Stingray changes (now with orange wheels)
RobotWorkshop
Posts: 2,307
I just noticed that the pictures of the Stingray kit now show that the robot has the Orange wheels. Is that what comes with the kit now? Are there any other changes?
Comments
Yea, The price!!!!
-MattG
You may want to add a note on the Stingray product page mentioning that the motors have an exposed shaft. That is a big plus that a lot of motors don't have. It would be good to call attention to that.
Robert
Roy: That's only 5 rev/sec, so what maybe 7-8 feet per second?
That's perfect for fine speed control in the LFO (line following open) at Expo. Maybe a little slow even... :P
Im planning on purchasing this kit in two weeks, I was wondering if one of the parallax employees could tell me if it will still be on sale? Also I emailed sales but never heard back, I really like the blue wheels much better, is there anyway to still get those with the kit? I noticed the motor only kit still comes with blue wheels.
Also, erco, I am shocked to hear you defending them, you were one of the folks blasting them in the past.
orange are medium and blue are harder...
http://www.parallax.com/Portals/0/Downloads/docs/prod/prop/28230-PropellerRobotControlBrd-v1.0.pdf
This is using the H-Bridge chip that I planned on using, I also use this chip to control my roomba, its an it is speced at STM l6205 2.8 continous to 5.something amps peak. If this is what you are using what exactly is wrong with the driver, it seems like it has more than enough power for the sting ray... Now youve got me a bit worried about driving this thing at lower speeds
Yes, the MSR1 was a board parallax originally sold with the Stingray, it's been discontinued for a while though.
The datasheet for that part says the operating supply voltage should be between 8 and 52 volts. However, those motors are 7.2v and I ran them at 7.2v (standard RC battery). Maybe that is why it didn't work so well for me?
The other motors I used that worked better were 12v, and I ran them from both a 12v SLA battery and a 3S Lipo (11.1v). Of course, they were also geared with a much higher ratio, so the output speed was much lower.
Sorry, I guess my subtle sarcasm didn't come thru my post. Yes, they are hopelessly undergeared and way too fast, as evidenced by the plethora of posts here about baseboard damage!
Yeah, ok, I wasn't sure, sarcasm is a bit hard to read in text sometimes.
rwgast_logicdesign, Check out these: http://www.pololu.com/catalog/category/116 I'd get the 12v, 100:1 or 131:1 ratio ones... I have those with the encoders. Got them during one of the black friday sales. They most fit right in, I think I might not have been able to get all 3 screws in without drilling, but I don't recall (it was over a year ago, and I can't easily check right now).
I have the Pololu motors in my Stingray, all 3 motor mounting holes match up with the Stingray. The shafts that drive the wheels are shorter on the the Pololu motors but are just barely long enough to reach the 2nd set screw on the Stingray wheel hubs. I bought my Pololu motors motors during their Blackfriday 2012 sale. My Stingray came with the orange wheels.
I like the top speed i see in the videos on youtube, but ill have to really test things things at low duty cycles, if I have the same issues as roy ill definately be trading them in for a pair of the polulu motors linked too. Speed is fun but if having it means theres not enough torque when going slow then its not worth it.
Has anyone thought about just regearing the things? The data sheet on parallax for stingray shows the gearbox its only 3 spurs, im not sure how easy popping the gearheads is though... the problem with most of these replacement motors is they lack a back shaft from what I can tell, and have no place to put encoders. Erco where did you get $10 replacements?
It's just the beast marking it's territory! ;-)
Are you talking about me, or the Stingray?
-Tommy
About how much weight can you put on this and still have it move smoothly?
Regarding the speed and torque issues. The motors are geared 30:1. if you drive the motors open loop you will find it very fast, and with enough torque to pull itself along quite nicely. Slow speeds are a little problematic requiring a minimum open loop setting before the thing will even move.
My interests, however, are in autonomous motion and have built navigate to waypoint and pid control into my bots software. I have found the issues with low speed control a non issue with pid control since pid will increase torque to achieve the set speed.
Wheel slippage and inaccuracies inherent in the motors and wheels especially when reversing direction and turning overwhelm any other issues. Never the less I am able to drive the bot fairly accurately indoors. for example I have a test program that drives the bot 5 meters forward then drive a 1 meter square making all right turns then another 1 meter square making all left turns and then drive back to the starting poing landing within 10-20 cm of the starting point most of the time (failures are very spectacular). I generally keep the speed at about 25-30% of max.
I do recommend the stingray for someone looking for something more advanced than the boebot and less expensive than the eddie but keep in mind it really needs the more sophisticated software control. Kye has placed a good (pid) motor control in the object exchange. Here is a link to a simplified version of pid control with a decent explaination.
http://www.ikalogic.com/closed-loop-speed-and-position-control-of-dc-motors/