Question about ESC and LiPo battery

[boeing_737]

Okay, I have been thinking about the issues here and it seems that you guys are right.. plus the size of the quad was going haywire. So, I have come up with a new config. Please let me know what you think.

Estimated weight of quad : 1Kg
Motors(4) : http://www.hobbyking.com/hobbyking/s...nner_10g_.html
Props : Not exactly the recommended props, but I did see a guy with a similar config using 4x2.5 and his quad looked pretty good, so I suppose this would be OK (http://www.hobbyking.com/hobbyking/s...ting_6pc_.html)
Battery : http://www.hobbyking.com/hobbyking/s...Lipo_Pack.html
ESC(4) : http://www.hobbyking.com/hobbyking/s...8_10A_ESC.html

Weight vise,
Motors : 10gx4 = 40g + 20g buffer = 60g
ESC : 6gx4 = 24g + 10g buffer = 34g
Battery : 135g + 25g buffer = 160g
Frame + Wiring + Electronics = 400g
Total : ~660g

As far as the flight time goes, the motor is supposed to have a peak efficiency current of 5.5A. If we assume it's going to be 8A for each motor, then we would have 32A drawn from the battery. The 2200mAh 30C battery will have a max current of 66A which would give a flight time of around 2 mins. So, drawing 32A would give a flight time of somewhere around 4 minutes. Hopefully, I would be more closer to the 5.5A draw and can hopefully manage a flight time near 8-10 mins. Would this setup work? what do you guys think?

[Rockin Robbins]

Originally Posted by boeing_737

I tried on 9x7 and 10x5 props and they were noticeably producing more thrust at the same power setting than the 7x5 prop. Btw, how do you guys convert from electric power (W) to mechanical force (grams of thrust)? Is it through a formula or more by experience?

I use a free program called drive calculator (google it) and Denny uses a commercial program called Motocalc. They tell you what performance to expect from a combination of motor (by brand and model number), electronic speed control (by brand name and model number) and propeller (same deal, by specific brand and model number). And the results are based on actual tests of the items, not on manufacturer claim

I highly recommend both.

[boeing_737]

Originally Posted by boeing_737

Okay, I have been thinking about the issues here and it seems that you guys are right.. plus the size of the quad was going haywire. So, I have come up with a new config. Please let me know what you think.

Estimated weight of quad : 1Kg
Motors(4) : http://www.hobbyking.com/hobbyking/s...nner_10g_.html
Props : Not exactly the recommended props, but I did see a guy with a similar config using 4x2.5 and his quad looked pretty good, so I suppose this would be OK (http://www.hobbyking.com/hobbyking/s...ting_6pc_.html)
Battery : http://www.hobbyking.com/hobbyking/s...Lipo_Pack.html
ESC(4) : http://www.hobbyking.com/hobbyking/s...8_10A_ESC.html

Weight vise,
Motors : 10gx4 = 40g + 20g buffer = 60g
ESC : 6gx4 = 24g + 10g buffer = 34g
Battery : 135g + 25g buffer = 160g
Frame + Wiring + Electronics = 400g
Total : ~660g

As far as the flight time goes, the motor is supposed to have a peak efficiency current of 5.5A. If we assume it's going to be 8A for each motor, then we would have 32A drawn from the battery. The 2200mAh 30C battery will have a max current of 66A which would give a flight time of around 2 mins. So, drawing 32A would give a flight time of somewhere around 4 minutes. Hopefully, I would be more closer to the 5.5A draw and can hopefully manage a flight time near 8-10 mins. Would this setup work? what do you guys think?

Could you guys please have a look at this config and let me know what you think? I have to order the stuff before hobbyking runs out and puts stuff on backorder. Thanks a lot.

[slipstick]

If you'd just read the comments on the page for that motor you'd see that people are getting around 4.4oz (120g) thrust at 3A from it on a 5x3 prop and 2S battery. So there's not much chance of 4 of them lifting something that weighs 1000g is there ?

Steve

[boeing_737]

Originally Posted by slipstick

If you'd just read the comments on the page for that motor you'd see that people are getting around 4.4oz (120g) thrust at 3A from it on a 5x3 prop and 2S battery. So there's not much chance of 4 of them lifting something that weighs 1000g is there ?

Steve

True, but being very conservative weight-vise, gave me ~660g. I don't think the frames+wiring+electronics is going to be 400g. That's why I think this setup would work.

[slipstick]

Unfortunately if you're giving us information that even you think is wrong we don't have much chance of doing a sensible evaluation .

If you think less than 500g static thrust will be enough to lift whatever you think your device will end up weighing then that setup should be o.k. You don't really need 8A ESCs because with that prop you'll be running about 3A but you won't save much by going for a smaller ESC and you may find you need to try a larger prop for a bit more thrust.

Steve

[boeing_737]

I am sorry for the confusion, since I haven't done something like this before, so I am not sure how conservative(or otherwise) I should be when estimating weights and sizing up the power system. I think I will go with this setup and try to limit the weight to below 500g.

Thanks a lot for the help.

[boeing_737]

Just a quick update:

I tested one of the SuperTigre motors with a 7x5 prop connected to 11.1V 3-Cell 3700mAh battery and I was able to get around 330g of static thrust at max power. Since I won't be running at max power always, it looks like 4 of these motors-props combo would have been able to lift a 1 Kg quad.

[slipstick]

That's good, but you might remember that what you were originally asking was how well they would lift 2Kg...and you only wanted to use a 2S (2 cell) battery .

But I'm glad you seem to be getting there.

Steve

[boeing_737]

^ @ Steve, you are right still climbing the slippery learning curve