Rubber

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lucwilder42
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Re: Rubber

Post by lucwilder42 » April 26th, 2011, 8:21 pm

Can you get better times by leaving enough winds that it doesn't deadstick? It seems like a waste of winds. Our copter deadsticks because the band runs out of torque, whether there are winds left or not. I guess I don't understand how to harness any leftover winds when the helicopter can no longer sustain its lift. Wouldn't the rotors just be spinning themselves from the air resistance on the descent?
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Re: Rubber

Post by lllazar » April 27th, 2011, 3:58 pm

Deadstick = ?

And also, more winds = more torque correct?
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Re: Rubber

Post by sj » April 27th, 2011, 4:03 pm

Deadstick is when the helicopter has no winds left in its rubber.

As for the torque im not a 100% sure but i think that is the basic idea...
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Re: Rubber

Post by sj » April 27th, 2011, 4:05 pm

lucwilder42 wrote:Can you get better times by leaving enough winds that it doesn't deadstick? It seems like a waste of winds. Our copter deadsticks because the band runs out of torque, whether there are winds left or not. I guess I don't understand how to harness any leftover winds when the helicopter can no longer sustain its lift. Wouldn't the rotors just be spinning themselves from the air resistance on the descent?
Also i was thinking that if the heli didn't deadstick on the way down then the powered rotors would provide more resistance than them just free spinning.
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Re: Rubber

Post by chalker7 » April 27th, 2011, 6:05 pm

lucwilder42 wrote:Can you get better times by leaving enough winds that it doesn't deadstick? It seems like a waste of winds. Our copter deadsticks because the band runs out of torque, whether there are winds left or not. I guess I don't understand how to harness any leftover winds when the helicopter can no longer sustain its lift. Wouldn't the rotors just be spinning themselves from the air resistance on the descent?
Ok, I've uploaded a sample graph of torque vs motor size with some made-up numbers. A couple things to note. First, those numbers are completely made up and just meant for example purposes. Second, I just made very basic shapes since it took less time, real torque curves don't have perfectly straight lines like that (I was just going for the general shape). Third, I made up units for torque. Common units include inch-ounces, foot-pounds or newton-meters (literally, some amount of force measured at some distance from the center of rotation). I'm just using an arbitrary value since I didn't actually measure real motors. Finally, I'm ignoring the differences in the shape during windup and wind down (energy input and release). The curves for these two are somewhat different, but for our purposes now just pretend these curves are showing the unwinding of a motor. Once it gets approved (it'll be in the helicopter gallery), hopefully this will help clear things up slightly.

Now, the short answer to your question is probably yes, deadsticking (running out of turns midflight) generally means you have too big of a motor. This is based off of freeflight airplanes knowledge, and could possibly be different for helicopters (hence the probably).
Here's the issue (using numbers from the graph I uploaded). In general, torque pretty directly corresponds to lift in helicopters. More torque means the rotors can turn faster and hence provide more lift. As such, for this conversation only, whenever I say "torque" or refer to some (arbitrary) value for torque you should also think "lift" or some (arbitrary) value for lift. Say your helicopter needs the motor to be providing at least 5 units of torque to hover. Above that it will climb, below it will fall. With the motors shown in the graph, you will start descending with ~50 turns left (thick motor) or ~375 turns left (thin motor). However, with the thick motor you only had ~800 turns to start and most of those provided torque way above what you needed. With a thinner one you had 1500 turns and all of them (until 375) kept the helicopter aloft. So, with the thick motor you had ~750 useful turns while with the thinner one you had ~1125. Obviously, the thinner one would keep you aloft longer.

Let's look at another common scenario that I think might affect a lot of teams. If you're well above 4 grams or have some construction errors, you probably need quite a bit more lift to keep your helicopter in the air. Let's say it needs 8 (arbitrary, according to my graph) units of torque to turn the rotors fast enough to keep it aloft. If you have too thin of a motor, you're only getting above 8 from ~1250-1500, so you have 250 useful turns on the motor. With the thicker motor you have above 8 from ~150-800, so 650 useful turns. Obviously, this means the thicker motor will be better for your helicopter. I see this pretty often when teams show up with well-built helicopters but just too thin of motors. They will put a huge number of winds in motor and only get 10-15 seconds. It isn't that the design is incapable of flying for a longer amount of time, it is that they have not found the correct motor for their helicopter.

Hopefully that explained the generic motor selection process for you a bit more. I'll clarify wherever possible, but please note there are no general answers that will solve all your flight problems. You just have to go out there and practice flying to try and come up with the right combination for your own helicopters.
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Re: Rubber

Post by lucwilder42 » April 27th, 2011, 7:44 pm

Thanks, and yes that supports what we've seen on our copters, I think we're at our max combo for the best copter we have
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Re: Rubber

Post by mrsteven » April 29th, 2011, 7:58 pm

For you guys going to nationals to compete: Im going to watch the helicopters and I was wondering when exactly the flights are from (time periods). and if theres a posted schedule of when what teams are going when...
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Re: Rubber

Post by thedoctor » May 16th, 2011, 5:54 pm

Does anyone know of any place that sells 5/32 in. rubber? We used that for our helicopter at states and it worked quite well I thought, but I can only seem to find 3/32, 1/8, and 3/16 on sites like a2z. If not, is it worth it to buy a rubber stripper?

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Re: Rubber

Post by mrsteven » May 16th, 2011, 6:01 pm

thedoctor wrote:Does anyone know of any place that sells 5/32 in. rubber? We used that for our helicopter at states and it worked quite well I thought, but I can only seem to find 3/32, 1/8, and 3/16 on sites like a2z. If not, is it worth it to buy a rubber stripper?
do you need them for this year (nationals this weekend) or just in general for in the future?
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Re: Rubber

Post by thedoctor » May 16th, 2011, 8:06 pm

mrsteven wrote:
thedoctor wrote:Does anyone know of any place that sells 5/32 in. rubber? We used that for our helicopter at states and it worked quite well I thought, but I can only seem to find 3/32, 1/8, and 3/16 on sites like a2z. If not, is it worth it to buy a rubber stripper?
do you need them for this year (nationals this weekend) or just in general for in the future?
For the future, so I'm in no rush.

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