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Motor Mount and Wheel Kit have — Parallax Forums

Motor Mount and Wheel Kit have

Computer Geek 101Computer Geek 101 Posts: 179
edited 2011-02-23 11:12 in General Discussion
Does anyone know how strong the motors in th Motor Mount and Wheel Kit( http://www.parallax.com/Store/Accessories/MotorServos/tabid/163/CategoryID/57/List/0/SortField/0/Level/a/ProductID/507/Default.aspx ) are? I am planning on building a robot that will weigh about 80 pounds. Will these motors work with that kind of load? Thanks!

Comments

  • TtailspinTtailspin Posts: 1,326
    edited 2011-02-21 17:37
    I was trying to find the picture of this same machine, except it has a large child on top...
    http://www.flickr.com/photos/parallax_inc_photos/4743508449/in/set-72157624385133344/
    I think the child was around 60 to 80 pounds, and he was rolling around at a pretty fast clip too.:lol:
  • Matt GillilandMatt Gilliland Posts: 1,406
    edited 2011-02-21 22:09
    Hi Computer Geek 101

    In another thread (#64) I reported on an impromptu load test of 40 lbs. or so, and then pushed it to the limit by giving Scott (our machinest) a ride on one of the new HDPE Robot Base Kits. @ a full 12 volts of power to both motors, he rode for about 12 feet and then lost his balance, fell forward and ended up breaking a caster bracket. Scott weighs 195 lbs. Both the Caster and Scott were repaired in relatively short order.

    Do we specify this as a load capacity? Of course not. However, there is a lot of power there, and only you and the terrain that you're running it on can decide what the upper limit is.

    I too, am putting together one of these robot bases that will easily be in the 60 lb range - and I don't forsee any problems as to it's ability to move well under different types of terrain. I've ran these things outside on fairly rough one acre lot and they do pretty well.

    -Matt
  • Computer Geek 101Computer Geek 101 Posts: 179
    edited 2011-02-22 03:58
    Thanks guys! I thought they would do fine, but just wanted to be sure.
  • LoopyBytelooseLoopyByteloose Posts: 12,537
    edited 2011-02-22 04:15
    80 pounds is pretty much the beginning of having to have a separate axle to support the payload. Motors, in general, are never really intended to directly attach to wheels. They are just suppose to supply torque.

    These Parallax units seem to be special designed to do both.

    If want more weight and power and you are trying to figure out a gear box, you might consider sprocket and chain (like bicycle chain) instead as these items are reasonably priced and you can easily adapt to a wide variety of wheels and motors.

    You might consider how many Watts equal one horse-power to get some idea of the kind of power you want. If you are taking to the hills, suddenly your need for power vastly increases. Flat ground is very friendly for low power, anything else is trouble.
  • $WMc%$WMc% Posts: 1,884
    edited 2011-02-22 18:30
    I'm with Loopy
    '
    Whats the duty cycle?
    '
    Is the robo working all day or just doing some five minute gigs here or there.?
  • Matt GillilandMatt Gilliland Posts: 1,406
    edited 2011-02-22 19:56
    Yes, bearings and bearing blocks are definitely preferable to just connecting a wheel to a motor shaft.

    I'm just noticing that our pics for the Motor Mount and Wheel Kit don't really show what their design is like. Inside the manual on page 4 you can kind of get a feel of what the structure is like.

    The drive shaft of the Motor is connected to a separate axle that is inserted through a ball-bearing assembly for an interference fit into a machined mounting block. The weight of the robot is thrust onto the bearing block assembly - not the Motor - which as Loopy points out, is the better way to carry heavier loads.

    I'll take some pics of my test platform in the morning so you can see an actual assembly - not just a model.

    -Matt
  • Computer Geek 101Computer Geek 101 Posts: 179
    edited 2011-02-23 04:33
    I've been thinking of an R2D2 robot, so it wont be running for hours on end. Just a toy to play with. The motor kit loooked really high quality, so I thought they would be nice for it.
  • Matt GillilandMatt Gilliland Posts: 1,406
    edited 2011-02-23 07:57
    Here's some close-up pics of the bearing block assembly...

    The ball-bearing unit is an interference fit into the machined bearing block. The axle is then inserted through the bearing and the motor is bolted to the bearing block as well.
    100_4382.jpg

    The two holes on the top (in the pic below), are what mount to your base platform (whatever that may be). Since the motor is part of the bearing block assembly, you can see how the *load* of the wheel assembly is riding on the bearing - and not the motor itself, since it "floats" with the bearing block. Hence, very little, if any load on the motor bearings themselves - the vast majority of the load is carried by the ball-bearing unit.
    100_4383.jpg

    This makes for a very smooth operating and reliable *ride* - quite a nice assembly I think. (no, I didn't design it :-)

    My first robot was built way back in 1985 - it used the same basic idea of supporting the load through bearings - rather than relying on the motor itself - it ran for years. However this assembly is WAY more robust than the one I built way-back-when.

    Don't forget to check out the new HDPE Robot Base - it's kinda "R2D2-ish" (as a foundation), and it's specifically designed to work with the MMWK too.
    Hope this helps...
    -Matt
    100_4383.jpg
    1024 x 768 - 49K
    100_4382.jpg
    1024 x 768 - 49K
  • Beau SchwabeBeau Schwabe Posts: 6,568
    edited 2011-02-23 09:06
    In addition to weight bearing loads, to answer the question 'how strong' the motors are, here are some torque tests I did with those particular motors. Later I confirmed my measurements with a torque wrench.

    http://forums.parallax.com/showthread.php?118861-Homebuilt-Robotic-Platform-AKA-Retrobot&p=873514&viewfull=1#post873514
  • Roy ElthamRoy Eltham Posts: 3,000
    edited 2011-02-23 09:31
    Another thing to note, the "motor shaft" in this case is not the actual motor's shaft. It's a shaft coming off a large gear that is driven by a worm gear that is connected to the actual motor.
    A friend and I are using this kit in a R2-D2 robot.
    Here's some info from my blog: http://rpef.blogspot.com/2010/10/new-robot-project.html
    And here is an entry showing our first test run (not at full power): http://rpef.blogspot.com/2010/11/first-test-run-of-r2-d2.html
  • Computer Geek 101Computer Geek 101 Posts: 179
    edited 2011-02-23 10:40
    @Roy thats actually what got me thinking about it!

    @Matt & Beau Thanks for the info on the motors. These will be perfect for the robot. They look well built, so I fifured they would do what I needed.
  • Matt GillilandMatt Gilliland Posts: 1,406
    edited 2011-02-23 11:12
    Thanks Beau!

    Roy - great point on the gears - they're seated in bearings on the inside too -the motor really doesn't have any vertical shaft load. And nice job on R2. Nice!

    Computer Geek 101 - good luck with your project - and be sure to keep us posted on your project and show it off here along the way!

    -Matt
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