Wednesday, April 28, 2010

High Current Motor Controller Shield Load Test

First off, I got my stackable headers in the mail today. They are Samtec SSQ .1" pitch square tail sockets, with tails about .39" long. I got my headers in 50 pin strips and cut them to size. If that isn't your style you can always buy stackable headers from SparkFun in the 8 pin and the 6 pin variety. Why the stackable headers? An xbee shield is on its way to me as we speak. Here is a pic of the motor controller shield with the stackable headers!

(Note, I also populated the programming header with a double row stacking header to keep compatibility with the original xbee shield)

Next, it's time to put the high current motor controller shield to the test! The plan, hook the shield up to a motor, stall the motor, see how the vnh2sp30's handle the heat, and see if my thermal management was good!

The result? They worked splendidly! When I stopped the motor, it drew 21 amps for an extended duration. The shield got a warm to the touch, but kept on going.

One last note, keep checking back, because the High Current Motor Controller Shield may soon find its way in a store near you!

Wednesday, April 21, 2010

Treaded Platform

I got my hands on a treaded robotics platform the other day. Treaded Platform from RobotShop

This is a perfect platform for testing the high current motor controller shield. More to come, including code and schematics!

Tuesday, April 13, 2010

Tuesday, April 6, 2010

Going gEDA

That's it. I'm transitioning to gEDA from Eagle. Why you might ask? Is it because I am a OSS dork that thinks that anything open source is better? No. Does gEDA have features that make it significantly better than Eagle? No. I like Eagle. There is just one problem. It is expensive.

Eagle provides a great service to hobbyists and students, or anybody non profit by making a free version for non-commercial use. I, however, want to start selling my designs. I probably won't make enough money to justify the truly expensive commercial version of Eagle.

So, long story short, I want to be legit! Expect a comparison of gEDA/PCB and Eagle in a month or so.

Sunday, April 4, 2010

High Current Motor Controller Shield in Action!

A video was promised, here it is!

High Current Motor Controller Shield for the Arduino

I've decided what to call it.  It will now be known as the High Current Motor Controller Shield for the Arduino.

Electrical Specifications

Recommended operating conditions:
Voltage input:7-12V
Continuous current output:15A
Peak output current output:30A

Absolute maximum operating conditions:
Voltage input:6-20V
Continuous current output:15A
Peak output current output:30A

Check out the datasheet for the VNH2SP30 for more specific information.

In short, though, the VNH2SP30 has some nice safety features. It features the following safety measures:
  • Undervoltage and overvoltage shut-down
  • Overvoltage clamp
  • Thermal shut down
  • Linear current limiter
  • Cross-conduction protection
  • Protection against loss of ground and loss of

The Skinny

Overall, these are very nice resilient chips that are designed for automotive uses. They feature a current sense allowing control loops to try to drive motors with a constant current (also meaning to some extent, constant force).

In the documentation for the VNH2SP30, ST provides ideas for ideas for controlling up to 3 motors with 2 of these chips. Because each chip basically consists of 2 high and low side switches, with separate inputs that force half of the bridge into high impedance, the VNH2SP30 is extremely versatile.

If you do the math, you can safely match the high current motor shield to 2 180W DC motors, or to 1 360W motor! Even better, you can stack these shields to expand capability.

Let me know if anyone is interested in purchasing these items. In larger quantities these could be sold for around $50 to $60 dollars. I originally made these because I could find nothing good that existed between the motor controller shield and the OSMC

Similar Boards

After some digging, I found out that Pololu actually sells something similar to this, and that SparkFun sells a serial enabled version for a little more. The main differences are that they include the reverse voltage protection FETS mentioned in the app note, they have holes instead of pads, and they don't fit nicely on the Arduino. In my experience a big fat pad can be more useful than a hole. For example, I have soldered Dean's Ultra connectors to the pads. Dean's Ultras can handle loads of current, and are polarized, thus helping to protect against reverse voltage.

Regular terminal blocks could be soldered to the pads as pictured.
Hirose DF5 series connectors also work with the shown pads.

Update: A video has been posted here