Mtripp, would you consider posting a short list of common throws divided by the categories you've mentioned. I think it's something I'd find quite helpful.
Take two foot techniques that are similar(ish) in action, but rely on totally different principles to work.
De ashi barai and Ko soto gari.
This video shows De ashi barai:
YouTube - Osawa Sensei: De Ashi Barai
Its in Japanese, but you don't need the sound to understand whats going on.
De ashi barai works by taking out the foot of the person you trying to sweep as they're trying to transfer their weight onto it. Think of it this way, ever been walking down the stairs in the dark and thought there was an extra step when there wasn't and fallen over? This is exactly how de ashi barai works. When we step forward there comes a point when the weight is all on the planted foot and there comes a point when all the weight is in the advancing foot, just before you plant the advancing foot on the ground. Just the same as when you fall down the stairs, you expect your foot to touch ground and all your weight is being focused into that point. If that ground isn't there all of a sudden, its too late your weight is already committed and you will fall.
De ashi barai works like this, but instead of the ground being lower than you thought it was in the stairs scenario. The person doing the throwing replicates this by sweeping your foot forward just as you expect to plant your foot. Alll you weight is already committed to this step and when you can no longer make it because your foot has been swept away you fall over.
This is easy to see for yourself, try doing de ashi barai a moment too early and the person stepping forward still hasn't transfered their weight fully and you just end up hooking their leg into the air and them hopping about. A moment too late and you just end up kicking a solidy planted foot, which doesn't move.
This video shows Ko soto gari
YouTube - ko soto gari
Ko soto gari works by reaping, note not sweeping, out a foot which has all of the persons weight on it. ALL the weight must be concentrated on that foot if it is evenly distributed between the feet, you will just lift their foot off the ground and they will hop about. If reaping their right foot the weight, preferable is 100% on the right foot, you can get away with 90% on the right and 10% on the left or if you have a really strong reaping action 80% on the right 20% on the left. But always aim to get as much weight on the foot being reaped as possible.
If you watch the last few seconds on the video I posted you can clearly see that the person being reaped has his left leg off the ground. This means 100% of his weight is concentrated in his right leg, so when it is reaped from underneath him. He has to fall, there's no other option he has no support for his bodyweight. Think of it like this, if i do a sidekick and you manage to catch it/ trap my leg with your arm against your side. The only thing stopping me falling over is my other leg, if you kick that out from underneath, well down I go. This is how Ko soto gari works.
Foot throws ending in barai/harai always rely on sweeping a foot just as weight is about to be transfered onto it. Gari always refers to reaping a foot when all the weight is planted on it and little to none on the other foot. Now if I were to use the Geoff Gleeson 'sweeper' terminology to describe both throws you wouldn't understand the important differences in weight distribution that are vital to making them work. So the sweepers, rollers and drivers idea. Is too simplistic and means you end up missing really important points about throws that you don't IF you understand why different Japanese words are used and when.
There are 6 major groups nage, otoshi, guruma, sasae, harai and gari. However, its not that simple, that is in part why Geoff Gleeson wrote about drivers, rollers etc... in his book because, there is no easy way to divide up the throws and still pass on all the important info, but by oversimplifying you miss masses of really vital technical detail.
The problem is that the throws are loosely structured and some are taken from old Jujustu others were devloped by Jigoro Kano etc... This isn't particularly helpful to a beginner, but its the way it is.