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From the Lab - September 1999

Steve Kranish calls on a guest columnist for extra info on "rolling your own" esc.

Thank You to the E-Zone and Eflight Community

In last month's 'From the Lab' (, I wrote about my father passing away. A number of readers wrote to me, expressing their condolences on my loss. I think I wrote back to everyone that I heard from, but I would like to take this opportunity to again thank everyone who wrote to me about this difficult time in my life.

I remain impressed and pleased by what a nice, friendly, helpful group of people I have met through the truly global E-Zone/Eflight community. Thank you everyone!


So You Want to Build an Electronic Speed Control...Continued

In last month's 'From the Lab' (, I wrote about several recently published Electronic Speed Control (ESC) designs. A number of readers emailed me to tell me about designs they had seen on the World Wide Web, but one reader, Soren Kjaer Nielsen SKN(at) of Denmark, wrote so much that I am presenting his material as a guest columnist. He covers a number of printed articles, and a lot of material that can be found on line. I have mentioned some of the web pages before, but I think Soren did a very good job of collecting the information together. The only things I have done is correct some of his English (which is a lot better than my Danish!), highlight the web links and add a few comments of my own, which are {bracketed and in italics}.

Electronic Speed Controls, by Soren Kjaer Nielsen

In the August ”From the Lab” you have a description of homemade Speed Controls, and you asked for some comments from E-flyers who have built and used these Speed Controls.  I have in the last few years built more than 50 Speed Controls for E-planes and boats, and I have collected a lot of information about homemade Speed Controls. Here is some information about where to find more information about good Speed Controls for “do it yourself” projects:


Elektro Modell
The German magazine Elektro Modell has printed a lot of articles about Speed Control construction (yes, it is unfortunately written in German, but the technical German is close to technical English - and then do it as I did, take the challenge to read the German about our fantastic hobby as a part of the challenge in building and flying the E-planes…....I don't like the German language - but it is not that bad !)  See or you can E-mail the company that prints Elektro Modell at: Neckar-Verlag(at)

I must especially point your attention at Milan Lulicīs designs. Milan's designs are made using the same good and stable analog design (but as you can see below Milan also have made designs using a microprocessor).  It is easy to adjust both start and stop positions in Milan's analog design. I have used these designs in very bad conditions on RX/TX running on 27Mhz, 35Mhz and 40Mhz both FM and AM, and I have never had problems with it.  Today it is unfortunately a general opinion that an analog design is not as good as a microprocessor controlled one. In my opinion the only advantage with the microprocessor is that you can build a Speed Controller with less components.

Some of Milan's Speed Controllers are built with leaded components, and they are therefore better to start with, if you don't have experience with building electronics.

Milan had also made a “do it yourself” charger for 6-30 cells, up to 6.5A. - I don't think that the charger has been printed in any magazine.

Together with Ingo Stal, Milan has made a “do it yourself” datalogger specifically for E-Planes for recording Voltage, Amp, rev/min, Height, Speed, Temp and used mAh - easy to build, and very fine working, Look in Elektro Modell 4/1996 and in No. 3/1998.

......Now back to the Speed Controls in Elektro Modell:

No. 1/1994:

“SMD-AKRO-REGLER” 8-30 cells, 40-50A, Power On Reset, High Rate, OPTO, Over Temp. Protection.  Designed by: Milan Lulic

No. 2/1994:

“SMD-NANO-REGLER” BEC, Under Voltage Cut Off, Brake.  Designed by: Heinz Jung

No. 3/1994:

“MINI-SMD-REGLER-S400” 6-10 cells, 10-12A, Power On Reset, High Rate, Brake, BEC, Under Voltage Cut Off.  Designed by: Milan Lulic

No. 4/1994:

“MAXI-SMD-REGLER” 6-12 cells, 40A, Power On Reset, Soft Start, BEC, Under Voltage Cut Off, High Rate, Brake, Over Temp. Protection.  Designed by: Milan Lulic

No. 4/1995:

”SMD-12CELLS-PYLON-REGLER” 6-12 cells, 45A, Power On Reset, Soft Start, BEC, Under Voltage Cut Off, Over Temp. Protection, High Rate.  Designed by: Milan Lulic

No. 3/1996:

”ROUND-S400-SMD-REGLER” 6-10 Cells, 12A, BEC, High Rate, Under Voltage Cut Off, Power On Reset, Brake,  Constructed by: Milan Lulic

No: 4/1997:

”MINI-REGLER-SLOWFLY” 6-10 cells, 4A, BEC, Under Voltage Cut Off,   Constructed by: Milan Lulic

No. 1/1998:

”HOTLINE-REGLER” NOT SMD – leaded-components! 8-16 cells, 40 A, OPTO, High Rate, Power on Reset, Over Temp. Protection.  Constructed by: Milan Lulic

N0: 2/1998:

”SOFTLINE_REGLER” NOT SMD – leaded components! 6-10 Cells, 40 A, BEC, High Rate, Power on Reset, Under Voltage Cut Off. Brake.  Constructed by: Milan Lulic

No: 4/1998

”MICRO-PROCESSOR-MINI-REGLER” 2-12 Cells, 20A, BEC, Under Voltage Cut Off, High Rate, …….And more. Microprocessor available from designer  Designed by: Peter Klare

No: 1/1999

”MC35-MIDI-REGLER” Microprocessor, 6-12 cells, 45A, BEC, Under Voltage Cut Off, Temp/high AMP Protection, High Rate, and more. Microprocessor available from designer.   Designed by: Milan Lulic

Elektor is an English magazine for electronic design - the magazine sometimes prints designs for RC use. In addition to the Speed Control I have built a microprocessor controlled servo tester - You will need some kind of servo tester for the Speed Control testing, and this one is very easy to build, you can use it both for testing RX/TX and for testing servo/speed controls, look in Elektor NO ?? one from 1999

Elektor: February 1996

A Microprocessor controlled Speed Controller for 8-10 cells, 40 A. BEC, Brake  This design can be built for forward only, and for both forward and reverse.  You have to buy the program for the Speed Controller from Elektor

Allt Om Hobby is a Swedish magazine - yes in Swedish!, but again, the technical part is close to English……… You can find ALT OM HOBBY at: 

No: 7/1995:

A fine forward/reverse design for 6-12 v max. 15A. For those who need a Speed Controller for your boat....or .for using the reverse power as a brake in a fan?


On the net, I have found the following links to pages with Speed Controls:

E.Behrs page:   One of the first pages on the net with Speed Controls, this page has a collection of speed control designs.  Here you can find some of Milan Lulic’s designs from Elektro Modell and some others e.g. a digital speed controller - without a microprocessor! Has someone tried that one? E. Behr has printed my comments about some of the designs on one of his pages. {SK: Eric includes a lot of background and theory, and one page has a good description of analog vs. digital (microcontroller) speed controls.}

Ken Hewit’s page:   A Microprocessor Speed Controller for 6-12 Cells, 40A, BEC, Under Voltage Cut Off, Fail Safe, Brake, Arming button, Two throttle response curves, High Rate, Speed Control or On/Off switch. The design uses a special fet-driver IC for driving the Power FET (that gives a better on/off control of the FET and therefore a higher efficiency in the FET). You have to buy the Microprocessor from Ken. Ken's page also shows some other microprocessor designs for RC use. {SK: Ken's page is the source for all electronic projects published in the UK magazine Radio Control Models and Electronics. You will find mixers, battery dischargers, testers, servo lead buffers, and the like - this page contains a lot of good projects.}

Michael Norton's page:   A Microprocessor Controlled Speed Controller for S400: 6-8 cells, 10A, High Rate, Brake, BEC, Low Voltage Cut Off,…..and more.  You can download the schematic diagram and the microprocessor program from the page.

Cords RC page:   A Microprocessor Controlled Speed Controller: 8-16 Cells, 40 A, OPTO, High Rate, Low voltage Cut Off, EEPROM for data, ……and more.  You can download the schematic diagram and the microprocessor program from the page. This page also shows a Microprocessor controlled tachometer with 1 rev/min resolution for a prop/fan with 2 - 7 blades. I have built it, a fine design.

Stefan Vorkoetter's page:   Several analog Speed Controllers. Stefan has a very fine description for how to build and test Speed Controllers. {SK: Stefan's pages include how to improve the Great Planes Spectra, and information about his Motocalc drive train performance analysis program}

What do I do ?

I like to change things, and add my personal fingerprints on the things that I build, therefore I have made new circuit board layouts for the designs that I have built. Today I build and use the following designs:

A) For GLIDERS - I only use S-400 in my GLIDERS

Milan's design from Elektro Modell NO: 3/1996. The only one where I use the original layout.

B) for S-400 + planes.

Milan's design from Elektro Modell No: 3/1994 without the brake. I have made 2 new layouts, one round for mounting directly on the S-400, and one “normal” in heat shrink tubing.  In both I use 2 FETs for driving the motor instead of the one FET that Milan uses. I don't think this gives a big effect on the max. 10-12A that an S-400 draws, but the extra FET gives me the possibility to use the “normal” size Speed Controller in planes with 2 pcs. S-400 and with S500/600 below 25A

C) For bigger motors:

Milan's AKRO-REGLER from Elektro Modell NO: 1/1994 plus the FET driver from K. Kewit's Microprocessor design.  My circuit boards are the size of the FETs that drive the motor. This one is a little tricky to build, because the components are mounted very close together. I build this controller in 2 versions:

  • for 7 - 20 cells and 80 A
  • for 7 - 40 cells and 50 A

The difference is the FET and a few extra components in the power supply.

You can get a copy of the the circuit board layout, but I don't have a description/diagram for the changes that I have made.

General hints:

  • Use the Power FET with the lowest Ron that you are willing to pay for (today one of the best FETs - for logic level driving - is the ILS 3803, with Ron = 0.006 OHM) 
  • The FET must run at the lowest possible temperature - the Ron goes up when the temperature goes up, and is a “bad circle”. {SK: actually, in a way this is good, because this is what prevents FETs from burning up the way Bipolar transistors do!} 
  • Add a cooling plate to the FET- I use a half PC-processor cooling plate (486-size) for the big Speed Controllers. Fresh air must move around the Speed Controller (also important on the Speed Controllers that you buy). {SK: don't connect the tabs of FETs, etc. together on a heat sink unless you are sure you know what you doing! The tabs of brake and drive FETS may be at different circuit voltages!} 
  • Add solder, thin brass-plate or wire to the part of the circuit board that carry the high currents, the resistance in the circuit board can easy spoil all the big efforts to get a low Ron by buying expensive FETs ! 
  • Test your homemade Speed Controller before you mount the FET (I think Stefan has a description for that on his homepage). If you have a power supply with an adjustable current limit, start the Speed Controller with the current limit at the lowest level, and then slowly open up, checking the AMP meter, the Speed Controller must not use more than 25 - 100 mA in this situation. Adjust START and STOP on the Speed Controller. 
  • When ready to the final test, do that with a motor without a prop, don't run the motor on full power, just check the function, then mount the prop and test full power. 
  • Remember that your homemade Speed Controller is NOT protected against short circuit - and over temperature protection will not help on this - You will destroy the FETs if you have a short circuit from the FET to the motor, if you have a short circuit before the FETs you may ruin the battery.  
  • If you have a OHM-meter check for short circuit before you connect to the battery. For some time ago I didn't check for short circuits before I connected the battery - a fully charged 28 cells pack of RC2000 connected to a short circuit was like a New Year's eve with display of fireworks. My friends told me that it looked very nice. I didn't like it, but I am sure that SANYO did, when I had to buy new cells ! 
  • An over temperature protection will protect the Speed Control against a complete melt down on a long duration run, not against anything more.

Soren Kjaer Nielsen SKN(at)

Some more Online sources for RC Electronics Projects

In addition to the web pages mentioned above by Soren, I have found the following pages about Electronic Speed Controls and their designs:

AMS Free Flight Controllers   Electronic controllers for competition free flight models, using RC servos to move the control surfaces. These are a lot more sophisticated than the mechanical timers they replace.

Brent Dane's Page   Servo reversers, slow down circuits for retract servos, and an on-board battery voltage tester. Parts kits are available.   This page from Australia includes a battery discharger/capacity tester, a battery backup circuit, and an extensive link list, which I have made no effort to duplicate here.

Dick Miller's page   contains characterization data for a variety of small electric motors, suitable for small electric RC and free flight applications.

4QD is a UK company that has published a lot of circuit ideas on the web. The page at includes some simple battery monitoring circuits, and the basics of a battery discharger.


This document and every single one of the photographs is copyrighted (c) 1999 by Steven Kranish, and may not be copied or used in other forms of publication (electronic or paper) without written permission from the author. I will probably grant permission, but I would like to know about it, so go ahead and ask.


If you have any questions, please feel free to contact me at skranish(at)



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