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Upside down Arlo? — Parallax Forums

Upside down Arlo?

dtaylordtaylor Posts: 17
edited 2014-03-18 09:14 in Robotics
I'm building a robot based on the Arlo platform. When I measured the threshold between my den and hallway, it is almost exactly the wheel clearance under the Arlo base which will make transitioning almost impossible. As I sat studying my Arlo, it occurred to me that the clearance between the top of the base and the top of the wheel was greater than the clearance below.

My question is this: Is there any engineering or design reason why I couldn't use the Arlo base upside down?

dogulas

Comments

  • RS_JimRS_Jim Posts: 1,762
    edited 2014-03-17 06:59
    dtaylor wrote: »
    I'm building a robot based on the Arlo platform. When I measured the threshold between my den and hallway, it is almost exactly the wheel clearance under the Arlo base which will make transitioning almost impossible. As I sat studying my Arlo, it occurred to me that the clearance between the top of the base and the top of the wheel was greater than the clearance below.

    My question is this: Is there any engineering or design reason why I couldn't use the Arlo base upside down?
    Wouldn't that make it an Olra?
    dogulas
  • GordonMcCombGordonMcComb Posts: 3,366
    edited 2014-03-17 07:58
    You'd have to use different (smaller) casters, but there isn't a technical reason (that I know of) that would forbid you from using it upside down. That said, the wheel clearance for the Arlo is often stated as the distance from ground to the bottom of the battery, which is slung underneath. You can use a slimmer battery. There's also the bulk of the mechanics of the drive motors, but I'm not sure how close they are to the ground. I have the older Madeusa platform, and its clearance is enough for the typical carpet threshold. It used somewhat different motors, though.
  • RobotWorkshopRobotWorkshop Posts: 2,307
    edited 2014-03-17 09:06
    I use that same base on a large robot and turn the base over. Instead of castors I am using a 1" ball transfer on the front and rear of the robot:

    http://www.mcmaster.com/#standard-ball-transfers-for-conveyors/=r4uc4f

    They look like the #4 version at the link above and I use the ones with a 1/4" thread. Just drill a hole in the front and rear of the base and use s 1/4" T nut for mounting. You can use either the steel ball or to be safe use the nylon version which is easier on floors.

    The battery is then sitting on top of the base instead of hanging down.

    The main issue you may run into is that this is meant for level surfaces and can only go over small obstacles. If you have a higher door threshold to go over that can be an issue for any robot. Not only clearance under the base but enough clearance so that when the front or rear castor hits that it doesn't lift a drive wheel off the floor.

    Robert
  • dtaylordtaylor Posts: 17
    edited 2014-03-18 06:56
    GordonMcComb wrote: »
    You'd have to use different (smaller) casters, but there isn't a technical reason (that I know of) that would forbid you from using it upside down. That said, the wheel clearance for the Arlo is often stated as the distance from ground to the bottom of the battery, which is slung underneath. You can use a slimmer battery. There's also the bulk of the mechanics of the drive motors, but I'm not sure how close they are to the ground. I have the older Madeusa platform, and its clearance is enough for the typical carpet threshold. It used somewhat different motors, though.

    Gordon, Thanks for the reply. Actually, there I a plate that goes across the bottom of the wheel kits that the batteries rest on but the documentation says is also necessary for structural strength. The motors also hang down to about the same level. There are two thresholds in question and they are wooden and about a inch and a quarter tall. I don't know the exact amount as I am not home right now. I measured them, though, and they are almost exactly the same distance as the edge of a wheel and the bottom of the battery tray.

    Doug
  • dtaylordtaylor Posts: 17
    edited 2014-03-18 07:04
    RobotWorkshop wrote: »
    If you have a higher door threshold to go over that can be an issue for any robot. Not only clearance under the base but enough clearance so that when the front or rear castor hits that it doesn't lift a drive wheel off the floor. Robert

    Robert,

    Yes, I have given a lot of thought about that and will be modifying the platform by putting both castors in the back. The batteries will be shifted back to move the center of gravity back and I plan to remove much material from the front half of the disk by drilling 1" holes partially through the disk from the bottom in a honeycomb fashion. This will allow the shape to still be a circle and will allow me to mount sensors along the front arc.

    Having the wheels in this configuration will allow me to mount much more uneven terrain.

    Doug
  • GordonMcCombGordonMcComb Posts: 3,366
    edited 2014-03-18 09:14
    dtaylor wrote: »
    There are two thresholds in question and they are wooden and about a inch and a quarter tall.

    If that's the case that's fairly excessive for a robot of this design. Even if you manage to account for the clearance that height may snag a caster, or cause the robot to go severely off course when it lands on the other side. That sort of defeats the purpose of a finely tuned robot. You may want to think about creating a ramp both sides of the threshold to accommodate the robot. This is not uncommon, even in lab settings.
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