RCX 1.0 Motor back-EMF measuring

[Urrakka]

Hello,

I've been learning how to program a RCX 1.0 brick using lejos to hopefully help my community college teach a range of programing classes. I've been having lots of fun building robot designs and programming them accordingly.
All I have to use is a 217 piece "Mindstroms for Schools" set.

I quickly learned that the touch sensors aren't very sensitive and that the light sensor is extremely versatile. It's a shame I only have one. I've successfully programmed the bot to avoid obstacles with the proximity sensor. The bot mindlessly runs around great but the only catch is the motors may stall from time to time on an object. Or the bot is easily foiled by carpet in which again the motors stall.

Is there any way to have the RCX recognize this stall?

I've been searching all around and I'm afraid I can't do this without purchasing extra sensors. I'd like to avoid this and see how far I can push the limits of this 217 piece set. Being able to do something meaningful with the back-EMF is like the holy grail to me. It would solve quite a few problems.

I've even attempted to attach a lead directly from the motor port to the sensor port. While I can read the load on motor (0 spinning free 100 loaded/stalled) I can't do anything useful with this as I lose functionality of either forward or reverse.

This is my last resort. From what I've learned after a few days of research all signs point to NO. But I am hoping that just maybe someone else can provide a bit more information on why I can or can't use the stock pieces to detect back-EMF and have the bot free itself from a jam.

Thanks.

[mdsmitty]

I've used rotaion sensors in the past to check for stalls. set the value of the sensor to a variable wait a few and compare. if its not staled set the variable again and keep going.