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 When your team becomes ubiquitous with the phrase "Always a bridesmaid, never the bride" - Peyton Yeung [more] |
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A close-up of our cam based chain tensioners.
Discussion
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23-08-2010 11:27
jspatz1
Re: pic: 221 Robotic Systems Swerve Demo Bot Steering Feedback
Could you give more info on the "continuous-rotation pot?" Does it have a dead zone?
23-08-2010 11:28
Brandon Holley
Re: pic: 221 Robotic Systems Swerve Demo Bot Steering Feedback
I'm assuming the actual tensioner pulleys are like a black delrin? If so, have you had any issues with wear and tear on them in your findings? I only ask because I used an almost identical steering gearbox setup as yours (kind of eerily similar actually) and had to replace the pulleys every so often.
-Brando
23-08-2010 12:55
Aren Siekmeier
Re: pic: 221 Robotic Systems Swerve Demo Bot Steering Feedback
Our team does something similar to tension our drive chains with black delrin, and we haven't experienced much wear. Our only problems have been the bolts loosening and the cams rotating away from the chain (loctite would probably fix this) or the mounting bracket being insufficiently supported. You also have to make sure the cam has enough play to take out more slack when the chain stretches (we had to drill a second hole in one of ours at competition for this very reason).
Btw, I like how you cut a slot for the chain in the tensioner material to keep it in line. We'll have to consider something like that for future drive trains. How did you machine it with the guide grooves?
23-08-2010 13:11
ajlapp
Re: pic: 221 Robotic Systems Swerve Demo Bot Steering Feedback
| Could you give more info on the "continuous-rotation pot?" Does it have a dead zone? |
My controls engineer may have to clarify, but I don't recall any dead band. They simply rollover at the zero point.
| I'm assuming the actual tensioner pulleys are like a black delrin? If so, have you had any issues with wear and tear on them in your findings? |
| How did you machine it with the guide grooves? |
23-08-2010 14:08
Joe Ross
Re: pic: 221 Robotic Systems Swerve Demo Bot Steering Feedback
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Originally Posted by ajlapp
From Digi-Key....made by Bourns. 6639S-1-103-ND
My controls engineer may have to clarify, but I don't recall any dead band. They simply rollover at the zero point. |
If you can live with the deadband, we very much like them. Continuous pots have been much more robust then any encoder we've used.
23-08-2010 16:16
Ether
Re: pic: 221 Robotic Systems Swerve Demo Bot Steering Feedback
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Originally Posted by Joe Ross
Continuous pots have been much more robust then any encoder we've used.
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23-08-2010 17:36
Marc P.
Re: pic: 221 Robotic Systems Swerve Demo Bot Steering Feedback
I spy an arduino with an ethernet shield. Is it controlling the bot on its own, or is it working with another microcontroller or IFI/cRio/other control system?
23-08-2010 18:23
jspatz1
Re: pic: 221 Robotic Systems Swerve Demo Bot Steering Feedback
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Originally Posted by Joe Ross
They do have a deadband at the rollover point, the rollover isn't a perfect "sawtooth". We've used Vishay 357s which after the rollover remain zero for 10-20 degrees. These appear to have similar specs.
If you can live with the deadband, we very much like them. Continuous pots have been much more robust then any encoder we've used. |
23-08-2010 18:30
Nikhil Bajaj
Re: pic: 221 Robotic Systems Swerve Demo Bot Steering Feedback
As an alternate sensor, one might consider the US Digital MA3, which has a much smaller dead band (it is pretty minuscule.) They are a little more expensive, though, at around $40+. However, you can get a ball-bearing version that can sustain higher rotational speeds.
http://www.usdigital.com/products/en...ary/shaft/ma3/
This is what we like to use for certain things on 461. I found out about them when asking some folks on 469 about their swerve drive a few years back.
I guess my method of dealing with dead bands is avoiding them entirely if possible!
28-08-2010 17:31
Gdeaver
Re: pic: 221 Robotic Systems Swerve Demo Bot Steering Feedback
I noticed that the sprocket on the steering drive is not the same diameter as the sprockets on the pivot modules. That combined with the dead band of the potentiometer would lead to some tough programing problems. I don't see any indexing on the steering system. So I want to know how are you guy's handling these problems? We used the window motors also. We have one for each module. Our steering sprockets are 1:1, so the value from the sensor always matches wheel orientation though 360 degrees. As to absolute rotary position sensors, I have not found any company that makes a classical potentiometer that has 360 degree mechanical and electrical ratings. The US Digital MA3's mentioned would be good for this application. We used the Cherry AN8 series. The Cherry AN8's are IP67 and automotive qualified. By being Automotive qualified you gain reverse polarity protection and higher ESD protection. Some teams have had problems with MA3's and ESD. They also are 0 to 5 volt and the out put is sloppy at the rails. The AN8's are 0.5 to 4.5 volts and have a sharp saw tooth slope.
30-08-2010 21:37
AdamHeard
Re: pic: 221 Robotic Systems Swerve Demo Bot Steering Feedback
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Originally Posted by Gdeaver
I noticed that the sprocket on the steering drive is not the same diameter as the sprockets on the pivot modules. That combined with the dead band of the potentiometer would lead to some tough programing problems. I don't see any indexing on the steering system. So I want to know how are you guy's handling these problems? We used the window motors also. We have one for each module. Our steering sprockets are 1:1, so the value from the sensor always matches wheel orientation though 360 degrees. As to absolute rotary position sensors, I have not found any company that makes a classical potentiometer that has 360 degree mechanical and electrical ratings. The US Digital MA3's mentioned would be good for this application. We used the Cherry AN8 series. The Cherry AN8's are IP67 and automotive qualified. By being Automotive qualified you gain reverse polarity protection and higher ESD protection. Some teams have had problems with MA3's and ESD. They also are 0 to 5 volt and the out put is sloppy at the rails. The AN8's are 0.5 to 4.5 volts and have a sharp saw tooth slope.
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30-08-2010 22:15
Gdeaver
Re: pic: 221 Robotic Systems Swerve Demo Bot Steering Feedback
The AN8's run about 40$ depending on the supplier. The AN8's come with a magnet assembly but it would not work in our use. We mounted a 15 tooth #35 sprocket on to the window motor and then mounted a 1/2" x 1/8" diametrically magnetized neodymium magnet on top of the sprocket. The Cherry sensor was then mounted 2.5mm away from the magnet. Look at the picture in this link.
http://wiki.team1640.com/images/thum...0124_csm_2.jpg
You'll also need the matching Delphi connector to make a cable for it. There are getting to be more and more sensors of this type in the market. Many are much more expensive.
30-08-2010 22:17
Joe Ross
Re: pic: 221 Robotic Systems Swerve Demo Bot Steering Feedback
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Originally Posted by AdamHeard
The sloppiness of the MA3's have been annoying, and the fear of ESD has bothered me (but never affected us). What do the AN8 costs?
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Originally Posted by jspatz1
So could you explain how you deal with the dead band in your logic?
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I'd also be interested in hearing how 221 Robotic Systems dealt with the deadband in this application.
31-08-2010 08:29
ajlapp
Re: pic: 221 Robotic Systems Swerve Demo Bot Steering Feedback
| So I want to know how are you guy's handling these problems? |
Our first focus was developing the three driving modes; tank, crab and monster truck steer.
Our wheel rotation is currently limited to 75 degrees in either direction from neutral....this is plenty good for monster truck steer.
31-08-2010 20:41
BEEKMAN
Re: pic: 221 Robotic Systems Swerve Demo Bot Steering Feedback
Was this the one on demo at IRI? If so, have you been able to control the jaguars with the Arduino yet?
02-09-2010 18:31
ajlapp
Re: pic: 221 Robotic Systems Swerve Demo Bot Steering Feedback
| Was this the one on demo at IRI? If so, have you been able to control the jaguars with the Arduino yet? |
We already control the Jaguars using the Arduino via pwm. We would like to add CAN communications using a 2CAN device but we haven't worked on this yet.
Its on the short list.
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