Accelerometer+Inclinometer] HWT901B-TTL MPU9250 9-axis for dish positioning
Pablo Lewin
Paul Oxley
I would be interested in your results. I previously tried using a compass as part of the positioning system. I could not get repeatable results on the azimuth measurements. I concluded that there was too much steel nearby. The Dish and mount supports were both made of steel. The motors were also mounted below the dish which would also cause magnetic fields.
The inclinometer worked well. The accelerometer and multiple axis measurements was not applicable to the slow motion of the dish.
Paul Oxley
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Pablo Lewin
Ciprian Sufitchi
For thos interested, I purchased a small and inexpensive ($16) inclinometer last week from Amazon, which seems to work great especially when adjustung antenna elevation. I don’t have a reference for the precision of this tool, but the device can be calibrated easily.
https://www.amazon.com/gp/product/B07R12DZQ9/
73 de Chip N2YO
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Paul Oxley
One of the techniques that I plan to use in my replacement system is nylon timing belts. These can allow the coupling of items without any ferrous metals. My planned uses include belts on the coupling between both the azimuth axis and elevation axis to the sensors.
The "timing" belts and pulleys are available from McMaster-Kerr (mcmaster.com). They are a large mailorder hardware distributor.
The sensors are rotational magnetic sensors that use the "Hall" Effect. The belts should allow the sensors to be placed outside any magnetic disturbances.
Paul
Paul Oxley
I have a similar one that I use to calibrate the elevation angle. The azimuth angle is accomplished by a compass by sighting back toward the antenna from a distance. For the exotic, this could be done with a level transit. I use the feed mount arm as a reference for the sighting.
The distance is necessary to avoid the ferrous metal in the antenna and mount.
Paul
Pablo Lewin
Pablo Lewin
mike....@gmail.com
Pablo Lewin
Jim Abshier
the ferrous metal problem, but, of course, the Sun must be shining.
Jim Abshier
On 11/2/20 11:58 AM, Paul Oxley wrote:
> Chip
>
> I have a similar one that I use to calibrate the elevation angle. The
> azimuth angle is accomplished by a compass by sighting back toward the
> antenna from a distance. For the exotic, this could be done with a
> level transit. I use the feed mount arm as a reference for the sighting.
>
> The distance is necessary to avoid the ferrous metal in the antenna
> and mount.
>
> Paul
>
>
> On Monday, November 2, 2020, 11:40:57 AM EST, Ciprian Sufitchi
> <csuf...@gmail.com> wrote:
>
>
> For thos interested, I purchased a small and inexpensive ($16)
> inclinometer last week from Amazon, which seems to work great
> especially when adjustung antenna elevation. I don’t have a reference
> for the precision of this tool, but the device can be calibrated easily.
>
> https://www.amazon.com/gp/product/B07R12DZQ9/
>
>
> *From:* sara...@googlegroups.com <sara...@googlegroups.com> *On
> Behalf Of *Pablo Lewin
> *Sent:* Monday, November 2, 2020 11:32 AM
> *To:* Society of Amateur Radio Astronomers <sara...@googlegroups.com>
> *Subject:* Re: [SARA] Accelerometer+Inclinometer] HWT901B-TTL MPU9250
>
> Hi Paul
>
> We'll see if this inclinometer works. The mount has a lot of metal so
> it might not, right now I only have implemented an elevation actuator,
> I don't have an azimuth solution as of yet, the base of the mount is a
> metal circle with a 38 inch diameter so I am now leaning towards a
> Dobsonian style wooden turntable with a stepper motor but it will be
> a while before I implement that solution.
>
> Pablo (WA6RSV)
>
> On Sunday, November 1, 2020 at 4:58:07 PM UTC-8 oxl...@att.net
>
> Pablo
>
> I would be interested in your results. I previously tried using a
> compass as part of the positioning system. I could not get
> repeatable results on the azimuth measurements. I concluded that
> there was too much steel nearby. The Dish and mount supports were
> both made of steel. The motors were also mounted below the dish
> which would also cause magnetic fields.
>
> The inclinometer worked well. The accelerometer and multiple axis
> measurements was not applicable to the slow motion of the dish.
>
> Paul Oxley
>
> On Sunday, November 1, 2020, 07:08:54 PM EST, Pablo Lewin
>
> [I just bought the Military-Grade Accelerometer+Inclinometer]
> HWT901B-TTL MPU9250 9-axis Gyroscope+Angle(XY 0.05°
> Accuracy)+Digital Compass+Air Pressure+Altitude, RM3100
> Magnetometer Compensation and Kalman Filtering which I will try
> on my 2.1 meter dish to position it and eventually to track radio
> sources.
>
> This is NOT the Bluetooth/Wifi version which are cheaper but for
> obvious reasons won't work with a radio telescope, but the TTF/USB
> kind.
>
> Does anybody have any experience with these? I have 30 days to
> return in case the experiment fails.
>
> Thoughts?
>
> Pablo Lewin (WA6RSV)
>
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Larry Mayfield
Company is McMaster-Carr…. I order al manners of stuff from them. I am in Southern Nevada and my orders are placed at the Los Angeles, Calif location and I get it usually next day. YMMV.
Larry
Pahrump, NV
To view this discussion on the web visit https://groups.google.com/d/msgid/sara-list/158369925.720130.1604335930479%40mail.yahoo.com.
Paul Oxley
Pablo
I have not completed the assembly. I have most of the parts. My health has prohibited the time necessary.
Paul
Larry Mayfield
Paul, all,
with some trepidation, I comment…
The use of the inclinometer to check the elevation angle is a the best application. These devices are essentially electronic levels but without a recordable output. So they are really inappropriate for any drive control systems. They are very useful for equatorial mounts that are used in drifting. Use one to set the latitude angle of the mount accurately then use it to set the declination or elevation angle at the zenith position of the RA axis (I think I got that right, lol). However, if you want tracking then an encoder is needed with an electronic output. For a couple of reasons. One is that you need to be on target and the other is that when you are recording data it is good to know actually where the antenna is pointed. If for nothing else, so you can develop some repeatability in observations over time. Rotary encoders, of some accuracy are available for around 25 bucks. I use ebay as my catalog, lol, and I search for what I am looking for, the cheapest prices and the most favorable specs. Most of the encoders are either optical, where they read a coded wheel, or magnetic sensors which work similarly, I guess. Optical is not bad, never fiddled with a magnetic one. There is a third type and that is a capacitance sensor unit. It works by varying the capacitance. Have not fiddled with one of these either but they are supposed to be accurate. Might even make one with an old radio tuning unit. Think of it as a tunable capacitor much like a radio used to tune to the radio stations. The calibrate it by measuring the voltage vs position of the meshing plates. Plot the results with excel and use the trend line to find the best fit of the curve then use that for control of where it is to be pointed via computer. No, I am not there yet, lol…
Regards the lazy Susan or Dobson type azimuth motion. I have reviewed a lot of things to use for that. I have a 3 meter dish that will set up as Alt-Az pointing because I decided that an Eq mount was cumbersome. Plus with Alt-Az I can cover just about all the sky with just 180 degree movements in the axes. For my AZ mount bearing, I have selected a ¾ or 1 ton truck floating rear axle and using only the hub and spindle from it. These are heavy duty units and if the spindle bearings are replaces with sealed ball bearings may outlast the pyramids, lol, because they are lightly loaded and will be very slow turning. And ball bearings generate very little bearing friction. For a small AZ bearing they can be found on ebay in the form of front wheel drive car replaceable front spindle hub bearings. Complete with all l new parts.
Paul mentioned the use of the cogged timing belt and pulleys for drive systems. Yup, good! For my large dish however, I want it to be robust so have come up with another scheme. I will use a link chain, like a large bicycle chain, as my sprocket! It will be sized so fit a large diameter base plate mounted the truck axle hub system mentioned above. This forms a large diameter sprocket! Then the drive motor will turn a jack shaft to reduce the speed and that will drive a small diameter chain sprocket for the final drive engagement. I plan on a NEMA 23 or 34 sized stepper motor with perhaps a planetary reduction gearbox. If I can do that then I won’t need an intermediate jack shaft speed reduction
chain drive set up. I know that I can get a 144:1 reduction planetary and with a 100 to 1 sprocket and drive I think I can get there pretty easy.
Now back to your regularly programmed schedule…..
Larry
Pahrump, NV
To view this discussion on the web visit https://groups.google.com/d/msgid/sara-list/1727707007.720373.1604336307516%40mail.yahoo.com.
Pablo Lewin
Larry, that's AMAZING! Do you have some pictures you can share with us? I love to see it so I can try to duplicate your work..I'm going to Ebay to see if I can get a reasonably priced truck floating rear axle
Pablo Lewin
Jim Abshier
image was made from an aluminum disc by drilling holes around the
periphery. The drive motor is an old TV antenna rotator. The holes are
sensed with an IR LED and detector. Although the resolution of this
encoder is only about 2.8 degrees, finer resolution (and greater torque)
could be obtained using some form of speed reduction gears or pulleys.
Jim Abshier
> *On Behalf Of *Paul Oxley
> *Sent:* 02 November 2020 08:58
> *To:* sara...@googlegroups.com
> *Subject:* Re: [SARA] Accelerometer+Inclinometer] HWT901B-TTL MPU9250
>
> Chip
>
> I have a similar one that I use to calibrate the elevation angle. The
> azimuth angle is accomplished by a compass by sighting back toward the
> antenna from a distance. For the exotic, this could be done with a
> level transit. I use the feed mount arm as a reference for the sighting.
>
> The distance is necessary to avoid the ferrous metal in the antenna
> and mount.
>
> Paul
>
> On Monday, November 2, 2020, 11:40:57 AM EST, Ciprian Sufitchi
>
> For thos interested, I purchased a small and inexpensive ($16)
> inclinometer last week from Amazon, which seems to work great
> especially when adjustung antenna elevation. I don’t have a reference
> for the precision of this tool, but the device can be calibrated easily.
>
> https://www.amazon.com/gp/product/B07R12DZQ9/
>
>
> *From:*sara...@googlegroups.com <mailto:sara...@googlegroups.com>
> <sara...@googlegroups.com <mailto:sara...@googlegroups.com>> *On
> Behalf Of *Pablo Lewin
> *Sent:* Monday, November 2, 2020 11:32 AM
> *To:* Society of Amateur Radio Astronomers <sara...@googlegroups.com
> <mailto:sara...@googlegroups.com>>
> *Subject:* Re: [SARA] Accelerometer+Inclinometer] HWT901B-TTL MPU9250
>
> Hi Paul
>
> We'll see if this inclinometer works. The mount has a lot of metal so
> it might not, right now I only have implemented an elevation actuator,
> I don't have an azimuth solution as of yet, the base of the mount is a
> metal circle with a 38 inch diameter so I am now leaning towards a
> Dobsonian style wooden turntable with a stepper motor but it will be
> a while before I implement that solution.
>
> Pablo (WA6RSV)
>
>
> Pablo
>
> I would be interested in your results. I previously tried using a
> compass as part of the positioning system. I could not get
> repeatable results on the azimuth measurements. I concluded that
> there was too much steel nearby. The Dish and mount supports were
> both made of steel. The motors were also mounted below the dish
> which would also cause magnetic fields.
>
> The inclinometer worked well. The accelerometer and multiple axis
> measurements was not applicable to the slow motion of the dish.
>
> Paul Oxley
>
> On Sunday, November 1, 2020, 07:08:54 PM EST, Pablo Lewin
>
> [I just bought the Military-Grade Accelerometer+Inclinometer]
> HWT901B-TTL MPU9250 9-axis Gyroscope+Angle(XY 0.05°
> Accuracy)+Digital Compass+Air Pressure+Altitude, RM3100
> Magnetometer Compensation and Kalman Filtering which I will try
> on my 2.1 meter dish to position it and eventually to track radio
> sources.
>
> This is NOT the Bluetooth/Wifi version which are cheaper but for
> obvious reasons won't work with a radio telescope, but the TTF/USB
> kind.
>
> Does anybody have any experience with these? I have 30 days to
> return in case the experiment fails.
>
> Thoughts?
>
> Pablo Lewin (WA6RSV)
>
> --
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Larry Mayfield
Pablo, what you want to do is find a salvage yard who specializes in wrecked trucks. All you desire is one side of the rear end and not even the drive axle . All you really want is the end of the housing and the hub with bearings.
No, no pictures, just my thoughts and meanderings and what I will probably do next summer. I have the big 3 meter dish, and several small sat dishes (Dish TV) pieces from long ago also. But I am new to RA and mostly a designer and fabricator. I do have my 2 meter dish though and I had it going for a while. Now parked for the winter though. I fabricated the feed system and on first light turn on had a pretty fair free hydrogen spectra. I am not an observatory type looking for oddities, but rather seeking Intelligent Extra Terrestrials. I am seeking a signal with a specific signature to it. I will dig up a photo of my 2 meter dish and send that to you. If I can’t find one I will go out and take another.
Larry
Pahrump, NV
To view this discussion on the web visit https://groups.google.com/d/msgid/sara-list/35912ea9-0cc9-43ea-9309-0b527b97bb9en%40googlegroups.com.
Larry Mayfield
For me, I will just buy a couple of the rotary encoders I mentioned. Here is one:
They are available is several different pulses per revolution. This one is 1024, but other are multiples up and down that point are available but price goes up. This particular one is 49 bucks. Here is an ebay link https://www.ebay.com/itm/Rotary-Encoder-1024-P-R-Quadrature/221588158663?hash=item3397aef8c7:g:4FIAAOSw9N1VmwzD
The 600 PR units can be had for as low as 13 bucks plus shipping from you know where.
Please be aware that fab skills are need to accomplishing stuff like this.
Here is a typical floating rear axle system. The parts wanted are buried inside all this iron. All that is needed is just the stub of the housing which has the spindle and the hub with the bearings and the flange where the wheel bolts on. About 80 percent of the stuff in the photo is NOT used . Brand is not particular.
Here is what you want to kind of wind up with although this would be good for a small AZ drive lazy Susan. If you buy 2 then the second one could be the bearing for the declination or elevation axis. The 3 hole flange is the earth side mounted rigidly, the rotating part becomes the bearing for the AZ and if you fab a mount for the second one and bolt it horizontally to the solidly mounted one then you have the elevation axis covered as well. Both are nearly friction free and because the loads as a telescope component are very light when compared to the rigors of hitting pot holes, curbs and just running down the road, will last nearly forever. This one is https://www.ebay.com/itm/2-Front-Wheel-Bearing-for-Buick-Century-Lucerne-Pontiac-Grand-Prix-Aztek-Montana/252076106550?hash=item3ab0e82336:g:L9EAAOSwK2Re-tvH
Hope these examples gives you some ideas on the how to make this kind of stuff. Reliable and very solid parts. I already have my elevation axis stuff. But need to head out to the junk yard and see if I can find a rear end that was damaged beyond repair on one side.
Good luck! Happy fabbing…
Larry
Pahrump, NV
-----Original Message-----
From: sara...@googlegroups.com [mailto:sara...@googlegroups.com] On Behalf Of Jim Abshier
Sent: 02 November 2020 14:50
To: sara...@googlegroups.com
Subject: Re: [SARA] Accelerometer+Inclinometer] HWT901B-TTL MPU9250 9-axis for dish positioning
You could also consider making your own encoder. The one shown in the image was made from an aluminum disc by drilling holes around the periphery. The drive motor is an old TV antenna rotator. The holes are sensed with an IR LED and detector. Although the resolution of this encoder is only about 2.8 degrees, finer resolution (and greater torque) could be obtained using some form of speed reduction gears or pulleys.
Jim Abshier
> *On Behalf Of *Paul Oxley
> *Sent:* 02 November 2020 08:58
> *To:* sara...@googlegroups.com
> *Subject:* Re: [SARA] Accelerometer+Inclinometer] HWT901B-TTL MPU9250
> 9-axis for dish positioning
>
> Chip
>
> I have a similar one that I use to calibrate the elevation angle. The
> azimuth angle is accomplished by a compass by sighting back toward the
> antenna from a distance. For the exotic, this could be done with a
> level transit. I use the feed mount arm as a reference for the sighting.
>
> The distance is necessary to avoid the ferrous metal in the antenna
> and mount.
>
> Paul
>
> On Monday, November 2, 2020, 11:40:57 AM EST, Ciprian Sufitchi
> <csuf...@gmail.com <mailto:csuf...@gmail.com>> wrote:
>
> For thos interested, I purchased a small and inexpensive ($16)
> inclinometer last week from Amazon, which seems to work great
> especially when adjustung antenna elevation. I don’t have a reference
> for the precision of this tool, but the device can be calibrated easily.
>
> https://www.amazon.com/gp/product/B07R12DZQ9/
>
> 73 de Chip N2YO
>
> *From:*sara...@googlegroups.com <mailto:sara...@googlegroups.com>
> <sara...@googlegroups.com <mailto:sara...@googlegroups.com>> *On
> Behalf Of *Pablo Lewin
> *Sent:* Monday, November 2, 2020 11:32 AM
> *To:* Society of Amateur Radio Astronomers <sara...@googlegroups.com
> <mailto:sara...@googlegroups.com>>
> *Subject:* Re: [SARA] Accelerometer+Inclinometer] HWT901B-TTL MPU9250
> 9-axis for dish positioning
>
> Hi Paul
>
> We'll see if this inclinometer works. The mount has a lot of metal so
> it might not, right now I only have implemented an elevation actuator,
> I don't have an azimuth solution as of yet, the base of the mount is a
> metal circle with a 38 inch diameter so I am now leaning towards a
> Dobsonian style wooden turntable with a stepper motor but it will be
> a while before I implement that solution.
>
> Pablo (WA6RSV)
>
> On Sunday, November 1, 2020 at 4:58:07 PM UTC-8 oxl..@att.net
> <mailto:oxl...@att.net> wrote:
>
> Pablo
>
> I would be interested in your results. I previously tried using a
> compass as part of the positioning system. I could not get
> repeatable results on the azimuth measurements. I concluded that
> there was too much steel nearby. The Dish and mount supports were
> both made of steel. The motors were also mounted below the dish
> which would also cause magnetic fields.
>
> The inclinometer worked well. The accelerometer and multiple axis
> measurements was not applicable to the slow motion of the dish.
>
> Paul Oxley
>
> On Sunday, November 1, 2020, 07:08:54 PM EST, Pablo Lewin
> <pabl...@gmail.com <mailto:pabl...@gmail.com>> wrote:
>
> [I just bought the Military-Grade Accelerometer+Inclinometer]
> HWT901B-TTL MPU9250 9-axis Gyroscope+Angle(XY 0.05°
> Accuracy)+Digital Compass+Air Pressure+Altitude, RM3100
> Magnetometer Compensation and Kalman Filtering which I will try
> on my 2.1 meter dish to position it and eventually to track radio
> sources.
>
> This is NOT the Bluetooth/Wifi version which are cheaper but for
> obvious reasons won't work with a radio telescope, but the TTF/USB
> kind.
>
> Does anybody have any experience with these? I have 30 days to
> return in case the experiment fails.
>
> Thoughts?
>
> Pablo Lewin (WA6RSV)
>
> --
> --
> You received this message because you are subscribed to the Google
> Groups "Society of Amateur Radio Astronomers" group.
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Paul Oxley
I would not suggest the use of nylon timing belts for the motion drive of the dish. Rather what I suggested is to use the nylon timing belts for coupling to a sensor that can then be moved away from the ferrous materials in the dish, mount, gears and chain drive, etc. The sensors have low torque and can use very small belts (i.e. 1/4 inch).
Paul
KD7JYK DM09
> wrecked trucks. All you desire is one side of the rear end and not even
> the drive axle . All you really want is the end of the housing and the
> hub with bearings.
radio magazine from around then showed a rear-end from a truck, with one
end set in cement, the mast on the other, the driveshaft input came into
the shack, with the steering wheel on it to rotate the antenna.
I like cleaner, more compact, and easier to integrate. Trailer hubs.
You can even get them with parking brakes to lock in a dish, tower,
mast, et cetera. Oddly, it's harder to fund hubs with manual brakes in
the US, but I've seen several on the European market over the years.
Here's an example of a hub:
https://www.crofttrailer.com/04369x-departure-hub-for-croft-tow-dolly/
Another style:
https://www.napaonline.com/en/p/BK_7304591
Research Trailer Hub, Idler Hub, Hub Drum Assembly, et cetera, see what
may work for various projects.
Shop around, they can be had for as little as $20 new.
I have a pair of very nice front end hub assemblies from a 1937 Ford
Coupe just waiting for some project.
What is old, is new, again!
Kurt
Larry Mayfield
Paul, the cogged timing belts are available is a zillion styles and sizes. One that is ½ inch or so wide can transmit a lot of torque without stretch. I looked into the use for my 2 meter dish on the equatorial axis. But, I also balanced the system so that the maximum torque was around 25 inch pounds to rotate the dish. That was at each end of its RA travel. I have all the pulleys that I was going to use along with a number of belts as I recall..
Larry
Pahrump, NVsomewhere, lol. And yes, they work well for turning a sensor shaft. My wife’s old Mercury Capri, ca 1972 had a cogged camshaft belt drive.
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Michiel Klaassen
Half a century ago I was a volunteer of a public observatory. I automated a 3m dish, polar mount, Neanderthal style.
It was built from a truck drive shaft/axle with one flange end welded solid, and the differential driven by a small motor.
On the other end the dish was mounted.
To track the sun automatically I mounted a mercury switch in the antenna boom.
With a timer the motor started on sunrise.
When in the evening the mercury switch reached the horizontal position, the motor was reversed and the dish turned 180 degrees and stopped when the mercury switch reached the horizontal position again.
Once a week on saturday I corrected the declination and the timer setting. The rest of the week it worked automatically.
We exchanged solar data with the Torun observatory in Poland every month.
So with just one sensor you also can build a solar radio observatory.
Regards,
Michiel
parac.eu
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Larry Mayfield
Michiel, I love the mercury switch idea I have some limit switches I was going to use but this is far simpler! Very good! Yes, if you can drive the ring gear in the differential slow enough then thayt mles a nice way to run the system: but I don’t like the backlash gear clearances that it might have. I have an old Jag differential the inboard type, that I might be able to use also. Nice ideas!
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Paul Oxley
Not sure that Mercury switches are still being made. The environmental hazard got them.
I looked on digi-key and they are now called tilt switches. They appear to use rolling balls. This would still work.
Paul
Larry Mayfield
Apparently they are, Ebay has them. And they have mercury warnings about toxicity etc. Here is a link to a typical offering…
I think the rolling ball idea is a better way to go, however. Wish I had thought of it, lol… And as mentioned, I have enough actual displacement limit switches that I am pretty set for just about anything.
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Pablo Lewin
Pablo Lewin
Pablo Lewin
Larry Mayfield
Pablo, sure it will work. When you purchase new stuff those it is sometimes a bit stiff. So keep in mind that “New” items will or might be a bit stiff. When purchased. Certainly should work, it is the same one that I sent with a second one in the phots. And it doesn’t matter if the wheel lugs are 4 or 5 bolt style. I suspect that if you are anywhere near a junk yard or breaker yard that you could get one from an old wrecked car that would work easier and also be dirt cheap. Just about any front wheel drive car will have these kinds of hubs. Some have 4 mounting bolts to hold them to the spindle mount or like the one below 3 bolts. Doesn’t matter at all for making a telescope lazy Susan table. If you are making something for a small Sat dish then I would get a furniture dolly from Harbor Freight add a deck to it and mount the hub to it. Then add the table piece where the lugs are. Then you have a rotatable table for pointing the dish in azimuth. Add your linear actuator to move the dish around a lower hinge point and there you have it. Add a wagon handle pull and take it where even you want to take it. Mount everything you can to the furniture dolly, lol. Heck I would put a pair of cheap levels on the dolly so you could level the base of it all when you park it. If you got your dish as a TV dish then it likely had some kind of tubular mount that was adjustable in RA and Declination. The installers had a sat finder and they hooked it up to the dish feed and pointed it in the general direction of the sat and then fine-tuned the dish pointing until they had a max reading. Tightened all the adjustments and removed the sat finder and it was done. Be creative!
Larry
Pahrump, NV
From: sara...@googlegroups.com [mailto:sara...@googlegroups.com] On Behalf Of Pablo Lewin
Sent: 03 November 2020 13:48
To: Society of Amateur Radio Astronomers <sara...@googlegroups.com>
Subject: Re: [SARA] Accelerometer+Inclinometer] HWT901B-TTL MPU9250 9-axis for dish positioning
What about this one here for 23 dollars with an abs connection? Do you think this will work?
Also they have 600PR encoders for only 14 dollars? What software does one use to connect to the computer?
Pablo
On Monday, November 2, 2020 at 4:45:46 PM UTC-8 Lawrence E. Mayfield wrote:
For me, I will just buy a couple of the rotary encoders I mentioned. Here is one:
They are available is several different pulses per revolution. This one is 1024, but other are multiples up and down that point are available but price goes up. This particular one is 49 bucks. Here is an ebay link https://www.ebay.com/itm/Rotary-Encoder-1024-P-R-Quadrature/221588158663?hash=item3397aef8c7:g:4FIAAOSw9N1VmwzD
The 600 PR units can be had for as low as 13 bucks plus shipping from you know where.
Please be aware that fab skills are need to accomplishing stuff like this.
Here is a typical floating rear axle system. The parts wanted are buried inside all this iron. All that is needed is just the stub of the housing which has the spindle and the hub with the bearings and the flange where the wheel bolts on. About 80 percent of the stuff in the photo is NOT used . Brand is not particular.
Here is what you want to kind of wind up with although this would be good for a small AZ drive lazy Susan. If you buy 2 then the second one could be the bearing for the declination or elevation axis. The 3 hole flange is the earth side mounted rigidly, the rotating part becomes the bearing for the AZ and if you fab a mount for the second one and bolt it horizontally to the solidly mounted one then you have the elevation axis covered as well. Both are nearly friction free and because the loads as a telescope component are very light when compared to the rigors of hitting pot holes, curbs and just running down the road, will last nearly forever. This one is https://www.ebay.com/itm/2-Front-Wheel-Bearing-for-Buick-Century-Lucerne-Pontiac-Grand-Prix-Aztek-Montana/252076106550?hash=item3ab0e82336:g:L9EAAOSwK2Re-tvH
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