I'm trying to create a bot that uses a lot of forward/backward motor action, and I'm hoping to make a low-power, small, lightwieght motor control using switch transistors. However, my electronics experience is -5. I came up with this idea that seems simple and effective, but I'm sure there's something I don't understand about the process. So with that in mind, here's my ultra-simple H-bridge.
The idea is that both "A" transistor bases are connected to one outpin, ditto for both "B" transistors. Obviously, I'll need some resistance along the way. But could something this simple really work?
In one of my previous In one of my previous classes, we made a forward/reverse motor driver. Of course it was on a larger scale (driving a car antenna motor) we used relays that were used in the EXACT same way. The concept is there, that is for sure! So i’d say with a little work it could be very effective. But im no genius at electronics.
More BEAMish A direct link to the h-bridge starter page mentioned above. One thing that needs to be considered before making a driver, is the requirements of the motor(s) to be driven.
beam library, who knew? that’s some good stuff. I hadn’t even thought about the “smokeproof” factor. That changes my approach a great deal (meaning: break down and just buy an IC). How do you use a 555 for an H-bridge?
I know -6 about electronics, so what I do is to hook up 4 relays. It is very easy, there is no loss in power, and you can chose whatever power you want for the motors.
Let me know if you want more info. It is used on the wall racers!
More info is always a good thing This bot i’m working on probably won’t be BEAM, but it will be very light and lean, so if i can use up less space and weight than an L239, I would be down. Plus if I get smoke, I’m only out a few transisors and not the motor, right?
to avoid the smoke factor to avoid the smoke factor you could do something like this: make the top motors PNP and the bottom motors NPN, then connect the motors on the left to the same output A and the ones on the right to the output B. This way you can be sure that transistors on the same side won’t be on at the same time. One problem about this setup is that, unless you disconnect the wires to your transistors, you won’t be able to coast the motor.
The first setup i posted or The first setup i posted or the second one (same but with PNP at the bottom) should work fine if, instead of BJTs we used FETs right? With p-channels substituting the PNPs and n-channels substituting the NPNs. There would be no shorting since the gate of the MOSFET is isolated from the source and drain.
Might be a good idea to do a bit of a search, and see if anyone has got a working NPN over PNP or even NMOS over PMOS h-bridge out there. There are a number of schematics on the web, some working, some not, and even devices with a couple transistors manufactured together to make P over N devices, not the other way around. Generally PNPs are on the topside next to the supply they switch off of, and NPNs are near ground which they switch off of; just as P channels FETs are near positive and N-channel are near ground. Just sayin’, may be fixing the switching problem in a wrong way.
Now by all means experiment if possible, and maybe there might be something new that hasn’t been developed before. Might even be a pretty cool solution that does actually allow things to work better than has been thought of before.
