How to program an ESC - Brakes

[sdabiker]

I have noticed that each time the "guys" fly without landing gear they never break a prop. How do they do it? Do they have a programmed ESC with a brake or just something that keeps the prop stopped in the same position. I would like to learn. Anyone that can help would be appreciated.

 

[Jaxx]

Yes, programmable ESCs have a "brake" function that can be turned on and off. It is used to stop the prop when there is no throttle input. If the aircraft is moving fast enough, the prop may still move a bit, but the brake will slow it down considerably, if it doesn't stop it completely. Now this will not guarantee you won't break props. I still break props with this featue enabled.

In my opinion, the easiest way to enable this feature is with a programming card. Your Tx can be used as well, but you have to listen to a series of beeps to identify and enable the specific functions. Here is an example of a programming card:

http://hobbyking.com/hobbyking/store/__2169__TURNIGY_BESC_Programming_Card.html

 

[Craftydan]

Gentle word of warning . . . There is no universal ESC programming card.

ESC programing cards are designed by product line. If you try to use a programing card on an ESC not designed to talk to that card (for example a turnigy card with a blue-series ESC) it will probably fail and *can* damage the ESC.

Proceede with caution and refer to the ESC's user manual for compatibility with programming cards or instructions on how to program it through your radio (it's a pain, but it works).

 

[stay-fun]

Actually I think programming a brake will CAUSE a prop to break. If the prop is stopped exactly when one of the blades is pointing towards the ground, it'll break. However, when the prop is still spinning slowly, as the plane comes to the ground, the chance that the prop will be exactly pointing towards the ground is minimal (1/180). In all other cases, the prop is allowed to spin in either direction to clear the nose for impact.

 

[quorneng]

stay-fun
The ESC brake is not a 'brake' in the conventional sense but a 'retarder'. With the brake on the ESC shorts out the motor windings so the motor becomes a generator so resists rotation but it still has to rotate to create any resistance.
I would agree that just setting the brake will not prevent breakage but as long as the blade comes to rest reasonably past vertical it should be ok.

The brake feature is often required with folding props as surprisingly they are quite likely to continue to windmill even with the power off.

 

[Jaxx]

Gentle word of warning . . . There is no universal ESC programming card.

ESC programing cards are designed by product line. If you try to use a programing card on an ESC not designed to talk to that card (for example a turnigy card with a blue-series ESC) it will probably fail and *can* damage the ESC.

Proceede with caution and refer to the ESC's user manual for compatibility with programming cards or instructions on how to program it through your radio (it's a pain, but it works).

I've just learned something new. I guess I've been lucky I havn't damaged any of my ESCs. I had no idea this was the case. I will have to start paying closer attention to the ESC manual. Thanks for the tip Dan!

 

[stay-fun]

stay-fun
The ESC brake is not a 'brake' in the conventional sense but a 'retarder'. With the brake on the ESC shorts out the motor windings so the motor becomes a generator so resists rotation but it still has to rotate to create any resistance.

Yes i know, may i ask what your point is? And to be exact, as i always want to be , when the prop has stopped there is resistance to movement, however, there is only friction when the prop actually moves.

The point of my post is that if the prop stops at for example, 45 deg angle, it could break on impact. If the prop would be allowed to turn freely, the prop would change its position upon impact, instead of breaking.

I hope I'm going an OK job at explaining this

 

[Craftydan]

I've just learned something new. I guess I've been lucky I havn't damaged any of my ESCs. I had no idea this was the case. I will have to start paying closer attention to the ESC manual. Thanks for the tip Dan!

If I hadn't seen it myself . . . I've got a buddy who builds beautiful airframes but has a penchant for letting the smoke out of electronics. He mixed the above turnigy card with one of the blue series ESCs and after changing a setting it promptly self destructed.

If you think about it, it makes sense. These cards throw the ESC into a programming mode then read/write a setting table. That'd be fine if every ESC ran on the same ROM (then the table would be the same values in the same place), but each manufacture writes their own ROM -- assuming they don't steal it from someone else. This also explains why a card will stop working for an ESC after you flash it to SimonK or BLHeli -- different ROM, different settings tables.

 

[quorneng]

Stay fun
The question is whether a rotating prop is more likely to get broken than a stationary one.
With the brake off the prop will be wind milling so if a blade touches the ground before it reaches bottom dead centre there is a good chance the prop will break.
If the brake is on and the prop is stationary with the blade before bottom dead centre there is a chance the blade will be pushed back out of the way as even with the brake on there is little or no resistance to small movements.
I would agree that if the blade is stopped close to bottom dead centre the prop is most likely to get broken.

Of course if you can see the prop is vertical and you have time, you can always give a very short blip of power to try to get the prop to stop at a different position. I have actually done this with my non folding prop belly landers.

 

[makattack]

I seem to have bad luck with motor braking enabled and belly landings taking out my prop. What are the odds of seeing your prop stop vertically, bumping the throttle only to see it stop vertically again? That happened to me last weekend. What was the end result? Half the prop cracked just before the hub.

That was an 8x4 on a small foamie "Fast and Furious" plane I was getting ready for a combat event this weekend. I mostly set the motor brake on so it would glide better on landings.

My versa wing, initially had motor brake on, but the motor I had didn't really do any braking until it dropped down to about < 4 meters per second... so it was kind of useless, I actually prefer the free wheeling prop on that one because it glides too darn well, when I want it to land. So, now, I have it set to freewheel to add drag.

 

[stay-fun]

quorneng: we can debate this forever I guess I just prefer to have the brake disabled on a non-folding prop. Same as makattack.

makattack: I would actually think that if a prop is allowed to freewheel, the drag will be less than when the prop can't freewheel. But either way, I think the difference in drag is insignificant.

 

[makattack]

quorneng: we can debate this forever I guess I just prefer to have the brake disabled on a non-folding prop. Same as makattack.

makattack: I would actually think that if a prop is allowed to freewheel, the drag will be less than when the prop can't freewheel. But either way, I think the difference in drag is insignificant.

http://www.djaerotech.com/dj_askjd/dj_questions/windmill_prop.html

Is a great article that explains the physics behind the drag on a free/windmilling prop. So you are correct, in that it actually has less drag than a stopped prop. It's odd though, because I have noticed that without the prop windmilling, I get much faster/longer glides on my smaller, light plane -- but that article did mention that for small planes with large props (8x4 on a 32" wing span) -- it "seemed to glide better" with the brake on...

 

[Jaxx]

If I hadn't seen it myself . . . I've got a buddy who builds beautiful airframes but has a penchant for letting the smoke out of electronics. He mixed the above turnigy card with one of the blue series ESCs and after changing a setting it promptly self destructed.

If you think about it, it makes sense. These cards throw the ESC into a programming mode then read/write a setting table. That'd be fine if every ESC ran on the same ROM (then the table would be the same values in the same place), but each manufacture writes their own ROM -- assuming they don't steal it from someone else. This also explains why a card will stop working for an ESC after you flash it to SimonK or BLHeli -- different ROM, different settings tables.

I suspect most of my ESCs were probably produced by the same manufacturer, and were simply rebranded.

 

[TexMechsRobot]

I know I'm resurrecting an old thread but I think it makes sense to do it for context rather than start a new thread.

I have come to the conclusion that I need to set the ESC brake for a belly lander. The BLHeli 30A ESC from Flite Test has 6 different settings: Low, Mid-Low, Middle, Mid-High, High, and Off. What are the differences? I can't seem to find anything.

My guess is the amount of brake applied. So High would take a lot of flowing air to turn while Low would only take a little bit of wind. Am I correct?

 

[Fluburtur]

I personally make only pusher prop planes and I never had any prop breaking (and believe me, the props I have are incredibly brittle)
So for pusher I couldn't recommend brake unless folding prop.

(I had a prop break once but the motor was running at full power when it hit the ground, don't land at full power)

 

[quorneng]

TexMechsRobot
Correct.
An ESC applies the brake to a motor by 'shorting out' the wires from the motor. The motor then generates a current which causes the motor to slow down. The power is dissipated via the ESC heat sink.
Where the brake has various settings it just means the maximum current (and thus the braking effect) is limited.
With a complete short circuit the motor will slow down very rapidly indeed.
Technically it is not a 'brake' in the conventional sense in that once the motor has slowed right down it is not physically prevented from turning but it will be quite hard to turn it at any speed.