I need battery advice.

Bill Chennault

All--

I am building my first robot. I need battery advice. I imagine you need to know some things about the robot. Here they are . . .

·1) Parallax BS2, BS2px, or BS2p40 with either the BOE or PDB.
·2) Parallax MMBe motor controllers.
·3) Two Banebot gearmotors; 1A no load, 3v - 9v operation, 7.2v nominal.
·4) Parallax eb500.
·5) Four photoresistors.
·6) Some contact sensors.
·7) 6"w x 8"l (approximate).
·8)·Two 3 inch diameter, 7/8" wide wheels.
·9) Front and rear casters.
10) I would like for it to operate at least three hours, if feasible.

I am looking at "2x 7.2 Volt 4200 mAh NiMH Battery Packs + Universal Smart Charger."

Will you please advise me?
Thanks!

--Bill

[noparse][[/noparse]Subject Added By Moderator]

Mike Green

Bill,
How long this can run depends on how much you expect the motors to run during this period. You say they're 1A no load. You are always going to have some load, so the motors will drain more than 2A (for both) and possibly several times that. The Stamp doesn't take much and I imagine the motor controllers and the EB500 take only a small fraction of the motor load. Their datasheets will give you the specific values.

The two battery packs total 8.4AH. At the kind of drain we're talking about, the actual mAH is somewhat less since the rated value is based on a 10 hour discharge rate (0.84A x 10h). If you figure that your motors draw 1.5A each with a light load and maybe run 60-80% of the time, you might get 3 hours of use. Really, it depends primarily on the motor drain.

Bill Chennault

Mike--

I understand and thank you.

Basically, this will be a cat plaything when it is not aimlessly roving about. Hopefully, I can "kinda" count wheel revolutions and send the info back to a PC that can map out the playing field of my house. Something semi-close is more than close enough. Basically, it will give me experience with Bluetooth and some other ideas I have.

When it hits something, it will·reverse a half-length and turn towards the strongest light detected then proceed. Additionally, the photoresistors SHOULD not allow it to get too close to anything that blocks the light. (I might have to get tricky with them at night. Maybe turn them off and turn some infra-reds on because the two cats ROAM at night! This sucker could come screaming out from under the couch or coffee table straight at a cat!)

I plan to run·the motors anywhere from 15% to 25% of their maximum rpm on a wood floor and a fairly hard, tight carpet. I do not know if it is correct to infer that means 15% to 25% of their "nominal" amp load, or not. Plus, I just made up the three hours. I will be happy if the thing runs for an hour.

I will buy a plastic, somewhat oval shaped bowl about 6"x8", my wife·will cover it with something that looks like fur, I will invert it and secure it·to the·top of the robot base, which will be either very thin steel or aluminum; I have not made my mind up.

I actually have two sets of motors. The first set will deliver 952 oz-in at stall torque and a "no-load" 164 rpm. Rather slow using 3" wheels, unless I run them flat out. (Max: Just a little over 2 feet per second.) The other set will deliver 238 oz-in at stall torque and a no-load 654 rpm. THIS is the set I really hope to use! They might move the little machine at up to about 8.5 feet per second. I figure that is about warp drive in cat terms! If I can use these motors, then I can write both Escape_the_Cat AND an Attack_the_Cat routine!

--Bill
ps I just finished a two-year project in a completely different type of technology and will have more time to spend on my microcontroller addiction. Parallax will be happy.


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