Wednesday, April 23, 2014

Nickel Metal Hydride Battery Story

This is another story about how trying to be cheap cost more in the long run.  Several years ago I purchased this heavy fiberglass, foam, and obeche wood 2-meter glider. It seemed so heavy I did not get very excited about installing radio equipment until last year. Fall of last year I finally made some flights with it and was amazed how well it flew, especially in windier weather.

Shadow 2 Meter Glider

For this year I upgraded to a Spektrum DX9 transmitter from the DX6xi, learning to re-program the glider was a challenge but I figured out most aspects.  Luckily I did tests glides instead of trying a hi-start launch from the start. The radio seemed to be shaky and the elevator control was not that responsive. I took the plane home and installed a longer arm on the elevator servo, feeling confident the next time test glides would be better.

Cells I Soldered in Front With Date Battery Put in Service

Next outing control was not any better and the radio took a long time to connect up, I should have recognized that as a bad sign.  I had charged the battery again before flying and the battery was only a little over a year old. On the last glide I threw the plane a little harder, it went up and it went down hitting the ground rather hard. One wing suffered damage that I fixed to be strong again but it is not very pretty. I also checked the battery condition and was shocked to find it was really low.

Sanyo Eneloop Battery

If the battery was charged, putting it on the expanded voltmeter would drag the needle to the left in a couple of minutes. I decided it was time to do some research, my inquiry on the Facebook Sailplane and Soaring group brought several suggestions as did some emails to someone that had just mentioned they had battery failures on batteries less than a year old.  This person like me had soldered the cells together instead of buying a pack that comes put together. Further research pointed to the possibility of soldered cells having a shortened life span because of damage from the heat.

I ordered 2 Sanyo Eneloop nickel metal hydride battery packs because I am going to replace another pack I soldered even though it appears to be working good for now. Battery monitoring will be done more frequently as well.  With the new battery in place the radio seems more solid, the servos are faster and do not make noises when not moving. 

Checking Voltage

Lesson learned; it could have turned out much worse if I had crashed from a high altitude, no doubt the glider would have been totaled. Looking back to last season the radio equipment did not work as fast or as smooth like it does now but I am not real experienced in the 2.4 systems yet.

Bill Kuhl

Comparing Two 2-Meter  Gliders

Basic Aerodynamics With a Lesson

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