Shinai weigh up to about 510g and the PVC lightsaber will be around 726kg, rounding up.
Shinai weight: 47" length
http://www.e-bogu.com/Shinai-Kendo-Bamboo-Sword-s/18.htm
PVC Weight: 1" width x 4' length
https://flexpvc.com/Reference/PVCPipeSpecsRigid.shtml
Note: This does not include electronics or buttons or batteries, but assume another foot of PVC weight, balanced just below the cross guard medium.
