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Author Topic: 12 Volt DC Motor Suggestions  (Read 5201 times)

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Offline robotcoderTopic starter

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12 Volt DC Motor Suggestions
« on: August 28, 2009, 10:13:40 PM »
I am trying to choose a 2 12V DC motors and was wondering if anyone had any suggestions.  I am building a 15 - 40 lbs robot with tracks.  I found this motor
http://www.robotshop.us/rbban31-banebots-spur-gearmotor.html
Calculated Performance*
Type Planetary
Motor RS-540
Operating v 4.5v – 12v
Nominal v 12v
No Load RPM 263
No Load A 1A
Stall Current 42A
Stall Torque 2527 oz-in / 17843 mN-m
Kt 60.2 oz-in/A / 425 mN-m/A
Kv 22 rpm/v

and this battery
http://www.all-battery.com/12v4200mahflatnimhbatterypackforairsoftgunanddcpower-1.aspx
Technical Specifications
    * Voltage: 12V
    * Batteries: 10 NiMH Sub C 4200mAh matched cells
    * Maximum Discharge Rate: 40A
    * Connector Type: Standard Tamiya.
    * Dimensions:   Width 9.1 cm; Thickness 2.2 cm; Length 11 cm
    * Weight:   1.4 lb.

Would these work together.

Any suggestions would be helpful Thanks

Offline SmAsH

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Re: 12 Volt DC Motor Suggestions
« Reply #1 on: August 28, 2009, 10:29:02 PM »
yeah... you see how the stall current for the motor is 42A and the battery is only 4.2AH?
i would either suggest you find a motor that draws less current or a battery that can supply more.
Howdy

Offline robotcoderTopic starter

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Re: 12 Volt DC Motor Suggestions
« Reply #2 on: August 28, 2009, 10:46:22 PM »
So the stall current is what I need to pay attention to then.  Any 12 v motor suggestions that you have used in the past.

Offline SmAsH

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Re: 12 Volt DC Motor Suggestions
« Reply #3 on: August 28, 2009, 10:57:03 PM »
ive never actually used dc motors before, just servos.
stall current is the current the motor will draw if you hold the shaft still...
if you are using that motor for tracks, the current draw will be quite high while turning.
i would probably suggest you get a bigger battery, maybe look into lead acid?
Howdy

Offline robotcoderTopic starter

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Re: 12 Volt DC Motor Suggestions
« Reply #4 on: August 28, 2009, 11:01:30 PM »
Would a lawn mower battery work?  12 Volt 162 cold-crancking amps

Offline SmAsH

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Re: 12 Volt DC Motor Suggestions
« Reply #5 on: August 28, 2009, 11:52:56 PM »
you mean 162AH?
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Offline Truckstop

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Re: 12 Volt DC Motor Suggestions
« Reply #6 on: August 29, 2009, 04:02:01 AM »
i think he means CCA ( cold cranking amps) Smash.  Its probably off a riding lawn mower. Batteries designed for starting engines that burn fuel such as petrol are not designed to provide constant power, just enugh to crank the motor over, then they die very quickly. So no that battery wouldn't be good to use, it would work but its not designed to be drained and recharged like the EV rated and other rechargeable battery's are and because of that it wont last very long, after a few use's it would no longer take a charge. Take a look here.

http://www.gruberpower.com/gruberpower/advertising/Batteries/Allbatteries/

i buy all my batteries from Gruber. the 12-90 i think would do it. a little heavy but fairly priced.
Note stall current is 42 Amps for each motor, so each motor (42 x 2 = 84) if both motors stall they will draw 84 amps, thats allot. but the 12-90 can deliver 90 amps so that leaves you 6 amps to play with. im currently using a 12-110 in my max project, the lead acid are heavy but reliable.

So in short, the battery you asked about, Yes it would work, but not for long, best chance is to go with something else. Also check into NiMH, Nickel Metel Hydrate. you can save allot of weight by using these instead of lead acid, Lithium is good too, but i have very bad luck with lithium. have scars to prove it

best of luck

Truckstop

« Last Edit: August 29, 2009, 04:27:25 AM by Truckstop »
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Offline Joker94

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Re: 12 Volt DC Motor Suggestions
« Reply #7 on: August 29, 2009, 05:54:18 AM »
i thought he was talking metephorically, like "162 (cold cranking) amps."

Offline Canabots

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Re: 12 Volt DC Motor Suggestions
« Reply #8 on: August 29, 2009, 06:26:42 AM »
Also remember that the battery needs to be able to supply the stall current X2, if you are going to use it for both motors.

I recommend Lithium batteries. They have higher a power density than Lead Acid. Though they're expensive since you need to buy the battery pack, an over-discharge protector, and the charger.

Try looking at all-battery.com They have good deals on these batteries.
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Offline ArcMan

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Re: 12 Volt DC Motor Suggestions
« Reply #9 on: August 29, 2009, 10:39:09 AM »
Going from experience...
My yard robot uses 2 5.4 kg-m torque DC gearmotors and it will easily haul 300 lbs. up a fairly steep grade with 10" dia wheels directly attached.
So I would say that your 1.8 kg-m torque gearmotors that you spec'ed will have no problem with a 40 lb. robot.
Battery size...
You may not have to worry too much about stall current.  It depends on how you use your robot.  If you don't stall the motors, you'll never see that kind of current.  My yard robot motors have about 40A of stall current each (about 80A total), but I fuse the battery at 30A.  I've only blown the fuse once in several hours of running - my wheels got wedged into a sink hole and stalled.  If my robot runs into a tree, the wheels just slip - they don't stall.
I'd think more about the average load vs. the capacity of the batteries.  Let's say you're drawing 10A on average (a fair estimate).  Those 4.2 AH batteries would give you about 2.5 to 3 hours of run time. (note that the AH capacity for the batteries is for a light load - it goes down for heavier loads).
In conclusion, I think the motor and battery you selected would work fine.  Fuse it at 40A.

Offline airman00

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Re: 12 Volt DC Motor Suggestions
« Reply #10 on: August 29, 2009, 11:10:29 AM »
Maybe you want to go with used wheelchair motors? - they are much cheaper and usually draw around 25 amps at stall current. Plus they definitely have the torque you need.
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Offline blackbeard

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Re: 12 Volt DC Motor Suggestions
« Reply #11 on: August 29, 2009, 02:35:25 PM »
Maybe you want to go with used wheelchair motors? - they are much cheaper and usually draw around 25 amps at stall current. Plus they definitely have the torque you need.


cheeper  :o you must show me now!

anyways i found these cheep window motors. what do you think? http://www.robotmarketplace.com/products/AME-210-1011.html
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Offline robotcoderTopic starter

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Re: 12 Volt DC Motor Suggestions
« Reply #12 on: August 29, 2009, 09:55:27 PM »
Thank you for the suggestions they have been helpful.

Offline robotcoderTopic starter

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Re: 12 Volt DC Motor Suggestions
« Reply #13 on: August 29, 2009, 10:21:53 PM »
Any opinions on this motor

http://www.robotmarketplace.com/products/ML-3506.html

and I am thinking about controlling it with this motor controller

http://www.dimensionengineering.com/Sabertooth2X25.htm

Offline ArcMan

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Re: 12 Volt DC Motor Suggestions
« Reply #14 on: August 31, 2009, 02:21:35 PM »
IMO, the motor is way too small for a 40 lb. bot.  Unless you plan on a very slow speed.

I use the Sabertooth 2X25 on my yard robot with wheelchair motors.  Great motor drive.  Worth every penny.  Very reliable, easy to use.  (I'm gushing).

Offline robotcoderTopic starter

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Re: 12 Volt DC Motor Suggestions
« Reply #15 on: August 31, 2009, 09:35:37 PM »
I am thinking about using this motor now

http://www.superdroidrobots.com/shop/item.asp?itemid=735

ArchMan, how do you regulate your power to your motors, and what batteries do you use?

Offline ArcMan

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Re: 12 Volt DC Motor Suggestions
« Reply #16 on: September 01, 2009, 10:49:15 AM »
You don't need to regulate power to your motors.
Choose a battery(ies) or battery pack to match the rated voltage of your motor.
The (fused) battery gets wired directly to the drive, and the motors are wired directly to the drive.  Easy peasy.
I have 24VDC wheelchair motors, so I use two 12VDC 32AH AGM (absorbed glass mat) lead-acid batteries in series.
I suggest fusing the batteries right at the battery terminals with inline fuse holders to avoid any unintentional arc welding.

Offline robotcoderTopic starter

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Re: 12 Volt DC Motor Suggestions
« Reply #17 on: September 01, 2009, 11:33:16 AM »
Isn't 32AH to many AH for the rated 2X25AH Sabertooth driver, I thought I needed to keep the battery below or at 25AH.

Offline ArcMan

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Re: 12 Volt DC Motor Suggestions
« Reply #18 on: September 01, 2009, 01:19:47 PM »
You're confusing amperes (A) with ampere-hours (AH).  A is a measure of current, AH is a measure of capacity.  I won't go crazy explaining the difference, you can do some Google-study  ;)
You size the drive according to the full-load current of your motors (note that full-load current is not locked-rotor current).  The Sabertooth 2X25 can handle two motors @ 25A max. each.  You spec your batteries to match the voltage of the motors (e.g. 24 VDC).  They will also need to be able to supply the full load current to the motors.  Then you select the capacity of the battery to match your desired run time.  e.g.  32AH batteries will supply 1A for 32 hours, or 2A for 16 hours, 4A for 8 hours, etc.  As the current increases, your actual AH capacity will go down, but I don't want to get too complicated here.

Offline robotcoderTopic starter

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« Last Edit: September 02, 2009, 09:31:57 AM by robotcoder »

Offline ArcMan

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Re: 12 Volt DC Motor Suggestions
« Reply #20 on: September 02, 2009, 09:20:51 AM »
I think you're reading that chart wrong.  The locked rotor current is ~17A.  Maximum power is produced at about 10A current.  You will almost always be running that motor between 0A and 10A unless you overload it.  That 18AH battery will produce the 20A (10A x 2) that you will need.

Offline Soeren

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Re: 12 Volt DC Motor Suggestions
« Reply #21 on: September 02, 2009, 07:26:21 PM »
Hi,

yeah... you see how the stall current for the motor is 42A and the battery is only 4.2AH?
i would either suggest you find a motor that draws less current or a battery that can supply more.
Why?
The motor won't stand drawing the stall current for more than a very brief moment anyway, so there's absolutely no idea in calculating in such a pedantic way. Besides, a battery rated to give 40A max. will easily give much more, it's just not within the specs that the manufacturer gives for nominal battery life.

I drive a motor with a stall current of 80A from a 7Ah SLA batteries with no problems whatsoever and I plan on downgrading to ~3Ah NiCds, as it only has to go for less than 3..4 minutes (or I have lost the race anyway).
Regards,
Søren

A rather fast and fairly heavy robot with quite large wheels needs what? A lot of power?
Please remember...
Engineering is based on numbers - not adjectives

 


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