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erco wrote: »
I tried unsuccessfully to obtain some from the manufacturer. If you have some 100:1 samples, send me some, and I'll put some encoders on a Stingray and show you some maneuvers.
Chris Savage wrote: »
erco, the motors used on the Stingray are compatible with many similar motors sold by various vendors. Trust me when I say, 100:1 would be way too slow...probably about BOE-Bot speed. 50:1 is what the original spec was and these motors had good torque and speed. The current motors are 30:1.
zappman wrote: »
What does everyone think about these motors?
Key Specs: 7.2Vdc, 1:52, 160 RPM, 6mm Shaft Diameter, Built in quadrature encoders
DC Gearhead Motor:
Rated Input Voltage 7.2Vdc
No Load Speed 160 RPM
1:52 Gear Reduction
Stall Torque: 100 oz-in (7.2 kg-cm)
Drive Shaft End Hole Thread Size: 2.5 x 0.45 x 8mm
No Load Current Draw: 300mA
Max Current Draw (Shaft Lockup): 4.0A
Built in Quadrature Encoder:
2 Channels, Plus +5V & Gnd Receptacles
12 Pulses per motor revolution
624 Pulses per output shaft revolution
12" 20AWG Lead Wires
Encoder plug compatible with 0.100" (2.54mm) headers
Roy Eltham wrote: »
So, the 50:1 (7.2v) motors are better than the 30:1 motors, but they are not good enough. I have code that attempts to run the bot in a square by driving forward 10 inches, then doing a 90 degree rotate in place, then repeating to get back to where it started.
I'm using the encoders available from LynxMotion. They are 400 counts/state transitions per motor revolution, which is 1/50th of a wheel revolution, so 20000 counts per wheel revolution. Should be pretty accurate if there is no slipping.
The slowest speed I can reliably run the motors at is 20% duty cycle pwm. Which is about 30-35RPM of the wheel (~1/2 rotation per second). Currently, when it does the square, it's always off by a couple inches when it gets back to near the start point. It seems that the 90 degree rotates are the main problem. Sometimes it appears to turn the right amount, but often it's at least a smidge off and sometimes it's as much as 5 degrees off. Since I am using the encoders, it's got to be that wheels slipping, right? Maybe if I add some weight? My test surface is a wood tabletop. It's not coated/painted or polished, but it's reasonably smooth. The wheels are still the stock wheels. I'll try adding some weight and see if that helps. If I can get it to do the square reliably then I'll share a video and move on to longer distances and more turns.
I've got those alternate wheels on order (two different hardnesses), and I went ahead and ordered some of the pololu motors. Some 75:1 6V motors ( http://www.pololu.com/catalog/product/2275 ) and some 100:1 12V motors ( http://www.pololu.com/catalog/product/1446 ). They both come with encoders and they look decent enough, we'll see if they suck or not. They aren't the little crap ones that you find on most of pololu's little bots.
Chris Savage wrote: »
Something that may be of interest to some of you are these new 12V Gear Motors that Parallax now carries. With a nominal voltage of 6VDC these should provide a better range of voltage for control as well as a 30:1 gear ration resulting in 200RPM output at full speed.
This powerful 12 V DC Geared Motor with 200 RPM output could be the muscle in your next robot. Manufactured by Hsiang Neng these motors are solid and a direct replacement for the 7.2 V motors used in our other compatible kits.
200 RPM Output Shaft (+/-10%)
Output Shaft Diameter 6mm
60mA Average Current @ No Load
44.5 V-12 V Range (6V Nominal)
Spur Gear Design
erco wrote: »
More 30:1 motors?
RobotWorkshop wrote: »
What about an exposed armature shaft for encoders? The one in the picture doesn't appear to have that feature. If not then we may not be able to swap out the Stingray motors for those of us using encoders.