far enough out to cause the problem. You could do it either way, I just find it easy to calibrate the esc.

Most of my esc's are Hobbywing, or HK/Nitroplanes rebranded units.

[Tim Wescott]

That's why I suggested the mod to the U/Tronics controller -- if you hold it to the same low-throttle setting as your timer, then you can swap back and forth with a will.

[john vlna]

Tim,
The problem is you still have to range set the esc anyway. They can't be trusted to hold their hi/lo setting. Since I fly electric carrier I want to know that high is high, low isn't too important, since carrier planes are seldom below 3/4 throttle.
john

[Tim Wescott]

They can't be trusted to hold their hi/lo setting.

Weird.  I wonder if a CC ESC would fix that.  Do they lose the setting at random, or only when you use them for electric carrier and then go back to stunt?

[john vlna]

I think it has to do with them sitting around not in use for a while. A good example is the other day I took a twin to the field. , first one motor would run and the other wouldn't, then it reversed. I re-calibrated both esc's and it was fine. Usually they won't start at all, but I have learned, when it is weird reset.Sort of like re-booting a computer when it hangs.

It could be because these are lower cost than some, maybe they fewer gates or something.

[Clancy Arnold]

Tim, John
Great discussion!  This is the first time the pulse width range problem has been brought to my attention. Thanks.

John is correct that my U/Tronics Control units will give a range of slightly more than the 1.0 to 2.0 msec. range as they were designed for use with analog Servos.  The use of them to control an ESC for electric power was tried and found useable. 

The Single Channel unit may have problems if the pot is at the handle but no problem if the pot is at the model and controlled mechanically (Three Line Handle). That is the way they have been used for Electric Navy Carrier for years. 

The addition of the two additional pots to set the end points should work fine.  The low speed end point pot I had recommended previously with a switch across it for engine shut off.  Adding the second pot will work fine but if you can no longer get full power add a fixed resistor in series with the 100K ohm pot. I would first try a 51K resistor.

The Single Channel U/Tronics Control unit has a wider output range than the Multi Channel system does so it may not have this type of problem.
Clancy

[john vlna]

Clancy,
I may incorporate the extra pots as you as Tim suggest in my new handle. It would solve the compatiblity issue with timers. I would still recalibrate on a routine basis though. It only takes a minute, and you are sure the U/Tronics and esc are matched.

The GWS box would be handy for setting up the extra pots since it directly reads pulse width. It also supplies a regulated 5v.
john

P.S.In thinking this over, all I need is the low speed pot, That is the compatability issue. High speed does not matter.

[Tim Wescott]

It could be because these are lower cost than some, maybe they fewer gates or something.

In this case it's probably cheaper engineering, for the most part.  Although there may be $0.10 worth of components left out that would give the microprocessor more reliability coming out of reset.  Like Chevrolet with the Vega, someone in charge doesn't know (or doesn't care) about the difference between "inexpensive" and "cheap".

[john vlna]

When you are making a quantity of a product, a few cents can be important. The cheap esc's are pretty good. I have run them over their amp ratings, actually let some smoke out of one and otherwise abused them over the years. Haven't had one break yet. So for the price I'll accept a bit of maintenance to keep them tuned.

Bought a 72 Vega in 1974 for my daughter for $350, burnt a lot of oil but she drove all through high school and for a while after. She sold it for $300. Amazing that the thing ran, should have called Ripley's

[Clancy Arnold]

I have just added information on adding Throttle End Point adjustments to my U/Tronics Control, Vendors Corner.

It is in the "Special Controls or uses of U/Tronics Control units" thread.

As you can see below, I have also added the information on an I.C. Engine Kill Switch.
Clancy

[john vlna]

Clancy,
Looks good, one point however. When you send the signal to the esc you only connect the control signal and ground.
Power is not needed snce the esc gets its power from the flight battery
John

[Clancy Arnold]

John
Thanks for spotting that!  You are correct there should not be a connection to the Red wire.
I Will try to fix that drawing.  I was only thinking about the end points and the kill switch when I as drawing it.
Clancy