1. Check that you are using fresh batteries. Weak batteries will decrease the range.
  2. Verify that the problem is with the cart instead of the receiver by methodically switching between different combinations of carts and receivers. If the problem follows the cart(s), it could be a mis-aligned or damaged LED.

If students mistakenly connect a power supply into the hole where the encoder cart IR LED emitter is, you can damage the emitter and push it out of line. Look into the IR emitter hole (below the stripes on the end of the cart) to see if it looks the same as a working unit.

In one case, we found that students were used to plugging in the WDSS (mounted to the top of a cart) to power. They were pushing the power connector into the recessed LED hole and damaging it. If you look at the IR emitter, it should be centered. If not, re-align the infrared LED with tweezers.

Be sure that you are looking at the IR LED instead of the blue light.
 
 
 

See also:
Motion Encoder System Troubleshooting and FAQs