Powersystem Comp 12 - weak servos

[Dumorian]

I have a new Powersystem Comp 12. I'm running a 6014 receiver, two 7.4v 1400mah Lipos. I have the ignition cutoff unit separated and on another battery. The model is a Dynaflight Decatlon, 36cc which weighs in a around 20 pounds when filled with gas. It has a 89" wingspan.

Flight controls include 2 servos on ailerons, 2 servos on flaps, 2 servos on elevators, one servo on rudder, one servo on tug release, one servo on bomb bay and one servo on throttle.

On the first day out, the power was on to all systems for maybe 4 or 5 hours. The model was likely either in the air or experiencing programming on the ground for maybe 1 hour. I ran the engine for maybe another half hour. This all to let you know that after this time, the flight batteries took between 400 and 450mah when charged. So, I think I have a pretty darned efficient setup with no extra drain due to a binding servo or something.

Yesterday, during the second flight, I thought I'd try a loop. Instead it looked more like a snap roll. So, I tried it again and same results? Odd.....

Back on the ground, we noticed that it didn't take much force to override the elevator servos. These were Hitec 635s which are around 80 ounce. Surprised by this, I changed them out for a pair of 5645s last night, which have about double the torque. I seem to get about the same results in overriding the elevators with my hand? I'm thinking I should feel like something is about to break before being able to do this, but in my unscientific by hand testing... it doesn't feel like something is anywhere near a breaking force.

OK, so, I popped the cover off the bottom to watch the whole system. I made custom CF tube control rods and nothing is flexing. The servo arms are simply being overridden.

Of note, first I am on the default voltage with the Powersystem, but I have not checked the output. First, I have 12" heavy duty Hitec extensions on these servos. When I hit this override point, it's like the servo just all but totally gives up... so it goes from pretty strong to almost no power at all, then when I ease up on my force, it regains it's power.

I'm wondering if I'm missing something? I know the system has a short protection function and wondering if somehow it's reducing power to these servos at a point below where it should, seeing my load as a short? Also, I didn't ask the first simple question of whether or not you consider the (2) 7.2v 1400 mah 10C batteries to be enough power for the system? It seems I should be able to put out nearly 30A with these. 3 or 4 should be plenty when testing only just one elevator servo with everything else being at the nuetral point.

Anyway, if I've missed something or you have a suggestion, please let me know. I'm hoping to fly this model at Joe Nall next week.

[Neogenesis]

Call the mfg.....they will know whats going on.

Neo

[rrritchey]

Hi,
If you did not set the servo voltage it will be about 5.5V. You should really check your servo output voltage to make sure of what it is. On this size plane you should be running servos that are at least 140oz from my experience. Other people may have a comment about this. You did not say if your other servos on ailerons and rudder are acting the same way? We will not reduce current to the servos, if they want 4 amps we will give them 4 amps. Let me know what I can do to help further.

[Dumorian]

Thanks Rob. I don't have much experience with these larger models. I guess I'm discovering the real power of servos. I guess I should do some quick calculations to discover how the torque ratings relate to force on a control surface with the mechanical (dis)advantages figured out.

Thanks for the great support of a great product!

[Neogenesis]

Those 5645's are plenty for that plane. I flew them in a 33% yak for 2 years without a problem. You have a issue somewhere else in the system, unless you've got the mechanical advantage setup wrong.

Neo

[bodywerks]

I can force a control surface back to center with Hitec 5955's but don't have problems in the air. I would look at your geometry, which should be 1:1 or better(meaning the servo arm needs to be the same size or shorter than the control arm), or you have unequal throw in your elevator halves, or you are trying to pull too tight of a loop, or you are too heavy and your plane is going to be snappy.
Or, if you really do have a problem with weak servos you should have the same problem with the other control surfaces. If it is only the elevators, you probably have a bad servo extension. If they are bargain brand extensions this is highly possible. Anything less than JR or Futaba brand leads are bargain brand, IMO - I've had bad leads from Cirrus and Expert, and bad connectors from Cemark and MPI.

[Dumorian]

Good info... thanks. I think the 635s were a bit on the weak side. The 5645s should do fine. It's a new build from a kit and after all this work I'm a bit more nervous than usual.

As for my controls... they are very near 1:1. When it looped like this my flying buddy who has been doing big planes for years and flying for 20+ years, vs my just over one year... started looking to see what might be wrong and found that he could move the elevators. So, that's why I posted. As for the odd roll, more like a snap... I managed to leave my angle meter on (I could have sworn I read it had an auto-off function!) and ran the battery down. And it's an odd battery. I live about 30 miles from town... Anyway, I normally set pretty aggressive rates. I might actually be experiencing an elevator stall. My angle is around 40 degrees and it just might not be able to handle that.

New plane... only three flights so far... still feeling it out and tuning.

Thanks for all the great input!

[exeter_acres]

how does it feel if you plug the servo direct into a RX??