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Sep 09, 2019, 05:22 PM
Bob418

Push pull on the Rudder?


All

I just picked up a Mythos, and trying to get the CG to balance at 220 for a starting point,

the only way I could get it close wat to put 60 grams on the rudder and my lipo all the way back.

I have to assume the guy that owned it before me did not know what he was doing

It has a pull pull rudder in it, so based on a few pictures it appears that in order to get close to CG I have to change to a push pull on the rudder. This would allow me to put my Lipo all the way back, and move my RX back as well.

Is this what most of you do????

Also would anyone have a spare Yellow / Black cowl laying around, mine is cracked, the guy had a hard landing and did so damage that needs repair, nothing too bad,

Thanks for helping out!
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Sep 09, 2019, 06:50 PM
Registered User
The rudder servo needs to be relocated to the tail. Only way to get the proper balance.
-Ken
Sep 09, 2019, 08:09 PM
Bob418
Quote:
Originally Posted by kdunlap
The rudder servo needs to be relocated to the tail. Only way to get the proper balance.
-Ken
I believe that, now I just have to find the right size control horn to convert it to push/pull from pull pull - anyone?????
Sep 10, 2019, 05:31 AM
Bo Edstrom, Sweden
Hibob418,
And to get Your MythoS 125E light in the nose I recommend You get a Falcon electric vented 75 mm carbon spinner (very light) and a Falcon electric V2 carbon 19x12 propeller (if You use 8 cell LiPo and Hacker A60-7XS motor). That prop is feather light and gives very good performance.

Also see if You can relocate the ESC to be slightly more back in the fuselage.

If You are going to install a rudder servo in the tail You may as well get a heavy 60 gram or so rudderservo if You need som extra grams in the tail. There will be some extra grams also by using close to 800-900 mm servo cable in the tail from rudderservo to receiver.

The rudder control horn in the tail is about 20 mm wide and goes into the rudder about 15 mm where it is glued with CA. Height of Control horn is about 20 mm and it is offset about 10 mm from rudder 45 deg edge to rudder center line (pivot line). The rudder rod is about 100 mm long with ball link ends. Servo arm from center to hole for the ball link is about 16-17 mm (in my case).
The control horn is made of 1.5 mm glass fibre plate.

/Bo
Sep 10, 2019, 06:03 AM
Bob418
Thanks Bo, Since I just got the bird, I want to do a test flight or 2 with some lead in the tail, to see how the CG is, Once I think I am close, I will start moving everything aft. I fly big 3d birds, but have always loved the Sebart birds. So I will give the bird the love it needs (have to fix the LG bay using your fix, thanks) and I have lots of slop in the rear stab, so I have to glue that in as well (crazy amount of movement in the stab- never seen that before)

Thanks for all the help!
Sep 10, 2019, 06:42 AM
Bo Edstrom, Sweden
bob418,
Yes I also had to glue the carbon rod for the stab, that goes through the fuselage in the tail, to get it firm. Very important.

/Bo
Sep 10, 2019, 06:54 AM
Bob418
Quote:
Originally Posted by bossee
bob418,
Yes I also had to glue the carbon rod for the stab, that goes through the fuselage in the tail, to get it firm. Very important.

/Bo
Thanks Bo,
Sep 11, 2019, 04:53 PM
Bob418

Does this setup sound correct


Guys

Since all of you have a long history with the Mythos does this motor/Prop/ESC setup sound like a good starting point. Remember I purchased this bird second hand so I got what I got.

Motor - Hacker A60-6xs-V2
ESC - 120 Amp
Prop APC 18 x 10
Running on a 5000mah 45c 6 cell lipo

It also as a life receiver pack

Should have enough power - I am not doing any IMAC yet, just love the look of the Mythos so I had to pick this one up (I know it is a sickness with me )

I am just looking to verify I am good with this setup, the guy before me said it flew great, but he also told me it flew fine as is, and the bird is WAY!!!! nose heavy - plus a few other issues which have been discussed here.

Thanks for the input - but I am trying to get this tread something to chat about!

Bob
Sep 11, 2019, 06:35 PM
Bo Edstrom, Sweden
Hi,
Although watt is watt so in theory a 6 cell Lipo with this plane should be reasonably OK, it has been proven that the MythoS 125E for more serious F3A flying (FAI Advanced and FAI F3A for that matter) is best equipped with 8 cell Lipo (and the A60-7XS motor) with Falcon electric carbon prop V2 19x12. I know of own experience how well that setup is (I flew it for two years and competed in FAI Advanced).
But as I said, at least in theory a 6 cell LiPo should be possible to give similar performance. But higher voltage on the LiPo pack seems to thriumph more for the power needed in vertical uplines and other more powerhungry manouvres. Less amp for a given performance also. If You put a Falcon Electric carbon prop V2 19x12 maybe You will stress that ESC You have Little too much?
A 120 amp ESC is probably not enough if you start to eperiment with optimal prop for Your LiPo and motor combination. I have somewhere here in this thread the amp my setup draw with 8 cell LiPo and A60-7XS with Falcon Electric carbon prop V2 19x12. I belive it was about 78 amp on full throttle in the air according to the Master Mezon 130 ESC log read with the Jeti Box. Max temp of ESC was 45 deg Celsius and max RPM was 7120. With APC 19x10 E I got 70 amp, 39 deg Celsius, 7550 rpm.
Personally I would try to get the most optimal prop for the setup You have, and be preparad to change to an ESC that can cope with higher current then 120 amp. You should have a good margin also on ESC so I would not stress a 120 amp ESC to it's limits, about 20% margin or more is better to have in my opinion if possible. Hard to tell how well Your present 6 cell LiPo can cope with the high current demand, if you want to prop for more power. As You know the C rating is not always much to trust on. But it is not uncommon the LiPo struggle after a while to keep the voltage up on high power. I have seeen that myself several times with my 10 cell LiPo F3A planes.
APC 18 x 10 prop is probably rather optimal. Measure the current draw with the props You test so You KNOW that, and can avoid to toast the ESC. I would not worry too much about overstressing the Hacker A60-6XS, the A60 series motors has probably rather good watts margins it can cope with.
On Hacker homepage for the A60-6XS (V4) they have some suggestions for props, maybe try them?
https://www.hacker-motor-shop.com/Br...ge&rdebox=box1
Try a Falcon Electric carbon prop V2 19x12 also if possible (it is an expensive prop).
APC props is not so expensive so to experiment with these props can be OK, but as soon as carbon props is involved the high cost set limits rather fast how many one can afford to test.

/Bo
Last edited by bossee; Sep 12, 2019 at 08:59 AM.
Sep 11, 2019, 06:50 PM
Bob418
Quote:
Originally Posted by bossee
Hi,
Although watt is watt so in theory a 6 cell Lipo with this plane should be reasonably OK, it has been proven that the MythoS 125E for more serious F3A flying (FAI Advanced and FAI F3A for that matter) is best equipped with 8 cell Lipo (and the A60-7XS motor) with Falcon electric carbon prop V2 19x12. I know of own experience how well that setup is (I flew it for two years and competed in FAI Advanced).
But as I said, at least in theory a 6 cell LiPo should be possible to give similar performance. But higher voltage on the LiPo pack seems to thriumph more for the power needed in vertical uplines and other more powerhungry manouvres. Less amp for a given performance also. If You put a Falcon Electric carbon prop V2 19x12 You will probably toast that ESC as well as the motor (A50-6XS) in the long run.
A 120 amp ESC is probably not enough if you start to eperiment with optimal prop for Your LiPo and motor combination. I have somewhere here in this thread the amp my setup draw with 8 cell LiPo and A60-7XS with Falcon Electric carbon prop V2 19x12. I belive it was about 78 amp on full throttle in the air according to the Master Mezon 130 ESC log read with the Jeti Box. Max temp of ESC was 45 deg Celsius and max RPM was 7120. With APC 19x10 E I got 70 amp, 39 deg Celsius, 7550 rpm.
Personally I would try to get the most optimal prop for the setup You have, and be preparad to change to an ESC that can cope with higher current then 120 amp. You shuld have a good margin also on ESC so I would not stress a 120 amp ESC to it's limits, about 20% margin or more is better to have in my opinion if possible. Hard to tell how well Your present 6 cell Lipo can cope with the high current demand, if you want to prop for more power. As You know the C rating is not always much to trust on. But it is not uncommon the LiPo struggle after a while to keep the voltage up on high power. I have seeen that myself several times with my 10 cell LiPo F3A planes.

/Bo
thanks Bo
Sep 11, 2019, 09:53 PM
Registered User
I used the 6S setup for a bit and then converted to the 8S. This is the difference between night and day. If you stay 6S my advice is to try to extract every single gram of weight from it. You need to have a CF prop and spinner. Next, go for Uber light weight batteries. On 6S 5000 I could fly exactly 6.5 minutes with a bit of reserve. To save weight I would go with 6S 4800 packs and realize you have 6.5 min period. I would also consider just using the BEC from the ESC and not adding a back up battery. If that’s too risky for you keep the back up to no more than 250 mah Lipo. Next I would swap out the tires for lighter ones and save 10g or so. Lastly keep all the wires short as possible. 6S is doable if you are militant about removing weight. Good luck. It’s a great airplane.
Sep 11, 2019, 09:57 PM
Registered User
FYI on this setup be extremely careful when using a light weight 18x10 prop. This will draw an immense amount of current. I toasted my motor and 90 amp esc because I probably drew well over 120 amps. Flew great for the 15 seconds or so the motor was operating. This is what lead to me going to 8S.
Sep 15, 2019, 01:03 PM
Team Futaba
Neilbo4's Avatar
I have a NIB Mythos 125E canopy for the Yellow/Black scheme - PM me if interested.

Neil


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