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where can I get strong motors affordably? — Parallax Forums

where can I get strong motors affordably?

WhelzornWhelzorn Posts: 256
edited 2006-04-07 02:36 in Robotics
I am looking for a pair (meaning two of the same, or one left hand one right hand) of motors with similar specs to these: banebots.com/osc/product_info.php?products_id=232. I like the RPM and torque of those, and I may order them, but before I do, I want to check up on a few things. Firstly, does anyone know of similar motors for a better price? I consider the price of those pretty good [noparse][[/noparse]$40 ea.], but if I can go cheaper, I would like to. Secondly, If I give my robot 6" wheels and those motors, what would be an acceptable weight for the robot if I wanted it to have a good amout of power? (it should be able to handle a mowed lawn, gravel, and some light woods). Another thing is, those motors seem impossibly small for their torque output, I mean that's over 1/2 HP! Is that believable? The stall current draw also concerns me. how can I possibly drive those with the stall current almose 40A? Does the HB-25 have over-current protection?

Thank you,
Justin W

Post Edited (Whelzorn) : 4/2/2006 9:43:00 PM GMT

Comments

  • PARPAR Posts: 285
    edited 2006-04-02 22:02
    Dunno about the specs meeting your needs, but regarding prices, how about used cordless screwdrivers that have planetary gears, lots of torque, modest rpms ? Especially the old ones that had non-replaceable rechargeable batteries --lots of folks tossed those to the recycle and they can be found in some recycle/used tools places for $5.00 or so.

    PAR
  • CatharsisCatharsis Posts: 27
    edited 2006-04-02 22:31
    Those are very low in price for that quality of motor. A much cheaper and worse solution would be to dissect a few drills but have no good mounts or shafts.

    Post Edited (Catharsis) : 4/2/2006 11:00:54 PM GMT
  • WhelzornWhelzorn Posts: 256
    edited 2006-04-02 22:45
    yeah, I was impressed by the mounting pattern on those motors as well as the large diameter of the output shaft and the fact that the shaft is supported by two ball bearings inside the motor. Perhaps I should just go with these. I am custom machining the whole chassis of the robot including the motor mounts out of aluminum, and figured these would be nice looking good quality motors for the purpose. Cordless drill motors ar OK, but I've found them hard to mount.
    Has anyone else used the motors from this company? I've never heard of them before, but they look pretty good. I'd just like to get someone elses opinion before I go for it.
  • CatharsisCatharsis Posts: 27
    edited 2006-04-02 22:56
    I ordered some smaller motors from them a few months ago and got them in 2 days. I never ended up using them though(it didn't have anything to do with the quality of the motors, I just gave up on the robot they were to go in to).

    Supposedly these motors hold up fine in fighting robots, so it's not like they are cheap or will fall apart. I think those(or maybe another size/ratio) would probably be your best bet for any type of robot.

    BTW, for the wheel size/weight question, this calculator should help:

    http://www.architeuthis-dux.net/tcr-home.asp

    Go to Tools>Torque / AH Calculator

    It has the motors you linked to.
  • Paul BakerPaul Baker Posts: 6,351
    edited 2006-04-03 20:53
    Heres what I turned up:
    http://www.allelectronics.com/cgi-bin/category/400400/DC_Gear_Motors.html· (1st, 2nd and 5th motors)

    http://www.herbach.com/Merchant2/merchant.mv?Screen=PROD&Store_Code=HAR&Product_Code=TM01MTR4488&Category_Code=DCGEARHEAD

    http://www.herbach.com/Merchant2/merchant.mv?Screen=PROD&Store_Code=HAR&Product_Code=TM03MTR4638&Category_Code=DCGEARHEAD



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  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2006-04-04 01:33
    On eBay currently Parallax is offering at least 4 of the EZ Roller Robotic Wheels kits...

    http://search.ebay.com/_W0QQfgtpZ1QQfrppZ25QQsassZpbasic1

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    Chris Savage
    Parallax Tech Support
    csavage@parallax.com
  • WhelzornWhelzorn Posts: 256
    edited 2006-04-05 02:06
    I ordered the 256:1 baneBots motors last night. I thing they are the best choice for this application. The 100:1 I mentioned in the first post are nice, but they were a bit too high RPM for my needs. The EZ rollers are nice too, but they are not big enough for my needs. Now I need to find a way to drive these. They draw 0.9 A no load, and almost 40 stalled. Thats quite a lot, but I don't expect to stall these (max, I expect the whole thing to weigh 30 lbs, and according to the AH Calculator posted by catharsis [noparse][[/noparse]thanks, by the way] this should be plenty of torque).
    So does anyone know what I should use to drive these? does my driver have to be able to supply 40A? should I just use relays?
    Thanks everyone
  • Paul BakerPaul Baker Posts: 6,351
    edited 2006-04-05 03:06
    You should design for the stall current, or take steps to avoid it (such as a fuse). If you bot runs into a wall, unless the bot starts to climb the wall·and flips itself over, you will stall the motors.

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    6+6=10 (Long live the duodecimal system)
  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2006-04-05 04:11
    The HB-25 from Parallax can handle motors up to 1/2 HP from 6-16V.· The continuous current rating is 25A.· They are also fused for protection and have thermal shutdown.

    http://www.parallax.com/detail.asp?product_id=29144

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    Chris Savage
    Parallax Tech Support
    csavage@parallax.com
  • CatharsisCatharsis Posts: 27
    edited 2006-04-05 14:43
    There is no way you should even come close to stalling those. The calculator should tell you what current it will draw just from driving.
  • Tom WalkerTom Walker Posts: 509
    edited 2006-04-05 17:59
    Catharsis,
    You're statement about not being able to stall these may be a little strong. Unless the device can push over any wall, chances are that it WILL encounter a stall condition at some point.

    Never say never...

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    Truly Understand the Fundamentals and the Path will be so much easier...
  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2006-04-05 18:05
    Tom,

    ·· Not taking sides here, but in my experience many wheel drive systems "slip" before they stall the drive motor.· It really depends on the drive-train and the surfaces it will be on.· If you pull a car up to a brick wall and then start accellerating, it will usually start spinning the tires after awhile.· Now on a standard that may vary depending on release speed of the clutch and RPM of the motor, but the point is it would have to be stress tested under normal operating conditions to gauge that.· Nobody can know without actually trying it, even the builder.

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    Chris Savage
    Parallax Tech Support
    csavage@parallax.com
  • Tom WalkerTom Walker Posts: 509
    edited 2006-04-05 18:19
    Chris,
    I agree with you as it has been my experience, as well. I guess that I just have let too much smoke out to not "assume the worst possible condition" and plan for that. (not to mention that even if it doesn't stall, the current still climbs above "rove")

    "Nothing beats building it so that it flies as it normally would...until the bird hits the engine..."

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    Truly Understand the Fundamentals and the Path will be so much easier...
  • CatharsisCatharsis Posts: 27
    edited 2006-04-05 19:48
    Tom,

    You bring up a very valid point. It is always best to build for the worst possible conditions. But in this case with 103 lb/ft of torque, even on a robot weighing 30 lbs, I can't see these motors coming close to stalling. As noted earlier in the thread, using fuses would be a good option.
  • Paul BakerPaul Baker Posts: 6,351
    edited 2006-04-05 20:34
    I can envision an elaborate situation where the bot wedges a drive wheel under an overhanging ledge, a situation where loss of traction for the wheel can't occur because its position is "locked in place"·and the bot can't be flipped over due to the ledge. In this case either the motor will stall or the frame for the bot would be ripped apart. Granted this type of situation is extremely unlikely to happen, but it is a non-zero possibility.

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    6+6=10 (Long live the duodecimal system)
  • WhelzornWhelzorn Posts: 256
    edited 2006-04-06 23:37
    Is there a simple circuit I could add to each motor to measure current draw? that way, if the current draw is close to stall, I could have the microcontroller reverse the motors for a few seconds. If the current draw is still high, I could simply have it shut down. The problem is, whatever circuit measures the current would also have to be able to handle 40A...
  • Paul BakerPaul Baker Posts: 6,351
    edited 2006-04-07 02:36
    http://www.edn.com/contents/images/502423.pdf#page=2

    and

    http://www.edn.com/contents/images/92503di.pdf#page=4

    you would meld the hbridge aspect of the second with the microcontroller control of the first.

    The idea is to measure the voltage across a very small value resistor (sense resistor)·to determine current flowing through it.

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    6+6=10 (Long live the duodecimal system)
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