Film-Tech Forum ARCHIVE: Direct Drive vs. Standard Drive?

This is topic Direct Drive vs. Standard Drive? in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.

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Posted by Carey Barber (Member # 1586) on 09-11-2009, 12:50 PM:

I have searched through the forums trying to find some info on the distinction between direct drive and standard drive projectors.

I got some sense of what this means, but could somebody give me a straightforward description of the difference between these two?

What exactly does it mean when we say that a projector is either direct drive or standard drive?

I also got the sense from other threads that some prefer one system over the other. Please enlighten me as to what you prefer and why.

Thanks!

Posted by David Zylstra (Member # 4230) on 09-11-2009, 02:55 PM:

For Century have a look at the R3-E soundhead manual (not the mag one) in the manuals section - page 17 shows the direct drive configuration where the motor drives the projector direcly and a shaft drops down to drive the soundhead sprocket. Page 38 shows the standard drive where the motor drives the soundhead sprocket shaft and a secondary belt off the same shaft drives the projector.

All the ones I ran or dealt with were standard drive so I have no perspective on preference.

Posted by Tim Reed (Member # 137) on 09-11-2009, 10:30 PM:

I always liked direct-drive, for simplicity and ease of service. Standard drive, however, is a little better on optical sound flutter, because the large drive pulley acts as a flywheel.

Posted by Louis Bornwasser (Member # 3063) on 09-12-2009, 06:39 AM:

While Tim is theoretically right about the flywheel effect of the large pulley, later ones were aluminum and minimized that effect.

We measured wow & flutter on about 30 Century soundheads and found that the direct drive preserved the positive effects of the Davis bridge, while the standard drive upset the bridge.

Main culprit is the tensioning roller that runs on the back side of the BE-529 belt. Unfortunately there is a lump on the BACK of the belt that introduces acceleraion & deceleration on the projector head.

Therefore, for critical applications, the direct drive "wins." (Both are way better than the sh1000/mi9030 due to offcenter gears on those.) Louis

Posted by Gordon McLeod (Member # 33) on 09-12-2009, 07:24 AM:

the older chain drive machines didn't have that lump on the back of the belt
I have found that the direct drive machines tended to shew up the main drive gear quicker
possibly because of the ration of speed reduction it had to do

Posted by Tim Reed (Member # 137) on 09-12-2009, 09:08 AM:

quote: Louis Bornwasser
We measured wow & flutter on about 30 Century soundheads and found that the direct drive preserved the positive effects of the Davis bridge, while the standard drive upset the bridge.

Well, this is good to know, since I really like direct-drives. [Smile]

quote: Gordon McLeod
I have found that the direct drive machines tended to shew up the main drive gear quicker

I thought that was just because I had more direct-drive machines! [Wink]

Fortunately, the 328 gear slips right through the bearing mount while on the drive shaft. [Big Grin]

Posted by Steve Guttag (Member # 268) on 09-12-2009, 10:44 AM:

The other problem with the standard drive machine is belt plucking as the gear belt engages and disengages the pulley. Heck, that alone has been the bane of Christie's design.

Century has also had problems in their machining...the bores for the bearings are not always concentric and often have too much slop in the bearing retainers. The lack of concentric bores will cause shaft binding and the slop can indeed cause the drum to not turn true.

The flex shafts for the direct drive have also been an issue for Century over the years...the rubber couplings eventually drink enough oil to swell up and fail. The spring shafts get deformed and fail...I haven't had as much problem with the current helical design though. Note, any slop in the flex shaft comes off of soundhead stability too.

I would say that the standard drive would have some issues from loading due to the fact that the main drive gear now has to power the soundhead and possibly a lower reel. However, its gearing (Ratio) is probably a bit more in its favor than the standard drive.

Steve

Posted by Mark Gulbrandsen (Member # 72) on 09-12-2009, 11:01 AM:

quote: Louis Bornwasser
We measured wow & flutter on about 30 Century soundheads and found that the direct drive preserved the positive effects of the Davis bridge, while the standard drive upset the bridge.

Then something is seriously wrong with the drive if the Davis can't compensate for it. There were also alot of tolerance issues with the Davis parts in many Century reproducers over the years. Too bad that Strong did not adapt the round tooth belt drive to the Century as they did to the 5 Star as it would have been the best of all of them.

Mark

Posted by Steve Guttag (Member # 268) on 09-12-2009, 11:30 AM:

Actually, they did...the current strong belt is a fine pitched round tooth.

Steve

Posted by Mark Gulbrandsen (Member # 72) on 09-12-2009, 11:40 AM:

Yea, but is the pulley alumnium or steel?