Your first Bike, first kiss, first date, first....never mind! And the first time you start flipping the heli around trying to do some 3D.
Life is good!
Monday, April 20, 2009
Saturday, April 18, 2009
Heli Chat
Come and join us propeller heads at the shop on Wednesday Evenings (7:00PM - 8:00PM).
Bring your helis and radios as we'll shoot the bull on setup, exchange crash stories and if anyone is building one when can help put it together and exchange ideas on building, setup and radio programming.
Bring your helis and radios as we'll shoot the bull on setup, exchange crash stories and if anyone is building one when can help put it together and exchange ideas on building, setup and radio programming.
A123 Batteries for the T-Rex 500 and like Helis
A123 Racing now has a 6S1P 2300mAh packs for the T-Rex 500 and similar helis. Max amperage is 138A and weight is ~500g. Voltage is slightly lower at 19.8v (3.3v/cell nominal) instead of 22.2v so they will not have the equivalent kick for the same number of cells. So think of them as 5S packs but gear them appropriately for the actual voltage.
Also, you will need an ESC that you can set the low voltage cutoff appropriately (stock T-Rex 500 ESC will not work. Castle Creations and Scorpion are options).
These packs are Li-Ion packs using nanophosphate and are safer and more durable than traditional LiPos and can be quick charged (15-20min) and handle more cycles, but they do weigh a bit more.
You will also need a charger that can charge A123 cells.
Also, you will need an ESC that you can set the low voltage cutoff appropriately (stock T-Rex 500 ESC will not work. Castle Creations and Scorpion are options).
These packs are Li-Ion packs using nanophosphate and are safer and more durable than traditional LiPos and can be quick charged (15-20min) and handle more cycles, but they do weigh a bit more.
You will also need a charger that can charge A123 cells.
Blade 400 First flights
Aftering learning to flip his CP Pro, living up to his word LHS customer taking his New e-flight Blade 400 for a ride.
Tuesday, April 14, 2009
RPM, Kv, And Current Rating
RPM stands for the number of rotations per minute, and signifies how fast a motor spins. Brushless motors are given a Kv rating, which is RPM per volt, that lets you determine how fast that motor will rotate with a given voltage supplied to it. A 980Kv motor powered by an 11.1V battery would spin at 980 x 11.1 = 10878 RPM with no load. The current rating specifies the maximum continuous and/or burst current that the motor is able to handle. When selecting a battery and speed control, choose ones with continuous current ratings equal to or greater that that of the motor.
Monday, April 13, 2009
What's up with Lipo Batteries?
Lithium Polymer batteries are used in many electronic devices. Cell Phone, Laptops, PDA's, Hearing Aids just to name a few. Most, if not all, lithium polymer batteries are not designed for RC use, we use them in different applications than they were designed for.
They are similar to Lithium Ion batteries in that they each have a nominal voltage of 3.6 volts, but dissimilar in that they do not have a hard metal casing but rather a flexible material encloses the chemicals inside. The "normal" lithium polymer batteries are thin rectangle shapes with two tabs on the top one positive one negative. The reason we use Lithium cells is that they are significantly lighter than comparable NiCad or NiMH batteries, which makes our planes fly longer and better.
Voltage and Cell Count:LiPolys act differently than NiCad or NiMH batteries do when charging and discharging. Lithium batteries are fully charged when each cell has a voltage of 4.2 volts. They are fully discharged when each cell has a voltage of 3.0 volts. It is important not to exceed both the high voltage of 4.2 volts and the low voltage of 3.0 volts. Exceeding these limits can harm the battery.
The way to ensure that you do not go below 3.0 volts while flying is to set the low voltage cutoff (LVC) of your electronic speed control (ESC). It important to use a programmable ESC since the correct voltage cutoff is critical to the life of your batteries. Use the ESC's programming mode to set the LVC to 3.0 volts per cell with a hard cutoff, or 3.3 volts per cell with a soft cutoff. If your ESC does not have hard or soft cutoff, use 3.0 volts per cell. You will know when flying that it is time to land when you experience a sudden drop in power caused by the LVC.
If your ESC has an automatic lithium mode. Use it, it will correctly sense the number of cells and set the auto cutoff appropriately.
If you have previously been flying with NiCad or NiMH batteries, switching over to lithium polymer will result in a different number of cells being used. If you had 6 to 7 round cells then 2 lithium polymer cells will correctly duplicate the voltage of those cells. If you had 10-11 cells then 3 lithium polymer cells would be right for you. There are a lot of 8 cell flyer's out there that are stuck between 2 and 3 cells. In my experience the best option is to determine how many watts you were using before and duplicate that with your LiPos, Motor, and Prop. For example. If you were running 8 cells (9.6volts) at 10 amps on a speed 400 airplane, then you have 9.6 x10, 96 watts. So if you went with 2 lithium polymer cells (7.2 volts nominal) then you'd need to change your prop such that you used 13 amps. If you went to 3 LiPoly's (10.8 volts nominal) then you'd need to reduce the amperage to 8.9 amps. These estimates are approximate, and some experimentation is required for best results but conserving Watts is a good way to start.
10C from 3S4P? Naming conventions explained. How fast a battery can discharge is it's maximum current capacity. Current is generally rated in C's for the battery. C is how long it takes to discharge the battery in fractions of an hour. For instance 1 C discharges the battery in 1/1 hours or 1 hour. 2 C discharges the battery in half an hour.
All RC batteries are rated in milli Amp hours. If a battery is rated at 2000 mAh and you discharge it at 2000mA (or 2 amps, 1 amp = 1000mA) it will be completely discharged in one hour. The C rating of the battery is thus based on its capacity. A 2000mAh cell discharged a 2 amps is being discharged at 1C (2000mA x 1), a 2000mAh cell discharged at 6 amps is being discharged at 3C( 2000mA x 3).
All batteries have limitations on how fast they can discharge. Because of this many LiPoly batteries are put in parallel to increase the current capacity of the battery pack. When 2 batteries are wired positive to positive and negative to negative they become like one battery with double the capacity. If you have 2 2000mAh cells and you wire them in parallel then the result is the same as 1 4000mAh cell. This 4000mAh cell has the same C rating as the original 2000mAh cells did. Thus if the 2000mAh cells could discharge at a maximum of 5C, or 10 amps then the new 4000mAh cell can also discharge at 5C or (4000mA x 5) 20 amps. This method of battery pack building allows us to use LiPoly batteries at higher currents than single cells could produce.
The naming convention that allows you to decipher how many cells are in parallel and how many are in series is the XSXP method. The number in front of the S represents the number of series cells in the pack so 3S means it's a 3 cell pack. The number in front of P means the number of cells in parallel. So a 3S4P pack of 2100mAh cells has a total of 12 cells inside. It will have the voltage of any other 3S pack since the number of cells in series determines the voltage. It will have the current handling of 4 times the maximum C rating of the 12 individual cells. So say our 3S4P pack had a maximum discharge of 6C. That means that it has a nominal voltage of 10.8 volts (3x3.6) and a maximum discharge rate of 50.4 amps (2100mAh x 6Cx4P ).
They are similar to Lithium Ion batteries in that they each have a nominal voltage of 3.6 volts, but dissimilar in that they do not have a hard metal casing but rather a flexible material encloses the chemicals inside. The "normal" lithium polymer batteries are thin rectangle shapes with two tabs on the top one positive one negative. The reason we use Lithium cells is that they are significantly lighter than comparable NiCad or NiMH batteries, which makes our planes fly longer and better.
Voltage and Cell Count:LiPolys act differently than NiCad or NiMH batteries do when charging and discharging. Lithium batteries are fully charged when each cell has a voltage of 4.2 volts. They are fully discharged when each cell has a voltage of 3.0 volts. It is important not to exceed both the high voltage of 4.2 volts and the low voltage of 3.0 volts. Exceeding these limits can harm the battery.
The way to ensure that you do not go below 3.0 volts while flying is to set the low voltage cutoff (LVC) of your electronic speed control (ESC). It important to use a programmable ESC since the correct voltage cutoff is critical to the life of your batteries. Use the ESC's programming mode to set the LVC to 3.0 volts per cell with a hard cutoff, or 3.3 volts per cell with a soft cutoff. If your ESC does not have hard or soft cutoff, use 3.0 volts per cell. You will know when flying that it is time to land when you experience a sudden drop in power caused by the LVC.
If your ESC has an automatic lithium mode. Use it, it will correctly sense the number of cells and set the auto cutoff appropriately.
If you have previously been flying with NiCad or NiMH batteries, switching over to lithium polymer will result in a different number of cells being used. If you had 6 to 7 round cells then 2 lithium polymer cells will correctly duplicate the voltage of those cells. If you had 10-11 cells then 3 lithium polymer cells would be right for you. There are a lot of 8 cell flyer's out there that are stuck between 2 and 3 cells. In my experience the best option is to determine how many watts you were using before and duplicate that with your LiPos, Motor, and Prop. For example. If you were running 8 cells (9.6volts) at 10 amps on a speed 400 airplane, then you have 9.6 x10, 96 watts. So if you went with 2 lithium polymer cells (7.2 volts nominal) then you'd need to change your prop such that you used 13 amps. If you went to 3 LiPoly's (10.8 volts nominal) then you'd need to reduce the amperage to 8.9 amps. These estimates are approximate, and some experimentation is required for best results but conserving Watts is a good way to start.
10C from 3S4P? Naming conventions explained. How fast a battery can discharge is it's maximum current capacity. Current is generally rated in C's for the battery. C is how long it takes to discharge the battery in fractions of an hour. For instance 1 C discharges the battery in 1/1 hours or 1 hour. 2 C discharges the battery in half an hour.
All RC batteries are rated in milli Amp hours. If a battery is rated at 2000 mAh and you discharge it at 2000mA (or 2 amps, 1 amp = 1000mA) it will be completely discharged in one hour. The C rating of the battery is thus based on its capacity. A 2000mAh cell discharged a 2 amps is being discharged at 1C (2000mA x 1), a 2000mAh cell discharged at 6 amps is being discharged at 3C( 2000mA x 3).
All batteries have limitations on how fast they can discharge. Because of this many LiPoly batteries are put in parallel to increase the current capacity of the battery pack. When 2 batteries are wired positive to positive and negative to negative they become like one battery with double the capacity. If you have 2 2000mAh cells and you wire them in parallel then the result is the same as 1 4000mAh cell. This 4000mAh cell has the same C rating as the original 2000mAh cells did. Thus if the 2000mAh cells could discharge at a maximum of 5C, or 10 amps then the new 4000mAh cell can also discharge at 5C or (4000mA x 5) 20 amps. This method of battery pack building allows us to use LiPoly batteries at higher currents than single cells could produce.
The naming convention that allows you to decipher how many cells are in parallel and how many are in series is the XSXP method. The number in front of the S represents the number of series cells in the pack so 3S means it's a 3 cell pack. The number in front of P means the number of cells in parallel. So a 3S4P pack of 2100mAh cells has a total of 12 cells inside. It will have the voltage of any other 3S pack since the number of cells in series determines the voltage. It will have the current handling of 4 times the maximum C rating of the 12 individual cells. So say our 3S4P pack had a maximum discharge of 6C. That means that it has a nominal voltage of 10.8 volts (3x3.6) and a maximum discharge rate of 50.4 amps (2100mAh x 6Cx4P ).
Sunday, April 12, 2009
Saturday, April 11, 2009
Throttle Hold (For emergency autorotations)
I often get asked about the importance of setting up throttle hold and here's an attempt at explaining it:
Autorotation - A way of 'gliding' a helicopter safely back to the ground without engine power. Autorotation is in itself a very demanding maneuver and challenging to execute correctly. To achieve this you need to be able to set the main rotor blades to a negative pitch. This allows you to keep the head speed up while you a rapidly descending, as you get closer to your landing you’ll want to “Flare” and give it positive pitch to slow the helicopter for your landing.
So the importance of programming throttle hold is if anything goes wrong with you heli during flight, say like a belt break, or something goes wrong with the tail. This would cause the tail to spin with the torque of the main blades. If you added more throttle it would only get worse. So in this situation, throttle hold (depending on your radio and programming) would cut the power of the engine, reducing the torque of the main blades which would cause the tail spin to stop and allow you to land your heli as seen in this video.
Pitch and throttle curves are totally personal preference though. These are only possibilities. I myself fly all modes with the same pitch range (+/-10 degrees or +/-11 degrees or +/- 12 degrees) This way I'm totally used to how the collective responds through all flight modes and it never changes.
Many people actually prefer it this way, although it's the most sensitive on the collective. It requires very subtle movements to climb or descend in a hover rapidly.
Here's a video to show you throttle hold in action:
Autorotation - A way of 'gliding' a helicopter safely back to the ground without engine power. Autorotation is in itself a very demanding maneuver and challenging to execute correctly. To achieve this you need to be able to set the main rotor blades to a negative pitch. This allows you to keep the head speed up while you a rapidly descending, as you get closer to your landing you’ll want to “Flare” and give it positive pitch to slow the helicopter for your landing.
So the importance of programming throttle hold is if anything goes wrong with you heli during flight, say like a belt break, or something goes wrong with the tail. This would cause the tail to spin with the torque of the main blades. If you added more throttle it would only get worse. So in this situation, throttle hold (depending on your radio and programming) would cut the power of the engine, reducing the torque of the main blades which would cause the tail spin to stop and allow you to land your heli as seen in this video.
Pitch and throttle curves are totally personal preference though. These are only possibilities. I myself fly all modes with the same pitch range (+/-10 degrees or +/-11 degrees or +/- 12 degrees) This way I'm totally used to how the collective responds through all flight modes and it never changes.
Many people actually prefer it this way, although it's the most sensitive on the collective. It requires very subtle movements to climb or descend in a hover rapidly.
Here's a video to show you throttle hold in action:
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