DPRG mailing list archives: [DPRG] Re: DPRGlist Digest, Vol 48, Issue 33

Tue May 27 16:06:15 CDT 2008

Brian,

I have a 9 x 20 Lathe sold by several vendors under various names that I 
purchased used several years ago.  I am a relative novice at machine 
working but I have had a lot of fun with mine and it seems to do 
everything I have wanted to do so far. My biggest complaint is that it 
seems that nothing you buy will be ready to use "out of the box" without 
some form of alignment or tweaking to get it set up properly. The lead 
screws on the ways are kinda sloppy and the swivel base of the tool post 
on my model is a very weak design. I have machined a lot of "parts" on 
it from Delrin, bronze ,aluminum and even some steel, and as long as you 
know the limitations of your machine and take your time you can do some 
good work. I generally agree with DPA in that you have to decide what it 
is you want to make with it before you can decide which one to by. I 
always tend to underbuy and really regret it later. Maybe I'll learn my 
lesson some day. I think DPA has some photos of his stuff online that 
show how he added DRO's, etc to his lathe. Its fairly easy to do and 
well worth the effort. I also made some attachments to do horizontal 
milling on the lathe and it works "okay". I did finally break down and 
spent the money on a vertical mill because some of the parts I needed to 
make were too large to fit on the lathe. Machine tooling makes great 
birthday presents from your family, even if you have to buy them for 
yourself. Now if I can just figure out how to keep the metal shavings 
out of the carpet.....

Steve Garmon

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> ------------------------------------------------------------------------
>
> Today's Topics:
>
>    1. Re: Absolute reference for angular position (Chris Jang)
>    2. Opinions on machine tools and sources? (brianmerritt at att.net)
>    3. RE: Absolute reference for angular position (Randy M. Dumse)
>    4. Absolute reference for angular position  (dpa)
>    5. RE: Absolute reference for angular position (Sluggy!)
>    6. Opinions on machine tools and sources? (dpa)
>    7. Re: Absolute reference for angular position (Dale Wheat)
>    8. Re: Absolute reference for angular position (Dale Wheat)
>    9. Re: Absolute reference for angular position (Dale Wheat)
>   
>
> ------------------------------------------------------------------------
>
> Subject:
> Re: [DPRG] Absolute reference for angular position
> From:
> Chris Jang <christopher.jang at yahoo.com>
> Date:
> Tue, 27 May 2008 10:14:47 -0700 (PDT)
> To:
> Eric Sumner <kd5bjo at gmail.com>, Dale Wheat <dale at dalewheat.com>
>
> To:
> Eric Sumner <kd5bjo at gmail.com>, Dale Wheat <dale at dalewheat.com>
> CC:
> DPRG <dprglist at dprg.org>
>
>
>>> Can anyone suggest an alternate method for measuring angular position with
>>>       
>> a
>>     
>>> high degree of accuracy and repeatability?  All I really need is an "index
>>> mark" to tell me when the robot returns to a specific heading and not a
>>> continuous readout of angular position.
>>>       
>> If you're only going to be using this to calibrate your rotation, you
>> could use a beacon and a directional receiver; a 38kHz IR receiver
>> module might work for this, if you restricted its field of view.  You
>> could do something similar with a laser pointer and a photodetector;
>> whenever the laser is directly falling on the detector, its value will
>> go up sharply.
>>     
>
> Another possibility is to take photographs of the robot as it rotates.
> Lay out some tape or other visual markers to establish a frame of
> reference. Then if there is a DRO of the angular position in view of the
> camera (maybe a laptop showing the angular readout - use a serial cable
> from the robot to take readings), there are no issues synchronizing data
> collection with the photos. One problem might be refresh of the DRO - may
> not look right to the camera.
>
>
>       
>
>
>   
>
> ------------------------------------------------------------------------
>
> Subject:
> [DPRG] Opinions on machine tools and sources?
> From:
> <brianmerritt at att.net>
> Date:
> Tue, 27 May 2008 12:57:03 -0500
> To:
> <dprglist at dprg.org>
>
> To:
> <dprglist at dprg.org>
>
>
> I am thinking about buying a small lathe and/or vertical mill, new or 
> used.  What are people's opinions on minimum sizes, the different 
> manufacturers, and ease of converting the mill to CNC at some point in 
> the future?  Also, anyone know of good sources for these tools?  I 
> have been watching eBay but it seems it would be tough to determine 
> the condition and would cost an arm and a leg to ship such big items.  
> All knowledgeable feedback will be appreciated.
>
>  
>
> Regards,
>
> Brian
>
>  
>
>  
>
>
> ------------------------------------------------------------------------
>
> Subject:
> RE: [DPRG] Absolute reference for angular position
> From:
> "Randy M. Dumse" <rmd at newmicros.com>
> Date:
> Tue, 27 May 2008 13:30:10 -0500
> To:
> "'Eric Sumner'" <kd5bjo at gmail.com>, "'Dale Wheat'" <dale at dalewheat.com>
>
> To:
> "'Eric Sumner'" <kd5bjo at gmail.com>, "'Dale Wheat'" <dale at dalewheat.com>
> CC:
> 'DPRG' <dprglist at dprg.org>
>
>
>> you could use a beacon and a directional receiver; 
>>     
>
> Even simpler. Use a trouble lamp, or other bright source on the
> floor in line with the robot, use a tube with a photo sensor on
> the robot. The peak value will be when the tube is pointing
> toward the lamp. The longer, narrower the tube, the more
> accurate the pointing.
>
> Randy
>
>
>
>   
>
> ------------------------------------------------------------------------
>
> Subject:
> [DPRG] Absolute reference for angular position
> From:
> dpa <dpa at io.isem.smu.edu>
> Date:
> Tue, 27 May 2008 13:50:38 -0500
> To:
> dprglist at dprg.org
>
> To:
> dprglist at dprg.org
>
>
> Howdy,
>
> Dale wrote:
>   
>> I'm trying to calibrate Daphne's wheelbase dimension.  Because the wheels are
>> not exactly round and the motor shafts are not exactly parallel, this is more of
>> an approximation than an actual measurement.
>>
>> The method I'm using is to spin in place and measure the difference between
>> measured and actual rotation.  To do this I need a very accurate method of
>> measuring the angular position.  Daphne keeps up with what she thinks is her
>> current angular position using odometry.  Comparing these two measurements will
>> help me determine the effective wheelbase dimension and allow me to increase the
>> accuracy of the odometry.
>>     
>
> I've done this with a two-wheel differential drive robot that is
> capable of rotating in place, i.e., zero turning radius.  The
> method used was to align the robot with an "X" marked on the floor,
> and then have the robot rotate in place multiple times, like 10 or
> 20 revolutions, to make the error large enough to measure, and stop
> when the robot thinks it's back to zero.  That is, if the robot's
> odometry error is .5 degree, then 20 revolutions will make it 10
> degrees, large enough to  easily measure and correct.
>
> However, it sounds from the following like you are looking for a
> way for the robot to calibrate itself.  Yes?
>
>   
>> I'm thinking about stereo sonar as a reference point.  Two identical sonar units
>> are aimed horizontally and diverge by 15 degrees or so.  The sonar array should
>> return equal readings when the array is normal (i.e., 90 degrees) to the wall.
>> I believe dpa has used this technique to true up SR04 during long journeys such
>> as our Can-Can contest.
>>     
>
> Our friends from the University of Michigan suggest that you can do
> this with a single sonar by placing the robot at a known location in
> a corner.  The robot uses the sonar to measure the distance to the
> two corner walls by measuring the distance to one, rotating 90
> degrees, and measuring the distance to the other one.   Then run
> your calibration procedure, and measure the distances again.  This
> gives both location and theta error, and the robot should be able
> to calibrate itself.  That would be pretty cool, and something
> that would be easy to run each time you change wheels, or take
> the robot apart and put it back together.
>
> Having said all that, the spin-in-place calibration is a good way to
> get a starting value for theta, but it has a couple of draw backs.
> It can't separate out the wheel base errors from the wheel size
> errors.  Consequently adjustments done using this technique are not
> reliable for general navigating, as the errors when turing one way
> will be more pronounced than turning the other.
>
> The previous "simplified navigation calibrating and tuning" post
> describes a method for using clockwise and counter-clockwise squares
> to do odometry fine tuning once a starting value for theta has been
> determined.  If you think about it, this is also a method for
> amplifying the errors, like spinning in place multiple times, in
> addition to isolating the software from the hardware error soruces.
>
>   
>> The only sonar module I've used before is the Devantech SRF04 module.  It's a
>> simple trigger+echo interface.  Unfortunately, I only have (or can only find)
>> one of them.  I have several of the Mini-S modules but don't know how to use
>> them.  They default to an automatic, fixed-distance operation.  Also, they
>> require 12 volts and Daphne's battery is 7.4 volts.
>>
>> I've also considered a small laser module and a pinpoint receiver.
>>     
>
> I've found that a small laser pointed accurately aligned to the
> robot's main fore/aft axis is a mighty handy thing to have, both
> for calibration and for general running.  It's difficult otherwise
> to tell exactly "where the robot is pointed."  Alternately some sort
> of boresight that can be sighted along for aligning the robot with
> a particular course, like sight marks on a telescope, might be
> helpful.
>
> Dale, how about "All of the Above?"
>
> cheers,
> dpa
>
>
>   
>
> ------------------------------------------------------------------------
>
> Subject:
> RE: [DPRG] Absolute reference for angular position
> From:
> Sluggy! <sluggy9912 at swbell.net>
> Date:
> Tue, 27 May 2008 12:16:58 -0700 (PDT)
> To:
> "'DPRG'" <dprglist at dprg.org>
>
> To:
> "'DPRG'" <dprglist at dprg.org>
>
>
> All the solutions given up to this point seem to be
> towards the robot being self-calibrating. The only
> problem with any of these is that it's adding another
> sensor, one that is intentionally narrow in focus,
> with all the problems that represents.
>
> If this measurement is for one time (or even
> occasional) manual calibration, how about a laser
> pointer attached to the chassis and pointed to a spot
> on the wall. Mark that spot. Rotate the robot under
> program control to what it thinks is 360 degrees.
> Using a high tech ruler, measure the error by where
> the laser ended up pointing. Repeat many times,
> perhaps averaging the results. Adjust the count in the
> software.
>
> Sluggy!
>
> ---
>
> "The idea that unicycling is intrinsically funny does not explain the findings." Professor Sam Shuster.
>
>   
>
> ------------------------------------------------------------------------
>
> Subject:
> [DPRG] Opinions on machine tools and sources?
> From:
> dpa <dpa at io.isem.smu.edu>
> Date:
> Tue, 27 May 2008 14:56:18 -0500
> To:
> dprglist at dprg.org
>
> To:
> dprglist at dprg.org
>
>
> Howdy,
>
> Brian, this is a huge topic.  What size of machine(s) are
> you looking for?  Table top?  Like Taag and Sherline.
> Sherline has a lot of CNC stuff.  I think Dave/Jon
> Hylands use Sherline and have quite a bit of experience
> therewith.
>
> You might also look at Grizzly
> <http://www.grizzlyindustrial.com/>
>
> and Blue Ridge Machinery
> <http://www.blueridgeshoponline.com/category.sc?categoryId=18>
>
> for medium size machine tools.
>
> A generally useful sequence is to start with a nice
> drill press and add an X,Y table for layout, etc.  Then add
> a lathe (I love my Emco-Maier Compact 8).  Between those
> two you can do most robot building tasks, and the lathe
> can be fitted with some fixtures to allow it to be used
> as a horizontal milling machine.  Later you can add a
> vertical mill.
>
> As always, assume you will spend about as much on
> tooling as on the machines themselves.
>
> A bench grinder for making and sharping tools is
> really a must, along with a precision flat plate,
> often made of granite, for doing layout.
>
> Ed K. has one of the 3-in-1 lathe/mills perhaps
> he'll chime in here and report on his experience
> with it.
>
> best,
> dpa
>
>
>
>   
>
> ------------------------------------------------------------------------
>
> Subject:
> Re: [DPRG] Absolute reference for angular position
> From:
> Dale Wheat <dale at dalewheat.com>
> Date:
> Tue, 27 May 2008 14:09:51 -0600
> To:
> dpa <dpa at io.isem.smu.edu>
>
> To:
> dpa <dpa at io.isem.smu.edu>
> CC:
> dprglist at dprg.org
>
>
> David,
>
> > However, it sounds from the following like you are looking for a
> > way for the robot to calibrate itself.  Yes?
>
> Ultimately, yes.  In the short term, I would assist somewhat.  :)
>
> > Our friends from the University of Michigan suggest that you can do
> > this with a single sonar by placing the robot at a known location in
> > a corner.  The robot uses the sonar to measure the distance to the
> > two corner walls by measuring the distance to one, rotating 90
> > degrees, and measuring the distance to the other one.   Then run
> > your calibration procedure, and measure the distances again.  This
> > gives both location and theta error, and the robot should be able
> > to calibrate itself.  That would be pretty cool, and something
> > that would be easy to run each time you change wheels, or take
> > the robot apart and put it back together.
>
> Is that described in more detail in the "Where Am I?" paper?  I have 
> enough sonar units (i.e., 1) for that procedure.
>
> > I've found that a small laser pointed accurately aligned to the
> > robot's main fore/aft axis is a mighty handy thing to have, both
> > for calibration and for general running.  It's difficult otherwise
> > to tell exactly "where the robot is pointed."  Alternately some sort
> > of boresight that can be sighted along for aligning the robot with
> > a particular course, like sight marks on a telescope, might be
> > helpful.
>
> Something I and Dr. Evil both plan to include in the near future, if 
> it's not too much to ask.
>
> > Dale, how about "All of the Above?"
>
> Probably the best suggestion so far!
>
>
> Thanks,
>
> Dale Wheat
>
> (972) 486-1317
> (877) DALE WHEAT
> http://dalewheat.com
>
>
>
>
> ------------------------------------------------------------------------
>
> Subject:
> Re: [DPRG] Absolute reference for angular position
> From:
> Dale Wheat <dale at dalewheat.com>
> Date:
> Tue, 27 May 2008 14:13:47 -0600
> To:
> "Sluggy!" <sluggy9912 at swbell.net>
>
> To:
> "Sluggy!" <sluggy9912 at swbell.net>
> CC:
> 'DPRG' <dprglist at dprg.org>
>
>
> Sluggy!
>
> > All the solutions given up to this point seem to be
> > towards the robot being self-calibrating. The only
> > problem with any of these is that it's adding another
> > sensor, one that is intentionally narrow in focus,
> > with all the problems that represents.
>
> Right now that's how I'm planning to use it, but a sonar array or even 
> a single unit would also be useful for general purpose obstacle 
> avoidance or targeting, once I get up to those lofty levels.
>
> > If this measurement is for one time (or even
> > occasional) manual calibration, how about a laser
> > pointer attached to the chassis and pointed to a spot
> > on the wall. Mark that spot. Rotate the robot under
> > program control to what it thinks is 360 degrees.
> > Using a high tech ruler, measure the error by where
> > the laser ended up pointing. Repeat many times,
> > perhaps averaging the results. Adjust the count in the
> > software.
>
> That sounds like the simplest way to achieve what I want to do.  I 
> have lots of lasers of all sizes laying around.
>
>
> Thanks,
>
> Dale Wheat
>
> (972) 486-1317
> (877) DALE WHEAT
> http://dalewheat.com
>
>
> Sluggy! wrote:
>> All the solutions given up to this point seem to be
>> towards the robot being self-calibrating. The only
>> problem with any of these is that it's adding another
>> sensor, one that is intentionally narrow in focus,
>> with all the problems that represents.
>>
>> If this measurement is for one time (or even
>> occasional) manual calibration, how about a laser
>> pointer attached to the chassis and pointed to a spot
>> on the wall. Mark that spot. Rotate the robot under
>> program control to what it thinks is 360 degrees.
>> Using a high tech ruler, measure the error by where
>> the laser ended up pointing. Repeat many times,
>> perhaps averaging the results. Adjust the count in the
>> software.
>>
>> Sluggy!
>>
>> ---
>>
>> "The idea that unicycling is intrinsically funny does not explain the 
>> findings." Professor Sam Shuster.
>> _______________________________________________
>> DPRGlist mailing list
>> DPRGlist at dprg.org
>> http://list.dprg.org/mailman/listinfo/dprglist
>>
>
>
> ------------------------------------------------------------------------
>
> Subject:
> Re: [DPRG] Absolute reference for angular position
> From:
> Dale Wheat <dale at dalewheat.com>
> Date:
> Tue, 27 May 2008 14:17:15 -0600
> To:
> Eric Sumner <kd5bjo at gmail.com>
>
> To:
> Eric Sumner <kd5bjo at gmail.com>
> CC:
> DPRG <dprglist at dprg.org>
>
>
> Eric,
>
> > If you're only going to be using this to calibrate your rotation, you
> > could use a beacon and a directional receiver; a 38kHz IR receiver
> > module might work for this, if you restricted its field of view.  You
> > could do something similar with a laser pointer and a photodetector;
> > whenever the laser is directly falling on the detector, its value will
> > go up sharply.
>
> The IR demodulator works too well at an angle.  They have AGC circuits 
> and other voodoo to pluck weak signals out of the air.  I need 
> something that falls off dramatically as the signal goes out of phase.
>
> What would be the best detector for a red laser beam?  CdS sensor?  
> Photodiode?  Any other ideas along these lines?
>
>
> Thanks,
>
> Dale Wheat
>
> (972) 486-1317
> (877) DALE WHEAT
> http://dalewheat.com
>
>
>
>
> ------------------------------------------------------------------------
>
> _______________________________________________
> DPRGlist mailing list
> DPRGlist at dprg.org
> http://list.dprg.org/mailman/listinfo/dprglist
>   

-- 

*Steve Garmon*
Geotechnical Manager
C&C Technologies
10615 Shadow Wood Drive
Suite #100
Houston, TX 77043
(713) 468.1536
steve.garmon at cctechnol.com <mailto:steve.Garmon at cctechnol.com>

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