I have been thinking about this and I think that this could really take the vex system to the next level.
It would be about the size of the vex blue controller and would have its own power supply to switch the relays on and off. Each relay would have a pwm cable to connect to a I/O port. Obviously the programming kit would be required but its the only way.
I can see the relays being rated at 5amps at around 24vdc power. They should be pretty cheap if bought in bulk $1 a piece or so. It would be a simple device, you would output a 1 to that port to turn it on and a 0 to turn it off.
The vex system has a lot of potential in controlling other deices like motors, lights, solenoids, and so much more. Its just very hard to have to get the $10 motor adapter, and all the other little parts needed to get the I/O interface working. So its much more cost effective to offer this and people will be able to build more complex robots.
I would be willing to pay $50 to $80 for this because it would be an essential part to any vex system.
You could use another microcontroller but that would add only 8 more full powered motors (with signal splitter)… maybe these with pwm input but pwm or dc output?
I have successfully used 5v relays (coils driven with 5v) with the controller. If you know how to use any generic transistor such as 2N2222 to turn on a relay, this will be easy. Google for some circuits.
I have the design for the circuit, Quazar made it.
It uses a diode and a transistor with two output wires. Its a very simple circuit but I would much rather have a relay board so that you would have plug an play. Making it yourself works but I would prefer vex to make it. And you can only draw 5v at 30ma which is not enough to power a large relay directly.
Check out the Relay Boards that I built for my EarthBot aka GardenBot robot. I described the construction of GardenBot for an article that I wrote for Nuts & Volts Magazine, which was published in 2001. It is remotely controlled and can carry payloads of 185 pounds or more.
I am in the process of upgrading it by designing a gardening tool for it using Vex components. It uses two very powerful surplus Swiss 24 volt DC Geared Motors that are switched for steering and direction using the relays. It can seed the lawn and pull an electric lawn mower under remote control.
Some reasons why we dont use a TIP110/120 to drive a relay: its overrated. A relay typically draws 30-100ma (max?). A generic transistor (and cheaper) BC3__ or 2N____ series will suffice. If not enough current from the 5v supply, tap directly from the battery or throw in an extra LM7805.
One cool thing about the small relays is that you can use a DIP socket to hold it instead of soldering it directly to the PCB. I made one with stripboard, a drill and a soldering iron, a spare LM7805 (TO220 package with tab soldered to the board to drain any heat)
I use 24-Volt relays to switch the power to my EarthBot Aka. GardenBot robot shown in the VEX gallery. The schematic for the relay circuit is also posted in the VEX Gallery. This hardware configuration allows me to use two Ananda 40 Ampere motorcycle controllers to independently control two 24-Volt Geared DC motors using a VEX Controller and two PWM cables.
Its a bit pricey but has some nice interface options. There are cheaper alternatives on ebay that also looks very nice for the money. I found one that had 8 relays each with an led and transistor to amp the signal up from the micro controller all on one board for $35. That’s cheaper than the one from Sparkfun but it doesn’t have the interface options like the Sparkfun one does.
On another note I just found out something really funny about my Vex robot videos I made a while back. Specifically this one
While playing around with the video statistics on my youtube account I found out where my videos had been embedded and I was quite surprised. An online retailer has been using my video to demonstrate the basic autonomous capability of the vex robotics system in their product description
