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Small motors for a small bot and a small wallet — Parallax Forums

Small motors for a small bot and a small wallet

Spiral_72Spiral_72 Posts: 791
edited 2011-02-09 17:19 in Robotics
I'm looking at a couple other things from this company. I'll probably add these too!

Yea, they're small, but it'd be just the thing for a little mouse bot or something :)

http://www.mpja.com/prodinfo.asp?number=18310+MD

Comments

  • Duane DegnDuane Degn Posts: 10,588
    edited 2011-01-21 15:36
    I've been tempted to add those to an order before. So far I've resisted. I have so many projects I'm already working on, I didn't need to add another project just so I could use these.

    They look like they'd need a nice smooth surface to run on. They still look fun.

    Duane
  • Duane DegnDuane Degn Posts: 10,588
    edited 2011-02-04 14:10
    Okay, I blame Spiral_72 for this. I just received my latest order from MPJA. I added four sets of these wheels to my order (you know who's fault).

    I'm very pleasantly surprised. I hadn't read the description very carefully. I saw "3/4" foam wheels" and thought they were little 3/4" diameter wheels. It's 3/4" wide wheels. I think you could easily power a Boe-Bot sided bot with these.

    I gave one motor 5V. Its free running current is 500mA. The stall current is 1.7A.

    These are surprisingly noisy in their cases. With some effort I removed one wheel and motor from the casing. It is much quieter without its case. The plastic house has just the right (really wrong) natural frequency to produce lots of noise when these things run.

    The motors have three noise (electronic) reducing capacitors each. (These make it hard to remove the motor and wheel from the housing.)

    Lets see . . . How many will I need for my robot army?
  • Spiral_72Spiral_72 Posts: 791
    edited 2011-02-07 11:58
    HAHA! I'm glad I could be of help...... or at least help in someone to blame :)


    So what do you suppose the wheel speed is? Slow 0-20rpm or fast 100+ rpm?? A good guess is fine.

    I haven't ordered mine yet. I'm waiting on the $60 for their variable bench supply. :)
  • Duane DegnDuane Degn Posts: 10,588
    edited 2011-02-07 14:36
    The wheels spin very fast without a load.

    Free spinning in the air I'd guess the speed of the wheels is over several thousand rpm.

    I drew a pencil line on the side of one wheel in hopes of being able to better judge the speed of the wheel. The line very quickly disappeared. If I add friction to the wheel and try to slow it down enough to see the pencil line the current draw quickly rises to near stall current.

    I'm starting to think who ever designed the toy these wheels were intend for didn't know what they were doing. I think there is a good reason these ended up as surplus.

    I'll probably try mounting these on some sort of platform to see if they are usable as is, but I'm not very optimistic they will be able to work without some sort of gearing.

    You might do well to think of them as cheap motors but don't expect them to work well without modification.

    The torque of these motors is very low.

    I have a tachometer I use with RC airplanes. I'll try to find it and get a better reading on the speed.

    Any tests I can do to help you decide if you want them or not?

    I'm not sure how to measure the torque on these. Maybe a weight on the end of a stick? I think I saw someone around here use this technique.

    The description on the internet mentioned a diode is used so these have two speeds (very fast and super fast). The diode has "6A4" printed on it. It's 9mm long and 9mm in diameter. There is a 0.746V drop across the diode when the motor is powered with 5V.

    The switch is double pull triple throw. Only one side of the switch is used.

    It would be great to figure out a way to use these. They are so darn cheap.
  • LeonLeon Posts: 7,620
    edited 2011-02-07 15:58
    Gearing will be essential with those motors.

    You'll find it easier to use the Tamiya gearboxes which come with 3V motors.
  • Duane DegnDuane Degn Posts: 10,588
    edited 2011-02-07 18:29
    Leon,
    Gearing will be essential with those motors.

    I was afraid of that.

    I wonder what the designer was thinking using these motors to directly drive wheels.
    You'll find it easier to use the Tamiya gearboxes which come with 3V motors.

    Easier yes. I was looking for cheaper. I have a little twin motor Tamiya gearbox. It works fine but it cost about $10 (I think). These little motors cost just under $1 each.

    One of these summers, I hope to hold a "Robot School" for kids. (I used to teach chemistry and physics and I miss teaching.) I keep looking for ways of making a lot robots for just a little bit of money. I was hoping these motors with wheels would work. It would be a lot less expensive than using hacked servos.
  • P!-RoP!-Ro Posts: 1,189
    edited 2011-02-07 19:44
    I'd be willing to help you with the "robot school" if you needed, provided you didn't put it off until I moved out of this freezing cold state. But if you're looking for a cheap way for kids to make robots then perhaps you should talk to Lambert Andrus of TechZoneCommunications (techzonecom.com) and get him to print you some robot parts. As it is, I'm thinking of creating a website dedicated to electronics and one of the first articles I'm thinking of writing is how to make printable components for a reprap (I am very good at that since it was my job to redesign the Huxley the way Lambert wanted it done).
  • Duane DegnDuane Degn Posts: 10,588
    edited 2011-02-08 09:35
    P!-Ro,

    Freezing cold state? Tell me about it. I grew up in San Diego, California. I had to buy a winter coat when I went off to college.

    It would be great if you could help with Robot School. Each summer I think about it. I thought I'd check with the local library to see if they'd let me use one of there large rooms. I'll let you know if it gets past the day-dreaming phase.

    I looked at those reprap machines. Pretty cool. I'll have to see if I have any money left after figuring out taxes. It would be great to "Print" a gear box.

    I saw printed gears on the site you mentioned. Are the gears strong enough to use in a small gear box? Assume the motor is similar to the one linked to by the OP.

    Duane
  • Spiral_72Spiral_72 Posts: 791
    edited 2011-02-08 13:11
    Well dang, I thought surely there would be some kind of gear reduction in the case!!!?? I'm sorry about that, at least your not out much I guess and you do have some cheap motors.

    Several thousand RPM. Wow, I have no idea what it could be used for.
  • Duane DegnDuane Degn Posts: 10,588
    edited 2011-02-08 14:01
    Spiral_72,

    I'm sure you know I was joking about my purchasing these being your fault.

    I'm still glad I purchased them.

    Heck, I think the switch that came with them is probably worth the two bucks.

    I don't think a person can have too many motors.

    I'll figure out a use for them.
  • P!-RoP!-Ro Posts: 1,189
    edited 2011-02-08 15:38
    Printing small gears is quite a challenge--from my work for Lambert I got a small Huxley reprap and I've been using it to try and fix a cool 4 tracked rc vehicle I'd like to convert into a robot. Unfortunately, it has a bunch of stripped gears which is causing me a problem, but I am currently trying to work it out by adding a dremel to the machine to carve the gears rather than print them. I also hope to use this to recycle pla by melting it into a slab and machining it--something very worthwhile since I have the ability to get a seemingly endless supply of scraps from Lambert.

    Also--I was at Lambert's house just barely and I found that he has a large number of cogs/belts that came off of his resent batch of motors that he is unable to use. If necessary, it really shouldn't be too hard to print a different attachment for it to connect to the small motors you bought.
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  • Duane DegnDuane Degn Posts: 10,588
    edited 2011-02-09 10:00
    I've been thinking about those cogs and belts.

    I'm don't think they would offer enough reduction to make these motors useable.

    I'm not really worried about using these motors. I only purchased four sets so I'm not out much money. It would be nice to have a source of cheap geared motors for robots.

    It would be great to be able to "print" gears. I'm not sure if the plasitc used by these reprap machines is strong enough.

    I wonder if I'd be better off with some sort of CNC router and cut out parts rather than printing them. There is something amazing about be able to "print" a part. I think I will eventually buy some sort of reprap machine.
  • P!-RoP!-Ro Posts: 1,189
    edited 2011-02-09 17:19
    I agree with you about the cnc, that's why I printed a head to hold a Dremel. Since I have a huxley it was simple to just mount it to the side so I can easily take it off to print if I'd like. The only problem I'm having is getting good support for the tool keeping it from wobbling separate from the x carriage, so I'm going to try soon here to print a different piece that will hopefully fix that. If I can get it to work well, then I should also later be able to mill myself some pcb's.
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