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BFD unit, M-One motor slipping


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#1 Lars Erik

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Posted 14 February 2008 - 06:38 AM

Hey all,

I own a BFD unit w/ M-One. Did a shoot with Arri UltraPrimes. 16, 24, 32, 50mm.

Sometimes the engine slipped a bit. Causing the markings on the T/x be unaccurate.

I used the 0.8m - 32 P ring for the lens.

Has anyone experienced this before?


LE
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#2 Robert Starling SOC

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Posted 14 February 2008 - 09:49 AM

I own a BFD unit w/ M-One. Did a shoot with Arri UltraPrimes. 16, 24, 32, 50mm.

Sometimes the engine slipped a bit. Causing the markings on the T/x be unaccurate.


Hi Lars, are you saying the contact point between the motor gear and focus gear is slipping or that something "inside" the motor or control mechanism is slipping?

I've occasionally had some slippage with lenses that are very tight or stiff if I have not "torqued" the motor onto the lens enough, especially when using just a set of rods w/o mattebox or a worn out set of rods on rental camera and the rods flex a little.
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#3 JimBartell

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Posted 14 February 2008 - 11:13 AM

The four most common causes of this are:

1. Mechanical mounting: Either the motor "jumps a tooth" where it mates with the lens gear ring or the motor slides or torques where it is attached to the camera.

2. Calibration knobs: If someone bumps the calibration knobs on the receiver all the motor marks be off.

3. Motor pot slippage: If the potentiometer in the motor gets stiff & hard to turn it will slip relative to the output gear. If this is the case the error will continuously worsen as you turn the lens.

4. Transmitter pot slippage: If one of the gears inside the transmitter becomes loose the marks will change as you turn the transmitter knob.

Problems 1 & 2 can be fixed in the field, 3 & 4 require retuning the piece of gear to the manufacturer.

Jim "slip slidin' away" Bartell
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#4 Lars Erik

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Posted 14 February 2008 - 11:25 AM

Hey Jim & Robert,

I would say that the problem was the first troubleshooting Jim mentioned. Mechanical mounting. I had to push the motor hard onto the lens not to slip. But this is "normal" then I guess? The solution would be to "torque" it more? Is that it? Just pushing the motor harder onto the lens?


Lars "always tryin' to keep it in focus" Erik
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#5 Dan Coplan

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Posted 14 February 2008 - 11:36 AM

I have occasionally had to wrap a bongo tie around the motor to keep it snug against the lens. This is more of a necessity when the rod to which the motor is mounted is loose or several brackets are used to get the motor in the right place offering less overall stability.

I have a dogbone for all my camera plates to insure the rods coming off the plates are rigid.

Dan
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#6 RonBaldwin

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Posted 14 February 2008 - 12:22 PM

Jim -- you mentioned "pot slippage" twice in your response. And it's not even 10am yet -- sweet.

the problem we've had is rarely with the motor, but with the rod either flexing or not able to be tightened enough to keep itself from spinning (mainly the panavision mb rods). I was thinking of asking Tom Gleason to make a dogbone to go between the two pana-rods so they won't spin. This rod issue has been a huge headache for my assistant and a time waster.

Ron "having a problem with my rod and Jim's pot slippage" B
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#7 Robert Starling SOC

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Posted 14 February 2008 - 12:51 PM

I have occasionally had to wrap a bongo tie around the motor to keep it snug against the lens.


Great suggestion Dan... I knew I bought a bag of those things (bongo ties that is) for some reason... at least it's not "pot slippage" which sounds like something that a production accountant turned dealer would create to improve his bottom line.
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#8 Joshua Harrison

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Posted 14 February 2008 - 01:52 PM

There is a (not so well known) problem with the m1 motor mount. I'm not sure if it's been fixed but mine and others I've seen do this. You can flip the side of the m1 to put the mount on either side of the motor. This will pull the motor away from or push it towards the lens depending on what side you put it on. Test this by putting the motor on a rod and slowly tightening the knob. You will see which way it goes, by flipping the mount onto the other side it will do the opposite. So attempt to mount the motor by having it on the side that will push towards the lens or get the dog bone (I think supplied with the motor) and tighten the motor and then use the dog bone to lock into place on the lens. Again this could have been fixed by now or may not be your problem but something to try out.

Joshua Harrison
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#9 Lars Erik

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Posted 14 February 2008 - 03:56 PM

Hey guys,

thanks for all the tips. Appreciate it.

LE
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