I can happily grow mungbean sprouts of the length for use in sandwiches (or, if you're my kids, fighting over while they're still in the sprouter) but have signally failed to grow them long enough for use in most East Asian cookery. I'm bookmarking this link in the hope that it will help me solve the problems I was having. I've never weighted them while growing before, for instance.
It inspired me to do some quick salad sprouting with the kids today. We inherited a three level sprouter from my Dad which is probably at least 20 years old. Although it's the kind which should be used with disposable filters for the smaller seeds like alfalfa, I never use them, and so long as I drain them well enough they're usually fine without. I couldn't find any mungbeans, but I did have a new bag of alfalfa and an old jar of fenugreek, alfalfa and mustard combo, so I did a tier of each. The mixture may be too old to sprout: we'll see in a few days.