ESC Programming

[Ross McWhirter]

I have a Hacker X70 speed controller on a Mythos 50e. On advice of fellow flyers I am changing the braking from hard to soft. I managed this OK using the Hacker USB cable and download programme. However I couldn't save a new setting without setting a voltage under the title "reduce power below". I selected 2 volts being the lowest option. Can anyone please advise the best setting for this?

[Gordon Tarling]

2 Volts is way too low if you're using a Lipo battery. The figure to which you refer is a 'per cell' voltage and it should really be set around 3.5 Volts, but the exact figure depends on what the current draw is. Try setting it to 3.5 Volts and see how you go - if you think it's reducing power too early, then drop the voltage a bit at a time. The aim is to end up with a battery that shows around 3.7 Volts per cell having rested for a minute or two after a flight.

Incidentally, I personally don't like the 'reduce power' setting and much prefer to have the motor cut completely when the low voltage figure is reached, as I've been caught out by it on a couple of occasions.

[Simon Chaddock]

Ross

Even a correct 'reduced power' setting can be an issue if you tend to fly at much reduced throttle settings - you simply won't know it has happened - unless you periodically apply full power and can hear that the motor does not speed up.

In practise you should not rely on the ESC low voltage settings as it does not do a LiPo any favours. Much better to good at judging how much capacity you have used and land. Treat the ESC cut off only as a final back stop if you get it wrong!

Just as an example. A fully balance charged 1500mAh LiPo gave close to its rated capacity when taken right down to the ESC cut off 3.3V but it would only accept 1258 mAh back suggesting such a 'deep' discharge significantly reduced its capacity.

[simon barr]

Why would you want braking on the Mythos anyway? Braking is usually used on the likes of electric gliders so that the prop folds when the motor is stopped to reduce drag...

[Ross McWhirter]

Thanks everyone.

Yes, I use my timer and land as soon as the beeper goes. It was when I tried to save a new setting on the ESC it wouldn't save until I chose a voltage. I'll set it to 3.5 volts and I'll switch off the braking.

[Peter Jenkins]

Simon

you may not be aware that ESC braking is used extensively in F3A (precision aerobatics) to slow the aircraft on vertical downlines. With an IC engine, the engine on idle provides prop braking and this is what the braking on F3A electrics is trying to emulate. The idea is to fly the model at a constant speed regardless of whether you are climbing or diving including going vertical in both - there's quite a lot of that in F3A!

Ross - I don't know what the Hacker X70 provides under soft braking but on a Jeti/Hacker Spin 99 you can set a wait period (I use 0.5 secs) and then an initial brake (~20%) then final brake (~40%). Adjust the final brake figure to provide the required braking. It may be the X70 just gives a single setting on soft brake in which case use that. Setting a hard brake gives minimal braking effect - ideal for gliders especially for folding props - but no good for aerobatics. I'm sure that someone in your Club of F3A experts will be able to help you further.

[simon barr]

Thanks, Peter.. No I didn't know that...

See, we all learn something new everyday

[Ross McWhirter]

Thanks for the advice on braking. I've just got the Mythos and wonder if having the brake off would help slow the plane on landing? Once I get better at landing I could turn it on at soft setting?

[Peter Jenkins]

Ross, remember that that throttle controls height and elevator controls speed. So, to slow down the Mythos approach at a shallower angle. Learn to fly a consistent circuit and your landings will also be consistent. The Mythos, like most F3A models, is usually pretty simple to land where you want - just takes a bit of practice.

I normally set an idle for my electric motor when landing. I aim for the minimum speed at which it will run so that i can get power immediately I move the throttle lever. This emulates IC I know but makes it much easier to land the aircraft and to adjust its descent rate. Closing the throttle with the hard brake means that you are just gliding in and when you start to undershoot slightly you tend to get a burst of power as you open the throttle. Also, if you are overshooting there is nothing you can do about it as the throttle if fully closed,

The secret to a good landing is to approach at the right speed with a bit of power on (how much depends on your motor setup and the model's characteristics) so that you can close the throttle to increase sink rate or open it to reduce the sink rate. Practice how slowly you can fly the Mythos at height and then come in a little bit faster for your landing. If it's windy, approach a bit faster i.e more steeply, as this will a) give you more control and b) give you a margin of speed as the aircraft comes through the wind gradient and loses airspeed close to the ground.