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Asked — Edited

B9 Robot And H Bridges

Hello All

So I'm a total novice at electronics and am on a steep learning curve so bear with me :-) I'm using EZ-Robot to control my B9 and have a question about H-Bridges. EZ recommends the L298N. I've reviewed the tutorial (see below) and think I grasp the process. What I'm unclear on is how much power the board can take. In the video the power source used is only battery. My system is 12 volts. Is that within the specs and how many H Bridges could I route through a single board?





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It will handle 12v like a champ. I am not sure about the amount of H-bridge, but my guess is one
Well, yes, EZB will run nicely on 12vdc. I have three EZB's in my B9 and all are running off 120v AC to 12v DC power converters.

Your EZB can run as many H-Bridges as there are digital ports. Depending on what style H-Bridge you get will depend how may ports each H-Bridge will take up. Some H-Bridges will only control one DC others will control more. The L298N sold here will control 2 DC motors. You can figure Two digital ports per DC motor. So, EZB has 20 digital ports, you can run up to 10 DC motors. Of course that means you wont have any ports left free for other things. When that happens it's time to get a second EZB.

EDIT: I originally said one port per DC motor. I forgot that you need to figure that each direction of the DC motor needs a different Signal wire meaning you will need 2 Digital ports per DC motor. I changed it in the above paragraph.

Remember the EZB is only powering the control circuit and trigger signal of the H-Bridge. The H-Bridge it's self is doing all the heavy lifting and should be sized to the current of the DC motor your controlling. The L298N sold here is a great little H-bridge for small DC motors, I use it is contorl the 2 small DC motors that rotates the radar and sensor ears on the head section of my B9. However I burnt up 3 of these when I tried to control the much bigger DC motors that operate the waist and hip rotation. Although the Amp specs were within the 4 amp max of the L298N the problem came in when the DC motor reversed. Fly back voltage created by the magnetic collapse of the coils in theDC motor throws back up to twice the original voltage into the H-Bridge. So I ended up buying a nice h-bridge from Pololu with a higher current rating, over voltage and reverse voltage protection. It's a VNH5019 Motor Driver Carrier and a good choice for your B9. If your using 24v batteries this is not a good choice do to the over voltage protection. Here's the link: http://www.pololu.com/catalog/product/1451 . It will only control one motor at a time. Here's a good choice if you want to control 2 DC motors from one H-Bridge. However it does not have a populated Current Sensing section: Dual VNH2SP30 Motor Driver Carrier MD03A - http://www.pololu.com/catalog/product/708 .

Good luck and have fun!
Dave Schulpius
Thanks for sharing Dave!:) ..bad experiances are a teaching benefit as well! "dont eat a molton marshmellow":)
Ya, I got a lot of bad experiences I can share. Sometimes I wonder if I'm learning anything from these "Teaching" moments as they keep happening. *blush*

Well, as an old mentor used to tell me; "What you don't have in your head, you make up out of your wallet". ;)

I've had a lot of people ask me how I know how to do all this stuff. I just tell them I don't have enough money to pay someone to build the things I want or fix the things I break and blow up so I have to try to learn how to do it myself. Sadly sometimes I don't learn fast enough and have to fix things two or three times. :P
Well I am in the same classroom in the "school of hard knocks" ..or soft black smoke ! another old saying wich I am sure your familiar with ..."old too soon smart too late" but WE have to break that one:)
Dave have you thought about using a "projector" to cast out a cool visual from a color lcd...I recently found an old slide projector..something I am sure technopro has only seen in a museum:) at a Lions sale for 5$ which I am going to incorporate in my robot...heres the link....in case your interested..
Nice find! No, I hadnt even considered this. However it's a very neat idea and something I need to consider.

Afternoon All

So I'm working with the single Pololu H Bridge VNH2Sp30 to operate a 12volt Dewert motor to rotate my robot left and right. My understanding was I only needed the white wire from my EZ Board to control voltage and then my + and - will tide to my outside power source but when I read the instructions on the board specs (http://www.pololu.com/catalog/product/706) it says use connection A and B to control the direction of the motor. How would that work if I only have a single white wire? Could it be I run two white wires to my EZ Board and then have a left and right control on the EZ interface? I'm attaching an image of the board.

Any advice would be greatly appreciated.


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Hi Daniel,

The two leads coming off your motor will attach to the Out A & Out B pins. These are the pins that will supply the power to your motor. It's OK to reverse these two wires. The only effect if you do this will be that the motor will run the other way.

Your 12v power will attach to the Vin & GND at the bottom of the H-bridge.

One White wire from one signal pin of a Digital port on EZB will be attached to the PMW pin on the left side of the H-bridge.
One White wire from a different signal pin of a Digital port on EZB will be attached to the InA pin on the left side of the H-bridge.
One White wire from a different signal pin of a Digital port on EZB will be attached to the InB pin on the left side of the H-bridge.

Red wire from the power pin of a digital port will attach to +5V(in) and finally a Black wire from a Ground pin of a Digital Port on EZB will be attached to GND on the left side of the H-bridge.

In ARC add a PMW control and set it's port to where you have the white (Signal) attached. You can now start you motor in a certain direction many ways. Movement panels or scripts by simply turning on the signal port attached to either Out A or Out B making sure one is on and the other is off. An important thing to remember is you need to have your PMW set up or the motor will not start. If left to zero your motor wont start.

Careful you don't reverse your motor too quickly. You could burn out half your H-bridge with fly back voltage. Those big Dewert motors are notorious for this.

Hope this helps.
I'm thinking the problem has got to be with my soldering. I've attached a diagram of my wiring along with a picture of my H bridge and the port settings. The PWM is set up and all the way to the top. The HBridge PWM controller with my right and left PWM both set at D8 (this was the only signal controller I saw that seemed appropriate). My motor connections are A&B on the right side of the Pololu board. My grounds are connected.

Anyone see a problem?

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Hi Daniel,

Sorry your having these problems. Unless something is burned out I'm sure we can get this up and runnng.

I've not used the PWM H-Bridge control but it looks like you have the right ports set and the wireing looks right. As long as you have the PWM sliders all the way up you should get movement. This is where you need to get your muil tester out to see if your etting the expected voltages you need.

First set your tester to DC voltage and review how to use and set it for your needs.
Then disonnect the 12vdc external power supply and motor wires from the h-bridge.
Turn on your 12vdc power supply and test the disconnected power supply leads to see if your geting 12vdc.
Next power on the ezb and test the 5vdc connection point on the h-bridge to see if you are getting the right power to the bridge. (do you see any lights on the h-bridge when it's powered up?).
Hook up your known working 12vdc power supply directly to the motor and switch it on. Your motor should start running if all is well. This will confirm the motor is OK. What are you useing for a 12vdc power supply? Can it supply enough amps to push the motor?
With all power off and the EZB turned off, reconnect your external 12vdc power supply. Do not hook up the motor leads.
Power up your 12vdc power supply and EZB.
Start up ARC and let it connect to EZB.
With your tester connected to the motor control pins connectors on the h-bridge toggel the on-off buttons on ARC's h-bridge conrtol (DO THIS SLOWLY AND DONT TOGGLE BACK AND FORTH QUICKLY! PAUSE BETWEEN ACTIONS! DOING SO COULD CAUSE FLYBACK VOLTAGE AND DAMAGE YOUR H-BRIDGE). Make sure your PWM sliders are up all the way. You should see your tester change between +12vdc and -12vdc when you push the buttons. Also you may be able to see LED lights on the H-Bridge come on and off as you move back and forth.

If all is OK till now reattach your motor to the h-bridge and see if ARC will now control it.

Following the above steps will tell you just what is working and where the problem starts.

Good luck and let us know what you find.

Oh ya; and have fun!
Thanks Dave

This is really helpful.

So using my multi-tester I confirmed I have 12 volts going into the H Bridge (vin and ground) however there is no voltage coming out of the A & B leads to the motor (I used the EZ control to test). I then re-soldered my connections but again no power to the A&B. I'm assuming I've damaged the Pololu board. My next approach will be with a second board (guess I'll buy them in bulk ) but this time instead of solder I'll use clips for all my connections and then test.

Did you test where are the five volts comes on too the H bridge? Do you have voltage there? Also test where the signal wires attach you should see 5 volts at each point when you toggle the movement on and off in E the builder.

Sorry for sounding like a cavemen above. What I meant to say was to test the Ina & INb connectors on the H-Bridge when you toggle on and off the control in ARC. You should see the voltage change from 5vdc to zero as you turn it on and off.
Greetings @Mulberry, from another fellow B9er.

I haven't gotten very far with EZ-B myself, and so I might be wrong on this, but I looked at the diagram that you posted, and it did not look right to me. I have gotten a few motor controllers to work on mine. I do not think that your power (red and black) wires should be hooked up to separate outputs on the EZ-B. Each "digital out" has a ground (black) a hot pin (red) and a signal pin (white). There are also two pins up top just for power.

Your power can be hooked up to any of the hot, and ground pins. It would make sense to use either the dedicated 5v pins, or one of the ones that you are already using. Since your diagram didn't show which pins you hooked up to, I am wondering if you connected your power to signal pins.

Here is a drawing of two ways that it can be done.

Again, I am pretty new to this. Dave has done an incredible job setting his up. Perhaps he could review what I have posted and offer more clarification.
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@Danger, thanks for clarifying this issue with a picture. I never thought Daniel may have attached to signal pins of each port. I've not see a picture of how he has it attached to EZB. However after looking at his pic of the port assignments closer he does have them pointed to the power and ground wires in his drawing.

@Daniel, Dangers Option 2 pictures above is exactly how I have all my h bridges set up. The problem with the PWM H-Bridge control your using is it has an extra set of direction toggle buttons and port assignments for a second motor. The H-bridge your using only controls one motor so the second input settings in your movement control panel needs to be set to ports that you have nothing attached to.

Each port has 3 pins, which are Gnd, +5 and Signal. The Gnd and +5 are for powering the device connected to the port. The Signal pin is connected to the EZ-B Microchip for reading or writing data from Digital or ADC. The Gnd and +5 pins are not connected to the Microchip, they are used only for powering the peripheral connected to the EZ-B.

For example, a servo has a 3 wire plug that connects to one of the EZ-B Digital Ports. The wires of a servo connector are Gnd, +5 and Signal. The Gnd and +5 power the motor and circuit within the servo. The Signal wire carries the information to tell the servo what position to move.

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BAZINGA! You guys were spot on. I had my port wires incorrect. Once I followed Danger's option 2 and switched to a standard H-Bridge control the bugger sprang into action. You two have no idea how much of a help you've been. This was the last block to actually connecting all the components and firing up the big boy. A big martini for you both if we ever meet .:D

Danger deserves the credit. He spotted your port settings and realized you may have had them attached to the wrong pins. That's why as a group we are able to achieve so much. I would never had come this far with my robot and had it turn out working so well without the help of people on this forum and others!

Glad all is working now. Post some pictures and video! I'd love to see him working.

I'm glad that I was able to help. So far I haven't gotten to the stage of putting actual motors into my B9. I am building it from scratch. It is very time consuming. I have done experimenting with motors, controllers, and EZ-B on the workbench though. I am pretty close to incorporating working parts into it.

As Dave said, it would be good to see some pictures, or video. I am always looking for ideas myself.
Thanks Guys. Again I am indebted. Videos ASAP.

Danger I have some extra B9 parts that you might could use. If you're interested contact me via email at danielscottangel@gmail.com.