Just curious… The H-bridge chip on the Baby-O does tend to get hot when in use?
I’m running two GM6 motors with RW2 wheels on them, but otherwise unloaded (they’re just sitting on the bench with the wheels up in the air). The H-bridge chip gets hot enough I have a hard time keeping my finger on it.
I know it’s got thermal cut-out, but I wanted to be sure I wasn’t doing anything really really bad.
Nice to see some forum participation from Waimea (I grew up there and got a lot of help from CFHT engineers)!
The motor driver power dissipation will be proportional to something between I and I^2, so the more current your motor draws, the hotter the driver will get.
However, the GM6 motors should not draw enough to make the motor driver too hot to touch. Perhaps you are using too high of a voltage (keep it under 9V) or too high of a PWM frequency (under a few kHz is better). Keep in mind that the Baby Orangutan has a mega48 or mega168 with 20 MHz crystal, while code you see for other AVR-based projects might be running at 8 MHz (internal oscillator) or 16 MHz (many AVRs don’t go faster).
Hey, I just showed this to Grant Matsushige. He’s told me all sorts of good stories about you, and when I mentioned your name he was seriously stoked! It’s certainly a wonderfully small world.
What you said about PWM frequency makes lots of sense. LOTS of sense. I’ve run into the 20MHz vs. 8MHz and slower clock frequencies in a couple of places already, but hadn’t made the connection with heating on the motor driver. It makes perfect sense, though, since most of the heat is going to be generated during the switching event. More switching, more heat.
Yay! This gets me back up and running. Time to plug in an oscilliscope and see what exactly is happening.
Thanks a ton!
It sure is a small world. Please say hi to Grant for me.
You hit it right on the nose.
The PWM setup I was using was doing about 24us between pulses, or 41kHz. Switching from clock/1 to clock/8 made things a lot happier. The motors work, the chip stays cool, and everything’s happy.
Grant says hi, too.
I am having a similar problem:
My Baby orangutan b-168 chip was working fine until recently. I am building a balancing robot for my physics ISU. The chip was fine before, it didn’t get hot at all, but recently the H-Bridge has been getting way too hot, even when no motors are plugged in. I tried changing the speed from 20 to 8 MHz, and I am pretty sure that is on clock/8:
// use the system clock/8 (=2.5 MHz) as the timer clock
TCCR0B = TCCR2B = 0x02;
I cannot figure out what’s wrong. If it helps, I am using the Tamiya double gearbox, and I have tried using a 9V and a 4-1.5V AA’s.
Any help would be gratefully appreciated, and as I said, i’m on a tight clock because it’s due soon.
Unfortunately I think you have probably broken the H-bridge on your Baby Orangutan. The Tamiya gearboxes have stall currents around 4 A, which is well above the 1 A/channel rating of the Baby Orangutan H-bridge. Though the H-bridge has thermal shutoff protection, it is not enough to protect the IC from such large current spikes. The typical mode of failure we have observed in such situations is that one of the H-bridge MOSFETs breaks, causing motor control signals to short power to ground in one of the states (this is why the IC gets hot even with no motors connected). It sounds like this is what has happened to your Baby Orangutan.
One possible option is for you to send your Baby Orangutan back to us so we can replace the motor driver chip, but I don’t know if your schedule will permit this. Please contact us to get an RMA number if you wish to pursue this course.
Another option is for you to disable your motor driver code or otherwise put the motor driver IC into a state that isn’t drawing power and use your Baby Orangutan to control an external motor driver that is capable of delivering as much current as the Tamiya gearboxes demand.
That is very unfortunate, I don’t think I have the time to get it repaired, and even if I did, I still wouldn’t be able to use the gearbox… so on to plan b, I got some Innovation first controllers from the first robotics competition so I’m going to try them. Thanks for your prompt help.
if I’m just running the motor either on or off, no PWM, I shouldn’t have to worry about the frequency thing & the motor getting too hot, correct? (assuming I run the proper amps and volts)
The heat problem described in the opening post was the result of using a PWM frequency that was much higher than the motor driver could handle. You have a newer revision of the Baby Orangutan that uses a different motor driver and would not experience the same shoot-through problem. To answer your specific question, you generally don’t have to worry much about shoot-through if you aren’t using PWM speed control, as shoot-through current spikes, if they exist, occur every time your H-bridge switches (so the heating is proportional to your switching frequency).
Note that you still need to make sure you avoid overheating caused by your motor drawing more current than the driver can deliver, though.