|
|
Post by Dillzio on Apr 22, 2010 15:30:22 GMT 1
|
|
|
|
Post by ginginho on Apr 22, 2010 16:46:22 GMT 1
Dillz, to be on the safe side I'd use a UBEC. The Turnigy/HobbyWing ESC's of similar size have 2A linear BEC which isn't particularly good.
I'm pretty sure the current draw listed isn't when under load so this will go up when installed, and I haven't found any further info with regards to the quality (also read accuracy of manufacturers bumpf) for those servos.
|
|
belem
Squadron leader
Posts: 210
|
Post by belem on Apr 22, 2010 18:37:32 GMT 1
I do. I lost a fuse after adding ailerons that may have been due to brown-out. Could have been a bad solder too, but for a couple bucks I added one when I rebuilt.
|
|
|
|
Post by flydiver on Apr 22, 2010 20:54:30 GMT 1
Did you look at the power draw used by servos in the other discussion we were having?
Good reading.
Nothing uses only 200mA, not even the best and most expensive. So....that's probably a fabrication. Surprise.
Now the part about a 3A linear BEC in there:
Some of the reviews right out off the link:
[I didn't test at 30A but deriving from the MOSFET types I would suggest to use it only for short bursts at 30A. Continuous rating should be about 22..25A.
The SO8 MOSFETs are not all the same height. Therefore the aluminum heatsink plate on top was only in contact with 7 of 12 MOSFETs. The other 5 will not be able to spread the heat.
The post above about keeping currents to 22-25 amps should be heeded. My SS30 ESC smoked in flight at 30 amps continuous. The BEC stayed functional for another 20 seconds as I raced to get it on the ground. After the crash, the entire ESC burst into flames.]
I'd guess that the thing is good for 2A BEC max. I'd think you particularly would like the heat sink problem.
|
|
|
|
Post by Dillzio on Apr 23, 2010 6:28:00 GMT 1
The post above about keeping currents to 22-25 amps should be heeded. My SS30 ESC smoked in flight at 30 amps continuous. The BEC stayed functional for another 20 seconds as I raced to get it on the ground. After the crash, the entire ESC burst into flames.] I'd guess that the thing is good for 2A BEC max. I'd think you particularly would like the heat sink problem. Yeah, I wouldn't try pushing it past 25 Amps, I won't be going much past 20 with my setup if I can help it, 20 is heaps of power for a cub anyway. Good call on the heat sink issue fly  I still have some heat transfer paste laying around here from my last project, perhaps I can just fill the gaps between the FETs and the heatsink with the paste. I think i've got a little 5v fan from an old computer processor laying around somewhere too. I'll be using an external BEC. $5 seems like a pretty good investment: www.hobbycity.com/hobbycity/store/uh_viewItem.asp?idProduct=10312Are the Turnigy Plush ESCs any better than the hobbyking ones? Ooohhh, one more question. If I set the BEC to 6v, can I then use 32AWG servo wire instead of 26? Hobbyking is out of stock of all the 26 gauge servo extenders. |
|
|
|
Post by flydiver on Apr 23, 2010 7:19:10 GMT 1
Turigy Plush are Hobby Wing Pentium. It's one of the better ESC out there. IMO the only thing worse than a HK SS is a TowerPro Mag8.
From what I know of computer CPU's and heat sinks the thermal compound wants to be exceedingly thin and you want maximal contact between the source and the sink. That's why the best ones are so polished. I don't think filling the gap with compound will get you anything at all but a mess maybe.
[If I set the BEC to 6v, can I then use 32AWG servo wire instead of 26? Hobbyking is out of stock of all the 26 gauge servo extenders.]
32g is smaller and you want to run higher voltage through it? 6v allows for faster and more powerful servo response. For a Cub, hardly an issue. I think the difference for the relatively short run required in a Cub makes it a non-issue - I think. I'm not versed at all in the particulars of wire gage and amp carrying capacity except in the most general way-more amps require bigger wires.
If you use an external BEC you essentially disable the BEC in the ESC anyway (red wire removal) so those FET's are no longer in service.
|
|
|
|
Post by ginginho on Apr 23, 2010 13:11:28 GMT 1
The post above about keeping currents to 22-25 amps should be heeded. My SS30 ESC smoked in flight at 30 amps continuous. The BEC stayed functional for another 20 seconds as I raced to get it on the ground. After the crash, the entire ESC burst into flames.] I'd guess that the thing is good for 2A BEC max. I'd think you particularly would like the heat sink problem. Yeah, I wouldn't try pushing it past 25 Amps, I won't be going much past 20 with my setup if I can help it, 20 is heaps of power for a cub anyway. Good call on the heat sink issue fly I still have some heat transfer paste laying around here from my last project, perhaps I can just fill the gaps between the FETs and the heatsink with the paste. I think i've got a little 5v fan from an old computer processor laying around somewhere too. I'll be using an external BEC. $5 seems like a pretty good investment: www.hobbycity.com/hobbycity/store/uh_viewItem.asp?idProduct=10312Are the Turnigy Plush ESCs any better than the hobbyking ones? Ooohhh, one more question. If I set the BEC to 6v, can I then use 32AWG servo wire instead of 26? Hobbyking is out of stock of all the 26 gauge servo extenders. I believe the Plush are the same as the Hobbywing Pentium. If so, then yes they are much better. I've tried some cheapo ESC's and had problems with stuttering motors. Replace with a HW ESC and it's all sweet. Ont he extensions side, how long are you planning on them being? You are safer to go bigger wire than smaller, do they have and 24, 22?? |
|
|
|
Post by Dillzio on Apr 25, 2010 16:07:31 GMT 1
Thanks for the tips guys. I've decided to spend the extra $3 to get the 25A Turnigy Plush. The servo leads need to be long enough to reach servos on the wings for the ailerons. They don't stock 24 gauge, and I thought 22 might be a little too heavy.
When running relatively high loads through 32AWG wire I think the voltage drop would become significant, running 6v should ensure that the servos still see at least 5v when they're under load... but lets work it out...
32AWG is about 1.64ohms/10 ft (http://www.powerstream.com/Wire_Size.htm), so with a 2ft length that's .33ohms. If you're running a servo at 5v 750ma, the servo's impedance would be 6.6ohms. The extra .33ohms imparted from the wire is going to cause a voltage drop of .25 volts (5v x 6.6/.33, or .75x,33, either work it out), so that when under load, the servos would be getting 4.75v instead of 5. By setting the BEC to 6v, the servos would still be getting about 5.7v when under load. In theory it should all work out fine, but things often work out a little differently in real life.
26AWG wire seems to be the ideal size, it's resistance is 4X less than 32 gauge wire, so the voltage drop over 2ft @750ma would only be .06v.
|
|
