dkshema
rrMaster
Location: Cedar Rapids, IA
| Don't get me wrong, the EP400XP is a fine little e-heli. I'm impressed by the upgrades Kyosho did to get the XP after they introduced the EP400 a year ago. I believe that it is capable of serving as an aerial camera platform. That being said, it sounds as if what you are really looking for is something on the order of a T-Rex 450 S/SA or SE since they already swing the 325 mm blades and a commercial camera mount is already available for the T-Rex.
(Recommending a T-Rex almost seems like blasphemy, but I own an EP400 XP, a couple of older T-Rex 450X and 450X-V2 versions, and just completed a 450SA that came courtesy of Santa). The SA is a pretty nice setup overall).
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As to your questions:
One thing you'll find with the EP400 at lower head speeds is that it will wobble. That's not a problem unique to the EP400, many of its larger brethren also wobble with a low head speed (my EVO 50 will do it, as does the Caliber 30. I've even seen my Freya do it).
Last year, when I was putting my original EP400 through its paces for this thread, the heli would wobble when it hovered. I had the wrong pinion at the time, and a couple of sick battery packs, so my head speed was down in the 2200 RPM range. As I got healthy batteries, and a better pinion selection, I found the EP settled down and became a stable, fun flying heli. With the addition of the XP upgrades, it is even more fun to fly as along with its "big helicopter feel", the new head and tail setups add precision control.
With a camera attached, you're not going to be worried about aerobatics, but I think you'll still want a respectable head speed, say in the 2400 to 2800 RPM range. This will keep the wobbles at bay and give you decent controllability, and much needed lift.
With the added weight of the payload, you will need to pay close attention to the power that your motor is able to deliver, as well as the current your battery pack will need to deliver without roasting the pack (and the motor current rating of your ESC). You would be wise to consider some of the newer 20C continuous packs such as the Thunder Power Extreme 2070 mah packs.
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One other thought that pops into my mind is that you might consider a 4S battery pack if your AXI can handle the extra voltage without going up in smoke. By going with an extra cell in the pack, you could get close to 2800 RPM with a 43 tooth pinion, or 2400 RPM using a 36 or 37-tooth pinion. Of course, you'd probably need to add an external BEC unless the ESC you've got is capable of running all the electronics with 14.8 volts nominal input without going up in smoke.
A 5S system -- would get you into a range of pinions that is more reasonable -- 34/35 tooth for 2800 RPM or 29/30 tooth for 2400 RPM.
A 4S or 5S system would also require less operating current for the motor when compared to the stock 3S system.
The trade-off is weight and $$$ for your battery charger.
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To answer some of your other questions:
The bolts for the current MR blades of the EP400 are 2.6 mm diameter x 12 mm long. I believe the MR grips and head would have no trouble with longer CF blades. I don't think you're going to get away with 315 or 325 mm blades, however, due to the short tail boom of the EP. Granted, you're not going to be doing aerobatics with your setup, but at those lengths, the MR is going to overlap the TR disc and put your heli at risk of whacking its tail feathers off. If nothing else, it would make for some rather dicey descents and landings!
Frankly, I'd like to find a source of 15 mm OD tail boom material so that I could lengthen the tail boom on the EP400XP to allow it to swing those 325 mm blades. A source of longer TR drive belts would also be nice to find at the same time. It's my gut feel that an EP400 swinging a set of 325 mm blades would be an excellent flying small heli and may give T-Rex-like performance.
Also, with regard to a pinion in the 50 - 57 tooth range, the diameter of the pinion is getting to be pretty large at those tooth counts. I'm not sure the motor with a pinion that size would actually fit in the heli without modifying the motor mount some. I'm also guessing that with a gear ratio in the neighborhood of 6:1 or 7:1 , there is going to be some healthy motor current required to turn the head. That battery pack and ESC you've chosen may not be up to the task. Also, can you GET 64 pitch diameter pinions with that number of teeth? Robinson Racing seems to run out of gas at 44 teeth. I would suspect that their competition does so, as well.
You may have that AXI laying around, but for about $50 there are a host of good 3000KV-plus motors on the market that would do the job with less hassle.
I'm not sure how you got a TP 3S 2000 mah LiPo that goes for 112 grams. I just looked at the TP website, and none of their 3S packs in the neighborhood of 2000 mah come in at 112 grams. I see a 2000 mah 3S pack at 120 grams, but it's only a 12C continuous pack. That pack is simply not up to the challenge. Best case scenario with that pack is that it gets real hot real fast and puffs up on you. You might get to witness a LiPo fire. That would be scary!
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To sum up this rather long post, I'm not trying to rain on your parade. I just think you need to rethink the motor selection. Dwight may choose to disagree, but healthy, legitimate discussion is good for all involved.
I believe the EP400XP could be a viable camera platform as long as you put the appropriate motor, pinion, ESC, and battery combination together. My gut feel says that a low KV motor, turning a LARGE pinion, with what appears to be a 12C battery pack will be a disaster.
A successful platform would use a higher KV motor, smaller pinion, and at least an 18C battery pack, and preferably a 20C or better pack.
If you can find them, a good set of 280/285 mm CF semi-symmetrical, even flat-bottom airfoil blades, would be a good solution for new blades. You'll sacrifice aerobatic ability for additional lift. But you may end up with more drag.
Longer symmetrical blades would be the ideal solution, but at this point, they are not a viable option without stretching the tail boom out an inch or so.
BTW -- you listed your electronics by weight, but didn't specify what kind of servos, RX, or ESC you've got in mind. The 401 for a gyro is an excellent choice.
Dave |
will seriously hamper your motor and helicopter's performance. It may even cause your ESC to shut down momentarily in flight.
