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Cessna 152, Balsa 30% Scale Rescue from Hostetler Plans

Joker 53150

Mmmmmmm, balsa.
Mentor
Well, no flying this weekend for the Cessna. I took it out to the sod farm/flying field to at least get some taxi-testing with it and ran into a couple problems. First, when it's running the servos are getting some interference and the tail surfaces are moving quite a bit as the throttle changes. Probably not the safest way to fly...! :) Next, the engine needs a little tuning. It fires up and idles well, but as I add throttle it cuts out a bit. Oh well, the engine is still new and should be broken in a bit more before trusting it to fly. Soon... soon...
 

Joker 53150

Mmmmmmm, balsa.
Mentor
A couple updates on the Cessna...

First, I'm able to get a little more done on it as my son's cancer treatments are working better and faster than I would have hoped for. He's still got a number of chemo treatments to go, but the treatments aren't hitting him nearly as bad as they do some people. He's run down for a couple days while getting chemo, and within a day is back to "normal" and feeling fine. Since he's hanging out with friends that frees me up to play with my toys! :)

Second update, I'm changing the electronics quite a bit. The phantom jitters experienced during the test-runs has me spooked so I'm trying to re-organize how it's wired. Although the two servos were working together and they gave me redundancy I decided to pull the plug on them and go with a power distribution box. I found one I like from Red Wing. It still gives me two battery inputs, 6 volts to the servos and regulated 5 volts to the receiver. It also has an alarm LED and beeper plus isolated voltage for the CDI box. The down-side is that I won't have as much programming flexibility as when I was running 16 channels, but on the good side I'm not powering a bunch of big servos through the receivers.

So far I've got channels 1 (throttle), 3 (elevators), 4 (rudder/steering), and 8 (throttle Opti-Kill) hooked up. The two elevators need some tweaking so they're even, which was very easy to do through programming when they were on different channels. I'm really hoping that the ailerons can be adjusted properly so they can share channel 2, but am pretty sure the flaps are going to need to be on different channels. The steering servo may also need it's own channel as it's got a ton of throw compared to the rudder. Neither can easily be adjusted manually to change that, so programming may be the best route. Another hour or so tweaking it and it should be ready for a run test, and hopefully the jitters will be gone!
Power_board_Pro_RC_plane_Red_03.jpg

Power_board_Pro_RC_plane_Red_06.jpg
 

Joker 53150

Mmmmmmm, balsa.
Mentor
The new power distribution box has the plane about ready to test-run again, and I'm looking forward to seeing if the jitters go away. If not I'll have to do some more trial & error to track it down. The servo extensions for the ailerons and flaps are going to be left unplugged until after I test it with channels 1, 3, and 4 only hooked up, and if it works properly I'll add the extra servos and wiring step by step to make sure it remains good.

I also found that this new power distribution box has a built-in optical kill for the electronic ignition. If I use it (and I am), it uses one channel on the receiver. However, I'd need to use that channel to run the external opti-kill anyway so I'm not losing anything except an extra piece of hardware. The box has a built-in light to show power is being sent to the ignition, and it isolates a separate battery dedicated to the ignition as well. I could also simply jump from one of the servos to the ignition battery input and use the same batteries for the ignition that I use for the servos, but I'd rather keep the ignition on it's own battery. So I'll run two batteries for the servos and receiver - both of them run through my power switch panel with redundant switches and then into the power distribution box which will also run just fine if one of the batteries dies. The ignition battery is also still run through my switch panel before being connected to the distribution box. It sounds confusing, and it kind of is... :) But I like what it does to clean everything up, and if it works as it should I'll add this kind of box to future giant-scale builds. Right now this one is simply added to the plane, but with some planning during the build it could be built-in and look much cleaner.
 

Joker 53150

Mmmmmmm, balsa.
Mentor
Not a huge update, but I finally fired up the Cessna with the new power distribution board installed and the servo twitching has gotten better, but has not been eliminated. A common area of concern would be the electronic ignition module, but in my case it's mounted in front of the firewall and far away from the rest of the electronics. It COULD still be causing interference so I'm going to swap it out with the module from the other 58cc Turnigy gas engine I've got for my L-19 project to see if the problem goes away. I'm also going to re-check to make sure all servo connections are tight. If neither of those help I've got another more involved thought or two that I'll look into. Either way, with the improved operation I did notice that the engine was running better/smoother, probably because the twitching was also hitting the throttle servo as well as the tail servos. In fact, it was running well enough that I took the plane for a "walk" around the yard. That 58cc gasser really has no problem pulling this heavy bird through grass!
 

PsyBorg

Fly Angry
Mentor
Would a filter cap or two strategically placed in the power system help better that twitchy servo issue like they do on high power quads.

I remember that noise in the radios years back from engine ignition. A simple capacitor cleared that all up and became a standard part of the cars since.