An Electric Primer for Fuel Guys

[Pagemaster]

Good thread!

You can get my book about FE from RCBM (shameless plug) but we can discuss questions about the differences of FE from fuel here for free. I invite any fuel racer to pose questions or comments, but let's try to keep it technical rather than political. Thanks!

.

Jay when are we going to see an updated book. The basic principles of the first book are still there, but a lot has changed in 10 or more years.

I'm first in line waiting to buy one!

Steven

 

[Mark Bullard]

The racing ESCs we use today do not change freqencies, they are programmed for a specific frequency and change the amount of time that power is fed to the motor to control the throttle. The most common frequencies are 9, 19 and 38 MHz, and with many controllers the end user can choose whichever frequency he wants. Some frequencies work better with specific motor designs, depending on the number of poles and the inductance of the motor windings. With some motors it doesn't seem to matter.

The 3 most common frequencies used in R/C brushless controllers are 9.6, 19, and 38 kHz.

As Jay noted, the frequency is not changed to vary the speed of the motor. The pulse wavelength is varied to change the speed. It is not a sinewave like the (industrial?) controllers that Mark is referring to. The waveform is trapezoidal. Full on or full off. The wave would be a squarewave but motor inductance rounds some edges.

Pulse wavelength was the wrong term to use.

The duty cycle or time that the pulse wave is in a high state is changed. Pulse width modulation. Speeds up by increasing the time the pulse is high. Slows down by decreasing the amount of time the pulse remains high.

The frequency of the waves remains stable at 9.6 kHz, 19 kHz, 38 kHz, or in some controllers a user setting somewhere between them. Not at the basic commutation frequency.

I think that it was the right term to use. The frequency that you declare is 9.6kHz, 19kHz, 38 kHz is what we call the

"Carrier frequency". Or another term would be the "Switching Frequency". This is how fast we turn the IGBT's on and off to build the Sine Waves. Now the higher the Switching Frequency is the more heat the controller will build and the motor will run cooler. The lower this Switching Frequecy is the cooler the controller will run and the motor will run hotter. Now that we have a switching frequency we can build the sine wave by how long we turn the IGBT on. Now remember that when we turn it on it is turning its self on and off at what ever the Switching Frequency is set at. Here is a picture of what wavelength looks like from a PWM drive. Now if you have a way to run these motors other than the controllers you find that they will only run Synchronous RPM that is available which is 60Hz.

 

[jayt]

Jay when are we going to see an updated book. The basic principles of the first book are still there, but a lot has changed in 10 or more years. I'm first in line waiting to buy one!

You know, I've asked AirAge several times about it in the past two years and they seem interested at the time, but they never followed up on it. Much of what is in the old book is still valid, but with modern cells and BL motors it can be confusing to a new boater. Threads like this one can help bridge the gap, particularly when we can get several viewpoints on the same subject instead of just one. You still have to be careful who you listen to of course - but that is true in print media too.

.

 

[JfromJAGs]

I think that it was the right term to use. The frequency that you declare is 9.6kHz, 19kHz, 38 kHz is what we call the "Carrier frequency". Or another term would be the "Switching Frequency". This is how fast we turn the IGBT's on and off to build the Sine Waves.

The type of brushless motors we use in model boats are not similar driven than industrial synchronious or asynchronious motors. The controllers don't form a sine wave, it's just a sqare wave like you would use for brushed DC motor.

Actually the best term for these motors and controllers is "brushless DC motor". The controller just replaces the brushes electronically. The motor/rotor spins as fast as it likes (just like for a brushed DC motor), switching the phases is resolved from back EMF or using magnetic sensors - so rpm is not given by the controller, it's determined from the motor.

The mentioned switching frequency is used for the PWM and stays constant; the amount of duty cycle is dermined from throttle position. Similar to brushed controllers. It's independent from switching the phases to make the motor spin.

The best switching frequency for the PWM depends on the motor construction. 2 pole, coreless BL motors are ok with low PWM frequency, as the inductivity of the coil is quite high. Higher pole toothed motors need higher PWM freuency, otherwise the current ripple will be too high.

Joerg

 

[brooks93]

Well I tried to enlighten ya'll on the simple principal electric motors and how they work. But it seem that ya'll know more about it than I do. I have over 40 years in the motor repair and rewind and your motors are no different than the ones that we repair. My primary repair that I do myself is repair servo, stepper, and spindle motors for CNC machines and robots. And yes I do have to work on the more simple motors too sometimes. And yes if I did decide to run electric I would be on top of the game and ahead of ya'll went I start.
Mark

Ok Mark I will take that bet. Build a FE boat and show us lesser FE people how its done. What you do is similar but, doesn't apply to everything. Don't think because you can hold your own in nitro that you would spank us in FE. I know you are a established hydro racers and you have a sweet twin but, please don't assume unless you are willing to prove otherwise. Even a old dog can learn new tricks. I have rebuilt some V8's in my time but, I don't try to act like I would beat everyone if i raced nitro because of that.

I do remember at the 05 internats you tried to tell me my Lehner Brushless was a 4 pole when its a 2 pole motor. I am sure Joerg will back me up that ALL Lehners are 2 poles only

 

[Pagemaster]

.....

 

[JfromJAGs]

I do remember at the 05 internats you tried to tell me my Lehner Brushless was a 4 pole when its a 2 pole motor. I am sure Joerg will back me up that ALL Lehners are 2 poles only

Correct. All Lehner inrunner BL motors use a 2 pole magnet rotor, made from a single piece of round neodym or glued together form neodym discs to reduce the eddy currents in the rotor.

 

[jayt]

Guys, this is supposed to be a thread for all of us to learn, not to pound our chests or put another R/C boater down. No politics! I really appreciate the input from those who are trying to be helpful - but much more BS from those who only want to argue and I'll have the thread locked. Play nice or find another thread.

I hope that Mark has a better understanding of the type of motor we run in FE boats and how they differ from the industrial models he is so familiar with. His input has been helpful for those FE guys who bothered to check the links he provided - the more we all can learn about the technical side of the hobby the better. I wish that he'd give FE a try - not because of his boast but because of his overall knowledge of R/C boating. The more input we have from all aspects of R/C racing - gas, nitro and FE - the better off the entire hobby is.

.

 

[brooks93]

sorry jay that comment just rubbed me the wrong way.

 

[Pagemaster]

sorry jay that comment just rubbed me the wrong way.

Same here Jay. I will edit or delete the post.

 

[jayt]

Thanks everyone. Fuel or electric, we are all R/C boaters here and we need to work together for the future of the hobby.

.

 

[jayt]

Starting in FE – Part One

 

I am often asked: 'What is the best starter FE race boat?" That question is usually asked by a complete R/C boat newbie and I tailor the answer to him. But more and more experienced fuel boaters are asking the same questions, and this seems like a good forum to answer that question.

 

There are really two routes to go for the experienced fuel boater. Perhaps the best is to race a Limited Sport Hydro (LSH) which uses a 700 brushed motor and 12 cells in a sport hydro hull at least 24" long. This class has several advantages:

• Virtually zero motor/ESC problems due to the mature brushed motor technology
  
• Relatively low cost due to use of spec brushed motors and nickel cells
  
• Easier to learn FE setup without risking expensive equipment
  
• A popular class so there is a good chance to have a lot of racing
  
• A "spec" class that ensures close races
  
• Fast enough (35-40 mph) to be of interest to most racers
  

This makes an excellent class for someone more interested in quality racing and less interested in raw power or spending lots of money to see if he likes FE. See the next Part for more information.

 

.

 

 

[jayt]

Starting in FE – Part Two

 

For the experienced fuel racer who wants to take advantage of the high speed potential of FE the possibilities are huge. Some fuel guys have already taken the plunge by building a boat to compete in the Open fuel classes (Open Mono and Open Cat in IMPBA). These are usually T-class boats of 32 cells/37 volts, and they can be highly competitive at this level once the new FE racer gets the big boat (same hulls as the Open fuel guys race) setup. However, a basic wiring error - that no experienced FE racer would make - can cost the new racer dearly at this level. The fuel racer wanting to race the big FE boats needs to weigh the risks against the rewards. He may - or may not - be better off starting with a less powerful boat first. This is analogous to a tunnel boat fuel racer building a twin rigger as his very first hydro – it may work for him, or it may not.

 

A more conservative route would be to start with a mid-level brushless boat, either mono or hydro. P-class (12 cells/14.8 volt) models can give high speeds and are probably similar to a 3.5cc fuel boat in size and performance. Entry cost is lower than with higher cell count boats, although the major differences are the larger hull and more cell costs.

 

At present, an approximate correlation between current FE and nitro classes are:

• N-2/6 cell/7.4v = 2.5 cc
  
• P/12 cell/14.8v = 3.5 cc
  
• Q/18 cells/22.2v = 7.5 cc
  
• S/24 cells/29.6v = 11 cc
  
• T/32 cells/37v = 15 cc
  

With the availability of newer cell technology the above will change somewhat, but as a general guideline the above chart works.

 

I attend several fuel races every year, and when we race the FE boats many fuel racers seem to be unimpressed watching them. I remember speaking to one CD during a P-Tunnel heat, and when I mentioned that the boats were traveling over 45 mph he refused to believe me. (I had a GPS in my own P-Tunnel so I knew how fast it was going.) Anyone who bothered to time the laps would have seen that the FE tunnels were faster than the .21 monos in the previous heat - but they looked slower. Why? The lack of engine noise is the answer! Watch a video of a fuel heat without the sound on and it seems a lot slower too. But what matters is the lap time, and FE boats can deliver the low lap times that win races. With fewer and fewer racing sites avaialble to R/C boaters due to noise restricdtions, running boats which are quieter but as fast or faster - just makes sense.

 

.

 

 

[Mark Bullard]

Guys, this is supposed to be a thread for all of us to learn, not to pound our chests or put another R/C boater down. No politics! I really appreciate the input from those who are trying to be helpful - but much more BS from those who only want to argue and I'll have the thread locked. Play nice or find another thread.
I hope that Mark has a better understanding of the type of motor we run in FE boats and how they differ from the industrial models he is so familiar with. His input has been helpful for those FE guys who bothered to check the links he provided - the more we all can learn about the technical side of the hobby the better. I wish that he'd give FE a try - not because of his boast but because of his overall knowledge of R/C boating. The more input we have from all aspects of R/C racing - gas, nitro and FE - the better off the entire hobby is.

.

Guys I do understand completely. And it is like I said it is all about the buzz words. The "Buzz Words" that ya'll use are not the same as the one that I use. And they don't match the industrial standards. But you all are saying the same thing that I am saying. I am just trying to place what you are saying to the standards. I work with all kinds of motors and the ones that are the most trouble to work on are the Servo motors. They have feedback devices and a lot of testing and documention has to be done before this type of motot is disassembled. Joerg talk about EMF or back-EMF or another name is counter-EMF. And some controllers use this to help control the Brushless motor. The feedback devices that I talk about and what you use to have on the earlier motors, control the motor by replacing the comutator and brushes. And controllers that has no feedback device must be control by the back-EMF. Now this is provided that your motors have magnetic rotors. This kind of control is not that tight or smooth but it does not have to be for what you are doing with it. One of the test that I do on servo is to backdrive the motor and measure the back-EMF voltage and to use the Oscilloscope to look at the Sine Wave on all of the phases to make sure the the magnets are in good shape and the winding is making a good wave form. See there I go talking about the Sine Wave again. Your controllers do make a Sine Wave, it may not be the prettest wave and it will have a lot of square edges but it is still a wave. But you can backdrive a motor the same way by driving the motor with another motor at a fix speed ( a 1000 RPM's is a good number) and measure and scope the motors windings. The reason to do this is to check your magnets and to make sure that they have not lost some of their pull. A brushless motor is build backwards compared to a DC motor. The Armature is the Stator winding and the Rotor is the Fields. By jumping two of the leads of the motor together and then marking the output shaft you may then turn the motor and count the number of lockups it take to get back to where you started. This number multiply by 2 will give you the poles of the motor. But the motor must have a magnetic rotor.

Now why would I check the magnets? First of all I when I bought a new motor I would run this Scope test on the motor and then document the Wave Forms and the back-EMF voltage. Fault currents that may occur from a malfunction of the control or if to much heat has been in the motor it will cause the magnets to lose some or all of their magnetic flux density. Heat is the worse enemy Ferrite Magnets assuming that is what is used. It will kill these types of magnets. Ferrite Magnets are the most commonly used. There is only three types of magnets and they are:

"Alnico" ( Aluminum, Nickel, Cobalt )

"Ferrite" ( Ceramic ) Ferrite 1 thru 8

"Rare Earth" ( Neodymium, Iron, Boron) or ( Samarium, Cobalt )

Now by checking the back-EMF voltage and the Wave Form I can be sure that my magnets are in good shape over the life of the motor. I can also do this to find the best motor or may I say to blueprint the motor or motors. If you generate a good Sine Wave and have a good back-EMF voltage then your magnets are doing a good job. And this means you can product the most torque the the motor will product. I do not know if you cool your motors or not but to do so would help make your magnets live longer if you overload your motor.

We have a old saying around here. And that is " These motors and controls run on smoke and when you let the smoke out they quit running." And I like it around here when they let the smoke out because we get to put it back in $$$$.

Mark

 

[Mark Bullard]

Starting in FE – Part Two 

For the experienced fuel racer who wants to take advantage of the high speed potential of FE the possibilities are huge. Some fuel guys have already taken the plunge by building a boat to compete in the Open fuel classes (Open Mono and Open Cat in IMPBA). These are usually T-class boats of 32 cells/37 volts, and they can be highly competitive at this level once the new FE racer gets the big boat (same hulls as the Open fuel guys race) setup. However, a basic wiring error - that no experienced FE racer would make - can cost the new racer dearly at this level. The fuel racer wanting to race the big FE boats needs to weigh the risks against the rewards. He may - or may not - be better off starting with a less powerful boat first. This is analogous to a tunnel boat fuel racer building a twin rigger as his very first hydro – it may work for him, or it may not.

 

A more conservative route would be to start with a mid-level brushless boat, either mono or hydro. P-class (12 cells/14.8 volt) models can give high speeds and are probably similar to a 3.5cc fuel boat in size and performance. Entry cost is lower than with higher cell count boats, although the major differences are the larger hull and more cell costs.

 

At present, an approximate correlation between current FE and nitro classes are:

• N-2/6 cell/7.4v = 2.5 cc
  
• P/12 cell/14.8v = 3.5 cc
  
• Q/18 cells/22.2v = 7.5 cc
  
• S/24 cells/29.6v = 11 cc
  
• T/32 cells/37v = 15 cc
  

With the availability of newer cell technology the above will change somewhat, but as a general guideline the above chart works.

 

I attend several fuel races every year, and when we race the FE boats many fuel racers seem to be unimpressed watching them. I remember speaking to one CD during a P-Tunnel heat, and when I mentioned that the boats were traveling over 45 mph he refused to believe me. (I had a GPS in my own P-Tunnel so I knew how fast it was going.) Anyone who bothered to time the laps would have seen that the FE tunnels were faster than the .21 monos in the previous heat - but they looked slower. Why? The lack of engine noise is the answer! Watch a video of a fuel heat without the sound on and it seems a lot slower too. But what matters is the lap time, and FE boats can deliver the low lap times that win races. With fewer and fewer racing sites avaialble to R/C boaters due to noise restricdtions, running boats which are quieter but as fast or faster - just makes sense.

 

.

 

Jayt,

You know I told and showed Tommy Lee about 15 years ago when he was setting some of the first FE records that the technology was there to blow these records apart when the brusless motors got smaller and the controllers got smaller to be able to run in a boat. It just took a little time for the technology trickle down into the hobby. I use to help him with wire and connections for him to set those records. And he still comes to my shop if he needs anything for whatever he is working on. These days since his eyesite has gone bad he has been working on a model drag line. Like the big mines use to remove ore. He has been over here many times and pick my brain to do his control the cheapest and simplest way he can get it done. He has been buying these battery power drills for very little money and using the motors and gears to build this drag line.

I know that I have watch Paul and others run their FE boats at the Nats and other races and I get a big kick watching the FE boat out do the Nitro and Gas boats. I have a lot of respect for FE racers because they have work hard to acheive what they have done. And yes if I had been running FE boats I may have been able to get ya'll there little quicker because of my knowledge. But for me to run FE would not be a hobby for me it would be to much like work. But if anyone wants to have a question answered on a motor I will try to do my best to answer it. Also if anyone need some wire to rewind there motor I have all sizes.

Mark

 

[BoatDoc]

mark-

ok...so i got a little curious about what you were saying about shorting together 2 wires on a motor. so i tried it...the motor was harder to turn over by hand. i think that was your point, right? as a non-electrical guru (i know just enough to build my boats) what causes that to happen?

 

[Mark Bullard]

mark-ok...so i got a little curious about what you were saying about shorting together 2 wires on a motor. so i tried it...the motor was harder to turn over by hand. i think that was your point, right? as a non-electrical guru (i know just enough to build my boats) what causes that to happen?

Your right. By shorting 2 of the leads together you are trying to cancel out the EMF voltage. The same thing will happen with a DC motor. And on a DC motor this is how Dynamic Braking is done. These types of motor will generate power when turn by a source. A DC motor will generate DC voltage. The Brushless motor will generate AC voltage. Now here is another little test you can do with a Brushless Motor. Take a 9 volt battery with some wires on it and by placing the positive on lead 1 and the negative on lead 2 the motor will lockup to that pole position. Now I do not know how your leads are numbered on the motor but the standard is 1-2-3 , A-B-C , R-S-T , or U-V-W. I myself like U-V-W but here is how to pole the motor thru one electrical rotation.

+ to U / - to V is pole position 1

+ to V / - to W is pole position 2

+ to W / - to U is pole position 3

This is one electrical rotation. If you had mark the shaft you will notice that the shaft may or may not have turned a complete 360 mechanical rotation. If the motor goes one mechanical rotation with one electrical rotation then the motor is a 2 pole. A 4 pole will have to go thru 2 electrical rotations to make one mechanical rotation. And the same for 6 pole has 3 electrical rotations, 8 pole has 4 electrical rotations for there mechanical rotation. Hope this helps

Mark

 

[Paul Pachmayer]

Hi Mark,

Also if anyone need some wire to rewind there motor I have all sizes.

Not trying to be a wise guy here but you do understand there are no windings on the arm of a FE brushless motor right? The rotors are made with rare earth (neo) magnets and are segmented, solid or slotted depending on the maufaturer. The coil which is compressed and fitted to the can would be impossible to rewind. If you happen to damage the coil in any way it's junk. Rotors OTOH can be replaced. The rotor is the constant in a given size motor, the windings determine the KV of the motor.

Paul.

 

[Andrewg]

Jay

Dead right about the value of nitro racers applying their knowledge to electrics. The last few months I have been working with them and the depth of their knowledge is very helpful especially as speeds rise.

BTW one thing with Lipo and the 6mm plugs we all seem to use now - has anyone established a convention about how these should be wired eg is polarity best determined by male and female plugs or by colour coding. Was there a convention with the 4mm and 3.5mm plugs when used on cell to connections?

If the former is the male positive or negative output from the battery. Should leads be a differnet length to reduce the likelihood of shorted leads.

Which is safest? And it may help in the future if packs and esc's were able to be swapped between boats.

 

[Mark Bullard]

Hi Mark,

Also if anyone need some wire to rewind there motor I have all sizes.

Not trying to be a wise guy here but you do understand there are no windings on the arm of a FE brushless motor right? The rotors are made with rare earth (neo) magnets and are segmented, solid or slotted depending on the maufaturer. The coil which is compressed and fitted to the can would be impossible to rewind. If you happen to damage the coil in any way it's junk. Rotors OTOH can be replaced. The rotor is the constant in a given size motor, the windings determine the KV of the motor.

Paul.

Paul,

No problem, but I think that you need to go back and read my posts. In the DC Brushless motor world the rotor is the Fields like the can of a DC brush motor. The Stator or windings ( you said coil ) is the Armature like the rotating part in a DC motor. I know this sound strange but these are the terms that are used in this type of motors.

The magnets that you say that are used are very good and give the best torque. Their name is really Neodymium, Iron, Boron or

Nd-Fe-B. Their typical air-gap flux density ( Teslas ) is the best that there is. Their Teslas rating is 1.0 - 1.3 Teslas ( 1.0 tesla = 10,000 Gauss 1.0 Gauss = 6.452 lines per sq. inch ). Or another way of looking at the Tesla number is that 1.0 tesla is equal to the earths gravity.

For your windings, I would have to look at it to see if it can be rewound. You say that they are compressed into a can but someone had to wind it. All motors do vary from size to size and their KV or HP rating does change with the size of the motor.

Here is some picture of a servo motor and some other pictures of motors that have been repaired. See if you can see the magnets in the rotor and the winding is bad in this motor. Other than having a feedback device on this motor it is the same as your motors. And if we took one of your controllers and hook it up to this motor it would run. This motor is a 1KW - 8 pole with a stall torque of 6 Nm at 5.6 amps. So if I put 5.6 amp DC volts on the winding across 2 leads for the motor to lockup, it will take 6 Nm (Newton Meters) to turn the motor if the magnets are good. I use a torgue wrench to test this and it is the same thing as running the motor on a Dyno. These are GE Fanuc servo motors. They say that they can not be rewound but I have devissed a way to wind them. The reason why they can't be wound is because of there mechanical construction. But I will try to post some pictures of the rewind and repair of this motor.

Mark