BS2 3 servo control

ultimateremedy

Hi

I want to use 3 standard servos with a PING)) using BS2 . Please help how much voltage&amp i should use all together and/or individually? I'm attaching a prototype BS2 board.

Mike Green

A typical servo will draw something on the order of 1/4 Amp average when moving lightly loaded. It can draw something like 1 Amp when moving under heavy mechanical load (lifting a heavy weight that slows it down to where it's barely moving). When stopped, it might draw 10-25mA. If you have 3 servos, they might draw 3 times those amounts at times. That's current.

Servos are designed to work at voltages from about 4.5V to 6V, sometimes as high as 7.5V. At the higher end, the motors will wear a little faster than at the lower end. There are "brushes" inside the motor that can spark and at the higher voltage, they spark more and the sparks cause most of the excess wear. Rechargable battery packs come in multiples of 1.2V (for NiMH or NiCd) and most models and robots would use 5 or 6 cells in series for a total voltage of 6.0V or 7.2V which works well. The Stamp is designed to run off either a 5V regulated supply or a 6-9V unregulated supply which it regulates. The PING))) runs off a 5V regulated supply. The Stamp can supply that if you're not running anything else (but the Stamp itself) off the regulator's output, otherwise you'll need some kind of external regulator like on the Board of Education.

SRLM

Take a look at the Board of Education schematic. You can duplicate that for correct operation of your servos and ping.

JD

ultimateremedy,

I would suggest using a separate voltage regulator for the servos, perhaps the LM2940, which is the same regulator that is on the Board of Education as SLRM suggested. That way you will not be possibly damaging the BASIC Stamp by pulling more current than the on-board regulator was designed to provide. You could get that done for $1.99 and that is far cry cheaper than replacing a BASIC Stamp at $49.00.

Here is a link to the datasheet for your review; and if you are interested is this option, also a link to the product page

LM2940 Datasheet:
http://www.parallax.com/Portals/0/Downloads/docs/prod/compshop/LM2940.pdf

LM2940 [noparse][[/noparse] product page ]:
http://www.parallax.com/Store/Components/IntegratedCircuits/VoltageRegulator/tabid/615/CategoryID/80/List/0/SortField/0/Level/a/ProductID/242/Default.aspx

Hope this helps,

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Joshua Donelson

www.parallax.com

ultimateremedy

Thank you all for your contributions esp Mike for his detailed help. I'm using 7806 for BS2 and 7805 voltage regulator for servo. earlier i tried 7805 for BS2 but it didn't work (may be the lesser amp) so i replaced it with 7806.

Now for more suggestion what you would recommend using LM2940 or 7805/7806? also i noticed BOE-BOT uses 3 servo and 1 Ping BUT i want to make and use my own PCB. Is there any similar project/semantic available with i can refer?

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An hour's contemplation is better than a year's adoration.

JD

Ultimateremedy,
·
You can use the Board of Education schematic; which supports the 3 servo connections and a connection for a PING))) as an example.
·
Were you looking for something more specific for your application or in different dimensions than the BOE?·In that case you may need to design something custom; however you can take the bits and pieces·and add it to your design·to make exactly what you need.
·
Board of Education [noparse][[/noparse] schematic ]:
http://www.parallax.com/Portals/0/Downloads/docs/prod/boards/BOE_USB_D_Schematic.pdf
·
The regulators seem to support roughly the same; however it looks like the LM2940 can handle more voltage input; but you shouldn’t be getting into that range anyways with powering servos and the PING))).


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Respectfully,


Joshua Donelson
www.parallax.com