Controlling Interest - September 2000

Bernard discusses the issue of self-calibrating ESC's, and looks at two micro slowfly controllers.

 

This time we're going to revisit one aspect of the main topic from the September 1999 column, and take a look at two tiny US made speed controls.

Self -Calibrating ESC's - A Good Idea or Maddening Complication?

In my September 1999 column I wrote at length about a feature of the throttle function of electronic speed controls which varies widely from maker to maker: matching the speed control's range and endpoints to your transmitter. Since that time I've seen a number of approaches to dealing with this question, and more recently, it has been a topic of some lively discussion on the Eflight mailing list. In particular there has been a discussion about the relative merits of "self calibrating" ESC's in comparison with those which have fixed endpoints and range or programmable endpoints which are "remembered" between flying sessions.

As those of you who have been reading my ramblings here on the E-zone for awhile know, I generally like the trend in microprocessor-based ESC's to self-calibrate the throttle function to my transmitter. I only own one transmitter that even has adjustable endpoints on any of the channels, and since I usually fly more than one plane with a given Tx (including that one), I don't like to mess with these adjustments. It's bad enough just keeping track of reversing switches. I suppose a microprocessor-based transmitter (a "computer radio") needs to be in my future, but I don't have one now. Even so, I like the stick motion to match the throttle’s response.

Back in the heyday of analog ESC's (say 6 or 8 years ago) many of the better throttles had two adjustments, one for span and one for an endpoint. Between these two adjustments, you could usually get a pretty good match between the ESC and the transmitter. When the microprocessor-based units first came on the scene, they simply had programmed into them assumed starting and ending points that were selected so as to try to work with most transmitters. But, since there was (and still is) quite a bit of variation in transmitters, for most of them this meant a noticeable amount of wasted throw at one or both ends of the stick’s travel.

Some ESC makers use this approach today – the control’s end points and range are what they are, and there is no way to change them. Some current examples are all the Astro Flight digital units, as well as Castle Creations controllers made before the middle of this year. If you have a computer transmitter, you can adjust the transmitter to match the throttle stick’s response to the ESC, rather than the other way around.

Astro Flight’s 215D, a fixed endpoint controller

Others, as I mentioned in the September 1999 column, have adopted various ways to allow the ESC to be adjusted to the transmitter, just like in the old days.  A few of these, however, allow you to adjust the ESC to a particular transmitter just once as you would with two adjustment potentiometers on an analog controller. Implementing that ability in software is rather more complex, I think, than putting in those two pots. Two types I have tried that allow you to set endpoints and retain them are Aveox 60 and 160 series brushless controllers (but not the 260s), and the Kontronik Star series of brushed motor controllers, when they are used in other than APM mode (more on these in a column in the near future).

Kontronik StarBEC 50-6-14, a control with one-time settable range and endpoints, or self-adjusting range and endpoints, depending on operating mode

Most adjustable microprocessor controllers use various approaches to automatically adjusting the start and endpoints each time they are powered up. There are many variations here. Some only adjust the upper endpoint, some only the lower, and some adjust both. Some adjust themselves only when first powered up; others will re-adjust anytime during use when they "see" a higher or lower signal from the receiver than they’ve seen before. You can get some sense of the wide number of variations by reading some of the mini-tests of speed controls in my columns published since last September.

For folks like me who are sport flyers, these self-adjusting throttles are great. Especially when coupled with a reverse-exponential throttle curve (Aveox 260 series, all current Castle Creations controllers, Kontronik Sun 4000, for example) they provide a very satisfactory "feel" of control. I expect that pilots of scale models would also find this type of ESC gives their power system a pleasing response.

Kontronik Sun 4000, a self adjusting ESC with a reverse exponential throttle curve

But not all electric model flyers fly the way I fly, or fly the types of models I fly. And for some of these folks, self-adjusting controls can be a problem. So, here are some other ideas about them that have been mentioned on the Eflight mailing list recently.

Doug Ingraham, who is the man behind the software in Astro Flight’s digital chargers, speed controls and the marvelous tool called the Whattmeter, remarked recently that if an ESC is self adjusting "…It means you cannot make the ESC do what you want. Changing endpoints and centering on your computer radio will have no effect. However, if there is some way to set the endpoints in the unit this is fine [like the Aveox and Kontronik units mentioned above – BEC]. It is the ones that figure it out on their own that cause no end of difficulties."

In a later message he added, "OK, here's the one that caused me to kill this feature in my own designs [the Lofty Pursuits LPSC-1 and LPSC-mini – BEC]. I fly a fun fly plane. At about 1/3 throttle stick I want the power to be off. The reason for this is below 1/3 I use a mixer to mix in a ton of spoilerons to provide landing drag. With a self adjusting endpoint unit you cannot make this work reliably.

"I have watched smart people swear at their self adjusting ESC when the behavior was not what they wanted."

A bit later in the same post Doug added "So if you want the ESC at full power with the stick at half for some reason, how do you do it? A reason that comes to mind would be a sailplane with an automatic launch mode setup mixed in on the full throttle."

So, one place where a self-adjusting throttle function would be undesirable is where you might want to mix in some other control or controls with the throttle. Another obvious example is in helicopter applications where it is routine to mix other controls with the throttle.

Ralph Weaver, who flies in some electric sailplane competitions as well as being the man behind Magellan Technologies, had a bad experience with a self-adjusting ESC. He posted this: "I've mentioned it before, but the ESC's with auto adjust endpoints can be a real problem for Limited Motor Run competition. I got my transmitter from the impound tent and about half way through the glide part, my motor started to barely tick over - disqualifying me. Turns out that if the end points are set when the TX is cool, the motor can come on as the TX warms up in the sun. I can duplicate the condition at home using the refrigerator."

"I don't like adjustable end points at all, but they are OK for sport and may be a benefit for use with simple transmitters. I set the end points and the throttle curve with my transmitter."

Others suggested (and I nearly did) that to get around this he simply have the throttle trim high when first powering up, then moving it lower after the ESC has "read" his signal and therefore assuring that "off" stayed that way. He replied that he tried that, but that the ESC he was using readjusted the "off" point, which defeated this solution. Some self-calibrating ESC's, as I mentioned earlier, will continuously reset both endpoints whenever they get a new signal outside the range they "know about". These include the Viper Models units and, apparently, the Schulze Ralph was using. (I just received some Schulze units to test, so I'll have more to say about them in a later column.) Other self-calibrating units either reset the endpoints only once (like the Jeti's) or do not reset the "start" point at all, such as the Tarling MicroStars and the FMA Direct (R/C Line) units.

But Ralph’s experience with the motor coming on uncommanded is something competitors need to be aware of in events where running the motor at a particular time counts against you. However, I’m not sure that this problem couldn’t occur with other than self-setting controls, depending on either the maker’s assumptions or the adjusted/programmed endpoints.

Greg Kamysz, head man at Specialized Model Supply, had another thought. He said, "Since many of the current ESC's are not using the reverse expo throttle curves yet, changing the endpoints and centers on the TX allows me to set half POWER at half stick NOT half VOLTAGE which you normally get. Half voltage doesn't get you half power when you have a motor connected to the other side. Half power at half stick makes taxiing and flying much more controlled.

"I will only buy ESC's with fixed endpoints, or like Kontronic, programmable fixed endpoints. The ones that set every time you plug in a new pack are a pain. Especially if you don't move the stick to full throttle the first time you power up."

Greg's first point echoes my own feelings about the advantages of reverse exponential throttle curves, as I've discussed in prior columns (most recently in the April, 2000 column). He apparently uses the endpoint and centering adjustments in his computerized transmitter to simulate this effect with linear throttle curve ESC's.

His second comment, about moving the stick to full throttle the first time you power up, refers to the behavior of those self-adjusting ESC's which only reset the upper endpoint and range once when you first advance the throttle, such as Jeti's or Kontroniks. Wherever you stop moving the stick (past the upper endpoint the controller assumes upon power-up) becomes the new upper endpoint. This setting remains until you reset that ESC, typically by unplugging and replugging the battery. Kontronik's instructions for the Sun 4000 and for the Auto-Programming Mode of the Star series controllers include the step "give 1 second full throttle or start with full throttle". Since I've been flying the Sun 4000 in the Electric Scout, I've learned to simply run it up briefly before releasing or launching it every time, which assures me that full throttle is where I expect it to be. However, one usually commences a takeoff roll or hand launch with full power, so that’s probably not really necessary. As I mentioned before, other self-adjusting units (including the Castle Creations Pixie-7, discussed below) will move the upper endpoint whenever they "see" a higher pulse duration than they’ve seen before.

Finally, weighing in on this discussion in favor of self-adjusting throttle functions in ESC's was Gordon Tarling, maker of the MicroStar line of ESC's in England. He said "....What more can you want an ESC to do other than give motor 'off' with stick all the way back and full power with it all the way forward and reasonably linear power change in between? If it self-calibrates to your radio, why on earth do you want to mess with endpoints and centering? You NEED to mess with those if you have a non-self-calibrating ESC!"

This expresses my own thoughts pretty well, also.

And in another post Gordon added, "So you'd prefer to program the ESC endpoints rather than have them set automatically? My MS40BEC allows you to program them once and they are then stored until you change them again - however, that facility makes the ESC larger, heavier and more expensive than competing types so, naturally, it doesn't sell so well."

And in a third: "In my experience, if the ESC doesn't auto-set both endpoints, then there is the danger that the customer will be running his motor at part throttle when he thinks it is at full throttle - result is either a complaint of lack of power or a burnt-out ESC!"

So, there you have it: some different ideas about the merits and drawbacks of the self-adjusting type of throttle function. Like other features of these collections of electronics in our power systems we call ESC's, they help make each maker’s products different, and give you, the electric model flyer, interesting choices.

This leads me to ask for some specific feedback. As I’ve mentioned a couple of times before, I want to put together a series of "buyer’s guides" of different groupings of ESC's, starting with one for 5A or so units for use in indoor/slowfly/parkfly types, one for 15-20A or Speed 400 type applications, and one for 30-40A sport speed controls. What I would like to hear from you about is this: What features or characteristics of these controls would you most want me to tabulate or comment on? I could do the usual table of weights and measures, but I think there are other things that are of interest as well. For example: for the throttle function, how are the endpoints and range set, and once set do they "remember" or continuously readjust? If there’s a brake, does it come on immediately, or with a delay? Does it stay on, or release after a delay? Can it be disabled? If so, how?

Anyway, I’d love to hear the one or two things you most want to know about a bunch of speed controls. Drop me an e-mail at abc_quiet_flight(at)operamail.com or ab_cawley(at)compuserve.com and let me know. Then, perhaps, I can do one of those guides next time.

Speed Controls of the Month: Sirius Electronics GFS! and Castle Creations Pixie-7

Sirius Electronics GFS! on top, attached to a Speed 280. Castle Creations Pixie-7 below

This time we’re going to look at two recent entries into the slow flyer/park flyer speed control market. Both of these are from small US companies, Don McGlauflin’s Sirius Electronics, and Pat del Castillo’s Castle Creations. Both are microprocessor-based controls, and both are rated for more than the usual 4 or 5 Amps for controls in this category. The GFS! (that stands for "glitch filtering software", by the way) is rated at 10 Amps continuos, and the Pixie-7 is rated at 7A. While both are aimed at the slow flyer/park flyer user, they take very different approaches to several features. So, let’s take a look at each one in turn.

Sirius Electronics GFS!

I spent quite a few minutes this past February visiting with Don McGlauflin in the Sirius Electronics booth at the Northwest Model Exposition in Puyallup. Don’s company is the maker of the various Sirius Charge NiCad chargers, as well as the Super Test discharger/analyzer. Sirius Electronics products have a well-deserved reputation for quality and durability, with their Pro Series fast charger for transmitter and receiver batteries probably the best device if its type available in the US. The GFS! is Sirius’ first foray into speed controls.  It blends Don’s newfound interest in many types of lightweight RC with his electronics design expertise, adding a purist’s bent.

One of the things Don told me that February afternoon was that many of the small speed controls he’d looked at were rough in operation and prone to glitching, especially when used with the less-selective receivers often used on/in indoor models. He also noticed that the battery eliminators of many small ESC's were overtaxed, especially when used in models running on nine or 10 cells, as has become common for some of the higher performance indoor models such as Todd Long’s Tiny.

His solution to these shortcomings is a slightly larger unit than some, though still quite small, with lots of metal clad heatsink area on the regulator side of the board (and nothing else). On the other side are the usual components – one surface-mount MOSFET, a tiny microprocessor and a couple of other items, as well as good sized discrete Schottky diode, with the leads left full length. These diode leads are to be soldered directly to the motor you are driving with the GFS!, and all other wiring exits the board on the opposite end. Ready to use weight, with a 7 inch (18 cm) receiver lead and a 5 inch (12 cm) battery lead ending in a 3-pin Deans connector is about 5 grams, or about 0.2 ounce.

In the accompanying instruction sheet (one sheet, both sides, with color illustrations) it is claimed to work with anywhere from 4 to 16 NiCad cells, with the BEC useable all the way to 16 cells. The instructions caution you to test when using 10 cells or more and check to see if the combination of equipment you are going to use is OK by exercising the servos continuously while checking the regulator’s temperature. They go on to say "if the BEC becomes too hot to touch, you are nearing the limits of heat dissipation, and should either reduce battery voltage, our use smaller servos." I ran it on 8 cells in my ModelairTech Skimpy and continuously ran the two HiTec HS-50 servos by simply moving the transmitter stick in a circular motion. The regulator did get quite warm when doing this while I held my thumb over the regulator. But with some air circulation it stays quite cool.

In operation the throttle function is indeed very smooth in operation at all possible motor speeds (there seems to be 16 steps between off and full power), even the slowest. It also appears to be of the fixed range, fixed endpoint variety, with no adjustments possible. I measured "on" at 1.28 ms pulse duration and "full power" at 1.83 ms with my trusty Ace Datamaster. However this range seems to match the HiTec Focus 3 AM transmitter I fly with my Skimpy pretty well. This means you need not worry too much about where your stick is when you power up. If it is above the start point, the unit will not arm. Pull it back and wait a moment, and then away you go.

In the rest of my battery of tests it performed quite well, being only slightly soft, but very smooth in response to speed change commands. When the transmitter signal is lost (turned off) the motor continues to run at the same speed for one second, then shuts down decisively with no glitching of the other controls. If the signal is restored, the control picks up where it left off.

Part throttle operation, at least at Speed 280 current levels, led to no discernable warming of the unit.

When the voltage cutoff is reached the motor is cut cleanly, and can be rearmed by moving the throttle stick to "off" and back up again. There seems to be no delay in rearming.

Flight testing was performed in my trusty ModelairTech Skimpy.  The Skimpy is powered by a geared Speed 280 (Titanic Airlines 3:1 gear drive) on 7 NiCad or 8 NiMH cells, and has a Hitec Focus 3 AM receiver (and matching transmitter). The receiver antenna is currently wound around a plastic drinking straw, as has been suggested on either the Eflight or Slow Flight lists, as a way to physically shorten an antenna without reducing range very much. With this setup, the GFS! was rock solid in the air with never a glitch, even when flying within the confines of a Little LeagueŽ Baseball diamond surrounded on all sides by a metal chain-link fence - a prime location for reflected signal interference. The 16 steps I noticed on the bench proved not to be an issue in the air – the control is responsive enough that I never felt I needed more "speeds". In the Skimpy’s flight log I noted that I liked the way it responds.

ModelairTech Skimpy, small speed control testbed

So, overall it seems to do just what it is supposed to do. I would be a little concerned about suspending it from the diode leads in the long run, but if you were to dedicate it to a model you probably wouldn’t have it sticking out like I have it in the pictures. Don’s trade show demonstration unit actually has the diode leads bent so that the control is above the motor, not sticking out behind it.

That one reservation aside, I am impressed. Even though it has fixed endpoints, they work well for me. I haven’t yet measured things to see if there is any reverse exponential in its throttle curve, but it had a quite acceptable feel in flight. Mine is going into my ModelairTech Slomowatt, where it’s relatively high capacity BEC will be used, in part, to power a tiny color video camera.  This will free up the Castle Pixie 14 that is currently in the Slomowatt for use in a Speed 400 powered project I’m working on.

See the table below for the various weights and measures.

Castle Creations Pixie-7

The Pixie-7 is the tiniest in the Castle Creations line of tiny speed controls. As its name suggests, it is rated at 7 amps continuos. It is the smallest production speed control I have yet seen, being both shorter and thinner than the JMP7 I wrote about in my October 1999 column.   The Pixie-7 measures about 0.5 by 0.3 by 0.2 inches (12 X 8 X 5 mm) and weighs about 0.15 ounce (a bit over 4g) ready to use, including a three pin Deans battery connector on a 4˝ inch (11 cm) battery lead, a JR type connector on a 5 (12.5 cm) inch receiver lead, and 5 inches (12.5 cm) of wire to go to the motor. This wire, by the way, is a custom-made very flexible silicone jacketed stranded wire about 23 gage (American wire gage – sorry, I don’t know the cross section in square mm).

It comes packaged in a small plastic bag with one sheet (double sided) of instructions including a color wiring diagram. In my last column I wrote about the new self-adjusting software for Castle Creations controllers, in particular in a Pegasus 35. The Pixie-7 ships with an implementation of the same software, and it runs very much as I described before. Here are the specifics:

The Pixie-7’s throttle function has self adjusting endpoints and range, and also gives you audible feedback (by "beeping" the motor) when it is powered up (one beep) and armed (two beeps). As an aside, the Kontronik Sun 4000 I’m flying in the Electric Scout (coming soon, I hope, as an E-zone review) also gives audible feedback that it is armed, as does the Jeti JES 350 discussed last time. I am quickly growing to like this feature very much.

Anyway, as usual, you power up a system including the Pixie-7 by first turning on the transmitter with the throttle stick where you want "off" to be. It will first beep once, letting you know power is on, then, 1˝ seconds later, it will beep twice more if the incoming pulse duration is between 1.0 and 1.25 ms, letting you know it is now armed. It assumes that the stick position when it beeps twice is "off". As you advance the stick from there the motor will start a couple of throttle stick clicks above the "off" point. It reaches full power after an increase of 0.6 ms of pulse duration. Any increase in pulse duration beyond the start point + 0.6 ms results in the full throttle point being moved up, and the range between there and the off point being re-scaled.

If the throttle channel pulse duration is higher than 1.30 ms when you power up, it will not arm (beeps once only). Pulling the stick back below that and stopping for at least 1.5 seconds sets the low point and arms the control (again, two beeps). By the way, on a Speed 280 these beeps aren’t very loud, so you need to listen closely. If there’s a glow-powered plane running anywhere around, you probably won’t hear them. I guess a Speed 280 just isn’t a very good loudspeaker <g>.

Also like other Castle controllers, the Pixie-7’s throttle curve is reverse-exponential, giving finer control over power at the upper end. What this means was discussed at length in my April 2000 column, so take a look there if you’re wondering what I mean. Unlike earlier Castle controllers, but like the Pegasus I mentioned last time, it throttles the motor very smoothly all across the range and has such small "steps" that I cannot distinguish them from the detents on my transmitter’s throttle stick.

In the rest of the usual tests it is well behaved, with no surprises, although in flight in my ModelairTech Skimpy (power and radio as described above) I did occasionally hear a little throttle glitch. As I said, I have the receiver antenna wound around a plastic drinking straw and that may have some effect here.

The BEC uses the same regulator as the GFS!, but it doesn’t have as much heat sink area available to it (the Pixie is about 1/3rd the size of the GFS!). Pat rates the BEC at 1.2A, and up to 8 cells with two servos. On 8 NiMH cells, putting the two HS-50s in Skimpy in constant motion causes the regulator to warm up very quickly (when held between my fingers). Of course, they aren’t in constant motion in the air and the regulator isn’t covered up by my fingers, either.

The motor cutoff is set at an unusually low 2.5V. The instructions say it will cut the motor when the voltage drops below 2.5V for more than ˝ second. I can’t say I’ve actually tested it to this point as Skimpy is long on the ground before the 7X350AAC pack gets anywhere near that low in voltage. I don’t even know what receivers are still working at that low a voltage. I would be interested to hear from Pixie users who are flying 4 or 5 cell power systems to learn how that is working for them. The instructions also say the Pixie-7 is good for up to 18 cells with the BEC disabled (remove the red pin from the Rx connector and insulate it or cut the red wire).

There is a software glitch that will cause it to arm and the motor to immediately start to run slowly, if the incoming pulse duration is between 1.25 and 1.29 ms. This is quite a bit above the lower throttle stop on most transmitters, but if you happen to power up with your stick just there, it is a bit of a surprise. I’m sure by now Pat has found and swatted this bug and can update your Pixie-7 (or other self-setting Castle controller – the Pegasus I mentioned last month does this too) if necessary. I had to go looking for this problem using my Ace Datamaster (it had been reported on the Slow Fly e-mail list) to find it. The range of throttle positions in which it occurs is VERY small.

Overall, I recommend it. It is so small that for any aircraft weighing more than a few ounces, its weight is negligible. I like both the self-adjusting endpoints and the reverse exponential throttle curve, so I would choose it ahead of a number of competing units.

Weights and measures below.

 

Sirius Electronics GFS! Specifications www.siriuselectronics.com

List Price $34.95 US

Physical

• Dimensions: 0.9 X 0.4 X 0.3 inches
• Weight as supplied: <0.1 ounces (about 1.5 g)
• Weight, ready to use**: 0.2 ounces (about 5g)
• Rx connector supplied?: No
• Power connectors supplied?: No

Throttle Function

• Microprocessor controlled
• Cell count range: 4 to 16
• Rated continuous current: 10 Amps
• Advertised resistance: no value listed
• Setup method: fixed endpoints, fixed range
• High rate switching?: Yes, rate not specified

Brake Function

• Brake?: no

Battery Eliminator/Cutoff Function

• BEC?: Yes, rated at 1.5 Amps
• Radio on/off switch? No
• Cutoff: at 3.6 V
• Motor Restart?: Yes, repeatable. Bring throttle to "off". No delay.

Additional Features

• Especially smooth speed changes and soft start.

**Includes 7 inch receiver lead with JR/Hitec connector and 5 inch motor lead with 3-pin Deans connector.

 

Castle Creations Pixie-7 Specifications www.castlerc.com

List Price $34.95 US

Physical

• Dimensions: 0.5 X 0.3 X 0.2 inches
• Weight as supplied*: 0.1 ounces
• Weight, ready to use**: 0.15 ounces
• Rx connector supplied?: Yes, JR/Hitec
• Power connectors supplied?: No

Throttle Function

• Microprocessor controlled
• Cell count range: 3 to 8 with BEC, up to 18 with BEC disabled
• Rated continuous current: 7 Amps (with cooling airflow)
• Advertised resistance: 9 milliOhms
• Setup method: continuously self adjusting, variable start point, variable range
• High rate switching?: 2.8 KHz

Brake Function

• Brake?: no

Battery Eliminator/Cutoff Function

• BEC?: Yes, rated at 1.2 Amps
• Radio on/off switch? no
• Cutoff: at 2.5 V
• Motor Restart?: Yes, repeatable. Bring throttle to "off". No delay.

Additional Features

• Audible signal for power on (one beep) and arming (two beeps)

*Includes 4.5 inches of 23 gauge wire silicone jacketed wire for motor and for battery hookups, 5.5 inch Rx lead and connector

**Includes above plus 3-pin Deans connector

 

A Look Ahead

My test "lab" (my hobby room) is virtually jammed with new controls to test right now. Next time I think I’ll report on the Kontronik and Schulze entrants into the micro speed control market (the Kontronik Micro 10, which is in Skimpy right now, and the Schulze slim-08be). I also have the Schulze slim-35be as well as the future-18be and –45bo brushless controls on hand, the Kontroniks I mentioned last time, the WattAge IC-50A, IC-55A and IC-380, and I am expecting examples of the new Great Planes ElectriFly controllers from our esteemed editor any day now. I plan to mate the two Schulze brushless controls to my Astro brushless 010 and my Aveox 1114/4Y for bench and flight testing.

So, a full plate to say the least. Here’s one more chance to ask you readers what information you’d like to see in a sort of buyer’s guide, as I’ve mentioned before. As usual, comments are welcome in e-mail at abc_quiet_flight(at)operamail.com or ab_cawley(at)compuserve.com . However, I’m thinking about dropping Compuserve as an ISP, so I’d suggest using the OperaMail address if you write more than a week or two after this article is "published".