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Old Mar 09, 2004, 05:22 AM
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Frank B's Avatar
Denmark, kbh
Joined Jun 2001
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Which Hacker?

I am looking for a new power system for my Supra 40, and have done some calculations in MotoCalc trying to find the best setup.

The following setup looks very promissing, but I am not sure if the motor is large enough (if it will get to hot):

Motor: Hacker B40 9L
Gear: 4.4:1
Accu: 12x3300 GP NiMH
ESC: TMM 6012-3
Prop: 13x10

MotoCalc says 56A static and about 20A in flight at 75% throttle.

Can the B40 handle this or do I need a B50 instead (assuming I want to use a Hacker)?

The best setup I can find with a B50 is a B50 8S (geared 6.7:1). It has similar power, but the flight time is reduced with about 2 minutes.

I could use a 12x10 prop instead. Then I get 47A static on the B40 9L.

The AUW with the B40 will be around 80oz (2265g).
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Old Mar 09, 2004, 11:13 AM
Supersonic Engineering
GordonTarling's Avatar
UK, Greater London, Uxbridge
Joined Mar 2001
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Without knowing the size and weight of a 'Supra 40', I can only guess that it's a model designed for a .40 size glow engine. If this is the case, the B40 is too small and you need one of the B50 series. When choosing a power system for a model like this, you should aim for max full throttle current of 40 Amps or less if at all possible. Propping for 56 Amps and then flying throttled back to 20 IS going to cook the motor. If you can't get the power you require at 40 Amps or less, then you need more cells.

If you can post wingspan, wing area and weight of the model, I'll be happy to specify a Hacker system for it.
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Old Mar 10, 2004, 04:37 AM
Giz
Tony Rogers
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Bath, UK
Joined Sep 2003
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Gordon

Quote:
Propping for 56 Amps and then flying throttled back to 20 IS going to cook the motor.
Why is this? As yet, I have not found it to be the case but I don't want to fry my motor.
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Old Mar 10, 2004, 04:42 AM
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Frank B's Avatar
Denmark, kbh
Joined Jun 2001
663 Posts
The Supra 40 is indeed designed for a .40 size glow engine.

Here are the specifications for the model:
Wingspan: 56.1 in (142.5 cm)
Wingarea: 491 sq.in (31.7 dmē)
Empty weight: 48.6 oz (1375 g)

The "empty weight" includes everything except motor, speed controller and batteries.

The model has a symmetrical aifoil (12%).

I have previously flown it on the following setup, but it really needs more power (it just barely takes off from grass):

Motor: Mega AC/22/20/3
Gear: 2.5:1
Accu: 10x3300 Sanyo NiMH
ESC: JES 40-3P
Prop: 13x10

I know that this Mega motor is too small, but I had one lying around so I tried it. MotoCalc says 48.6A static with this setup.

I would really like a Hacker-setup. I already have two others (a B2 18L and a B40 10S) and they are great motors. Also I can buy them locally.

Note that my new setup is not restricted to using 12 cell packs. That's just what I tried out in MotoCalc in order to get some more power than with my old 10 cell setup. I would, however, like to stay at max. 12 cells so I can use a speed controller with BEC (the weight of more cells and an additional receiver pack concern me). I will build brand new packs for the Supra, but they have to be 3300 GP's (I'm not using li-po's).

I hope this is info enough.
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Old Mar 10, 2004, 03:05 PM
Supersonic Engineering
GordonTarling's Avatar
UK, Greater London, Uxbridge
Joined Mar 2001
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Frank B - My suggestion is to use a Hacker B50-7L with 6.7:1 gearbox and a 14 x 10 prop on your 12 cells. Motocalc predicts 38 Amps and a climb rate of 1500 ft/min. Watts per pound is a bit on the low side at 87. You'd be better using 16 cells, when you could go to the B50-8L with 6.7:1 - 14 x 10 prop now gives 41 Amps (just about OK) and a climb rate of over 2000 ft/min. Watts per pound is 114!

Your insistence on sticking to 12 cells is really restricting your power too much. If you MUST use BEC, the go for the Hacker 70-3P Opto controller (up to 16 cells) and use either a UBEC or SBEC unit to supply receiver power. 4 servos, 12 cells and a normal BEC in an ESC is really asking for problems.

Giz - ESC's and motors are less efficient at part throttle, so it's easy to cook motors if you're not careful. 56 Amps is WAY too much full throttle current for a B40 which is running for most of the flight, so the part throttle current would also be way too high.
Note that the very same motor could, however, be propped up for 90 Amps or so in a glider which uses the motor in short bursts - it's all to do with heating.
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Old Mar 10, 2004, 06:49 PM
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davidleitch's Avatar
Sydney Australia
Joined Feb 2002
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Gordon's suggestions are bound to be good. Another setup commonly used on models of this size is a B50 13S with a 15x10 prop on 16 cells.

A major weight saving could be achieved by going to lipos of course. A B50 13S and 4S3P pack or 5S3P pack would be sure to pull the Supra around fairly well.
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Old Mar 10, 2004, 09:39 PM
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Ed Lyerly's Avatar
Rutherfordton, North Carolina, United States
Joined Apr 2001
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Quote:
Originally posted by davidleitch
Gordon's suggestions are bound to be good. Another setup commonly used on models of this size is a B50 13S with a 15x10 prop on 16 cells.

A major weight saving could be achieved by going to lipos of course. A B50 13S and 4S3P pack or 5S3P pack would be sure to pull the Supra around fairly well.
Good advice David. Use the 5S 3P, B50 13S+6.7:1 & APC 15x10-E prop.

Ed
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Old Mar 11, 2004, 04:59 AM
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Frank B's Avatar
Denmark, kbh
Joined Jun 2001
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Thanks a lot.

It seems that I was on the wrong track there. I didn't think about the 4 servos + 12 cells + BEC combination.

My main goal was to keep the weight down, but that seem to be the wrong approach. On 16 cells it really looks god.

One thing though (sorry I didn't mention it before): I think that a 13" prop is the largest one that the Supra will take. I haven't tried anything larger, but the 13" just cuts the grass as it rolls along. Maybe I could make some modifications to raise the motor a bit.

Assuming that 13" is max. and going with you suggestions of 16 cells and max. 40 amps static, I would pick the B50 11S. Does this sound reasonable?

Regarding the li-po setup, that looks totally wild, and I would love to have it in my Supra, but I do have some concerns about the safety of these cells. And my wallet isn't to happy about it either.
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Old Mar 11, 2004, 08:08 AM
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Frank B's Avatar
Denmark, kbh
Joined Jun 2001
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I have done some searching here on the E-zone, and found that people actually fly the Supra 40 with both 14" and 15" props.

So, I think I will go for one of the following two setups:

16 cells + B50 13S + 15x10 prop.

16 cells + B50 12S + 14x10 prop.

According to MotoCalc the first setup has a pitch speed that is slightly too low. Should I be concerned about that?
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Old Mar 11, 2004, 09:30 AM
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Ed Lyerly's Avatar
Rutherfordton, North Carolina, United States
Joined Apr 2001
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Quote:
Originally posted by Frank B
I have done some searching here on the E-zone, and found that people actually fly the Supra 40 with both 14" and 15" props.

So, I think I will go for one of the following two setups:

16 cells + B50 13S + 15x10 prop.

16 cells + B50 12S + 14x10 prop.

According to MotoCalc the first setup has a pitch speed that is slightly too low. Should I be concerned about that?
Frank,
Don't worry about the pitch speed Motocalc predicts. I have seen this combo (B50 13S+6.7:1 w/15x10 APC-E on 16 cells) fly a Venus 40 ARF with excellent speed and authority. If you need to, block up the landing gear to get more prop clearance, or purchase some taller gear for your Supra.
Ed
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Old Mar 11, 2004, 09:48 AM
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Frank B's Avatar
Denmark, kbh
Joined Jun 2001
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Thanks Ed, I will go with the setup you recommend.

One last thing: I have never used a separate receiver pack in a plane before. Do I need 4 or 5 cells, and how much capacity is necessary?
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Old Mar 11, 2004, 10:00 AM
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Ed Lyerly's Avatar
Rutherfordton, North Carolina, United States
Joined Apr 2001
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Quote:
Originally posted by Frank B
Thanks Ed, I will go with the setup you recommend.

One last thing: I have never used a separate receiver pack in a plane before. Do I need 4 or 5 cells, and how much capacity is necessary?
Frank,
Get yourself a UBEC from these folks (or one of their distributors)and you won't need a separate receiver pack. I would get the new 6V model as it gives the servos a bit more power and zip.
http://www.koolflightsystems.com/products1.htm
Ed
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Old Mar 11, 2004, 01:43 PM
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Frank B's Avatar
Denmark, kbh
Joined Jun 2001
663 Posts
Quote:
Originally posted by Ed Lyerly
Frank,
Get yourself a UBEC from these folks (or one of their distributors)and you won't need a separate receiver pack. I would get the new 6V model as it gives the servos a bit more power and zip.
http://www.koolflightsystems.com/products1.htm
Ed
I really like that UBEC. It only weighs .7 oz, so there's really no need to worry about additional weight. (I have just ordered a 6V model).

Thanks again for the superb help.
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Old Mar 12, 2004, 05:27 AM
Giz
Tony Rogers
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Bath, UK
Joined Sep 2003
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Gordon,

I mis-read the original post. I thought it was a B50 not a B40. Do you think a B50 12XL would be OK propped for 56 Amps and run at part throttle?

I am testing this and I have found that the motor shaft gets quite hot but you can still keep you finger on it so maybe 60 deg C? I am using a heat sink.
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Old Mar 12, 2004, 08:45 AM
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Frank B's Avatar
Denmark, kbh
Joined Jun 2001
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Hmm, I think I'm missing something here. Is the goal to have a model where you fly full throttle all the time? It seems that flying on part throttle is bad for the motor. I have always thought that flying on half throttle was the optimal solution, and that you only used the extra power when taking off from grass, doing loops and such. That's why I originally propped my B40 for 56 amps.
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Last edited by Frank B; Mar 12, 2004 at 09:00 AM.
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