|Dec 06, 2003, 09:31 PM|
U-S-A! U-S-A! U-S-A!
Joined Dec 2003
Got my Black Widow AV order fast! Plus, some questions.
Usually, when I order something via U.S. Postal, I have the unpleasant experience of having to wait for my order. I was expecting the package to arrive, at the earliest, this coming Monday. Much to my surprise, it arrived today. Considering that I ordered it early last Thursday morning, that's pretty quick. Thanks to Bill (yb2normal) for shipping it out so quickly!
I have a couple of questions that some of you (including Bill) might be able to answer for me. I do know enough about electronics that I can usually make an educated guess about how to hook some components up, but considering the sensitivity and cost of these devices, I'd rather not take any chances. I tried doing serches here, but none of my questions could be answered for sure.
Two of the components that I had ordered, the Panasonic CX161 CCD camera and the 2.4 Ghz 50mW transmitter, were chosen because they need a power source of 5 volts, and I wanted to power both of them (in at least one of my applications) with a dedicated 4 cell NiMH pack (4.8 volts). The thing that made me question whether this was the safe thing to do was the fact that the instruction sheets for both devices stated that the use of a voltage regulator is recommended. Are the input voltages needed on these devices critical enough that running .2v below 5v will mess things up? I didn't really want to add a voltage regulator because you usually have to run the input voltage at least 2 volts higher than the desired output voltage. (Or am I wrong here?) More volts means more cells, which in turn means more weight.
So, does this mean I have to use more than 4 cells, or will that be enough?
On to the next question. Sorry.
Most people (including yb2normal) say that you shouldn't power the camera and transmitter off of the same battery pack that's running your reciever and servos. Is this strictly just because you'll just end up running the battery down faster, or are there other reasons, such as radio interference in the video signal, or worse, voltage spikes from the motors that can damage the camera and transmitter.
The reason I ask is because in addition to using this camera on a heli (which I do intend to use a dedicated battery pack for the camera system) I plan to use it on an electric Team Losi XXXT. I was planning on using the 5 volts from the BEC of the Novak ESC. (Which IS a regulated voltage source, correct?) I'm pretty safe when it comes to the amount of miliamps being pulled by everything on the BEC... I think.
Panasonic Camera - 160ma
50mW transmitter - 70ma
Novak reciever - 8ma
Total - 238ma
The BEC is rated at 500ma. Which leaves 500ma - 238ma = 262 ma. The only thing left is the steering servo, which I seriously doubt would pull over 200ma. I doubt that my run time would be much affected either, since it's a 2400 mah NiCD.
So the only reasons that I can think of as to why I shouldn't hook up the camera and transmitter to the BEC is possible noise introduced in the video signal and damaging voltage spikes. If that is the case, can't capacitors and a schottky diode be used to help curb these threats?
Any input would be helpful.
|Dec 07, 2003, 04:35 AM|
Snoo - using a 4 cell Nicad or NiMH pack should be fine, the voltage ought to be quite stable enough. Just don''t try hooking up a LiPo pack!
The reason a separate supply for camera and transmitter is recommended is twofold. One you've already guessed - it cuts down drastically on both interference with the video signal and possible interference with your radio equipment. Second reason is safety - it just makes common sense to use a totally independent supply for the video equipment in order to safeguard the radio as much as possible. This last doesn't apply quite so much if you're going to be using it in a car or truck, so I guess it would be worth a try to see if you can get it to work. However, I should point out that you should expect the steering servo on a car or truck to draw a LOT more than 200mA. Frankly, I wouldn't consider a 1/2Amp BEC to be up to the job.
|Dec 07, 2003, 04:09 PM|
Everything Gordon says is spot on. I'll reiterate a couple points and add some comments.
1) a 4 cell pack will work fine. The voltage tolerance of the transmitter and camera are well up to the task. Low voltage won't cause any damage, it will simply stop transmitting.
2) Sharing the BEC: my philosophy is that I never add more possible points of failure to the RC system other than the pilot
Now having said that, I will frequently share the RC battery directly, but that is with my RTF system which has a 5v regulator added to it.
On the subject of regulators, the one I recommend in the documentation is a 'Low Drop-out' model which will operate down to just 0.5 volts over the regulated value (5v). Furthermore, the regulator will simply pass the voltage through when you go below 5.5v, so your transmitter and camera will always get juice. If you are going to expend the effort to play with capacitors and diodes to provide some filtering, then I would highly recommend that you implement the voltage regulator instead and add the supporting capacitors recommended in the app notes for the regulator on National's website.
|Dec 08, 2003, 08:43 PM|
U-S-A! U-S-A! U-S-A!
Joined Dec 2003
Thank you both for your advice. It's good to hear that using just a 4 cell pack will suffice. Since that's the case, I'll probably just go with 4 AAA NiMH cells soldered together. 600 mah sould give me over a couple of hours, which is plenty.
Gordon brings up a good point, concerning the servo. If I were still using a cheap, slow, weak servo that comes with a RTR truck, then I probably wouldn't have anything to worry about when it comes to pulling too many milliamps. But since I have a much faster and more powerful steering servo installed, it probably is pulling more than a 1/4 of an amp. He probably saved me from blowing my BEC.
Again, thanks to you both! You put my mind at ease. Now I can start playing with this stuff.
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