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Mini Ultra Stick, Not Happy With My Setup

Old 05-04-2008, 01:49 PM
  #1  
Sam_K
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Question Mini Ultra Stick, Not Happy With My Setup

I have an E-Flite Mini Ultra Stick which I have kitted out as follows.

Motor: Turnigy 35-30C 1100Kv B/L Outrunner
Prop: APC 10x7e
ESC: Tower Pro Mag8 30A
Battery: A123 3S 2300mAh
BEC: Dimension Engineering ParkBEC
Data Logger: Eagle Tree MicroPower eLogger
RX: Spektrum AR7000
Servos: 6x Hitec HS-55 (quad flaps)

The flying weight is 910g (32oz). I realise that this is quite a lot more than the recommended weight of 610-725g (22-25oz) but I am using a 3 cell A123 pack (250g (8.8oz)). I have also beefed up the landing gear attachment area (completely redesigned is probably a better term, I tore out the original mounting plate 3 times) and put on slightly larger diameter and much wider treaded foam wheels so that it has a fighting chance at take-offs and landings on our pretty rough grass field. There is also the extra weight of the quad flap servos and linkages, ParkBEC and eLogger.


My problem is that the performance is just not quite strong enough. I want this plane to be my aerobatic trainer but it feels really underpowered in the air. It can't quite maintain straight and level altitude at 50% throttle, 75% is typically required for just flying smoothly around the circuit. When I am practising aerobatic manoeuvres I have it at 100% the whole time.

I have to dive before pulling a moderate sized (say 10-15m diameter) loop and even then I have to keep it fairly tight so as not to stall out. From top speed at straight and level, if I pull into a vertical climb it will climb for about 20-30m (hard to judge, let's say 3 to 4 seconds) before stopping and falling backwards.

One thing I find disappointing is that I based my power system selection on the "watts per pound" rule. With a flying weight of 2lbs and averaging around 210W at WOT (measured with the in-flight logger), this comes out to 105W/lb. According the sticky at the top of this forum that should give "Sport aerobatic and fast flying scale models" performance. Would you say that my earlier description of my planes performance matches that? Perhaps I am expecting too much, but I don't think so.

I have tried a few different props, all ACP E props of the following sizes: 10x7, 11x5.5, 12x6 and 8x6. The 10x7 seems to be the best of those. The 12x6 only gives a small improvement in performance but pulls a lot more amps so I think it is too far outside the efficient area of the motor's operation. Surprisingly the 8x6, although not as strong, does not cause nearly as much drop in performance as I would have though and is still quite flyable, but I am looking for more performance not longer flights here.

In looking at motor upgrades, I thought the Turnigy 35-36C might be a better choice, but the patchy motor info from Hobby City makes it hard to figure out what the difference in performance would be.

I'd like to keep the upgrade costs to a minimum so I'd rather change the prop than the motor, and I'd rather change the motor than the battery, etc, etc. Also, if you are going to recommend an upgraded motor then please use the Turnigy range from Hobby City. I simply can't afford name brands like Hacker, etc. In fact if the upgrade requires much more than a $25 HC motor then I'll probably just have to live with what I have.

Thanks for reading and thanks in advance for any replies

Cheers
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Old 05-04-2008, 03:48 PM
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Check out www.bphobbies.com for motors. I've used their "Bp" motors and they're quite good. They're based in New Jersey and the prices are reasonable. By the time you pay shipping from Hong Kong, and wait, and wait somemore, you would have your plane in the air and maybe a few dollars left in your pocket.

http://www.bphobbies.com/view.asp?id...7&pid=B1898545 may suit your needs quite well.
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Old 05-04-2008, 03:53 PM
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I just realized that you are "down under". That changes things a bit. I will get back to you with something else....
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Old 05-04-2008, 04:08 PM
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Have you concidered taking some things out of the bird that are really not needed? The logger for instance? The stats for that motor should be enough for that bird, and then some. What I'm thinking is that you are loading the wings too much for the lift available. I may be wrong (probably), but you are creating an aweful lot of weight and it's changing the flight characteristics of the aircraft.

From what I have been able to find... the 35-36c "should" produce around 1200g of thrust (2.65lbs). That would put you in the ball park of a 1:1 ratio.
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Old 05-04-2008, 04:12 PM
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http://www.hobbycity.com/hobbycity/s...idProduct=2047 May work well too, but it's power hungry.
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Old 05-04-2008, 06:37 PM
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If you increase the wing loading, you will have to increase the speed. The pitch of the prop needs to increase. When the prop pitch increases you need to decrease the diameter to keep the amp draw the same. Try 9x6, 9x7.5 9x9. 8x8 and 10x10 props. You skipped the 9x6 so I would try that first followed by the 9x9, if the current is ok but still short on preformance try 10x10. If the 9x9 is too much current try the 8x8.

Having been there and done that I would say that making the plane lighter or using a plane with more wing area is a far better choice
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Old 05-05-2008, 03:04 AM
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The logger weighs 20g (0.7 oz), so taking it out won't make much difference but I suppose every bit counts.

The real culprit is the A123 pack which weighs 250g (8oz). If I switched to a lightweight 3s LiPo then I'd shed 100g (3.5oz). But I really don't have the budget to buy new packs and I really enjoy the convenience of the fast charge time on the A123s.

The only other possible option is to remove the landing gear. I haven't weighed it yet so I can't say how much difference it will make, (I am at work atm) but given the long aluminium legs and oversized foam wheels it might be 2oz+.

So without buying new batteries, the most I could expect would be to get it down to about 820g (29 oz).

If I did buy new batteries I'd have to get at least 3 packs to be able to fly anywhere near as often as I can on my two A123 packs that I have atm.

Currently the batteries charge in the same time it takes me to have a fly and then come back to the pitts and get the wing off to change the pack.
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Old 05-06-2008, 02:33 AM
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I had that plane with a KD A22-20L motor (about 200W) and a 3S1P 2200mah battery with a 30A ESC and it flew great. You are just to heavy with that set-up. Hobby city has the motor and everything else you need and the price is right too. If you really fly that much, then you will need 3 batteries, but you REALLY need to get some weight out of that plane. It's to small for that kind of weight and that is why you are struggling through the air. If you can't fly at 1/2 power, you are just to HEAVY. Those A123 batteries may be nice in some ways, but weight is NOT one of them. Every oz hurts in that small of a plane and the mini is small. If you want to fly with A123 batteries and a big motor, then I would go with the 25 size and it will handle the weight much better with the bigger wing. Not everything is watts per pound. You are forgetting pounds per sq.ft too. That's about what you have and mine flies BIG loops with a 200W motor and 9X7.5 APC prop with a 2200mah battery. I pull about 20 amps at WOT and get about 15 min flying time out of it. I even had to add a little led to the tail to get the CG right, but it was only 1/4oz I think. With the system you have I think you would be much happier with the 25 size stick. Cheers.
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Old 05-07-2008, 03:46 PM
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I weighed the various "optional" components tonight. Before I go on, please note that my scales are just analogue kitchen scales with 10g as the smallest unit, so if these figures don't gel exactly with previously mentioned weights then that would be why.

The landing gear weighs 70g, the logger weighs 20g and the A123 pack weighs 240g. Removing the logger and the landing gear gets me down to an absolute minimum A123 powered weight of 805g. If I then also remove the A123 pack then the weight with no battery or gear is 565g.

If I was then to add something like, say an ABF 2200mAh 3S which weighs 170g then that would bring me up to 735g which is almost the recommended weight. If I put the landing gear back on then that puts me back up to 805g which is starting to get up there again and is also, incidently, the same weight as it would be with the A123 pack but without landing gear.

Yeah, I know those ABF packs are of seriously questionable quality, but it fits in my budget.
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Old 05-07-2008, 10:13 PM
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I have a 35-36 from Heads Up RC (Ebay store) that generates 42 oz of static thrust with an APC 10x5E (at about 24 amps if I remember correctly). It powers my 39oz Super Sporster very well, all the performance I want. The motor can take an 11x5.5E which would create more thrust but I don't need it and I like 20 minute flight times with 2xTP21003S connected in parallel. Hope this helps; I'm not sure how the Heads Up 35-36 compares to the Turnigy 35-36c. Good Luck
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Old 05-08-2008, 02:24 AM
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I have a 28X29mm motor in mine and puts out around 200 Watts. I don't know why you had to put a 35mm motor in there, but that is a little on the large side for this plane. I started to put a 35mm motor on mine and changed my mind fast after I got it mounted. I took it off and put the 28mm motor on it and it flies great. That little KD A22-20L motor really pulls it along good and I can do rather large loops with it. I got rid of it simply because I wanted something else, not that the plane flew bad. Everyone at my field is flying it on 200 Watts or so and it flies great. I don't know why you went to the 35mm motor, but the smaller motor does fine and I have none of the problems you are talking about and neither is anyone else. My motor will take a 9X6 to 11X5.5 prop with no problems, but I flew it with a 9X6 or 10X6 most of the time and had great results. I have a Super Sportster with a 35mm motor and it flies great too, but it is a bigger plane and can handle the bigger motor. It puts out 450 Watts and for the SS it is over kill, but it flies good with the motor. I just think you are going to big with everything. Try something like the KD A22-20L with a 2200mah LiPo and I think you will find it flies much better.
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Old 05-08-2008, 03:21 AM
  #12  
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The reason I went with the Turnigy 35-30C was because it was the closest cheap alternative to the E-Flite Park 480 that everyone on the forums says is the best motor for the MUS. I also went up a little in KV to try to compensate for the lesser voltage of the A123 pack.

At this stage I really can't afford to buy a whole new power system, especially not with name brand parts.

I think I will just have to remove the gear and logger and then put up with however it performs after that.
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Old 05-08-2008, 03:46 AM
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I got the motor from Hobby City as well as the battery and they don't cost that much. They cost a LOT less then the so called name brands. Take a look around Hobby City and see what you think. You can change them out for a lot less then the name brands.
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Old 05-08-2008, 03:50 AM
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I agree with Flubber, you need more pitch speed. Try the 8x8 and 9x9 props if your motor can handle the amps (doesn't say what the max amps are on the web site).
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Old 05-08-2008, 12:24 PM
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Originally Posted by mred View Post
I got the motor from Hobby City as well as the battery and they don't cost that much. They cost a LOT less then the so called name brands. Take a look around Hobby City and see what you think. You can change them out for a lot less then the name brands.
Ed

Sorry, you didn't mention the brand or supplier and I thought it looked like an Align brand model number.

The KD A22-20L actually weighs 7g more than the Turnigy 35-30C and has very similar performance figures. I'm not sure how this motor would make any significant difference.

I will try out those higher pitch props, I think a 9x9 might be the ticket. I actually tried to buy a 9x9 or 8x8 last time I went to pick up some extra props for testing, but the LHS didn't have anything higher than a 7" pitch on any of their 8" to 11" props. I'll keep trying on this front.
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Old 05-08-2008, 03:04 PM
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OMG I just remembered I do in fact also have a spare TowerPro 2409-12 motor! I've got the scales out again and started weighing everything. Again the disclaimer applies about my crappy scales, the best I can do is 5g resolution.

Airframe, no undercarriage, with servos installed, Spektrum AR7000 RX, servo extension leads, TowerPro Mag8 30A ESC and ParkBEC = 430g

Turnigy 35-30C motor with prop nut, spinner, motor mount and APCe 10x7 prop = 125g

TowerPro 2409-12 with prop nut, motor mount and APCe 8x6 prop = 75g (50g less than Turnigy!)

3S A123 2300mAh = 250g

Undercarriage with my larger foam wheels = 70g
Eagle Tree logger = 20g

So if I was to use the TowerPro motor, with the 8x6 prop, A123 battery and no undercarriage I should come out at 430+75+250 = 755g. That's a saving of 50g of weight over the Turnigy motor and is putting me very close to the upper end of the recommended weight range (610-725g) while still using my A123 pack! The question then would be if the weight loss is enough to compensate for the smaller motor and prop. I'm hoping so.

Also if I start doing belly landings I may need to attach some small skids to the underside of the wings to prevent my servos being stripped due to either the flap surfaces or servo horns contacting the ground on landing.
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Old 05-17-2008, 03:27 PM
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When I tried to fit the TP 2409-12 motor, the supplied screws (M2x5mm) were not long enough to reach all the way through the motor mount and firewall so I haven't been able to do anything about it until I found some longer screws. Today I found that my local electronics supplier (Jaycar) sell M2x8mm which were just right.

After fitting the motor, an APCe 8x6 prop, and removing the undercarriage and logger, the MUS sat on the scales ready to fly at a weight of 760g.

Next came the power test.

I plugged in my logger and connected it up to the computer for "live mode" testing where you can see the amps/volts/watts etc on the screen in real time. I revved it up over half way and it went up to 25.8A, I then revved it up almost to full and it went up to 32A. Then just as I was starting to throttle back the motor suddenly tore free from the front of the plane! :O

Thankfully nose was hanging off the end of a bench and the motor just swung around suspended on it's wires and the prop didn't actually hit anything. Two of the three ESC wires had pulled out of their banana plugs but the third one held on.

After switching everything off I found that the motor had come out of it's base. Closer inspection revealed that one of the two grub screws that hold the motor to it's base was missing. I looked around on the floor and found it near were I had been doing the power test. This is the first time I had ever run this motor so clearly these grub screws were not done up properly at the factory!

I've just put it back together but have yet to test it again. I hope the incident has not done any permanent damage to the motor.
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Old 05-17-2008, 04:31 PM
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Well it looks like the motor is OK. After putting the motor base back together, and using some thread lock to ensure it stayed that way, I ran another power test and everything seems OK.

When the battery is drained a little it sits at 25A on full throttle which is just right. I will have to go easy on the throttle when the pack is fresh off the charger though as 30A+ is too much for both the motor and ESC.

I've chickened out on flying without the undercarriage for tomorrow as a quick check showed that the linkage connecting the aileron servo horn to the push rod is the first thing to hit the ground if I push down a wing tip with the belly on the ground. I struggle to see how this could NOT result in a stripped servo on the majority of landings on our grass field.

I will make up some skids to protect the servos so I can fly without the undercarriage but it won't be ready for tomorrows flight.
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Old 05-17-2008, 04:40 PM
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Good luck.
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Old 05-19-2008, 11:20 AM
  #20  
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It didn't go well.

The plane flew for about a minute and then the ESC cut out. Thankfully I use a separate BEC so I didn't lose radio contact. Even though I didn't quite make it back to the field for a smooth landing, no serious damage was done.

After talking to a friend at the field he explained that you can't use throttle management to keep the amps below the acceptable maximum. Regardless of throttle position, the ESC still sees full WOT amps part of the time. So if the ESC can't handle the power system at WOT then it can't handle it at all, which turned out to be the case.

I will have to try a smaller prop.
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Old 05-19-2008, 12:16 PM
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How was it flying for the minute before your esc quit?
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Old 05-19-2008, 05:45 PM
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Originally Posted by Sam_K View Post
After talking to a friend at the field he explained that you can't use throttle management to keep the amps below the acceptable maximum. Regardless of throttle position, the ESC still sees full WOT amps part of the time. So if the ESC can't handle the power system at WOT then it can't handle it at all, which turned out to be the case.

I will have to try a smaller prop.
That may be fine for getting the amps down, but the performance is going to suffer with a smaller prop. You need to get a motor that does not use more then 30 amps, or an ESC that can take more then 30 amps if you want the same performance. You need a little head room on your ESC, so a 40A ESC would be needed unless you can fine a 35, but I have never seen one. You cannot use a 30 amp motor and 30 amp ESC together as you will have problems with part throttle using this system. You need to go to 40 amps.

Your friend is also correct about using the throttle to bring your amps down. Your watt meter reads the average of the square wave that the ESC is putting out, not the peak. The only time your watt meter will be right is at WOT, not part throttle. The motor and watt meter respond to the average amps that the ESC is putting out, but the ESC is always putting out max (whatever that is) amps that the motor is drawing. Take care.
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Old 05-25-2008, 07:55 AM
  #23  
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To answer your question smoke, I didn't try anything fancy at all in the time I was up, climbout seemed strong but I really didn't test it much as I was trying to be conservative for the first minute or two, however it was definitely faster compared to the old motor and prop, pitch speed is definitely up significantly compared to the old set-up.

I downloaded and read the logs today from last weekend, turns out the system wasn't pulling over 30A at all during the flight, in fact the peak was 25A at take off and settled down to around 19A before the ESC cut out. Turns out the reason the ESC cut out was just plain old LVC which was set to LiPo. The pack had dropped below 2.8V per cell (no problem for A123 cells) and so the LVC had kicked in.

I never usually fly to LVC so I wasn't prepared for this eventuality it just didn't occur to me last weekend to go to 0% throttle and then up again to re-arm. I just immediately assumed the worst and thought the motor was gone.

Today I switched the LVC to NiMh mode (there is no option to turn it off) the instructions are confusing and don't really state clearly what the actual LVC voltage is supposed to be, so I did a full power test on the bench at WOT for 3 minutes straight. Voltage sagged down to 8.2V (2.7v per cell) and the ESC did not cut out at all. Current started at 26A and settled down to 21A. According to the Tower Pro spec sheet this motor is most efficient at 23A so that seems pretty much spot on.

The motor was hot to the touch afterwards, not hot enough to burn instantly but hot enough that I couldn't hold my finger on it for more than a second. I'm hoping that in the air it will get better airflow and stay a bit cooler. I will keep an eye on this though.

With respect to earlier readings at 32A, that was the initial momentary peak when I slammed open the throttle on a pack that was fresh off the charger. The readings I got today were from a battery that was charged last night and then sat for about 8 hours before the power test.
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Old 05-25-2008, 08:46 AM
  #24  
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Reading the specs in the instruction sheet for the ESC, it says this ESC can do 30A continuous and 35A max. So it seems that even a 32A initial spike isn't going over the limit.
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Old 06-01-2008, 03:40 PM
  #25  
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I finally got time today for a quick trip to the field to try out the TP2409-12 motor.

The first flight was with the 3S A123 pack and an APCe 8x6 and it went well! Performance was definitely improved over the old setup. Pitch speed was significantly higher and it pulled easily through several cuban 8s in a row. What's more it strolled around with no problems at half throttle. I was feeling good about this setup.

I then tried my old FlightPower 2S 2500mAh LiPo pack that I use with my Easy Star. I also changed the prop to the 10x7 which had it pulling 25A at WOT on a freshly charged pack (already tested at home on the bench). I really thought this would fly great, as it is a weight saving of 100g over the A123 setup but still pulling the same amps. However the performance was very similar to the original setup detailed in post #1, at half throttle it could not maintain altitude during one lap of the field.

Then 3 minutes into the flight somthing went pop and I had no motor power. Luckily the plane was pretty much exactly were I have it when I turn onto final approach, so I brought it in to land, as it got closer I could see the motor was hanging down of the front of the plane suspended by it's wires. I botched the landing slightly and stalled it about 1 foot off the ground which ripped the landing gear off again (6th time).

On closer inspection it turned out that vibration from the motor had simply vibrated the nuts off the mounting bolts. Silly me, I had not used Locktite on them. I had intended to put it on after a successful power test. They were done up nice and tight but obviously that is simply not enough.

Now I am up for even more repairs. I'm really starting to get tired of the constant repairs that I have to do on this plane. I can't remember the last time I came home from the field without some sort of damage to fix. I suppose I should consider myself lucky, I've had quite a few scrapes with this plane and never really done any serious structural damage to it.

I also now need to find a source of M2 nuts as the nuts that vibrated off were lost and I have no others. I have in fact already looked for these before and none of my local places have any. (BTW, if anyone is going to make any suggestions for where to get them, just remember I am in Australia.)

EDIT: Oops I meant M2 nuts, M3 are easy to find...

Last edited by Sam_K; 06-01-2008 at 04:01 PM.
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