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What's wrong with stationary motors?

Discussion in 'General Talk' started by msaeger, Nov 26, 2017.

  1. msaeger

    msaeger New
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    What is the disadvantage to having the motors being stationary on a belt driven cnc vs hauling them around? All the designs using timing belts I am seeing have the motor on the moving gantry.

    On my 3D printer I am using v-slot and have the motor on rear of the extrusion with both ends of the belt attached to the build plate. I realize the load is much less on the 3D printer but is there a disadvantage to having the motor stationary? I have worked with other much larger belt driven machines (flatbed inkjet) that do it this way.

    I am just thinking it may be better to not be hauling around the 12 pounds of motors.
     
  2. Scotty Orr

    Scotty Orr Veteran
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    On a 3D printer, the moving motor is usually driving the filament extruder, not the gantry. (The gantry is indeed driven by a stationary motor.) The alternative to having a direct-drive extruder (with moving motor on the gantry) is to use a bowden tube setup. That is what I use on my 3D printer. The advantage is what you would think - not hauling around all that weight makes for faster speeds. The disadvantage of using bowden is that you might be limited with certain filaments (flexibles often have a hard time with bowden setups).
     
  3. msaeger

    msaeger New
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    Sorry I guess I am not writing a good explanation I am asking about a cnc router and was just using my 3D printer as an example. Look at the OX build they have the motors that move the Y direction attached to the X gantry so the X gantry is hauling around those motors as well as the one moving the X.
     
  4. Rick 2.0

    Rick 2.0 OpenBuilds Team
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    Unlike the head on a 3D printer, the CNC router head puts a lot of back force on the system as it is cutting. By moving the motors with the gantry this reduces belt length and thus potential belt stretch which would result in lower quality cuts.
     
  5. msaeger

    msaeger New
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    That does make sense the belt would be twice as long. Does anyone use larger belts than the GT3 ones I see on openbuilds. I look on McMaster and they have a bunch of different sizes but I don't know if they would be the right thing to use. I suppose if the tooth pitch is the same a wider belt would not change the resolution if there is such a thing.
     
    #5 msaeger, Nov 27, 2017
    Last edited: Nov 27, 2017
  6. Rick 2.0

    Rick 2.0 OpenBuilds Team
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    The magic behind the GT3 belts that OpenBuilds uses is that they are narrow enough to fit in the slot and run beneath the wheels. Wider belts are a possibility but they have have to be dealt with in a different manner, generally having to set up in air above the wheels which requires additional hardware to accommodate. Larger tooth belts are also a possibility but this increases pulley size and increases step length which is not good for resolution.
     
  7. msaeger

    msaeger New
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    That makes sense but for what I am picturing how I want to try and do it that wouldn't be an issue but that will probably change when the parts come and I get something going.

    I am thinking something like how these guys are doing it WorkBee CNC Mechanical Kit – A Workshop CNC Router. Instead of using the mini v-wheels I could use whatever pulley would fit in the c-beam channel.
     
  8. Gary Caruso

    Gary Caruso Veteran
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    Dual belting works very well too.
     
    Joe Santarsiero likes this.

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