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FEZ Motor Controller & 4 motors? (electronics question)


#1

I have the FEZ Motor Controller (not the shield) and my Domino. It’s works very FEZzy :slight_smile:

Look at items like this:

Dagu Wild Thumper 4WD chassis.
http://www.pololu.com/catalog/product/1567 (Image: http://www.pololu.com/picture/view/0J2891)

It has 4 motors.

Could I drive 2 motors one 1 side with 1 output from the controller? It would move/turn much like a tank.

Would this just drain the battery twice as quickly?
Would this drain at the same rate, just move at 1/2 speed?

Would doing this increase/decrease the resistance and cause problems to the controller board?

Thanks
(obviously I’m an electronics n00b)

My only point of reference is the concept of the wiring of speakers.
2 4ohm speakers in parallel = 2 ohms resistance
2 4ohm speakers in series = 8 ohms resistance


#2

Also a chassis like this one:

http://www.dfrobot.com/index.php?route=product/product&product_id=97

image: http://www.dfrobot.com/image/cache/data/ROB0003/dfrobot4wdpackagedetails-500x500.jpg

It comes with 4 motors


#3

It works the same as with the speakers.

2 motors in parallel will run at the same speed as one, but have half the resistance and use twice the power. The battery will last half as long and the controller needs to be twice as big.

If one motor draws 1 amp, then two in parallel will need 2 amps so the controller needs to handle 2 anmps per channel.

If the controller is PWM and it can handle both motors at 100% then you can run them at half speed and the battery will last twice as long.

You can run the motors in series but they will run at half the speed. The problem with running motors in series is that one can steal power from the other and you’ll struggle to get them to run at the same speed.

Most controllers have over current protection so you should be okay to try it out. Just watch the heat on the controller. If it gets too hot too touch, back off. If it releases magic smoke, put it back with a syringe and try again. That last part was a joke :wink:

Hope this helps.


#4

Thanks for the reply. I’m a software guy who struggles mightily with the electronics part.

The controller I am using is this: http://www.inexglobal.com/products.php?type=addon&cat=app_motor&model=zxdcm2
2-Channels DC motor driver board
Drive DC motor 2 channels with bi-color LED indicator.
L293D H-Bridge driver Max. load current 600mA.
Fully 3-Control signal wires
Suitable supply voltage +4.8 to 30Vdc. Separate control voltage (+5V) and Motor supply voltage (+V)

Most of these motors have 2 ratings – no load & stall

For example:
• No-load current(3V):60mA
• No-load current(6V):71mA
• Stall current(3V):260mA
• Stall current(6V):470mA

or
Free-run current @ 6V: 70 mA
Stall current @ 6V: 800 mA

I assume that No-load/Free run, is the motor not connected to anything other than power. Is this correct?

The stall current I’m not sure about.

I fried one of my motor boards in the past and don’t want to do it again.

Thanks again!!

(I guess worst case if I go with one of those platforms, I could always just power 2 motors and leave the other 2 unconnected)


#5

No-load would be when the motor is running, but not attached to anything. Free-running. No work to be done. This won’t happen in a real robot because the motor should be powering the wheels.

Stall current is when the motor is held so it can’t move. It is putting all the power it can out. This could happen if the robot stops against a wall and the wheels stall.

With a 600mA controller and a motor with 800mA stall current, you will fry it if it stalls for extended periods. The simple solution to that problem is simply to put a 600 mA slow blow fuse in the circuit. It is much cheaper to lose the fuse than the controller.

In the setup you are describing the motors will probably run at 300 to 500 mA or so lugging the robot around - so you should be fine. Measure the amps if you are worried.

By the way, the most common cause of frying a controller is short circuiting or putting the controller in forward and reverse at the same time. Most modern controllers shouldn’t allow you to do this, but just watch your control logic anyway.


#6

Thanks for the info.

In my case, I accidentally reversed the polarity of the external power. :-[


#7

Oh yes - and of course that too :slight_smile:


#8

So would it be wired up like this then?

Note - this is from an old flowchart software, so the lines that cross wouldn’t be connected.

Is it correct to assume that the fuse would be on the + side. Or does it not matter?

Thanks


#9

That looks fine.

The fuses will add resistance. You can remove them once you are comfortable that your motors are not overloading the controller.