If you own a Vernier Cart and Track system and wish to update to use the Go Direct® Sensor Cart (GDX-CART-Y) and Go Direct® Sensor Cart (GDX-CART-G) you will need to purchase the Go Direct® Sensor Cart Accessory Kit (GDX-CART-AK) in addition to the Go Direct Sensor Cart. One accessory kit is adequate for two carts.
Depending on the vintage of your existing cart and track system, you may also want to purchase the Pulley Bracket (B-SPA). The older models of this bracket had a center slit that was closed with a v-notch at the top. The Pulley Bracket has been redesigned with a longer slit that is open at the top to allow the pulley to be positioned lower. This allows a string attached to the force sensor hook on a Go Direct Cart and draped over the pulley to be parallel with the track. This provides the best alignment between the cart and the pulley in a half-Atwood experiment.