PDA

View Full Version : Home made Arduino robot - crawler/tank



jaosef
05-07-2013, 04:43 PM
Just finished the code and I'm finally happy with the performance.
Most of the parts are bought from ebay, low budget build.
http://s23.postimg.org/v310egpqj/2013_05_07_16_35_41.jpg


https://www.youtube.com/watch?v=YblSltHDbIU

CasperH
05-09-2013, 03:59 AM
I think it's cute. :o The video was very explanatory.

Any particular reason why you decided to build your own h-bridge instead of buying an off the shelf part?

hwan we
05-09-2013, 06:00 AM
Very well made ​​~
clean and good design.:o

jaosef
05-10-2013, 02:09 AM
I think it's cute. :o The video was very explanatory.

Any particular reason why you decided to build your own h-bridge instead of buying an off the shelf part?


Very well made ​​~
clean and good design.:o

Thanks guys! The reason i built my own H-bridge is mostly because it's more fun than buying it of the shelf.. And I was afraid the ready-made h-bridges would not handle the current. They are often rated between 1-2 amps, and the one I made can handle up to 10 amps.

jwatte
05-10-2013, 12:33 PM
I was afraid the ready-made h-bridges would not handle the current

Actually, some of those are just intended to provide gate current for big MOSFETs to deal with whatever current you want.
The reason they need a full amp or more is that powerful MOSFETs need really quite a lot of current very quickly to switch on or off.

I can't see much of your circuit board; it looks like maybe you're using pull-up resistors to turn on P-channel and off N-channel, and then use a smaller transistor to pull to ground for the inverse? If that's what you're doing, you're current limited on the pull-up resistor value. Looks like maybe 100 Ohms? If so, then I would expect (based on experience!) you can do OK with Arduino-level PWM (400 Hz or so) but if you try to raise the PWM frequency, you'll start blowing the MOSFETs.

jaosef
05-11-2013, 03:38 PM
Actually, some of those are just intended to provide gate current for big MOSFETs to deal with whatever current you want.
The reason they need a full amp or more is that powerful MOSFETs need really quite a lot of current very quickly to switch on or off.

I can't see much of your circuit board; it looks like maybe you're using pull-up resistors to turn on P-channel and off N-channel, and then use a smaller transistor to pull to ground for the inverse? If that's what you're doing, you're current limited on the pull-up resistor value. Looks like maybe 100 Ohms? If so, then I would expect (based on experience!) you can do OK with Arduino-level PWM (400 Hz or so) but if you try to raise the PWM frequency, you'll start blowing the MOSFETs.

You've got a point, buying ready-made h-bridge and using a MOSFET would probably be the easiest way. In this H-bridge there are no MOSFETS though, only NPN and PNP -transistors. I dont think the pwm-signal will damage the npn-transistor, but I guess one could make a low-pass filter if it becomes a problem. The high current does not pass through any resistors along the circuit (except the motors themself). It is more or less the same circuit as this and it seems to perform nicely;
http://wilf.solarbotics.net/PSHbridge/PShbridge.gif