Let's Make Robots!

Using 4 Motors?

Hi all, I've made my first robot using a picaxe 28x1 project board. This uses the L293D to drive my 2 motors (connected to a & b). My question is, if I wanted to power 4 motors from a robot, what would I need to do? Is this hardware capable, or should I be looking at something slightly different?

Also, I have a AXE230 PICAXE-08M Module...which says it can be attached to the board and enable the use of additional servos or other output devices, but does not specify motors.

Any advice is welcome, I've been through so many different websites and can't seem to put this together myself :(

Comment viewing options

Select your preferred way to display the comments and click "Save settings" to activate your changes.

4 motors should not be a problem, as long as they are small enough. Everything here comes down to current draw, how many Amps your motors pull and if that total is less than what your L293D can handle. In theory, that L293D is probably good for maybe 700 or 800 mA (.7 amps / .8 amps) fairly constantly without getting too wicked hot. (4) motors, such as a GM9 (the start here robot's motors) would probably be ok --But, if you want to be completely safe here, you should calculate the total current draw of a motor when stalled --when you physically stop the motor from moving, and then tell it to go full-speed. The current draw at this point will be the highest the motor will ever pull. Double this number for your two motors wired in parallel, and that is the total current draw. Again, if this number is less than say, 800 mA or so (for each side, left and right), you are probably good to go.

Your little 08m board is a super awesome board and you will find 1000 uses for it. It does not however have a motor driver onboard. Servos, yes,  --motors, no.

 

Will someone else tell him about the L293D drop-in replacement chip --the 1A one...  I can't remember the number.

Thanks for the detailed response, appreciate it. You'll have to excuse me because I'm so new when it comes to simple electronics as well, I'm re-teaching myself everything, school was a long time ago :P

so that said, if the 2 motors I currently have are taking up both the two A and two B pins, do I just connect 2 additional motors to the standard output ports? Or did I just embarrace myself by asking that? :)

Looking at the datasheets, the L293D says it can handle 600mA per channel. Does this mean for each motor? Both my current motors have a stall of 600mA, so right on the threshold. If I were to run parallel motors, both circuits of 2 motors should not exceed 600mA?

(Double Post)

You are correct, I misspoke, the L293D is good for 600mA, not the 800mA I said. Good catch. Everything else I said is good, I think. And yes, that is 600mA per channel (per side).

Well, it looks like your motors (when stalled) are already at the limits of this chip. This is of couse, if you stall them or run them very, very hard. I say go for it (and don't let them stall). Double up your motors, run the robot around for a minute or so and touch the L293D. If you burn your finger, it is too much juice. If we are talking warm or hot but not crazy hot, I would not worry about it. Worst case, you blow a motor driver --you are out $2 and 2 weeks to get a new one from ebay. No biggie.

Your motors will be wired in parallel. Parallel/ series is wicked important and there are 1000's of tutorials out there. In your case, you will now have 2 wires total going to each motor outputs on your board. 

 

Thanks again, can I just ask you to elaborate on the last point you said. I'm still a bit thick, but this is how I understand it, I currently have 2 wires from each motor (obviously lol) going into the board, one positive and one ground per channel. I will no doubt find a tutorial on wiring it parallel but are you saying that I WILL have 2 sets of wires per channel (ie, fixing 2 wires per pin?) rather than the one set of wires per channel?

Lastly, when wiring parallel, am I likely to have a reduction of power between the 2 motors in that circuit?

Just to be clear, you'll be running four motors, but only two independant channels. Two motors on each side of your robot will turn together, sharing a channel. 

The board has an A channel and a B channel. Each channel has two pins. So you could connect the + wire from the two motors on the left to one pin of channel A, and the - wire from the two left motors to the other pin of channel A. 

The right motors connect the same way to channel B. What I mean by the + and - wires of the motor is, make sure the two motors on the same side turn the same way when you connect them.

One other thing, some people have successfully soldered one l293d chip on top of another. Each leg of the chip on the top is soldered to the same leg of the chip on the bottom. This effectively doubles the current handling capacity.

The other chip Chris mentioned is the SN754410

One other thing, some people have successfully soldered one l293d chip on top of another. Each leg of the chip on the top is soldered to the same leg of the chip on the bottom. This effectively doubles the current handling capacity.

oh i like that - an entirely new concept i hadnt considered - parralel chipping

 

This whole series/ parallel thing is incredibly important, you would do well in learning the concept over just "how to hook up these particular motors". You really, really need to find a tutorial that makes sense to you and get this one down. Like I said, there is 1000 tutorials out there for this --"series parallel tutorial" on the googles or the youtubes.

And yes, 2 wires per pin. Basically, connect a motor to say, Motor output A on the board like you normally would. Now do it again with the second motor (again, going to motor output A). It should NOT be motor_output_A-->first_motor-->second_motor-->motor_ouput_A   (this would be series, and it is not what you want) 

Gotcha, understood :) thanks for your help