Archive for the 'Radio Control' Category

Storing Lipo batteries for faster charging times and longer lipo life

I just finished a quick flight at the park with my Trex 550e. What a fun bird to fly.

Trex 550e Upside down hover

That picture was taken last year on a nice summer morning. No pictures today but it's the same heli.

Anyway, the point of this post is about lipo batteries. I just brought up the heli fly because I had such a great experience with it's battery. Coincidentally, I was just talking today with someone about charging batteries and they wished they could charge 4 6S batteries in 20 minutes. You need a lot of Watts to do that. A 6S lipo is 22.2V nominal and the batteries for these helis are 5000mAh. So if W=A*V then 4 of these things take ~444W to charge in an hour. Triple that to do it in 20 minutes. The only charger I know of that can do close to that is the Powerlab 8. Given a big enough input power supply it can do 1344W output.

Step back a bit. When I first started flying RC airplanes and helis I wanted to fly all the time. Well, I still do but I was pretty gung ho from the beginning. I'd do like 3 or 4 flights per day if the weather wasn't bad. Morning, evening, it was all good. We live by a park big enough to fly my small trainer so I'd just run out for a couple quick flights and then go back to doing whatever. I didn't have time to charge my batteries before every flight so at the time I just charged them after the flights and left them charged all the time. It worked out pretty well except after a while I started learning that it might be best to not store them charged all the time. Apparently it breaks down the chemistry faster when they have a full charge. A day before you're probably fine but charged all the time is going to wear them out much faster.

Ok, side note again. All my batteries that I did that with are still fine. I use them in planes and even an EDF still and as far as I can tell that early storing stuff didn't do much harm to them. BUT... you know, the experts must have something they know so I better heed advice.

Fast forward a bit. I decide I should probably not store my batteries charged. I think this is the point I started flying less often. If I wanted to go fly something I had to take a moment and charge some batteries. You can see why someone would want to be able to charge their batteries FAST.

I got a better charger.

OK, so I have this charger that can charge faster than the original one I had but I have a lot of batteries by this time too. I hook them all up and charge most of them at the same time. It can take over an hour still. In the mean time, I keep learning and reading things and I find out that the experts are advocating not storing the batteries all the way discharged too. Apparently storing them discharged has a similar effect to when you store them charged. How much? I have no idea. My philosophy is that I'll probably destroy the battery before I find out if the way I stored it has much effect. However, this is good news because 1) My fancy pants charger has "store" mode and 2) I get to fly faster if they are already charged a bit.

Store mode on these chargers puts the charge on the pack back to about 70% capacity. Somewhere around 3.85-3.9V/cell. So now I get to feel all dandy because I'm storing my batteries in such a way that the experts won't complain AND, my charging time is cut in half. I just charge the packs before a flight, go fly, then stick the packs back on the charger for their storage charge and I'm good to go for next time.

Back to the heli flight today. I was smiling because I just stuck that one 6S 5000mAh pack on for a quick charge and 20 minutes later I was ready to go.

Graupner MX16-iFS vs Spektrum DX7

I started my RC hobby with a Graupner MX16-iFS. I've been quite happy with it and don't have any plans to change in the future. As part of a package deal I purchased, I obtained a Spektrum DX7. While I won't be keeping the DX7, I don't have a receiver for the Heli I bought yet so I'm using the existing radio system in the mean time. Having thus had a chance to play around with them both, I thought I'd post a few of my observations.

MX-16 Pros:

  • 8 channels instead of 7.
  • Rotary knob. This can be used for flaps or throttle limit.
  • More customizable buttons/switches. You can tie any function to whichever switch you like. The DX7 has fairly standard switch assignments and I found it hard to change the functionality. e.g., your elevator dual rate functionality can't be assigned to the aileron dual rate switch.
  • Push button. Just another different style selector switch the DX7 doesn't have. The DX7 and MX16 have the same number of extra switches but it's nice to be able to use different types as suite your personal tastes. For instance, I find using the push button to switch my gyro functionality nicer than using a switch. Not that big of a deal really though.
  • Easier to program. I found the menu system on the DX7 a little difficult to get used to. You have to push two buttons to activate the menu for instance. The MX16 feels a little more intuitive.
  • Automatic timer. I tie my timer to my throttle channel or auto-rotate for helis. With the DX7, I couldn't find any way to start the timer besides pushing the button. (And it's hard for me not to forget to do that.)

Spektrum DX7 Pros:

  • DSM2. You can bind-n-fly.
  • Slightly more complex radio functions are available. You can add expo to your pitch and throttle curves for a heli for instance. Also has Revo mixing. (The MX16 has more free mixes though so you can do the same thing as revo with the MX16).
  • More complex heli setup. MX16 only has two flight modes for helis. Normal and IDLE-UP. The DX7 has normal, idle-1 and idle-2.
  • More model memory. The DX7 holds 20 models and the MX16 holds 12.

Anyway, I can't talk to much on the reliability of either system. They are both 2.4 Ghz systems and are not subject to interference from other transmitters. They both have to have an adequate power supply to the Rx which will reboot if voltage drops too low (not good).



css.php