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Archive for August, 2018
Posted by edwen303 | Aug 26, 2018 @ 07:51 PM | 3,255 Views
  • Use hand file to make saw teeth on the end of brass tube or cf tube. This is to act like cutting piece when used with hand drill inside the foam
  • Secure a brass tube or cf tube, the same way as holding a drill bit, in a power drill (an example: https://www.amazon.com/dp/B077FSNHX4...d-777fa7fb2507 )
  • Carefully pulsatingly place the tube with teeth into where you plan to add wingspar and drill slowly. Make sure the tube stay in the correct path inside the foam. You can add some pressure on the drill/tube to slightly adjust which direction the tube inside the foam. Even the hole is a little bit rough or too large, don't worry.
  • After the drilling, remove the foam debris from the drilling tube. Place the cf tube inside the wing to test the fit.
  • Gluing: Put on glove, apply Gorilla polyurethane (foaming) glue to the tube, use disposable piece to spread the glue on the cf tube, then spray some water on the glue and mix glue/water with disposable stick.
  • Insert the cf tube into the hole with twisting move all the way to the desired depth. Gorilla PU glue with water will soon foam and expand, so use masking tape to whereever the glue might "outgrow" to maintain the smooth surface once glue is cured and hardened. Gorilla glue is notorious for the messiness in terms of cleaning but it is my goto glue if working on foam models.

Posted by edwen303 | Aug 07, 2018 @ 10:00 PM | 3,316 Views
There are many Lipo battery vendors online or in store, not all of them are rated equally accurate.

Capacity:
Once I purchased a lipo from Amazon for its low price. The lipo arrived in good shape, voltages for each cell are consistent 3.80 V +/- 0.02 V. Then when I charged the battery to 4.20 V, my charger showed the charge it received was significantly below 50% of the rated capacity. For example, with a new 3s 2200mAh lipo, one would expect to charge 1100 mAh into the lipo from 3.80 V/cell (11.4 V total) to 4.20 V (12.6V). Anyhow, based on what I found out, this lipo has capacity that is much less than rated and I had to return the lipo as "significantly different from the description".

I fly mostly EDF, the maximal amp in the model is typically 20C of the capacity. So the current at full throttle will be ~100Amp when running a 5000mAh (aka 5 Ah) battery. The actual amperage in flight should be less than the static test. Suppose the average amp in flight is 50 Amp, the amount of discharge from 4.20 V to 3.80 V is 50% of capacity or 2.5 Ah. The flight time can be calculated as = Ah / A = 2.5 Ah x 60 min/50 A = 3.0 min

If at the same amp but a lipo of larger capacity is used, the longer flight time. For a 6000mAh lipo, the flight time = 3.0 Ah x 60 min/50 A = 3.6 min
If you find a lipo battery last very short amount of time, it is very likely your lipo has lower capacity than rated. To find out the true capacity of your lipo, put your lipo to storage voltage 3....Continue Reading
Posted by edwen303 | Aug 07, 2018 @ 09:25 PM | 3,219 Views
In addition to physical appearance of Lipo pack, there are several factors that affect the health of Lipo:
  • Storage voltage: If lipo will remain unused for more than two days, use your charger or drain your lipo to 3.80V per cell. This will make your lipo last longer time.
  • Charging: Never charge lipo above the suggested maximal charging current. Charging at 1C is always the safest. Example: maximal charging current for 3s 2200mah lipo is 2.2 Amp
  • Discharging current: Avoid continuously discharging at amperage higher than the rated C value. For a 3s 2200mah 30C battery, keep the maximal amp below 66Amp.
  • Overcharging: Charging lipo to voltage above 4.2 V per cell is damaging to the battery, can even cause fire. This happened to me
  • Overdischarging: Avoid discharging lipo to below 3.5 V per cell. Many chargers will not charge a lipo if the voltage is below 3.0 V. If the lipo was slowly discharged to low voltage (such as pilot forgot to unplug the lipo from ESC), it is possible to "revive" an overly discharged lipo by charging the lipo as Nickel-Metal or Ni-Cd battery. Ask an experienced RC modeler who knows well about the use of lipo to handle this.
  • Storage temperature: Research showed fully charged lipo loses the capacity faster at high temperature, so store your lipo at low temperature (like in the refrigerator or just room temperature, ~25 C or 75 F)
  • Discharging temperature: The internal resistance of Lipo affects the performance of your battery, the C rating. Low temperature increases the IR and reduces battery performance.
  • "Break-in" of Lipo battery: This is controversial topic but this will NOT hurt your battery health. For a new lipo battery, charge at 1 C to full, then discharge the battery to storage voltage 3.8 V at low current, such as 2C to 10C. Then repeat the charging/storage cycle again.