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Thread: Is there an alternative to using pillow blocks?

  1. #11
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    Re: Is there an alternative to using pillow blocks?

    So the bearings have a 'sort of spherical' outer surface on the outer race that permits the bearing assembly to rotate a little bit inside the pillow block housing to compensate for up to a couple degrees of axle misalignment, but the combination of load and pillow block mounting/placement is such that the bearings end up rotating too far inside the housing and seizing up?
    Please pardon the pedantry... and the profanity... and the convoluted speech pattern...
    "You have failed me, Brain!"
    bleh

  2. Re: Is there an alternative to using pillow blocks?

    Exactly. Even without any payload, they are being pulled out of place by the track tensioning around the drive wheels. If I don't tension it to the level of failure, then when I add the payload they will fail.

  3. #13
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    Re: Is there an alternative to using pillow blocks?

    If you cannot space the pillow blocks further apart to lessen the amount of deflection, then things will be difficult. One option is what I described above with the fixed shaft and free-spinning hub on preloaded tapered pin roller bearings (often called 'timken', after the major manufacturer).

    Another option is to machine a single block of metal to hold the opposed pair of tapered pin roller bearings and mount that to the frame. It will require machining the shaft to have steps and threads that will permit the bearings to be preloaded so they do not self-destruct and ensure they run true (castellated nut with cotter pin to press on one bearing in housing and step in shaft to press on the other bearing).

    Probably a few more methods, but none are immediately coming to mind.
    Please pardon the pedantry... and the profanity... and the convoluted speech pattern...
    "You have failed me, Brain!"
    bleh

  4. Re: Is there an alternative to using pillow blocks?

    Ok that is exactly what I needed to hear. I'm going to rebuild the frame and add some plate in the middle to mount the pillow blocks to. This will spread them about 12-15" apart from each other. The guy I was buying the bearings from told me that as long as I had 2 , they wouldn't slip so I mounted them next to each other. I will report back with success or failure

  5. #15

    Re: Is there an alternative to using pillow blocks?

    Tician: Why the castellated nut with cotter pin, instead of a shaft collar?

  6. #16
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    Re: Is there an alternative to using pillow blocks?

    Quote Originally Posted by jwatte View Post
    Tician: Why the castellated nut with cotter pin, instead of a shaft collar?
    Partly because I'm paranoid, but mostly: if you're going to the trouble of machining a housing for taper roller bearings that require quite a bit of constant preload to not self-destruct, why not secure it proper? Stepped shaft, castellated nut and cotter pin means you can torque it down to ensure full seating of the bearings and races, back off the nut, then torque down again to the required preload; all without worrying about losing preload because the collar slipped or you didn't compress the bearings hard enough before tightening the collar.

    Since the shaft is not transmitting power, the 'best' way would be a fixed shaft (preferably short as possible and machined from/into larger assembly attached to frame/suspension) and free-spinning hub with the drive and track sprockets. No continuous rotation of the 'too small diameter' and/or excessively cantilevered shaft means no (or at least far less regular) cyclical tension/compression loading that will often cause rapid fatigue failure like happened with Mule (which had it all: too small diameter for supporting bot's weight, too long/cantilevered, and transmitting power); just the usual shock stresses from the terrain and you can easily make the shaft/assembly larger/stronger to compensate and/or add suspension and/or just go slower.
    Last edited by tician; 05-25-2015 at 03:09 AM. Reason: added link
    Please pardon the pedantry... and the profanity... and the convoluted speech pattern...
    "You have failed me, Brain!"
    bleh

  7. #17

    Re: Is there an alternative to using pillow blocks?

    bearings that require quite a bit of constant preload to not self-destruct
    I see -- I read up some more on the tapered-pin bearings, and now understand why they need pre-load. (Being a mechanics n00b, I've just used ball bearings pressed into machined blocks before.) Thanks!

    Sounds like a dead shaft would be ideal for djbutter22, if he has access to the necessary resources.

  8. #18
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    Re: Is there an alternative to using pillow blocks?

    Even ball bearings can require a bit of preload for high precision operation. If you have any easily rebuildable stepper motors (NEMA sizes, not pancakes), you should usually find a wave washer, or similar device, at one end of the motor pressing on the bearings to ensure the bearings always run true. Remove the washer and that tiny bit of play in the bearings will often be enough to let the magnets in the rotor stick to the stator and prevent proper operation.
    Please pardon the pedantry... and the profanity... and the convoluted speech pattern...
    "You have failed me, Brain!"
    bleh

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