Hi Dave

Yep. Its me from San Francisco and you're right about the B9. I want to control my waist rotation and my soil sampler with this bridge. I'm using two EZ boards (following in your lead): one for the leg/tread section and then one for the torso/brain.

I'm slowly getting there

Daniel

Hi Daniel, Welcome to the EZ life. Glad to see you here. you are good to love it.

What are the amps each of the motors pull. make sure your hbridge is rated to handle them. What hbridge are you using here?

Hi Dave

I'm using the H bridges sold through EZ Robot. They're rated at 2.5. The heaviest motor I'm using is a Dewert and they're rated at 1-2 amps. At least that's what I found on the B9 Builder's Club. As far as I can tell that's correct...I hope.

Daniel

Okay, here's my fear. The motor is rated at 2 amps. The H bridge is 2. 5. Why back voltage can be almost twice as high as supply voltage. This happens when you reverse the DC motor quickly. Soul, if you do the map, you're fly back voltage can be more than 4 amps. This will burn out your fridge. It happens to me and I am using the same motors you are

Is there any way to block flyback current? Diodes or something? This (flyback) is all new ground for me so it's very interesting.

Here is a Link to some theory about DC motor EMI DC Motor braking

Well, you cant really block the flyback voltage but you can bleed it off to ground through quick switching Shottky diodes. Here's a post I made last year when I was destroying H-Bridges and trying to figure out why:

>>>>>>>>>>>>>>>>>>>>>>>> I've come up with why I'm destroying h-bridges. I installed another working one and got things working properly with the H-Bridge movement control in ARC. Push an arrow, push Stop, push the other arrow and the motor would reverse nicely. I did that a few times and all went well until....... I decided to switch the motor direction back and forth without pushing the "Stop" button. Well, it did change direction a few times nicely but then it just locked on in one direction again and would not respond. Remember, I'm supplying 24vdc through the H-Bridge to the DC motor (which is OK).

The problem happens when I reverse the motor quickly and it sends a serge back into the H-Bridge causing damage. I read that this is normal and dammage happens when there is no protection diodes to block the back shock. Seems that the back voltage ( counter-electromotive force also known as back electromotive force) can be as high as twice the supply voltage. So the answer is to surround the motor with Protection Diodes and a of course a fuse. The best type of diode to use is a very quick switching diode and they recommend a Shottky diode rated just above (not below) the value of the supply voltage and rated above the current you will pull. In my case I need a 30v, 3 amp diode sense my supply voltage is 24vdc and my motor pulls just above 2 amps under load (a 1N5821 is just right). Well, now to build the circuit and see if it helps. They also suggest adding caps to save the motor and add more power smoothing. Here is a drawing of how it should look:

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Here's a picture of one of the diode protection boards I made to keep the flyback voltage away from my h-bridge. It's the little tan one on the left:

Most people building small robots with small DC motors will not have this problem. I'm running a couple small DC motors that turn my Radar and Ears and have no protection diodes. No problems with them. It the bigger DC motors that turn my robots waist and bend the hips that were blowing my H-Bridges. I suspect this has been the problem of a few people on this forum that has had problems with one side of their H-bridge not working and it not being a faulty product. Perhaps it was working properly till Flyback voltage took it out. Well never know though.

Hope this helps. Dave Schulpius

I just wanted to note that the 2.5A L298 motor control board we have in our store does include the flyback diodes, so you don't have to worry about back EMF voltages from your motors as they dissipate voltages up to 1000V.

While I'm here One thing I would recommend if you are using the L298 near it's current limits and finding that it is thermally shutting down is to use a lager heat sink on the back of the chip or a fan on the current heatsink to keep the L298 cooler. The L298 will be able to run as long as it doesn't reach it's internal thermal limit.