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Author Topic: Are these components compatible? (chassis/motorshield related)  (Read 1026 times)
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I already have this chassis with the motors already included :
http://www.robotshop.com/dfrobot-4wd-arduino-mobile-platform-4.html

but I need a motor shield to hook up to my arduino uno.  I'm pretty much decided between these two:
[1] http://www.adafruit.com/products/81
and
[2] http://www.amazon.com/DFRobot-Motor-Shield-for-Arduino/dp/B006D85PAS/ref=sr_1_4?s=electronics&ie=UTF8&qid=1323643740&sr=1-4

Now, I've done some light research and as far as I can understand, I THINK they're both compatible, but I'm not completely sure.  I think [1] is my best bet but that be just me.

This is where you guys come in, if you guys could help me and and tell me which one is the best one for my needs on this project that would be awesome.
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Either should work fine, but if you wanted the most headroom (not really needed for that chassis, though), the second would be the better option.
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Would someone verify I am looking at this correctly?  It looks like either could handle the green motors, but not the yellow motors unless you prevent the motors from stalling.

http://www.robotshop.com/dfrobot-4wd-arduino-mobile-platform-4.html
Indicates a stall current of 470mA @ 6 volts for the green motor and 2.8A @ 6 volts for the yellow motor.
The chassis appears to use 4 motors, so if your driver is 2 port, you would need to double the stall currents as you would have 2 motors on each port.

http://www.adafruit.com/products/81
provides 4 channels of 0.6A continuous capacity (each sufficient for the stall current of the green motors)

http://www.amazon.com/DFRobot-Motor-Shield-for-Arduino/dp/B006D85PAS/ref=sr_1_4?s=electronics&ie=UTF8&qid=1323643740&sr=1-4
provides 2 channels of 2.0A continuous capacity (each sufficient for the stall current of 2x green motors)
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Would someone verify I am looking at this correctly?  It looks like either could handle the green motors, but not the yellow motors unless you prevent the motors from stalling.

http://www.robotshop.com/dfrobot-4wd-arduino-mobile-platform-4.html
Indicates a stall current of 470mA @ 6 volts for the green motor and 2.8A @ 6 volts for the yellow motor.
The chassis appears to use 4 motors, so if your driver is 2 port, you would need to double the stall currents as you would have 2 motors on each port.

http://www.adafruit.com/products/81
provides 4 channels of 0.6A continuous capacity (each sufficient for the stall current of the green motors)

http://www.amazon.com/DFRobot-Motor-Shield-for-Arduino/dp/B006D85PAS/ref=sr_1_4?s=electronics&ie=UTF8&qid=1323643740&sr=1-4
provides 2 channels of 2.0A continuous capacity (each sufficient for the stall current of 2x green motors)

Ok, so correct me if I'm wrong? According to you, I should use the adafruit shield?  I don't understand what the term "stall current" means, or how those relate to the current going to the  motors. 
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http://www.robotshop.com/dfrobot-4wd-arduino-mobile-platform-4.html
click on the Specifications tab

it has 2 different motor types listed: "green" and "yellow"

the green has the following stats listed for 6 volt supply:
No-load current(6V): 71 mA
Stall current(6V): 470 mA

This means with no load (IE holding your robot in the air with the wheels not touching anything), the motor draws 71 mA.
Stall current means that if you were then to grab the wheel and prevents it from moving it would draw 470 mA.

Your motor driver needs to be able to handle the strongest current draw of your motor without overloading.  My understanding is that to do this it needs to be able to handle the stall current of the motor that is connected to it. So for this motor you would need to handle 470 mA per motor.  The chassis has 4 motors.

If you were to use the following controller: http://www.adafruit.com/products/81
It has 4 channels that each can handle a maximum of 600 mA per channel (1200 mA peak -per spec sheet -> non-repetitive, t ≤ 100 µs).
Since 1 "green" motor needs 470 mA, you could connect 1 motor per channel with out going over the maximum current per channel.
There is 4 channels and 4 motors, so this would work.

if you were to use the following controller: http://www.amazon.com/DFRobot-Motor-Shield-for-Arduino/dp/B006D85PAS/ref=sr_1_4?s=electronics&ie=UTF8&qid=1323643740&sr=1-4
It has 2 channels that each can handle a maximum of 2000 mA per channel DC (see spec sheet for peak info).
Since 2 "green motors need 940 mA, you could connect 2 motors per channel with out going over the maximum current per channel.
There is 2 channels and 4 motors, so this would work.

Now for the "yellow" motor:
No load current (6V): 160 mA
Locked-rotor current (6V): 2800 mA
The first controller can't handle 2800 mA per channel. therefore will not work for "yellow" motors.
The second controller can't handle 5600 mA (2800 mA x 2) per channel. Therefore will not work for "yellow" motors.

So the conclusion I have is this: are you getting the "green" motors or the "yellow" motors?
"Green" = you can make either work
"Yellow" = neither can handle the peak current usage, so your controller might burn out if your robot got stuck.

Does that help?
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Yes, I see what the problem is.  Farther back than the jargon, I was confused with the different colored motors. The motors are all yellow, but when I was reading the spec sheet before I ordered it I didn't even think about which motors I was getting.  That's something I'll have to deal with now, because I'm pretty sure they didnt give me any kind of option to choose while I was ordering it.

No comes to the question about motor shields.  I already have an uno and I'm gonna stick with that and I don't want to spend a LOT of money on the shield.  What if I were to piggy back the adafruit shield?  Would that work for me.  I'm gonna try the calculation myself but it wouldn't hurt to have a second brain thinking about this with me.
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If I decided to piggyback on the adafriut shield, it would essentially double everything, correct?  And since I have the yellow motors, which draw a max of 2.8 A, the new piggyback'd shield will output a new 2400 max.  Will this 200 mA really make a difference and burn out my shield or what?
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the adafriut only handles 600 mA per channel doubling that only gives 1200 mA which is still well below 2800 mA.

You need a driver that can do 4 channels of 2800 mA or higher draw or 2 channels of 5600 mA or higher draw.
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