Pells are an incredibly useful tool for training. Creating muscles memory through repetition, the ability to ascertain the precision of your strikes etc. Here are two good sites for building one.
A simple Pell
very portable pell
Here is the one I made today.
Here is something valuable that you can make for solo practice!
Not to crossover into training too much but when using a pell, be sure to work slowly at first, getting good form, and using good structure. Then work on speed, not hitting hard, just good form, and faster. Then you can play with power, vary it between light medium and hard hits choosing which you want to use. That way you can calibrate accordingly depending upon the protection your partner is wearing and such.