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Request For Information (Stingray Experimenters) — Parallax Forums

Request For Information (Stingray Experimenters)

Chris SavageChris Savage Parallax EngineeringPosts: 14,406
edited 2013-09-09 14:26 in Robotics
Hey everyone,

Some of you, at some point were trying motors (I think erco was involved) trying to find one that was an ideal solution for the Stingray. Our motor supplier at the time went dark on us and we were unable to get better motors for you all. We recently got back in touch with the company and are interested in getting some better motors. This won't bring the Stingray back, per se, however it will provide motors for the motor mounting bracket kit we have. The thing is, since we have to wait for samples, we'd like to get the gear ration correct and I know some of you did empirical testing and found something that worked well with the wheels we have. Looking for the results of your findings. Anyone want to share? :thumb:

Comments

  • zappmanzappman Posts: 418
    edited 2013-08-14 10:02
    I am using these 12 V Motors from Pololu;

    100:1 Metal Gearmotor 37Dx57L mm with 64 CPR Encoder

    The integrated quadrature encoder provides a resolution of 64 counts per revolution of the motor shaft, which corresponds to 6533 counts per revolution of the gearbox’s output shaft.

    It is really nice to have the quadrature encoders built into the motor !!!
    You simply mount the motor including the encoder with 3 screws. You don't need to worry about seperating mounting the encoders.

    I am powering them from a 9.6Vdc NiMH battery that actually charges to a measured voltage of 10.7 Vdc.

    The mounting holes in the motors match the Stingray perfectly, however the motor shafts are shorter then the original Stingray motors.
























    General specifications
    Gear ratio: 100:1
    Free-run speed @ 6V: 50 rpm1
    Free-run current @ 6V: 250 mA1
    Stall current @ 6V: 2500 mA1
    Stall torque @ 6V: 110 oz·in1
    Free-run speed @ 12V: 100 rpm
    Free-run current @ 12V: 300 mA
    Stall current @ 12V: 5000 mA
    Stall torque @ 12V: 220 oz·in
    Lead length: 11 in

    Notes:

    1
    This motor will run at 6 V but is intended for operation at 12 V.
  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2013-08-14 10:58
    Do you have a video showing how fast the Stingray moves with that configuration at 12V? With such a high ratio it would seem to be fairly slow. The original motors I tested had 50:1 ratio and were quite slow.
  • W9GFOW9GFO Posts: 4,010
    edited 2013-08-14 13:00
    I have a source for more powerful Stingray sized motors w/encoders. I believe I emailed you about them some time ago but never heard back. They are less than 1/5th the price of the Pololu motors if purchased by the thousand.

    attachment.php?attachmentid=103324&d=1376510356
    Stingray motor.jpg
    1024 x 765 - 67K
  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2013-08-14 13:56
    Sorry for not getting back to you. Sometimes it gets tricky to keep all relevant information in one place. We recently switched from one mail system to another and mail before a certain point now isn't easy to get to for me. One thing we're looking for too is that the motors use all metal gears. Do you happen to know if these have any plastic gears inside? Also, how's the speed and torque when used on the Stingray? Wish I had a set to try.
  • W9GFOW9GFO Posts: 4,010
    edited 2013-08-14 14:16
    They gears are all metal. I believe the voltage range is 6 - 12V. They are 30:1. I can send you a pair if you want. RPM is listed as 82 @ 6V.
  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2013-08-14 14:35
    If you can send me a pair (here at Parallax) and purchase information I will see about carrying them. I am trying to solve the motor issue first (keep stocking motors) and then move on to the robot issue. But not going to make any empty promises there. One step at a time.
  • zappmanzappman Posts: 418
    edited 2013-08-14 15:33
    Chris Savage wrote: »
    Do you have a video showing how fast the Stingray moves with that configuration at 12V? With such a high ratio it would seem to be fairly slow. The original motors I tested had 50:1 ratio and were quite slow.

    Sorry I don't have any video yet.

    The motor’s rated speed is 100 RPM at 12 V which equates to a robot speed of approximately 2.1 feet/sec (0.65 m/s) or 1.45 mph or 1531.5 inches / minute. The encoders will generate 426.587 pulses per inch of travel or 5119 pulses per foot of travel. This is using the Stingray's wheels.

    These speeds seem great for an indoor robot. If you have a 20 x 20 foot room you can get across the room in about 10 seconds.

    Remember, since the motors are geared slower, you get more torque, so the robot can be heavier.

    Also most motors can output more Torque when operating below their maximum speed, you need to look at the manufactures data sheet / graph.
  • WhitWhit Posts: 4,191
    edited 2013-08-14 19:20
    @Chris,

    Here is erco's video on the subject...

    On the YouTube page erco says"A visibly lower RPM/higher torque motor for a Parallax Stingray robot to obtain finer low speed motor control. ~$10 Ebay China, called a "DC Gear Motor 12V 70rpm 37mm High Torque 8kg.cm" Bolts right in, almost identical size/weight, an easy swap.

    An eBay search for the above will find - http://www.ebay.com/itm/DC-Gear-Motor-12V-70rpm-37mm-High-Torque-8kg-cm-Micro-DC-Gear-Box-Motor-/150990875645?pt=LH_DefaultDomain_0&hash=item2327c1ebfd

    I ordered some of these, but have not installed them yet. Will probably try them at 7.2 volts first...
  • Ron CzapalaRon Czapala Posts: 2,418
    edited 2013-08-14 19:37
    Here is a video using the 50:1 Pololu motors at 12v on my homemade Stingray - I don't think It was running flat out - I was trying for straightline accuracy with quadrature encoders

    There are more videos and pics in this thread: http://forums.parallax.com/showthread.php/131522-Homemade-StingRay
  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2013-08-15 10:14
    Whit, thanks for the video...had I been at home I am subscribed to erco's channel and would have seen them. ;)

    Ron, I know you listed the ratio (50:1), but do you happen to know the RPM@V rating with that gear ratio?
  • Ron CzapalaRon Czapala Posts: 2,418
    edited 2013-08-15 11:34
    Chris Savage wrote: »
    Ron, I know you listed the ratio (50:1), but do you happen to know the RPM@V rating with that gear ratio?

    Here are the specs http://www.pololu.com/catalog/product/1444/specs
  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2013-08-15 12:29
    Ron, those motors have the same specs as the motors we were supposed to get to replace the high-speed ones. We're still waiting on samples and I am still looking at other suggestions. The ones we're waiting to sample don't have encoders, but they're the same case as the old motors so ready for U.S. Digital or our own encoder board. I am also going to look at the ones W9GFO mentioned.
  • NWCCTVNWCCTV Posts: 3,629
    edited 2013-08-15 20:08
    Rich, I don't need a thousand but what's the chance of picking up 4 or so of those motors?
  • W9GFOW9GFO Posts: 4,010
    edited 2013-08-15 20:43
    I can probably get more the first week in September, so let me know how many you would like. Expect to pay about $20 ea.
  • ercoerco Posts: 20,256
    edited 2013-08-15 22:13
    I still maintain that most people would be happier with a gear ratio of 100:1 or higher. When's the last time you heard a complaint about too much control? OTOH, there are numerous posts about runaway Stingrays and jokes of baseboard damage.
  • ajwardajward Posts: 1,130
    edited 2013-08-16 06:17
    I agree with erco on the higher gear ratios. I didn't get a Stingray, but built a 'bot with a kind of similar layout. Using the 30:1/310 RPM motors, the wee beastie was =way= too fast, hard to control and the torque was minimal. I replaced them with a pair of Pololu 131:1/80 RPM motors. The difference was dramatic!
    I realize 80 RPM might be a little slow for some folks, but my critters seldom operate in the wide open spaces and speed isn't much of an issue. Also the torque is much better. Installing the motors in my tracked chassis, I find it can climb an approximate 45 degree slope... (with a decent surface, that is).
    Just my two cents.

    Amanda
  • Ron CzapalaRon Czapala Posts: 2,418
    edited 2013-08-16 07:33
    erco wrote: »
    I still maintain that most people would be happier with a gear ratio of 100:1 or higher. When's the last time you heard a complaint about too much control? OTOH, there are numerous posts about runaway Stingrays and jokes of baseboard damage.

    I had similar thoughts and considered swapping out the 50:1 for 100:1.
  • ercoerco Posts: 20,256
    edited 2013-08-16 11:07
    Ron Czapala wrote: »
    I had similar thoughts and considered swapping out the 50:1 for 100:1.

    That speaks volumes, Ron, especially considering the amazing accuracy you've achieved & documented already!
  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2013-09-06 14:29
    W9GFO wrote: »
    They gears are all metal. I believe the voltage range is 6 - 12V. They are 30:1. I can send you a pair if you want. RPM is listed as 82 @ 6V.

    Just wanted to double check...these are marked 6V...is 12V a safe voltage for them?
  • W9GFOW9GFO Posts: 4,010
    edited 2013-09-06 14:37
    Chris Savage wrote: »
    Just wanted to double check...these are marked 6V...is 12V a safe voltage for them?

    Good question, I think so but I will ask. I do know that you can get them in 12 or 24V versions as well.
  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2013-09-06 14:42
    Okay, well I will check more into it. I'd like to cover the widest range of use, including for power sources up to 12V (which can be as high as 14.5V).
  • W9GFOW9GFO Posts: 4,010
    edited 2013-09-09 01:58
    Just heard back from the manufacturer, they say they are good for up to 24V.
  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2013-09-09 08:30
    The units marked 6V are good up to 24V? Well, that is good news! I didn't want to add power until I had an answer because my supply is above 7.5V currently and I wanted to try it with the SLA as well. Thanks for the information.
  • W9GFOW9GFO Posts: 4,010
    edited 2013-09-09 12:55
    Chris Savage wrote: »
    The units marked 6V are good up to 24V?

    I think so. hard to decipher their answers sometimes. Here is what I asked...
    I have a sample motor here in my hand. On the label it is marked GM37-555PM-30-EN, 6V/DC 82rpm. Can you verify what the maximum safe operating voltage is?

    ... and their answer.
    within 12v.max 24v,but that will become louder noise.
  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2013-09-09 14:26
    Sounds good. ;) Thanks again.
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