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Arri cForce Plus motors compared with Preston´s

Arri cForce Plus motors compared with Preston´s

Saul Oliveira

Hello there!

Did you have a change to compare Arri Cforce Plus motors with Preston motors (speaking about Focus channel) in terms of power and speed?

If yes, what are your conclusions?

Best regards, hope everyone is ok

Saul Oliveira
First AC

jeffrey truong

I own a DM1x, cforce plus, cforce mini and used to own a heden 26Ve. I have also used the RTmotion motors, cine gears, clm-4 and clm-3 but only a handful of times.
The DM1x is a world of difference in terms of speed, size and responsiveness that isn't be matched by the others but gosh it's darn heavy. There are some focus timings where you can only do it with a DM1x. Especially when shooting slow motion. You've got to pay close attention of which torque you use. Many rental houses here have had some lenses damaged from focus pullers using them on high torque for low friction lenses, please be very careful with it and always re-calibrate when putting it back on a lens.

Cforce plus is my usual go to when I have older lenses like mk3 superspeeds. The sort of lenses where if you had a manual follow focus you'd have to pay a little bit of attention to changing the frame if your operator was handheld.

The mini is good for newer smooth lenses like master primes. The sort where if you were handheld and had a manual focus you wouldn't ever accidentally change the frame by pulling. Also Lbus cabling is neater and this is my usual iris motor.


Here are the specs according to manufacturers:

Clm-4 = 0.5Nm (1Nm peak) @ 2Rps (100 teeth/s), 270g
Cforce mini = 0.5Nm @ 3.75Rps (150 Teeth/s), 173g
Cforce plus = 1Nm @ 3.5Rps (210 teeth/s), 325g
Preston DM1X = 1.15Nm @ 4Rps (224 teeth/s) 415g
Preston DM2 = 0.84 Nm @ 2.1Rps (118 teeth/s) 290g
Heden 26Ve = 1.8Nm @ ??? (???) 222g 
Cforce mini RF, has 0.25Nm (0.3 peak) @6rps (240 teeth/second)
Power in Watts (ignoring gear size):
Clm4=  104.73W
Cforce mini=196.36W
Cforce plus =366.54W
Preston dm1x=481.74W
Preston Dm2=184.74W
Heden 26Ve=??? Need to find out rpm to work out
Cforce mini RF=157.9W
I hope this helps!
Jeff, Australia

jeffrey truong

Oops the calculation in Watts was inaccurate (however the numbers were still accurate for comparison)
Clm-4 = 6W (13W peak)
Cforce mini = 12W
Cforce plus = 22W
Preston DM1X = 29W
Preston DM2 = 11W
Heden 26Ve=??? Need to find out rpm to work out
Cforce mini RF = 9W (11W peak)

Saul Oliveira

How do we read these numbers?, does teeth/s mean the higher the fastest the motor?. Does Nm mean the higher the stronger the motor?.
I don't think i´m understand it correctly.

Saul Oliveira 
First AC

jeffrey truong

-Nm (Newton meters) = The torque on a motor, the higher it is the better it is at turning stiff lenses. The value isn't important if you're only turning slick master primes.
-Teeth/s (Teeth per second)= How fast the motor is when turning a lens. Use this value when you want to go for close focus to infinity as fast as possible (if your lens stiffness requirements is met)
-Rps (Revolutions per second) = how fast the actual axle turn, useful when you need to calculate how fast your lens will be when you swap to a larger gear.
-Watts (combined value of speed and torque) = Total power in motor. Use this when comparing motors to each other. All other listed above are dependent on each other i.e if you use a smaller gear on the same motor the Nm will increase due to the extra leverage the smaller gear provides but the teeth per second will reduce since there is less teeth per revolution. This value doesn't take into account gear sizes since you can get all kind of sizes which would not be a fair comparison.

-g (grams) =weight