Servo Voltage Drop

CanyonMann

I've built a little battery powered submarine that uses (among other things) a BS2 and a servo (Hitec HS-55). I'm slimming it down into a smaller package and want to use smaller batteries. (it was monstrous using D cells), The servo runs perfectly on a 6V tiny camera battery as does the stamp BUT when i try to run them both off the same battery theres a 10 ms blip I can see on my osscilloscope right when the servo starts to move that crashes my voltage to low enough that the Stamp resets...then the servo stops, stamp reboots, servo starts to move, voltage drops stamp reboots and around and around we go.

I think what's happening is the instant the servo starts to move, for that instant, the circuit acts like a short until the servo starts moving and then the current decreases to something reasonable. I tried to insert a capacitor in the circuit to try to hold the voltage for the 10 ms but unless i use a capacitor the size of a D cell (which is the whole purpose) it won't hold the voltage up. I could always use two batteries but that's so inelegant, there has to be a better way.· Thanks for any and all suggestions. Graham

RickB

You might try enough supercaps in series to meet or exceed the battery voltage, but a small battery just for the bs2 will be the cheapest route. There's no free lunch here.

Rick

Chris Savage

Graham,
·
·· Without increasing battery capacity I don’t see any other way. ·Large capacitors and Super Caps may or may not work, but if your power source cannot handle the sudden current draw then you will need to increase the battery size or add a separate battery for the BASIC Stamp side. ·With separate power sources that problem will go away.· Take care.

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Chris Savage
Parallax Tech Support

Bruce Bates

Graham -

How much physical room is there to work with. What is the largest dimension - length, height, width?

What battery technology are you presently using: carbon-zinc, alkaline, Ni-Cad, Ni-MH, Lithium?

Regards,

Bruce Bates

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CanyonMann

I'm embarressed to admit this, but I went ahead and got some 0.5F superCaps and they worked...rather erratically but when I was looking at Bruce's suggestions trying to figure out what kind of battery technology I realized that the cute little 6Volt from Radioshack has listed a maximum current of 60 miliamps, I got a CR2 battery from Panasonic which 1/3 bigger and only 3Volts and it can crank out 1000 miliamps. Two of those and I'm golden.

Since I'm going to go ahead and do a run of 1000 subs and try to start make my millions (don't laugh), I could obviously not afford to use Stamps (I hope that statement doesn't kick me out of the forum, Don't worry moderators, I'll give you guys props on Oprah)) So I'm using a IC_1187 which is cheap as hell. That involved learning assembly language which was TORTURE (hence, stick with the STAMP unless you're an absolute masochist)

So I can use only one 3Volt battery now for all the component of the sub and the sirens and the lights and the chip...but now the fricking Servo won't work since it needs 4.8 volts.

Anybody know how to get 3 volts up to 4.8 volts in under 2 cubic cm's with a 3V battery that puts out 1 amp but still needs to but out 300 miliamps when at 5Volts?

Speak slowly, I have an MD and but no electrical or computer engineering training. Graham

Mike Green

There are lots of solutions for taking 3V and producing 4.8V, but they get physically big and expensive when you expect them to supply significant current, like for a servo. You're probably better off devoting the space to using another battery in series with the 3V one. The servos should be happy with 6V. You can still use just the 3V from the one battery for the other circuitry. You'll drain one battery faster than the other with the extra load, but the main load probably is the servos.