Since there seems to be many different ways of describing motors, is there a chart on the web which compares the various descriptions? For example, is the HeadsUp PowerUp 25 (which I happen to have) the equivalent of the Turnigy 3542 1000 Kv? Such a chart showing equivalency would be very helpful when comparing or choosing a motor. Thanks. Gary
So far as I know, there is no such chart of equivalence. However, you can compare the power ratings in watts and the Kv rating to come out ballpark close, which is all a chart could do anyway.
So take the Power Up 25 Sport. There are two Power Up 25s, a sport and a speed version. The sport version is rated at 620 watts and is 900Kv. We'll arbitrarily choose that one.
There are also multiple Turnigy 3542 1000Kv motors. We'll take the Turnigy Aerodrive SK3 3542 1000Kv. It's rated at 670W and 1000Kv. So it may be just a bit more powerful.
Then you have to take into consideration that the Chinese motors tend to be rated higher than their capabilities. Having an SK3 myself I know they're pretty honestly rated, but you don't know that. So you would run it at 620W safely and would have a motor that is fairly equivalent to that Power Up 25 Sport.
By the way, when Heads Up tells you the rating of their motor, they aren't taking the word of the manufacturer. They TEST and publish their test results. If they say that's a 620W motor you can take it to the bank.
These motors have a few characteristics to be aware of:
Max rated Amps
Max rated Watts
Zero load ampere draw
Just about all motors specify their "KV" rating, or approximately how many RPM's the motor turns per volt of battery power.
Also, they specify maximum Amperes and Watts rating.
Most of the motors specify the zero load ampere draw. This is an indication of quality, for a given size motor, the lower this current the better.
Again, most motors specify the motor weight.
Not all motor suppliers provide the motors Winding Resistance. This is a critical value that is involved in the maximum Amps and Watts the motor can handle. This winding resistance doesn't require multi-thousand dollar micro-ohmmeters, it can be accurately measured with a pair of digital multimeters, a battery, resistor and not much else.
The motor weight and maximum watts capability are related to each other. If you take the motor maximum wattage rating, and divide that number by the motor weight in ounces, you get watts per ounce of motor weight. Decent values would be around 100 Watts per ounce of motor, so an eight ounce motor can usually handle 800 Watts.
Some of the real cheap import motors are claiming 150 or 200 watts per ounce of motor weight. Actually running them that hard will often result in short life, or worse.
And, the winding resistance of a quality motor versus a cheap import also can vary widely. I've seen the winding resistance of a cheap import measure three or four times higher than the winding resistance of a quality motor such as the Hacker or Hyperion line. Generally, when most of the winding area of the motor is air, rather than copper windings, the winding resistance will be higher.
Take a look at a $$$$ Hacker A40-10L motor, versus another well known motor mfg. The well known motor had a mfg defect, where one winding shorted out, frying it. All of the other windings in this motor are OK. The well known brand motor has double the winding resistance, double the no load current, and two ounces more weight than the Hacker. I've also installed one Hyperion motor of similar size to the Hacker, but it sells for a very reasonable $49.00.
Hope that helps.
If you are looking for a rough and ready comparison then IMHO weight and Kv are the two best general guides. I find claimed power rating to be unreliable because different manufacturers come up with wildly different ratings for effectively the same motors.
Then you have physical dimensions and mounting details which are also hard to compare because there are numerous different ways of specifying a motor's dimensions. You really need to compare spec sheets to figure if it will actually fit in your plane size wise.
The motor can size and kv are a good way to compair motors, it will get you very close, the heads up power 25 sport, is a 3549 900kv motor, the turnigy motor is a 3542 1000kv motor, the 3549 is a tad more powerful, and bigger, also the motor size is important too, depending on how much room you have in the cowl, if the 3549 is to big, and if the 3542 will fit into the cowl, thats what you want to use, also the use of different cell counts affects the power too, the 3542 will be more powerful on a 4 cell lipo than the 3549 on 3 cells, lot of things to take into consideration, I use heads up RC motor specs on other motors to get a good idea of how much power / thrust it will produce, it will be a very good ball park figure, and what size props to use with different cell counts, It wont be Exact, but it will very close. and of course, check your amps and watts with a Wattmeter to be on the safe side.
I generally find the off-brand motors to be good motors that are rated optimistically enough that if you run 'em by the numbers you make lots of smoke. It's important to find out what your motor's REAL capabilities are as opposed to its ADVERTISED capabilities are.
With some motors, Hacker and a few other manufacturers, Heads Up RC and a very few retailers, you get honest numbers. For the rest, you can either reject them outright, which can cost you a lot of money, or use one of two proven computer programs that will evaluate your power system based on test results.
The first is a paid program called MotoCalc. It evaluates how your system: battery, ESC, motor and propeller will perform, and flags any problems you might have. It also tries to predict how a given airplane will perform with that power system. MotoCalc has a smaller and older database but if you buy components which are in the database the predictions will be on the money. Why would you restrict your purchases to the contents of an arbitrary database? Because the alternative is to buy $$$$$ Hackers or Heads Up motors only. More choices equals more opportunities.
The other is a free program called Drive Calculator, which is what I use. It has a live database, contributed to by qualified modelers all over the world. Test results are signed. One major contributor is Dr Kiwi of that other RC forum which shall remain nameless here.:D Just like MotoCalc, you pick components by brand name and model. You can also have it spit out a list of props that match the rest of the system, for instance. You can start out with a prop and match the other components to it. I put a Slow Stick together using Drive Calculator when the recommended motors just were not available. I may still be the only one who has used a Turnigy 2217-20 motor with one. HK says it's a 230 watt motor. Drive Calculator says it's safe to run at 200 watts. It's been flawless and I only had to buy components once. The motor was $13.
Either way, you leave the jungle of uncertainty and widen your safe choices for components. If you choose the Hobby King route you're still performing with no safety net. Heads Up gives you rock solid information and although their prices are a bit higher, their two dollar shipping and the fact that you're only going to have to buy something once more than balances out the equation.
Motocalc is a very good computer program that, unfortunately is only as accurate as the specifications provided to it by the motor mfg's.
If the major specs provided by the motor mfg are provided (KV, No Load Amps, Winding Resistance, Motor Weight) motocalc will flag any motor that has questionable power ratings. I've seen some name brand motors where Motocalc indicated the motor will be running at 450 degrees F, when running at the rated "Amps" and rated "Watts".
I've found that the name brand motors, such as Hacker, Hyperion, and a lot of other motors do provide fairly accurate specs. And, you can run those Hackers and Hyperions at their maximum rated Amps and Watts, and have no issues with overheating, or smoke.
One important spec is the motor's winding resistance. This is a very easy to measure value that can be measured with a multi-thousand dollar micro-ohmmeter, or with a simple pair of digital multimeters, a power source and resistor. I've measured winding resistance both ways many many times. We had dozens of those micro-ohmmeters at work, and they were EXPENSIVE!
IMHO, I'd be a bit reluctant to buy any motor where the mfg does not provide the motors winding resistance. Unless its real real cheap, and a burnt up motor won't hurt the budget.
Things are a bit different when running at well over 1000 watts, or in my case, 3000 watts on one of my models. A motor failure in flight can cost a lot more than the value of the motor if the model lands off field and crashes. I've got eight Hacker motors, ranging from the A30 series, two A40 series, three A50's and two A60's. All are running at their max current/power rating, none have had any sort of problem.
Lipos, chargers and power supplies. The somewhat more expensive Lipoly packs may have better quality controls and may give longer life with good performance than cheap ones which may be mismatched packs sold under other brand names. Good quality packs may cost up to twice the price of cheapies but "buy cheap buy twice". Revolectrics/FMA direct chargers and lipo packs and power supplies are considered good stuff but are not cheap. A friend of mine swears by Turnigy Nanotech lipos sold by Hobby King. Try to learn as much solid "no-hype" information as you can about good versus poor lipos, chargers, and power supplies.
There are many brands of medium cost lipos, chargers and power supplies that may satisfy your current and forseeable needs. Proper use, charging and storage of lipos will help extend their useful life.
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