How to add limit switches to VEXplorer...


Every time I let a new driver loose on my VEXplorer, they have to go through the learning curve of how to avoid stripping the arm gears. Without an arcade-style mix mode, you have to use tank-style driving. The problem is that one of the joints has to be assigned to a horizontal joystick axis, and this tends to gradually drift since they can’t keep the stick centered horizontally while driving. It takes some practice to notice what is going on and correct it. (Hey, what does that “pop pop pop” sound mean?)

My solution? Add limit switches! This is a bit more involved than my usual half-page projects, so I’ve put up a website for this (and future) projects. I still have to work out where to mount the limit switches, but the circuit itself is all worked out.

You have to make a simple mod to standard VEX limit switches (they still work with VEX afterwords), and you have to build an adapter that ties the motor and limit switches together.

Since VRC isn’t programmable, I thought it would be nice to push the envelope a bit in what you can do with it. Check it out and let me know what you think!


  • Dean

[EDIT] I just noticed the VEXplorer Discussion sub-forum. This thread should probably be moved there. [/EDIT]

Great Idea…

I had noticed a year or so ago, that the Limit Switches seemed to be both NC and NO. I was thinking of re-wiring the Switch so that the normal mode was to be pressed, and trigger when release (the opposite of how it is normally used)

(Again, I say) Nice Graphics… Clean, Neat, Clear (I’m envious, no Mac)

Yep. The other neat trick you can do is to flip the switch in the housing so that you have limit switches that are a mirror image of the normal limit switch. I’ve done that to a few of mine and it comes in handy sometimes.

Thanks! I’m continuing to build up my library of photo-realistic parts, but it does take a while to get each one to look just right. I am not an artist (more of a craftist) and I’m not really using the right software, but it seems to come out OK.


  • Dean

Finally the macs are in control, hmm? :slight_smile:

Its a really nice site. of course the current mods are no use to me yet as I don’t have a vexplorer.

would this work with vex if you changed the dc cables to pwm and then sent a signal in some way to the motor… i know this would be somewhat pointless, but hey, it frees up two sensor ports…


This kind of limiter only works on DC motors where you reverse polarity to change direction, so you can’t use it directly on PWM control signals.

It would work with the PWM->DC Motor Controller, though, so you can use it with the VEX that way.

If you are good with solder, you could remove the heatshrink over-wrap from one of those and add this circuit directly to the output, basically combining the controller and limiter into a single package.

True, but it also means you don’t have to add the limit switch logic to your program. There is no way for a programming error to cause a limit switch to be ignored. On the downside, there is no way for the software to know the limit switch has closed. Depending on exactly what you need, that could a plus or a minus…


  • Dean

yep, i was thinking that later

My Microchip dsPIC30F6014 Sensor Controller Board collects sensors for my Gilbert IV Explorer robot shown in the Gallery and can also be used on my Vexplorer robot. It reports the sensor readings including GP2D12 Sharp IR Ranger readings and Freescale XYZ accelerometers using its 12-Bit Analog to Digital Converter (ADC). In addition it can also read and de-bounce the Vex bumper switches and limit switches that I have mounted on the front and rear of the robots.

The Sensor Controller firmware is written using Microchip MPLAB and C30 C and programmed using the ICD2.

The sensor telemetry from the Gilbert IV Explorer or Vexplorer Robot is transmitted back to my remote laptop using an XBEE Pro Wireles UART (WiFi) at 115200 Baud using its two UARTS. Even though the Vexplorer is currently not programmable, the feedback I get from the sensor telemetry allows me to detect objects that are not in the field of view of the wireless video camera so that I can use the Vexplorer joysticks to avoid it, thus increasing the field of view.

hello. good idea with the limit switches. I, for one would have flipped the vexblue with the vexred. I have had the same pop pop poping noise.
I studied this. It is the motors being told to move ever so slightly even though you dont touch the conroller. I have no Idea how to fix this on vex blue but vexred is easy.

Yep… VEXblue does not have trim adjustments, so you either need to keep an eye on the moving parts, or you need limit switches.


  • Dean