Bolex H16 1:1 Drive Shaft - torque

[carllooper]

Does anyone know the torque of the 1:1 drive shaft on a Bolex H16 (Rex5)?
Or have a torque gauge, and a Bolex they can test, to see what that torque might be.

Carl

[JeremyC]

Thanks for asking this question I would like to know it as well as I have a 1:1 bolex H8 Rex plus a motor and plate to fit the motor onto the side of the camera but I need to put together the rest of the bits to drive the motor at the right speed/torque for the camera so this would be a great help if anyone knows it.
I also have a 8:1 shaft Bolex H8 so the torque for that would be great as well.

[carllooper]

I'm going to acquire a torque gauge in a couple of weeks time, so will be able to answer the question then.
I'll measure both the 1:1 shaft and the 8:1 shaft. I've only got an H16 though ... I assume the torque will differ somewhat from an H8.

In terms of what motor rating would be required to drive a Bolex, the only online info I could find (so far) was this site:

http://sparetimelabs.com/animato/animat ... bolex.html

where he's using a 6 watt 24 V AC motor (that needs 0.25 Amps) to drive the Bolex.

Carl

[bolextech]

The only specs that comes close to what you are describing is the resistant torque of the mechanism.
This is measured on the 8:1 shaft and should be no more than 320 grams.
This is the mechanism's internal resistance to movement.
If it is higher than this value, the motor will have difficulty maintaining a constant speed and the speed will slow down unacceptably during the run cycle.
It it could be measured through the 1:1 shaft, it should be considerably less.

Cheers,
Jean-Louis

[carllooper]

The only specs that comes close to what you are describing is the resistant torque of the mechanism ...

Thanks Jean-Louis. That diagram is useful. I've got a force gauge here.
Following the same idea in the diagram I can get a good idea of the
torque using the force gauge on a pulley pivoted to the shaft.

cheers
Carl

[carllooper]

I need to put together the rest of the bits to drive the motor at the right speed/torque for the camera so this would be a great help if anyone knows it.

The speed side of the equation is easy enough. For 24fps, the 1:1 shaft needs to rotate at 24 rotations per second, and on the 8:1 shaft, at 3 rotations per second.

For a stepper motor application, based on purely ad hoc tests I'm doing with a force gauge on the 1:1 shaft, I reckon you could get away with anything capable of 100g-cm torque or better

For example, I reckon almost all of the stepper motors listed here would be more than capable
http://www.phidgets.com/products.php?category=23

Of technical interest is what the smallest motor required would be, to do the job. Could a 30g-cm motor do it? For that I need to do a much more fine tuned test on the shaft.

Carl

[carllooper]

I tested the torque on an Elmo K100 Super8/Standard8 projector.
I found it requires more force to rotate the shutter shaft of the Elmo projector than it does to rotate the 1:1 shaft of the Bolex.

The Elmo I tested produced a peak torque of 540g-cm.

I've yet to set up a proper test on the Bolex. I have to get the mounting right if I'm to get a good test.
On the Elmo it was easy.
All I had to do was just wind some string around the shutter wheel and pull on that with the force gauge.
The radius of the shutter wheel was 2.7cm and the force required to rotate the wheel peaked at 200g.

So Elmo torque = 200g x 2.7cm = 540g x 1 cm

Carl

[MovieStuff]

To a large degree, the torque is less important if you are not trying to use the Bolex in "running" mode where the shutter makes the exposure. As I understand it, you are going to essentially stop the Bolex with the internal shutter open and let the PC create the exposure. In this case, any cheap Dayton gear motor that moves as slow as you probably desire for the duty cycle of your process would have more than enough torque. If you were using the internal shutter to create the exposure in continuous run or for animation purposes, then the torque, particularly the start up torque, is critical to prevent getting flicker from uneven exposures. But the way you are employing it, just use a small gear motor and you are good to go.

Roger

[carllooper]

To a large degree, the torque is less important if you are not trying to use the Bolex in "running" mode where the shutter makes the exposure. As I understand it, you are going to essentially stop the Bolex with the internal shutter open and let the PC create the exposure. In this case, any cheap Dayton gear motor that moves as slow as you probably desire for the duty cycle of your process would have more than enough torque. If you were using the internal shutter to create the exposure in continuous run or for animation purposes, then the torque, particularly the start up torque, is critical to prevent getting flicker from uneven exposures. But the way you are employing it, just use a small gear motor and you are good to go.

Roger

Thanks Roger.

Yes, it's for animation purposes. The proof of concept one I've been using is fine but I want to replace it with a small one, or rather, the smallest one that can still drive the camera, ie. without having to buy too many motors to find out which. Last year I tried a small motor on the Elmo and it didn't quite have enough grunt, so I just got a big high torque one that would do the job (the better safe than sorry approach) With respect to the Bolex I'm re-designing the camera mount so that it's more user-friendly, portable, and easy to setup.So looking to find what the most lightweight solution would be that won't have me going back to the motor shop

Last week I mistakenly acquired a force gauge to test the shaft (not thinking) and realised I'd need a torque gauge instead. But looking at Jean-Louis diagram I realised torque can also be measured with a force gauge - using pulleys. In the Elmo it effectively has it's own pully (because the shaft is belt driven), so some simple string did the trick. For the Bolex I just to have finish making a proper pully for it - which is my mission this weekend.

C

[David M. Leugers]

I don't know the torque value, but I do know that the H8 requires a higher torque than the H16 to run the camera at 24fps sync speed.

[JeremyC]

I don't know the torque value, but I do know that the H8 requires a higher torque than the H16 to run the camera at 24fps sync speed.

Interesting.