Caution: Savox SB-2271SG Cyclic Servo Bench Test Results

[Flying Dutchy]

Originally Posted by akschu

Should be fine, but use the 16v version. The lower internal resistance is good since they will react faster.

schu

Thanks! Will use the 25v version as they have the lowest resistance.

[akschu]

I talked to castle support this morning, and the tech asked the engineer about this. He said that there isn't any issue with backfeeding the bec pro, and that the only reason why say not to run buffer packs is because the unit can't constant current charge, it's just a voltage source. If they didn't specifically say don't run a buffer pack then a customer would plug a lipo into 6v regulator or other silliness.

Knowing what I know, and after talking to castle support, I would feel comfortable charging a buffer pack to 8v, setting the bec pro to 8v and running them together. I would put a switch in for the buffer pack and turn it off when I'm not using the heli, but other than that it should be fine.

For now I'm very happy with the cap mod, and think that the dcup is probably vast overkill, but it's a good way to go for those that don't want to diy.

schu

[Chris Sexton]

Originally Posted by akschu

I talked to castle support this morning, and the tech asked the engineer about this. He said that there isn't any issue with backfeeding the bec pro, and that the only reason why say not to run buffer packs is because the unit can't constant current charge, it's just a voltage source. If they didn't specifically say don't run a buffer pack then a customer would plug a lipo into 6v regulator or other silliness.

Knowing what I know, and after talking to castle support, I would feel comfortable charging a buffer pack to 8v, setting the bec pro to 8v and running them together. I would put a switch in for the buffer pack and turn it off when I'm not using the heli, but other than that it should be fine.

For now I'm very happy with the cap mod, and think that the dcup is probably vast overkill, but it's a good way to go for those that don't want to diy.

schu

Thanks for the information. It might be overkill, but with my soldering skills I will take overkill.

Thank you for all the time you have put into helping diagnose this issue!

[Rob Cherry]

Originally Posted by cdsexton

Thanks for the information. It might be overkill, but with my soldering skills I will take overkill.

Thank you for all the time you have put into helping diagnose this issue!

I second this. thanks for your time, you've helped me out a ton!

[akschu]

You guys wanna give me flying lessons? I'm much better at electronics than flying the heli. I would be pretty happy if I could just do inverted backwards flight (well for a week anyway.)

schu

[Rob Cherry]

Originally Posted by akschu

You guys wanna give me flying lessons? I'm much better at electronics than flying the heli. I would be pretty happy if I could just do inverted backwards flight (well for a week anyway.)

schu

HA! the only lesson i'm good at giving is "use the sim more". Where do you live? lol

[akschu]

50 miles north of Anchorage.

[Rob Cherry]

Originally Posted by akschu

50 miles north of Anchorage.

Stick to the sim, I can't help you much from here. LMFAO



I just thought it was crazy, because I live in Big Lake, MN.

[CraneGrus]

Originally Posted by akschu

...
For now I'm very happy with the cap mod, and think that the dcup is probably vast overkill, ...
schu

First, thanks for all your input and efforts.

On your last point I have doubts though, from practical experience.

1. On a normal flight voltage does not drop below more than two points on the DCUP scale. But with a bit of extra load on the blades, it is easy to get significantly below that.
(OK, I need a better BEC )

2. Some people install it as a buffer, to use for safe landing in case of BEC failure. I do not believe that is a good idea anyway (how would you know?). However, I also believe with these servo's you will have less than 5 seconds for landing, even if you would know.

3. As last point i would like to mention the interaction between DCUP and vbar I noticed, when the DCUP drains out. If I move the servo's, they regularly end with a glitch, where one or two servo arms end up in a awkward position, 90degree up or down, swash being severely tilted. Not a position one would like the heli to end if control fails.

[CraneGrus]

Originally Posted by akschu

You guys wanna give me flying lessons? I'm much better at electronics than flying the heli. I would be pretty happy if I could just do inverted backwards flight (well for a week anyway.)

schu

Sorry, I have just acquired inverted forwards flight, and are now working on normal backwards flight. Could not help you with that.
(besides the small geographical difficulties)

[akschu]

Originally Posted by CraneGrus

1. On a normal flight voltage does not drop below more than two points on the DCUP scale. But with a bit of extra load on the blades, it is easy to get significantly below that.
(OK, I need a better BEC )

What voltage are they dropping to and for how long? I wouldn't be concerned if it dropped to 5v for 100us. Basically, I don't really care what the DCUP scale says because that all depends on how quickly they are sampling.

Also, keep in mind that there is a difference between the amount of capacitance and how fast the caps can react. My solution doesn't have anywhere as much capacitance, but they react very fast due to the extremely low internal resistance. I did this because the scope showed the event to be less than 1ms.

Anyway, I should have my dcup today, so when I get a sec I'll compare it to the scope.

Originally Posted by CraneGrus

2. Some people install it as a buffer, to use for safe landing in case of BEC failure. I do not believe that is a good idea anyway (how would you know?). However, I also believe with these servo's you will have less than 5 seconds for landing, even if you would know.

That is just plain silly, that isn't going to do anything. If you loose the BEC you are going to crash. Period.

Originally Posted by CraneGrus

3. As last point i would like to mention the interaction between DCUP and vbar I noticed, when the DCUP drains out. If I move the servo's, they regularly end with a glitch, where one or two servo arms end up in a awkward position, 90degree up or down, swash being severely tilted. Not a position one would like the heli to end if control fails.

Yea, I'm not surprised at that. I suspect that they are using caps designed to store a lot of energy, with relatively high ESR values. If that is the case then the DCUP won't filter as well as smaller caps with high ESR ratings, but as long as the RX doesn't brownout, it doesn't really matter since nothing in these helis is perfect DC anyway.

I'll know more this weekend.

schu

[MrMel]

That is just plain silly, that isn't going to do anything. If you loose the BEC you are going to crash. Period.

Actually, I can say that I have done more than one emergency auto with DC-Up, so you need to rethink that one
Only have a few seconds so it's no Place it nicely auto, it's Down on the ground now auto, but yes, it works.

I use them as buffer when I do beta-testing on dubious systems

[akschu]

How do you detect when the bec fails and your running on the dcup?

[MrMel]

Originally Posted by akschu

How do you detect when the bec fails and your running on the dcup?

as I use them when I use ESC's with built-in bec, when the BEC dies the motor ALWAYS stops (ESC quit working)

[akschu]

Ok, that makes much more sense. With a dedicated BEC I think my comment holds true.

[akschu]

Finally got an avatar setup. That's me welding in the autopilot servo on my full scale.

schu

[MrMel]

Originally Posted by akschu

Ok, that makes much more sense. With a dedicated BEC I think my comment holds true.

Except for one failure and that is main packs getting unplugged
*cough*, tried that one too.

[Chris Sexton]

Ok got my DCUP last night. Since I am not an electrical expert I thought I would post my plan before trying it.

My X7 has a Mini Vbar which limits the places I can plug becs and such into.

My scorpion sbec offers power through the throttle lead and a second power lead to spread the load. My plan is to use a parallel Y and plug the DCUP and the second bec lead into the same port on the mini vbar. In my case this will be the RXC port. RXa is the phase sensor, RXb is the throttle.

Will this work?


Sent from my iPhone using Tapatalk

[akschu]

cdsexton, That should be fine. That way you have two power wires for the bec and a single power wire for the dcup.

All, I got my dcup last night and looked at what caps they are using. I feel these are better for our application than the caps I spec'd, however, I haven't had a chance to look at it on my scope since I'm in the middle of a move.

I plan to run the dcup on my heli instead of my own cap mod. Not so much because I don't think my caps won't work fine, but the dcup is better and I bought one to look at it. On future helis I won't buy the full dcup, I'll just get the caps they use directly. Though they are expensive:

http://search.digikey.com/us/en/prod...1001-ND/946801

Also, these are 2.7 volt caps so they need to be wired in series instead of parallel like my caps do.

schu

[dantemcc]

Now after reading this thread im a little worried. I'm bidding on a set of these on ebay and was going to run them at 7.4v through a bec pro on my X7 with a RX pack powering them. Now i wonder if i should just get a different servo setup.