Would someone simplify answer to previous thread

[flyyy]

I asked about limiting the throttle stick in order to not exceed amperage on the esc awhile back and something in all the technical answers puzzles me [which isn't hard to do]. Does it damage any of the equipment [motor,batteries,esc] to putter around at low throttle settings? I thought I was saving the equipment now I'm not so sure because something about the motor wants to run at full current? One more thing about twin motors. In the thread about twins awhile back it mentioned a way to hook up twin motors with separate throttles using a v tail mixer hooked to channel 3 and 4. My v tail radio is on channel 2 and 4. Which way would you move the 4 stick? I think I might be misunderstanding something in their setup and I should Y the escs together and hope for the best.

[Larry3215]

Flying the plane at part throttle will cause the esc to run hotter than it does at full throttle.

Its even worse if you are using an esc that is too small.

So, yes, you will be hurting your esc by doing that. The motor and battery will probably be ok unless you are also running them over their max rating.

I didnt see a thread about using V-tail mixers on twins so I cant comment on that.

Normally you just use a standard Y connector on the throttle channel.

[baz49exe]

Flyyy I used differential throttle control on my Wellington build. Here is a link to the page which contained the info.

http://www.wattflyer.com/forums/show...t=60141&page=2

post 32.

The simplest way is to buy a cheap V -tail mixer. Plug the inputs of the mixer into the throttle and rudder channel outputs of your receiver and plug the outputs from the V tail mixer into the left and right ESC inputs.
I did use a separate UBEC to power the radio system as I was on Spectrum 2.4 so I isolated the red wire coming from both ESC's by simply pushing down the little plastic tag in the socket, pulling out the brass connector and taping it over. This way the ESC's are not supplying power to the system and only the signal ( white) and the negative ( black) are operating.
The fun part of this system is that it transfers the throttle controls to the left stick where you would expect them to be. Stick forward as you would expect gives increased throttle on both motors but move the stick left or right as you would to operate the rudder and the opposite motor will slow down. Hope this helps!
Barry

[Larry3215]

LOL Barry, I like the flying brick

Now I see why the V-tail mixer.

What Barry is using the mixer for is to link rudder inputs to the throttle controll on each motor.

What this will do is make one motor speed up and the other one slow down when you make turns using the rudder.

Be careful if you try this. It cam make a tame, easy flyer into a wild beast. It can be a lot of fun if you are an experienced flyer. if not, then Id highly recomend you just use a normal Y lead from your throttler channel to the esc's.

Disconnecting the red wire on one of the esc's is a must unless you are using Castle esc's. Or you can do like Barry and disconnect both red wires and use a separate bec.

[NJSwede]

Originally Posted by Larry3215

Flying the plane at part throttle will cause the esc to run hotter than it does at full throttle.

I've always wondered about this. Given what I know about electronics, it should work the opposite way. I think brushless ESCs use pulse-width modulation to shape a sine wave (or three phase shifted sine waves to be exact). Since RPM is proportional to voltage on brushless motors, the sine waves should have lower frequency as well as lower amplitude (i.e. peak voltage) at low throttle. The result should be that the chopper stage in the ESC is more off than on and that should result in less energy being transferred (and lost as heat).

What am I getting wrong here?

[Larry3215]

The frequency of the PWM doesnt change in our esc's even though the commutation frequency does change with rpm. Also, the peak voltage is constant which means the peak amperage is also constant which means the peak I x I x R values are also constant.

The other factor is how the FETs handle the OFF phase. Im not an expert on that aspect of it but the end result is more heat generation durring PWM than during full on.

Patrick Castillo of Castle Creations did a great explanation - with math - a while back. I'll see if I can find it.

[NJSwede]

Originally Posted by Larry3215

The frequency of the PWM doesnt change in our esc's even though the commutation frequency does change with rpm. Also, the peak voltage is constant which means the peak amperage is also constant which means the peak I x I x R values are also constant.

The other factor is how the FETs handle the OFF phase. Im not an expert on that aspect of it but the end result is more heat generation durring PWM than during full on.

Patrick Castillo of Castle Creations did a great explanation - with math - a while back. I'll see if I can find it.

I feel bad hijacking the thread, but this is really interesting!

What I meant was that the commutation frequency changes, not the chopper frequency.

It's still a bit counter intuitive to me. FETs shouldn't really draw any current when they're off.

You're right that the peak power (wattage) is the same, but that's only part of the equation. You have to look at the energy (power integrated over time), which would be less for lower throttle input, since the total time you have power on will be less. The ESC "leaks" energy (as heat) to the surrounding air at a fairly constant rate, which means that it gets more time between the peaks to bleed off heat, which should keep it cooler. In theory...

Sorry... You pushed my geek button. I'll stop hijacking the thread, but it would be cool if you could show me that explanation. I've always wondered about this and it's never made sense in my head!

[flyyy]

Don't be concerned about hijacking. All of this went right over my head. I thought maybe the reason for increased heat in esc was due to less airflow. You go right ahead because it is all Greek to me. One thing though, do you think that going slow more than fast will damage the esc either now or over time?

[gyrocptr]

Originally Posted by flyyy

.... One thing though, do you think that going slow more than fast will damage the esc either now or over time?

You need to check the current draw of your motor-prop combination at maximum, wide-open-throttle (WOT). You may want to invest in a high-capacity ammeter or "wattmeter". It's a really useful/essential piece of equipment.
If the WOT current exceeds the amperage-rating of the ESC, you will damage the ESC, even if you operate at partial-throttle. To provide a margin of safety, some people will select a prop that provides a WOT current of not more than 80% of the amperage-rating of the ESC.

[CrimzonRider]

Originally Posted by Larry3215

Flying the plane at part throttle will cause the esc to run hotter than it does at full throttle........

Sorry Flyy, I am a bad hijacker too. But what larry said really caught my eye.

To Larry....... HUH? Please explain further, that is the first time I have read that and it makes my brain hurt!! LOL Not debating that statement, I just might have had this prob with my warmliner, a ST Models Blaze, 10x6 folder, 960kv, 11.1v 50amp esc, even at part throttle the esc is unbelievably hot, barely can touch it. These results after a WOT launch to a average (1/2 throttle) 12min flight with nominal airflow. Even after increasing airflow, batt(2000mah) and motor are cool, esc is still hot...... Wattmeter shows 260w, 24amps. A near WOT flights results in 6mins flights, everything hot. Thanks.

have a good one
cr

[Larry3215]

Originally Posted by Gohmer

Sorry guy, hard to get simple, or even accurate answers here. Someone's always dragging topics off where they want them to go.

LOL Where have you been hanging out that threads DONT get dragged off topic to one degree or another??

This isnt really off topic anyway - its just expanding on the answers.

I did a quick search and couldnt find the specific post I was looking for by Patrick where he goes into details on why esc's run hotter at part throttle. I really wanted to look at it again so I didnt screw up the math

The short version is that the rpm in our motors is controlled by the esc switching the voltage ON and OFF very rapidly. Thats called PWM controll or Pulse Width Modulation.

Motor RPM is a direct function of the voltage applied, so if you switch the voltage on/off at varying rates you can control the average voltage the motor 'see's'. In other words, if you switch the voltage OFF 50% of the time, the motor will act like its only runnng at 1/2 the voltage and so turn at 1/2 the rpm. If the voltage is OFF 25% of the time, the motor will see 75% of the voltage and run at 75% of max rpm.

The problem - and the extra heat - comes in because the FET's in the esc that do that switching are less efficient when they are switching than when they are full on. Lower efficiency means more waste heat which can only do one thing - make the controller run hotter.

Now if your running at under say 1/8-1/4 throttle, then maybe the controller would run cooler. But thats probably a very IN-efficient range for the motor to run in so then IT will run hotter

So, its no good to over amp your esc and think you can run at 1/2 throttle and be safe. Your actually making it worse than if you go ahead and run it at full throttle.

[Larry3215]

Originally Posted by flyyy

Don't be concerned about hijacking. All of this went right over my head. I thought maybe the reason for increased heat in esc was due to less airflow. You go right ahead because it is all Greek to me. One thing though, do you think that going slow more than fast will damage the esc either now or over time?

Airflow is always an issue. if the heat isnt being removed, then it has no choice but to build up.

Originally Posted by gyrocptr

You need to check the current draw of your motor-prop combination at maximum, wide-open-throttle (WOT). You may want to invest in a high-capacity ammeter or "wattmeter". It's a really useful/essential piece of equipment.
If the WOT current exceeds the amperage-rating of the ESC, you will damage the ESC, even if you operate at partial-throttle. To provide a margin of safety, some people will select a prop that provides a WOT current of not more than 80% of the amperage-rating of the ESC.

Excellent advice. Every electric flyer needs a watt meter

Originally Posted by CrimzonRider

Sorry Flyy, I am a bad hijacker too. But what larry said really caught my eye.

To Larry....... HUH? Please explain further, that is the first time I have read that and it makes my brain hurt!! LOL Not debating that statement, I just might have had this prob with my warmliner, a ST Models Blaze, 10x6 folder, 960kv, 11.1v 50amp esc, even at part throttle the esc is unbelievably hot, barely can touch it. These results after a WOT launch to a average (1/2 throttle) 12min flight with nominal airflow. Even after increasing airflow, batt(2000mah) and motor are cool, esc is still hot...... Wattmeter shows 260w, 24amps. A near WOT flights results in 6mins flights, everything hot. Thanks.

have a good one
cr

Which controller? Quality makes a huge difference. Those Hobby King controllers for example are not very efficient when compared to name brand controllers. Plus they are almost always over rated.

There are several other factors that can make the esc run hot as well.

Are you using the internal BEC? If so, how many servos? Linear BEC's generate a good bit of heat all by themselves.

How good are your packs and how long are the battery to esc wires? Hi Ir packs and/or long battery leads or poor connections can all increase ripple voltage which will also add to controller heating.

Another factor on cooling is how the esc is positioned. You may have large air intakes, but is the airFLOW actually moving over the esc efficiently?

Are your air EXITS large enough? I see that one a LOT. You need air exits at least 50% larger than the air intakes or you dont get good airflow.

Finally - how hot is TOO HOT?

Again, quality makes a huge difference. You can run Castle controllers hot enough to melt the solder off the boards and the components will keep working just fine.

Not so true of lesser controllers, but even the cheap ones should be safe when run too hot to hold your finger on.

Most people start to say "ouch" at around 140 degrees or so.

Even the cheapest controllers should survive that kind of temp all day long.

Check the temps with a heat gun and see where they are. if your under 180 or so your probably fine.

If its a castle esc, then under 280 is perfectly safe.

[NJSwede]

Larry,

What you're saying is true for a brushed motor. The chopper modulates the duty cycle to create a signal that, when filtered, produces a DC voltage that's proportional to the duty cycle. At WOT, the duty cycle is 100%, and the chopper isn't chopping anymore, but its power FET is constantly conducting. This is the most efficient state and you'll get the smallest amount of losses.

I'm with you that far. But a brushless controller is more complicated, since you have to produce AC for the motor phases even at WOT. That's what known as the commutation frequency. This signal is always overloaded on the output, even at WOT, which means that the chopper still has to switch the signal on and off.

So you won't have the same kind of "always on" state that you'd have with a brushed controller. What you *may* have is longer periods of "on" at full throttle, and that may increase efficiency compared to a lower throttle input, but not nearly as much as for a brushed controller (is my guess at least).

My web searches came up with some pretty strong evidence that it's an issue for brushed controllers (not surprisingly), but a lot of the people claiming the same thing for brushless controllers seemed to use the old "I have been in the hobby for 30 years" line and offered very little evidence.

There seems to be some consensus that there may be a peak in power loss (and heat production) around 80-90% throttle, but my guess is that the effect disappears quickly towards lower throttle inputs, simply because the effect is canceled out by the fact that the ESC handles a lot less power.

Anyway. I've already gotten yelled at for hijacking the thread, so I think it's time to stop. It was fun hijacking with you Larry!

[CrimzonRider]

Originally Posted by Larry3215

Are you using the internal BEC? If so, how many servos? Linear BEC's generate a good bit of heat all by themselves.

How good are your packs and how long are the battery to esc wires? Hi Ir packs and/or long battery leads or poor connections can all increase ripple voltage which will also add to controller heating.

Another factor on cooling is how the esc is positioned. You may have large air intakes, but is the airFLOW actually moving over the esc efficiently?

Are your air EXITS large enough? I see that one a LOT. You need air exits at least 50% larger than the air intakes or you dont get good airflow.

Finally - how hot is TOO HOT?

Again, quality makes a huge difference. You can run Castle controllers hot enough to melt the solder off the boards and the components will keep working just fine.

Not so true of lesser controllers, but even the cheap ones should be safe when run too hot to hold your finger on.

Most people start to say "ouch" at around 140 degrees or so.

Even the cheapest controllers should survive that kind of temp all day long.

Check the temps with a heat gun and see where they are. if your under 180 or so your probably fine.

If its a castle esc, then under 280 is perfectly safe.

thanks larry as always.....temp of esc on average runs is at least 120, (I have a infared thermo, just forget to bring it when flying) after what you said I am not so worried, it is a cheap Grayson Hobby 50amp with 3amp bec with 4 servos, other than the heat "problem" not a hint of any problems. I easily doubled the size of the "air scoops" and enlarged the exhaust holes by about 50% larger, I use velcro to hold esc vertical on it side to provide more cooling on the two flat sides. IMHO Wires are not too long about 3 inches from batt to deans connector, esc is same. 6.5" total battery to esc.

Really what this comes down to is for me not to be so worried about, pretty much. I have only bought about 10 different motor/esc combo's and never had a single esc or motor get anywhere near this temp, even flying in the same real world conditions. HOT! On my other thread, Denny pretty much has me convinced to start buying switching ESCs from Castle Creations instead of cheapies that I have been buying. Phoenix I think he called them.
Thanks for all the info Larry...I tried to soak it all in!

Thanks Flyy for letting me "borrow" your thread

have a good one
cr

[flyyy]

I agree with crimzon rider. I don't have money to burn, but making my own planes out of foam and buying cheap Asian products I guess I don't really need to understand why things work just the general guidelines of how to hook things up and what size to use with what. I appreciate someone who really understands electronics and I've even been through electronics school, but I was just passing through. I knew that I wouldn't be earning a living working on tv's if you know what I mean. One final thing. Is it best to use an external bec if you have plenty of them on hand? Also if you use a external bec with a twin do you undo both esc red wires? Thanks all.

[Larry3215]

Originally Posted by NJSwede

Larry,

What you're saying is true for a brushed motor. The chopper modulates the duty cycle to create a signal that, when filtered, produces a DC voltage that's proportional to the duty cycle. At WOT, the duty cycle is 100%, and the chopper isn't chopping anymore, but its power FET is constantly conducting. This is the most efficient state and you'll get the smallest amount of losses.

I'm with you that far. But a brushless controller is more complicated, since you have to produce AC for the motor phases even at WOT. That's what known as the commutation frequency. This signal is always overloaded on the output, even at WOT, which means that the chopper still has to switch the signal on and off.

So you won't have the same kind of "always on" state that you'd have with a brushed controller. What you *may* have is longer periods of "on" at full throttle, and that may increase efficiency compared to a lower throttle input, but not nearly as much as for a brushed controller (is my guess at least).

My web searches came up with some pretty strong evidence that it's an issue for brushed controllers (not surprisingly), but a lot of the people claiming the same thing for brushless controllers seemed to use the old "I have been in the hobby for 30 years" line and offered very little evidence.

There seems to be some consensus that there may be a peak in power loss (and heat production) around 80-90% throttle, but my guess is that the effect disappears quickly towards lower throttle inputs, simply because the effect is canceled out by the fact that the ESC handles a lot less power.

Anyway. I've already gotten yelled at for hijacking the thread, so I think it's time to stop. It was fun hijacking with you Larry!

First, I dont think this is hi-jacking. Second, even if it is, the OP gave his permission

A few points.

Yes, the FET's are most effieient when full on. BUT, they arent full on at part throttle. Which is what I said earlier, they are switching on/off at the PWM rate and therefore less efficient.

Second, our brushless motors are actually brushless DC motors, not AC. That simplifies things a lot

The comutation cycle is the rate at which the esc drives each seperate phase of the motor. Each of the three phases in the motor is driven by its own seperate bank of FET's in the controller. The comutation pulse is timed to coincide with magnet position relative to the stators based on back emf pulses that the non-energised phases of the motor are generating as it turns. The comutation rate varies according to rpm and the number of poles the motor has. the timing setting on the controller fine tunes when the power is applied as the magnets move in relation to the stator.

Thats completely independent of the PWM which is occuring while each phase of the motor is being driven. The PWM and comutation rates are not related in any way.

The comutation rate determines when a bank of FET's and a phase of the motor can have power. The PWM rate determines the average voltage thats applied during that comutation cycle.

Here are a few quotes from Patrick del Castillo - owner and founder of Castle Creations and the guy who designs all the esc's.

PWM is used to change the power level. However, you have to realize that power loss in an ESC is not linear -- so you can't setup a 25A controller on a motor that draws 40A, and then limit the throttle to stay under 25A. The controller always sees 40A when in the on PWM state. Because the power loss is i^2R + SW, the power losses are higher. (SW= switching losses)

I know it seems backwards, but partial throttles can actually be harder on a controller than full throttle.

You should always check the full throttle amperage, and size the controller based on that. About 87% throttle is hardest on the controller, and will cause the highest temperature rise in the controller.

First of all, a controller always sees full throttle current, even at partial throttle. So you have to be sure that the full throttle current is not above the rating of the controller, or you will see lots of heating. (for example, you can't prop a motor for 50A, and then just throttle up to 10A and expect the controller to be happy with it. The controller still sees 50A of current.)

Secondly, if you are pushing a motor too hard, the controller will suffer from heating. The reason is that the motor iron can saturate, which causes really high currents for short periods. The iron saturation causes a huge drop in the motor inductance, which creates shoft duration REALLY high currents. These won't show up on a meter (which averages over time) but can be seen on an oscilloscope with a current probe or shunt. These short duration high currents cause TONS of extra heat to be dissipated in the controller.

No, voltage has nothing to do with the life of the Phx-10. Current and heat do. The higher the current, the more likely you are to hurt any controller. If you are constantly "on the edge" (for example, if you run a Phx-10 at 15 amps all the time) you will shorten the life of your controller.

Also, (and especially with helis) you cannot simply reduce the throttle to reduce the current and then run a system which draws too much current for the controller. For example, if you have a setup that draws 20 amps at full throttle, you can't just run 50% throttle at 10 amps and expect the controller to survive.

Typical full throttle controller efficiencies are very very high (99% or better.) But at partial throttles the controller efficiencies drop (and therefore, temperatures rise.)

At full throttle, the mosfets are only switching during commutation. At partial throttles the mosfets switch during both commutation and PWM period. Switching losses are therefore higher. Also, there are additional losses during recirculation, and when the FETs are in reverse recovery. These losses all increase in partial throttle.

[Larry3215]

Originally Posted by flyyy

I agree with crimzon rider. I don't have money to burn, but making my own planes out of foam and buying cheap Asian products I guess I don't really need to understand why things work just the general guidelines of how to hook things up and what size to use with what. I appreciate someone who really understands electronics and I've even been through electronics school, but I was just passing through. I knew that I wouldn't be earning a living working on tv's if you know what I mean. One final thing. Is it best to use an external bec if you have plenty of them on hand? Also if you use a external bec with a twin do you undo both esc red wires? Thanks all.

When to use an external bec depends on how many amps your servos are drawing. if you are pushing the internal BEC on the controller, then you must use an external bec. The other reason is for insurance or if you happen to trust the external one more than the internal one.

That second question proves something Ive suspected for a long time. Most people dont read all the way through a post if its more than 3 sentences long

See post #4 above - last sentence

[baz49exe]

Larry, glad you like the flying brick! I used to build solid balsa wing funfighters powered by 25 glow motors and they were flying bricks!! Hence the avatar seemed appropriate when I turned to the darkside and went lightweight electric LOL
I found your comments on UBEC use spot on and I know it's been mentioned so many times on this forum . There are still flyers losing control of small foamies when flying Spektrum 2.4 and using micro servo setups at low amps with a bec speed controller which is capable of delivering 2 amps or thereabouts on the bec feed. When I read that the current draw on cheap 9g servos can be 600 plus milli amps each I realised that running three was marginal and four was asking for trouble ( as has been mentioned many times)
Barry

[bbqflyer]

OMG! My brain hurts reading all of this!! I feel even more dumb now. I just prefer to look at it this way: fly plane around (weeeee), land, change battery, don't touch thingy with wires coming out of it (HOT), fly some more WEEEEEEEEE!

[NJSwede]

Larry, I finally get it!

It's all Wikipedia's fault. I was looking at this diagram on their article about brushless DC motors:



It looks like they're using a chopper to create sine waves (after filtering) for the phases (like you would for an AC motor). But you're saying the commutation is just DC on/off pulses. Then it makes sense to me.

You sure know your stuff, Larry!

[flyyy]

"That second question proves something Ive suspected for a long time. Most people dont read all the way through a post if its more than 3 sentences long

See post #4 above - last sentence" from Larry. You see it's not that I don't read all of the post it's a retention thing. At #18 I'm not concentrating on #4. About the bec. If everything is sized right does it just help the esc using an external bec. For instance would the esc run cooler using a bec than just using the esc alone. Just hypothetically.

Ps. I haven't learned how to change colors and all that fancy stuff in post yet.

[CrimzonRider]

Originally Posted by bbqflyer

OMG! My brain hurts reading all of this!! I feel even more dumb now. I just prefer to look at it this way: fly plane around (weeeee), land, change battery, don't touch thingy with wires coming out of it (HOT), fly some more WEEEEEEEEE!

LMAO.......I thought you fly plane around, land, change battery, "eat four delicious smoked ribs, drink two beers, eat more beans, thennnnnnnnnnnnn.....fly some more!!!!!

have a good one
cr

[CrimzonRider]

Originally Posted by flyyy

"That second question proves something Ive suspected for a long time. Most people dont read all the way through a post if its more than 3 sentences long

See post #4 above - last sentence" from Larry. You see it's not that I don't read all of the post it's a retention thing. At #18 I'm not concentrating on #4. About the bec. If everything is sized right does it just help the esc using an external bec. For instance would the esc run cooler using a bec than just using the esc alone. Just hypothetically.

Ps. I haven't learned how to change colors and all that fancy stuff in post yet.

I would imagine that temp would be about the same as when everything is working correctly is also getting the same voltage. I would think airflow is more important concerning the temp of an esc, than where its voltage is coming from......I think..lol

have a good one
cr

[Larry3215]

Originally Posted by flyyy

"That second question proves something Ive suspected for a long time. Most people dont read all the way through a post if its more than 3 sentences long

See post #4 above - last sentence" from Larry. You see it's not that I don't read all of the post it's a retention thing. At #18 I'm not concentrating on #4. About the bec. If everything is sized right does it just help the esc using an external bec. For instance would the esc run cooler using a bec than just using the esc alone. Just hypothetically.

Ps. I haven't learned how to change colors and all that fancy stuff in post yet.

Yes to some degree.

If you're using the internal BEC, then it is generating at least some additional heat, so using an external bec will let it run somewhat cooler. It may even let it run a lot cooler if you were pushing the bec too hard with too masy servos.

However, using an external bec probably wont help enough if your pushing the esc too hard or if you dont have enough cooling to begin with.

Like crimson rider said - cooling air flow and correct sizing of the esc are more important.

On the other hand, it cant really hurt to use an external bec as long as its as reliable as the internal one. Its more expense and more set up work and one more part to potentially fail, but I dont see those as major hold backs.

If you feel like using an external bec "just because', I dont see any real reason not to do it

[Glacier Girl]

Lot of really great info posted. Going back to part one of post one, where flyyy asked about using part throttle to control amps.

Maybe a layman's explanation would help him out instead of technical talk that's even over my noggin.

Flyy, how it was explained to me a long time ago, and where newbies get confused.

The old brushed controllers/esc's you could think of as a water faucet. The more you open up the faucet, the more water (power) flows from it.

On a brushless version, think light switch. On/off. That in simple terms is what the esc does to control motor speed. At WOT it's on almost all the time. Say at mid throttle it's more like on for a short while, off for an instant, back on for a short while. Down at low throttle, it's on for an instant, off for a while, on for an instant.

But every time it turns on, the motor is pulling the full amps it pulled at WOT.
Granted the duration is lower at reduced throttle, but the amount is still the same.


And if you use a meter, it will trick you into believing that the amps drop as the throttle does. Where it leads you astray is that it averages readings over a period of time. For example say in 10 seconds it takes 10 readings. At WOT it will see 10 readings of X amp draw, so it reads that.

At lower throttle, remember the on/off esc to run the motor, it may only catch 5 amp ratings of X. So it tells you the amp draw is 1/2 of X. You thinking it is safe to run up to that point could easily lead to the magic smoke leaking out of your system, and putting a frown on your face.

As for your second part, that's what is called differential steering, using motor speeds to help in turns, like the others have posted. Not really something to try until you have some time under your belt. If you aren't paying attention and don't have it on a switch, it can make a nice flying bird a beast.