An Electric Primer for Fuel Guys

[jayt]

I am delighted that more and more fuel racers are looking at and participating on the electric forum, but like any new aspect of the hobby there is a learning curve before the fuel racer understands about FE (fast electric). I started R/C with fuel boats many years ago so I have a basic understanding of them - but to many fuel guys the electrics are a mystery.

I hope that this thread can function as a learning center dealing with questions that fuel racers have about FE. 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!

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[Mark Bullard]

I am delighted that more and more fuel racers are looking at and participating on the electric forum, but like any new aspect of the hobby there is a learning curve before the fuel racer understands about FE (fast electric). I started R/C with fuel boats many years ago so I have a basic understanding of them - but to many fuel guys the electrics are a mystery.
I hope that this thread can function as a learning center dealing with questions that fuel racers have about FE. 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!

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Post from other thread:

"No Limits" on batteries.! The Amperes and Voltage is already as high as a arc welder. Someone will die.

Jayt,

The post that I made in the other thread was not to mislead anyone on electrics. I have talk to our Electric Director many times on this subject of batteries. I for one would like to see a limit on the voltage and not the cells. These are not flashlight batteries we are using. Even though a flashlight battery will make a good fire if shorted out.

And yes I run Nitro! I will never run electric but I can say that if I did, I could show you a thing or two. Why, because my business is electric motors. And I will not play with what I work with every day. I sell, repair, rewind and service all kinds of electric motors including VFD's and DC drives. I have repaired motors from as small as the ones that are used in boats to 20,000HP @ 13,000VAC.

If you have any techincal issues with these motors I will be glad to try and help. Out of talking with some the electric guys I have found that the buzz words that are used are nowhere near what the industry uses but I think that I can give you some good information.

Mark

 

[jayt]

Thanks for your offer Mark - all of us can learn from each other. We don't have problems with electric motors, they are very simple devices - we do have occasional problems with the electronic speed controllers if we try to get too greedy.

To start: FE classes are defined by voltage. Amperage has been unregulated in the past, which is fine because the speed controllers we have now can handle only so much amperage before they burn up. Very simply put - horsepower is the watts output of the motor, about 746 watts per horsepower. With a fixed amperage - restricted today by the speed controller - a 6-cell/7.4volt class boat can produce around 1 hp continuous, a 12-cell/14.8 volt class 2hp, etc. Clearly the various power levels/classes are defined by voltage, just as classes are defined by displacement with fuel engines.

The battery has voltage, but it also has capacity, similar to a fuel tank – the higher the mAh capacity, the more energy is stored. The difference is that the Lithium Polymer (LiPo) batteries are different from the old nickel cells we used for many years - they offer far more amperage delivery. This delivery is related to the capacity of the LiPo battery - the higher the battery capacity the higher the amperage the battery can deliver. Today a quality 5000 mAh battery can deliver 100 continuous amps, and a 10,000 mAh battery can deliver twice as much, or 200 amps. The higher the capacity of the battery, the more amps it can deliver. So the LiPo cells offer more amps (power) and capacity. You can set up an electric boat to have more speed and power, or more run time. This is done by varying the prop loading; up to a point, the larger the prop the more power is delivered by the battery.

I had wanted to keep this thread free of politics, and the rules debate certainly is political. Let's please try to keep it that way.

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[sjslhill]

Don't forget to do some cost comparisons......

 

[Tim_Duggan]

I've got a few;

Question relating to ESC's.

When they fail - how often is it terminal and how often are they a viable repair? I hear talk of cost comparisons all the time, but when a nitro or gas engine has a failure they are usually repairable with spare parts.

Question relating to advances in motors etc.

Once upon a time it was quite common to see geared drive set-ups. Is this still as relevant with the brushless motors available now as it was in the old brushed motor days? Any advantage to gearing the 700 brushed motors or has that sort of thing died as the cells have improved in capacity?

Question relating to 700 motors - specifically LSH. What is the optimum current draw from these engines on 12 cells? I'd imagine if you know that figure then fine tuning the prop would be done this way?

Thanks in advance Jay, This sort of clarification is just the ticket to increase interest from the IC guys.

 

[jayt]

Question relating to ESC's. When they fail - how often is it terminal and how often are they a viable repair? I hear talk of cost comparisons all the time, but when a nitro or gas engine has a failure they are usually repairable with spare parts.

The vast majority of brushless speed control failures are not user-repairable, but most are repairable by the maker. Castle Creations for example will repair (replace actually) a $220 ESC for no more than $75, regardless of how badly burned up the ESC is. For the first year they will usually replace it for free. The european controllers must be sent overseas for repair, giving the Castles a logistical advantage. Fortunately Castle identified a software problem in their marine controllers a few months ago, and their re-programmed controllers are much much more reliable now than they were just last summer. ESCs are still a weak link, but if the racer is careful and not too greedy his controllers can last a long time. I have burned up controllers at SAW events, but only one during normal oval racing over the past five years. I'm still running the very first brushless ESC I ever bought, and I even set a SAW record with it once.
Brushed controllers as used in LSH and LSO boats are virtually bullet proof. The best IMO are from RC-Hydros and are waterproof. A failure with one one of these controllers is almost unheard of.

Question relating to advances in motors etc. Once upon a time it was quite common to see geared drive set-ups. Is this still as relevant with the brushless motors available now as it was in the old brushed motor days? Any advantage to gearing the 700 brushed motors or has that sort of thing died as the cells have improved in capacity?

Gear drives are still used on occasion, but instead of a performance advantage they are used to give an advantage in flexibility. With the vast variety of brushless (BL) motors available the racer can choose the exact motor needed for his specific application. But if he wants to use the same boat for more than one class he can use the same motor and prop, just change the number of cells and the gear ratio. If he wants to compete in an enduro/offshore event, he can gear down the motor so that he can run fast for the amount of time needed without completely discharging the battery. He doesn't need to buy different motors or props, just use different batteries and gears. This is great flexibility for racers who only have one or two hulls but want to race a number of classes.
The 700 motors are seldom run on gear boxes unless they are running on more than 12 cells. These motors can really wake up on 16 cells, but in order to last very long a reduction gearing is really needed. This lets it wind up and reduces the load on the motor. In most cases the faster any electric motor runs the less current it draws and the cooler it runs, as long as all else is equal.

Question relating to 700 motors - specifically LSH. What is the optimum current draw from these engines on 12 cells? I'd imagine if you know that figure then fine tuning the prop would be done this way?

For top quality 700 motors the "best" performance is probably between 35 and 45 amps draw. Drawing more amps can sometimes give higher speeds, but it will shorten motor life. I raced on 700 motor in my LSH boat for two years, running three heats twice a month, and it ran great for over 100 heats. Then I ran it at a summer race with 106 degree ambient temperatures and over-heated the motor - it was never the same, and the LSH motors cannot legally be rebuilt. But two years of racing with the same motor and virtually no maintenance is pretty good!
Prop choice is usually based on measuring speed and temperature after a heat. If the motor comes back at under 145 degrees, the prop is probably a good choice. If it comes in over 145F, reduce the prop size/loading. A well-setup LSH hydro with good cells will run between 35-40 mph on GPS, and an LSO mono between 30 and 35 mph. As with any boat, set-up is just as important as the motor and prop choice.

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[Mark Bullard]

Now I know that these Brushless Motors are what we call three phase motors. What is the average poles of the motors and the rpm's that you are running them at by the pole number.

Mark

 

[jayt]

The most common BL motors used in FE race boats are two- and four-pole motors. The Kv values (rpm per volt) run from 800 rpm for high voltage oval setups to over 9000 rpm for lower voltage SAW setups. The rpm on the water for oval racers is usually in the 25,000-30,000 range, for SAW racing it is between 40,000-50,000+ rpm. The number of poles makes little difference - both types spin over 40K easily - motor design and execution play larger roles in motor performance. Motor efficiencies generally run from 80% to 90%, again based on design and execution.

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[Don Ferrette]

Since jayt made the statement in the other thread-

Don, I wish you'd post in the primer thread so you would get a better understanding of the basics of FE. The apples and apples comparison is voltage and displacement for differentiating the different classes. Amperage is the same for most all classes, it is differences in voltage which determines the ultimate power level of each particular class. Amps times volts = watts = horsepower. 200 amps with 7.4 volts is 1480 watts = 2 hp. 200 amps with 14.8 volts = 4 hp. 200 amps with 37 volts = 7400 watts = 10 hp. The amps remain the same, it is the voltage which changes the power level. Think of voltage as displacement, and amperage as the amount of energy in a pint of fuel. The bigger engine burns more fuel and produces more power. The higher voltage amplifies the cell's amperage. Is that a more clear analogy?

I have a bunch of motors in my shop. They are all wired for 110 volts. Some draw a couple amps and the biggest draws around 12 amps. The biggest one has way more power than the smallest ones. Why is it that they can make more power if as you say, the only variable is voltage? Answer is simple, voltage is not the only part of the power equation, amps drawn also matters. Vary the amps in your calculations instead of the volts and this will be obvious. If the battery being used can output more amps, a motor can be chosen which will draw more current and therefore have more power.

Chuck beat me to it. Voltage is only HALF the power equation in FE so again I don't buy the voltage only angle in that it is only what equals displacement. Some of you ampheads make broad based assumptions that we IC guys are completely clueless on how this stuff works. I work with electric motors on a much grander scale in controlling output levels of the HVAC systems in my building. The voltage always remains the same to the HVAC supply fans but when we up the load by pitching up the inlet guide vanes (this would equate to adding a bigger prop ) , & draw more amps the fans deliver more volume, only difference is I'm pushing air not water. Using your own math example of amps x volts = watts = horsepower-

100 amps @ 14.8 volts is 1480 watts

200 amps @ 14.8 volts is 2960 watts

400 amps @ 14.8 volts is 5920 watts

Watts equals horsepower so higher capacity batteries, i.e. MORE AMPS equals MORE POWER.

You want to have the motor draw more amps you load it harder, in this case a bigger prop. What does a bigger prop mean? It means you go FASTER. The guys who have the motors that can handle the higher amps (read more expensive) & the batteries capable of delivering the same high amps (again read more expensive) will have a huge advantage over the guy who can't afford that mega buck stuff but has to run in the same class. And BTW- there is simply no comparision to say a nitro motor where one guy runs a stock motor & one guy runs a modded motor as you won't double or triple you power output if somebody grinds on it (if only it were that easy) like you can when you double or triple your amp output with batteries.

So tell me again how amps remain the same and it is the voltage which changes the power level. <_<

Like I said before, I'm not picking sides just looking at this in a broad based spectrum. My concern is because of the recent ability of newer and MORE EXPENSIVE battery technology the guys with the deepest pockets and/or sponsorships will have a grotesquely unfair advantage over the "little guys" and ultimately shoot yourselves in the foot when all you have left is a small group of financially armed racers. It would seem to me a voltage AND amperage cap (an in-line fuse?) and adding some unlimited classes would serve the best of both. Guess that seems too simple.......

 

[Ken Retallick]

I like this idea to teach us nitro burners all about Mr EMF!

What difference do different turns in a motor do?

If one motor is rated at 900 Rpm per Volt, and another at 2000 Rpm per volt, how does this

work in the real world? does the lower rpm motor have more torque? cant be that simple

 

[jayt]

Don, I never meant to imply that you were clueless about electricity - just that you may not understand the whole FE picture including the physically-imposed limits. Right now the amperage limit is imposed by the speed controllers. No matter how much amperage any cells might be able to supply, the ESCs can only handle so much. This maximum amperage possible is independent of voltage, and this is why the amperage is the same for most any voltage class (excluding the limited and spec classes). The best controllers available now can handle about 200 amps reliably, but most not for a long period of time. We can stack up LiPo cells until we are blue in the face, but the ESCs (and to a lesser degree the motors) can only handle so much amperage. Your example of 400 amps is blue sky, not possible today. Kinda like trying to run 90% nitro - ain't gonna happen in an oval racing glow engine. So it is still voltage which determines the total power achieveable, and it is voltage which determines the different classes....just like displacement does.

I want to keep the politics (rules) out of this discussion, please. I have my own opinions about what is the "best" path forward for NAMBA, but I won't discuss them publicly until everyone has the proposals in front of them, and it won't be in this thread. Thanks Don.

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[Don Ferrette]

Hey It's cool Jay, just soaking it all in. While you are correct that, at the moment, the limiting factor is the ESC do you not think higher amp ESC's are not already in the works? I'm kinda trying to get people to look ahead at what most likely will be rather than what's on the table at the moment. We all know there has been phenomenal advances recently in batteries & common sense tells one that the ESC's will be right behind. Would it not be better to stay on the leading edge as opposed to playing catch up?

 

[jayt]

I like this idea to teach us nitro burners all about Mr EMF! What difference do different turns in a motor do? If one motor is rated at 900 Rpm per Volt, and another at 2000 Rpm per volt, how does this work in the real world? does the lower rpm motor have more torque? cant be that simple.

Thanks Ken, that is the intent of the thread - learning about the other guy's stuff.
FE Motors

Electric racing motors can be classified by two main criteria - size and turns. Generally, the larger a motor is the more heat (watts) it can absorb and the more torque it can produce. A 7.4 volt motor is smaller than a 14.8 volt motor (usually shorter, but definately weighs less) and is more appropriate for a smaller boat.

Turns

Turns describe the amount of wire through which the electricity passes within the motor. The higher the number of turns, the more wire there is and the more resistance within the motor. This resistance determines the Kv, or rpm per volt, of the motor. A motor with a high Kv has less resistance and needs to spin at a higher rpm than a motor with a lower Kv.

An example is the Hacker line of brushless motors. The most common motors are the B50 size, about 1.4" in diameter. This line has three different lengths - S, L and XL - and each one is about 1/2" longer than the last. The XL motors are the longest and have the most torque in this line. But each size comes with a variety of turns, usually from 6 to 26. One of the most popular motors is the 8XL, used mostly in 14-volt hydros and monos. Below is a chart showing the different Kvs of 8-turn motors in the Hacker B50 line:

8S - 4613 rpm/volt

8L - 3019

8XL - 1973

Each motor has the same number of turns, but because the 8S is a lot shorter than the 8XL the amount of wire in each turn is less, the resistance is less, and the Kv is higher.

Choosing a Motor

The best way to choose a motor for a specific FE boat is to use what other racers have run successfully, but there are very general guidelines. These have worked well in the past with the nickel chemistry cells but may need to be modified as we gain more experience with lithium cells. In the chart below, the number of cells refers to the number of nickel cells you want to run. Each nickel cell has a nominal 1.2 volts.

Sport Running - number of cells x Kv = 15,000 - 20,000

Oval Racing - number of cells x Kv = 25,000 - 30,000

SAW Racing - number of cells x Kv = 40,000+

Remember that the physical size of the motor has to be considered too. You would not want to run the small, lightweight 'S' motor on 22 volts because it would lack the torque needed for the larger boat's larger prop, and it's lack of mass would overheat quickly.

The above is a very general picture of motor design and while it applies mostly to brushless motors, the general principles are the same for brushed motors. But the classes in which the brushed motors are the most popular are limited, and the motor is specified so there is little to choosing a brushed racing motor.

I hope this has helped you gain an understanding of FE motors - if it is not clear please let me know and I'll clarify. Thanks.

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[sjslhill]

Jay,

Is there a limit to the number of motors now in the larger classes? I use to run 2, 3 or even 4 - 05 motors on a gearbox.

 

[Darin Jordan]

Jay,
Is there a limit to the number of motors now in the larger classes? I use to run 2, 3 or even 4 - 05 motors on a gearbox.

For Reference (NAMBA Electric Rules):

D. CLASS SPECIFICATIONS

1. POWER SPECIFICATIONS

a) The following motor and cell configurations will be considered official for electric racing in NAMBA:

M-2 A single .05 motor with brushes, any endbell, ferrite magnets. 1-4 cells are permitted

N-1 Any ROAR-approved stock motor as defined by current ROAR parameters. 1-6 cells are permitted.

N-2 Any single motor, any endbell, bearings, and magnets. 1-6 cells are permitted.

O Any amount and/or size of motors, any endbell, bearings, and magnets. 7-8 cells are permitted.

P Any amount and/or size of motors, any endbell, bearings, and magnets. 9-12 cells are permitted.

Q Any amount and/or size of motors, any endbell, bearings, and magnets. 13-18 cells are permitted.

S Any amount and/or size of motors, any endbell, bearings, and magnets. 19-24 cells are permitted.

T Any amount and/or size of motors, any endbell, bearings, and magnets. 25-32 cells are permitted.

 

[Mark Bullard]

Amps, Voltage, Horsepower!!! I have been reading a lot of what ya'll are saying but I think that ya'll have missed the boat on alot of this. And it may be from company's that say but don't know themselves.

Here it is in simple terms and don't everyone throw this back at me but I am trying to make it simple.

Voltage is the medium that is used to carry the product to make the motor turn.

Voltage on a motor to make it turn must be greater than zero and is unlimited on the upper end. Now the voltage must be great enough to over come the inertia of the rotor and the max voltage is only in the limit of the insulation of the windings. Will the higher the voltage make the motor run faster, Yes and No. A DC motor with brushes will increase speed with the more voltage applied or untill the limit of the rotating mass. A AC brushless motor or what we would call a induction motor will not increase speed. Their speed is base on the number of poles at the Synchronous RPM. The Synchronous RPM in AC motors is a very simple math formula.

Hertz X 120

Synchronous RPM = ---------------

Poles

So with this formula a 4 Pole motor will turn only 1800 RPM's at 60hz. So the end results is the motors that ya'll are using will not increase speed with voltage but only with a change of Hertz.

Amperes is the results of the motor turning at load.

This is what it is. The more load on the motor the more amps the motor will see. The limits here are the size of the wire or conductors/devices that carry the voltage to the motor and the motor winding themselves.

Horsepower is the end results to what the motor's limit can product at the giving amperes and voltage.

Now with all of this said the larger amp per hour batteries will allow a motor to product the same horsepower for a longer time or more horsepower for the same time of the lower amp per hour batteries. The limit will be the motor. The higher voltage will not product more RPM in the brushless motors. Motors with magnetic rotors will have more torque at lower speeds than motors that do not have magnetic rotors. To tell if you have a magnetic rotor, short two of the leads of the motor and then turn the motor by hand. If the motor appears to be lockup then the motor has a magnetic rotor. A motor with out a magnetic rotor will have what we call "slip" and this will be a decrease of RPM as the motor is loaded until it reaches it rated "slip".

I have talk about DC motors and AC motors. And the motors that are being used these days are AC motors. You may think that they are DC because of the batteries but they are not the batteries are just the storage medium. The ESD that ya'll use are making the voltage into AC voltage at a variable Hertz. And there is 3 lines of this voltage at 120 degrees of phase shift. Thus this is what we call 3 phase. We could use 5 or 7 or 9 or 11, etc of phases but when NiKola Tesla invented the power we used today, he decided on 3 phases because it was the small number that could be used to make a motor turn. Thomas Edison was the one that created DC. But this is a whole different history lesson. But one thing thay you may not know is that a DC motor run on AC inside the armature. DC voltage is applied to a DC motor brush. As it passes thru the comutator to the winding it is converted to AC. AC is then used in the winding and then when it leaves the comutator on the other side it is converted back to DC before it exits the other brush.

I did not talk about your housewhole motors because they are different type of motor all together. They are what we call Single Phase motors. They are still AC induction motors but work on a different way.

I hope this will help you understand Amperes, Voltage, Horsepower, and Motors.

Mark

 

[jayt]

A AC brushless motor or what we would call a induction motor will not increase speed. Their speed is base on the number of poles at the Synchronous RPM. The Synchronous RPM in AC motors is a very simple math formula....So with this formula a 4 Pole motor will turn only 1800 RPM's at 60hz. So the end results is the motors that ya'll are using will not increase speed with voltage but only with a change of Hertz.

I am not certain how to respond to this Mark; what I do know is that any FE brushless racing motor will most certainly run twice as fast with twice the voltage - there is no argument here, just fact. As I understand the BL ESC's function, it uses a fixed frequency (9KHz, 19KHz, 38KHz, whatever is programmed), but the controller turns the power on and off at that frequency. The more time the power is turned off, the less goes to the motor so the motor speed is lower - that is how the motor is throttled. With no interruption of the power, the motor runs at maximum speed. That speed is determined by the maximum voltage applied and the resistance/efficiency of the motor windings.

The limit to output power today is the ESC, not the motor (at least not with the better-quality racing motors). No matter how much amperage is available from the battery, the ESC will fail before the motor will, and with most ESCs today that is below 200 amps. That's today....tomorrow who knows....but we need to understand what today's limits are first.

The output power of an FE motor is based upon the input voltage/amperage at the motor after the ESC and the efficiency of the motor. If 14.8 volts and 100 amps are supplied to the motor, the max output will be around 1200 watts, or 1.6 horsepower (ca. 746 watts per horsepower). The rest of the power is wasted generating heat. (One of the main reasons that BL motors produce more power than brushed motors is their efficiency; BL motors are usually above 80% efficiency at maximum power while brushed racing motors were often only 60-70% efficient. The rest of that energy was wasted as heat.)

While many seem fixated on amperage, experienced FE boaters know that if possible it is better to achieve power by increasing the voltage. This gives high power without having to use high amperage - that means lower temperatures in the cells and the ESC. High power means larger boats, and since power is volts x amps there are two different ways to get there. With today's technology, voltage rules.

I've tried to answer Mark and include some additional information - I hope this isn't too confusing for anyone. If so please let me know. :blink:

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[sjslhill]

"High power means larger boats, and since power is volts x amps there are two different ways to get there. With today's technology, voltage rules."

How would you explain the need for 150 amps for the N2 class? How do more amps affect these motors at such a low voltage? Does more amps create more RMP or Torque or what exactly?

This is a serious question, not playing politics here.

thanks,

Steve

 

[Paul Pachmayer]

Hi Jay,

I hope this isn't too confusing for anyone. If so please let me know.

TMI, TMI, TMI! I can't take it anymore, I'm selling my FE stuff and buying a gas boat. :blink:

Paul.

 

[Paul Pachmayer]

Hi Steve,

How would you explain the need for 150 amps for the N2 class? How do more amps affect these motors at such a low voltage? Does more amps create more RMP or Torque or what exactly?

More amps are drawn because people use bigger props and/or higher KV motors. They can do that because Lipos will deliver those amps easily without heating up. You could do the same thing with sub-C cells, you just have to replace them often. For example, the rigger Joerg went 140 with. If he pulled the 32 sub-cs out and swaped with a 10S pack changing nothing else his amp draw would still be the same or slightly lower but he would have gone faster because lipos don't drop voltage like Sub-cs do. Why, internal resistance of the cells, Sub-Cs being much higher.

A 32 cell pack peaks at around 40 volts, a lipo 10S pack at 42 volts. Under the high amp loads the 32 cell pack would drop to roughly 29 volts and the lipos around 39 volts. At least that's how it's been shaking out in my open class 10S2P boats compared to running 32 cells.

Paul.