360 Rotating Platform With Fixed Central Platform
Intro: 360 Rotating Platform With Fixed Central Platform
Hopefully the instruction below along with the photos will allow anyone with some basic DIY skills to create their own version of this platform and hopefully improve on the design somewhat. Reading around on the interweb looks like the DIY shops in the US are much better equipped than in the UK so maybe those based in the states will have more choice on what to use, I had to make use of what was available in the stores and what I could get
off eBay quickly.
STEP 1: The Requirement
I need a rotating platform to be able to take photos and 3D scan images of objects. However due to the way the 3D modelling software works the device must stay fixed in the centre position with either the scanner
or camera rotating around the object.
If at all possible it would be very helpful if the platform rotated automatically by use of a variable speed motor. This would help with taking time lapse photos as the platform could be calibrated to rotate 1full turn within a set amount of time meaning photos can them be taken at set positions via the time lapse settings.
STEP 2: The Solution
As I had to rotate a camera around a fixed object the centre cannot move. In order to rotate the platform I needed a bearing. Nearly all bearing are designed to have a spindle in the centre, this wouldn’t work. I knew of something called a “lazy susan” bearing, these are a large bearings, generally 100mm plus that basically have a large hole in the centre and the bearing actually rotates around it.
This is just what I needed to make the project work. Above is the bearing I chose for my platform and is 300mm across, and will take a load of 250kg (strong enough to rotate a person). If you look around on Google you will see all difference types, this one is aluminium with ball bearings that hold the two parts together, and others can be pressed steel. Depending on you size and load requirements will ultimately dictate the type you need.Also the ultimate aim is to rotate the platform with a motor I have taken into account the various ways of doing this. At the moment I’m not quite sure how or what I will use to rotate the platform, my two main options seem to be
Direct drive - Motor with a wheel that rests against the bottom or side of the main platform
Belt drive – belt attached to the platform with the motor separate
STEP 3: The Material
My whole platform was cut from a single 8’x4’ 19mm sheet of MDF. I live in the UK so I purchased this from B&Q for £20.00. They cut it into 2 x 1000x1220mm pieces with the offcut for me so it would fit into the car. You will see why I choose those sizes below.
STEP 4: Router Jig for Creating Round Discs
The first obstacle was to make the discs for the platforms. I wanted my platform to be round so I did consider a jigsaw but I wanted a better finish and also knew that it wouldn’t be properly round by the time I finished. As I already had a router and 6mm straight cut bit I decided to use that but I needed a way to cut circles with a router so googled that and realised I needed a jig. I didn’t have one so had to make it.
The jig is made from a 6mm thick off cut of MDF but anything that will allow you to attach the router and is fairly solid will do the trick.
NOTE – before you cut anything I would suggest marking out the shape of the jig and then you MUST mark a centre line along the whole length of the MDF. This centre line is based in the dead centre of the router bit when the router has been fixed to the MDF. This centre line will be used for the pivot points meaning you get an
exact circle every time.
The router fixing were made first, my router is a basic home DIY Bosch model that allows you to screw into the base. On the MDF I just traced around the base plate of the router, cut the hole in the centre for the router bit and marked the holes for the 3 screws. The screw holes on the bottom of the MDF was countersunk so everything ran smoothly when rotated.
Along the centre I have drilled holes every 50mm with the first one being 100mm from the centre of the router bit ( this is because 50mm was to close to the router base plate ) The holes I have drilled are 6mm but that’s only because I had a spare 6mm bolt which I was going to use as the centre pin. What I would say is make sure you do not drill holes bigger than whatever you decide to use for the centre pin as the tighter the fit the more
accurate the jig will cut.
As modification to this would be to create a long slot rather than individual holes, this would then allow for any size disk to be cut but you would have to make sure you get a very good pin as any movement would ruin the cut.
Just for info…. My Jig goes up to 500mm which means I can cut a 1mtr circle… that’s a pretty big platform but just to be safe and as I was having fun on a sunny day I also made a much larger version that goes up to
1500mm….. a 3Mtr circle … may that will come in useful for a garden table one day!.
Anyway that’s the jig. To use if just drill a hole in the material you want to cut NO BIGGER than the size of your pin. Insert the pin through the jig and into the material you are cutting and if you haven’t used a router before take it VERY SLOWLEY… I generally set the cutter bit down 5mm at a time, that way theres not to much pressure on the cutting bit and you get a better edge finish. Every now and again move the jig backwards to clear the dust and cuttings and remember if you’re using MDF either do it outside or wear a mask. MDF dusk is dangerous.
Also, this may sound obvious but ALLWAYS cut the outside diameter first. If you cut the inside hole you will have no place for the centre pin !
STEP 5: The Platform
As I mentioned above I’m not sure how to rotate the finished platform by means of a motor yet so I decided that I would need 4 disks.3 above the bearing and one as the main base.
Out of the 3 above the bearing the main one would be the top, then two below which would allow me to create a pulley wheel that I could use with a belt if that’s the route I was going to take. If you know you are going to use a direct drive method, i.e. the motor attached directly to the main platform you only need the top and bottom.
Obviously the three top disks would also need the centres cutting out. As my bearing is 300mm across I decided to cut the hole in the middle as 200mm, no coincidence that’s the smallest hole my jig would allow to cut. The top main platform is 1000mm, the next one is 400mm and the one below that is 500mm. The base was basically cut from whatever I had left from the sheet of MDF, from memory I think it worked out at 650mm.
The 2nd image show what it will look like when put together, image 3 and 4 are assembled but the whole platform is upside down to give you a better indication.
The belt will fit around the middle disk and the bottom will stop it from coming off. The image’s below shows it slightly better upside down.
I then decided to cut a final disk that could be used as the very top, this smaller platform is what the object will be placed onto and will sit on some sort of riser fixed to the very base of the whole platform.
This will not turn and purely acts as a fixed platform.
This is shown in image 5 & 6.
So that’s the wood all cut for the turn table, just need to put it all together now.
STEP 6: Putting the Turn Table Together
I got my bearing from eBay, just search “Lazy Susan Bearing” and choose the size and type that you need.
Unfortunately when my bearing was delivered it wasn’t as smooth as I hoped for. As I mentioned above my bearing is aluminium and is held together with ball bearings, there is a small grub screen on the outside that provides access to the ball bearings so took the grub screen out and emptied all the bearings into a cup. The bearing just falls apart when all the bearings are out and I proceeded to sand the edges with 600 grit wet and dry sandpaper, cleaned it up and then put it back together by simply placing the centre ring into the outer one and started to drop the ball bearings back in through the grub screw hole. Once full I dropped in a few drops of 3 in 1 oil and gave it a spin, much better.
Another type of lazy susan bearings is a pressed steel version, i personally haven't used one of these so i'm not sure if or how they come apart.
Next I had to attached the bearing to the MDF, this wasn’t as easy as I hoped for because in my wisdom I forgot to mark where the bearing would go on the MDF and now with a gaping huge hole in the middle it wasn’t that straight forward. In the end I just placed the bearing roughly where it needed to go and used a ruler to make sure the edge was the same distance from the inner hole at various points. I got there in the end but it took a while.
Note to self, before cutting the final hole use the pin hole and the router jig ( with a pencil not the router ) to mark a 300mm ( size of bearing ) circle. This will show where the bearing needs to go.
My bearing also came with pre drilled holes in each ring that were counter sunk, these were useful but didn’t really work. It also had rubber pegs as spacers, again useful but not up to the job I needed.
I took the rubber pegs out and used small washers as my spacers, these washers MUST NOT be any bigger than the width of the ring or they will cause friction when being turned. The inner ring was attached to the top section of the platform by means of the pre drilled holes and machine screws as they fitted flush into the pre drilled counter sunk holes.
Now this is where it got complicated. I had no way of getting screws into the outer ring and into the base disk of the platform. This was because the bearing was already attached to another piece of MDF! To fix this I decided to tap the holes ( I used M5 tap ) and then screw in from the bottom of the MDF into the bearing. Result… works great and also means I can take the base platform off to get to the bearing as and when I need to.
Unfortunately I forgot to take some photos of the final assembly as I was to excited in getting it all put together and there was much head scratching going on. The assembly is quite tricky to put together on yourself as you need to hold the base plate, alight it with the main section and bearing and then screw in the screws without the washers falling off… arrgghhhh… BUT if anyone really wants to see it I can take it all apart and take some photos.
The 2nd image shows the finished platform taken from the side so you can see the various components, you can just make out the bearing near the bottom.
Now all need to do it work out how to rotate it with a motor…..
STEP 7: Automating the Rotation
So… I had an old cordless drill that is on its last legs so decided to donate it’s part to this project.. The drill is 18 volts and in theory should have enough oomph to rotate the platform.
Firstly I needed to manage the speed in which the motor rotates as taking photos when the top platform is going around at drill speed wouldn’t be that useful.
Again… UK shops are useless so I resorted to eBay… and came up with this 6 volt to 40 volt speed regulator ( image 1 ). Very simple, has +/- input… twisty round know to control the speed and +/- output to the motor… I think it cost around £6.00 with free delivery! Wired it up to the drill battery and the motor and hey presto a VERY controllable small drill motor, in fact the speed control goes from zero… i.e. nothing to stupid fast… just what I needed.
So plan 1 is to attach the motor to the platform by means of a drive belt. The idea is to somehow fix a rubber wheel to the motor spindle… get a drive belt long enough to go around my platforms middle disk and around the
wheel on the motor… hopefully that should make it turn around and remain controllable.
Next I needed to find a way to fix the motor into some kind of housing that keeps it upright and strong enough to take the strain of the drive belt.
This is what I came up with…
Just off cuts of the sheet of MDF for the platform with a hole drilled in the middle to take the motor ( image 2 )
In the end I cut 4 plates so that I could then attach the whole thing to a small base plate along with the speed controller attached to the side ( image 3 ). The thing on top of the motor is some tin I cut out and screwed to the top of the motor and then the MDF. Everything is very secure and I doubt it’s going to move much. Image 4 shows the finished motor assembly with speed controller and cordless drill battery.
The square base plate will be attached to a side board on the platform…. ( image 5 )
This is again an off cut from the original MDF sheet and will simply just push up again the bottom of the base of the platform itself. The tension from the belt drive should hold it all in place.
In order to keep tension in the belt drive I intend to only use a single fixing in one corner when attaching the motor base to the side plate and then a spring to another fixing, this will then ensure the belt drive it kept nice and tight when in use.
And unfortunately that’s where I am up to… at the moment I am trying to source a wheel to attach to the motor, the plan is to use something like an RC car wheel that has a rubber tyre. Image 6 is an example of what I am thinking of using a lego car wheel. This will help the drive belt to get grip and if all that fails I could re-jig the whole motor mount and use set it up as a direct drive version… we will have to see where I get to.
STEP 8: Finished ( Manual ) Turntable
This video shows the turntable in action, all be it in manual mode. As you can see the top ring of the platform rotates around a fixed centre and provides enough space for a camera or scanner to be mounted. The centre platform is just sitting on a spacer ( old paint tin ) and the object is then placed on top.
I hope you find these instructions useful. As and when I get the whole thing rotating with a motor I will update or add an new set of instructions following on from these.
Any comments, questions, suggestions would be gratefully received.
21 Comments
dirtstarr 9 years ago
Thank you for the tutorial and idea, but why did you decide to have the camera rotate instead of the object?
pigsfoot 9 years ago
Hi dirtsarr... The camera / scanner has to rotate around an object where 3D scanning is involved as the calculations used to map an object takes the background into account. The background is used as a fixed point which then gives each photo grabbed a point in space. When the "stitching" of the images grabbed is performed the software uses the background to map the location of each image.... hence why I need to rotate around an object so that the background is always static. This is especially required if you are taking single photos to create a 3D object with software such as Autodesk 123d Catch.
Plus... just making an object go round and round is easy :-)
Another cool idea is to stand on the fixed centre platform and have a video on a boom rotate around you, this gives a really good video effect as you are static with everything around you moving. Movies use it a lot.
Hope that helps... if you haven't tried 123d Catch you should give it ago... it's what got me into the whole thing.
falk_m 3 years ago
I think this answer is only partially correct. The background is only taken into account if it provides technically extractable features. If it is blurry, e.g. by reduced depth of field, then only the object features will be considered for registration and reconstruction.
So it depends on photo settings; I think rotating the object is possible. Even a "greenscreen" behind the object could work.
I in fact came here because I will try out and report back soon ;) Thank you very much for giving me a start!
From my stationary objects with photogrammetry, I can highly recommend to put an irregular pattern on the center part which holds the object. That will provide a lot of features!
I collected some more settings and tips here: http://www.mielke-bio.info/falk/photogrammetry
Cheers,
Falk
DazzlingDukeOfLazers 9 years ago
McMaster Carr has a really good selection of off the shelf turntables:
http://www.mcmaster.com/#bearing-turntables/=wk35f...
500 Pound Capacity!
mathom33 9 years ago
padbravo 9 years ago
Yeap... why this aproach?
Usually... the subject is to be rotated (the background remains fixed... in order to be "eliminated" more easily)
wilwrk4tls 9 years ago
Most of the 3D capture software packages want the object that you are trying to capture to remain still, while the camera changes its vantage point- that way the software can render out the differences in the background around the object and calculate what the subject actually is. I tried movign the object and it really messed up the capture!
wilwrk4tls 9 years ago
*moving*
pigsfoot 9 years ago
Padbravo... Your question is already answered in other comments and in the brief of this project.
Please bear in mind that this project was specifically designed with 3D scanning in mind. 3D Scanning works best when the camera / scanner is rotated around the object as the background is used for mapping purposes. What is also useful with this design is if I just want a rotating turntable I can drop the top platform ( the one the object sits on ) onto the camera platform and the whole thing will rotate..
wilwrk4tls 9 years ago
I had a very similar idea, but I haven't built mine yet. I was also going to add a piece to allow capturing from different heights around the piece being scanned since they suggest different camera angles to better capture various details. I did a quick model to show what I had in mind. The slot would allow the camera rest to move up and down, and the post sticking up would be a standard 1/4"-20 camera tripod mount thread.
Also, you may want to put something patterned on the table, such as newspaper or something that differs graphically all over. The more unique the design from each angle the better the software can process the location and stitch the images together more accurately.
Jayefuu 9 years ago
Fantastic build! A better title picture and this will get featured for sure!
pigsfoot 9 years ago
Awesome, will try to get a better picture, maybe a still from the video.
Jayefuu 9 years ago
Much improved!
Jayefuu 9 years ago
Also, are you planning on using 123d Catch for the 3d scanning?
pigsfoot 9 years ago
Hi Jayefuu... Thanks for the comments. The whole design and idea actually came about because I was using 123d Catch and I wanted better control of the images I am capturing. I also have a Sence Scanner which I haven't tried yet with this design but that should also work. One thing I have yet to do is to paint the centre platform and add individual graphics at 12 0'clock, 3, 6 and 9 o'clock as I have found doing that allows 123d catch to stich the separate images back together much better.
tovey 9 years ago
When you paint the center table put a grid with circles on the top. This will make it easier to center your objects when scanning.
Add indexing marks on the edge/side of your object table and at the inside edge of the camera platform. This will give you exact positioning for each image you take. It will also allow you to control the quality of your scans and determine the most efficient number of images to model conversion.
Jayefuu 9 years ago
"One thing I have yet to do is to paint the centre platform and add
individual graphics at 12 0'clock, 3, 6 and 9 o'clock as I have found
doing that allows 123d catch to stich the separate images back together
much better."
Good! That was my concern with the current setup, without any marks to reference it by 123d will struggle. Bilal talks about it a bit in this Instructable if you're interested:
https://www.instructables.com/id/Prosthetics-Modification-for-Pain-Relief-of-Pressu/
Tony Gouveia 9 years ago
Hi ProfFreddie,
I,m in the process of building a variation of a similar turntable with the difference that it will be powerful enough to rotate a human. Instead of using a turntable bearing the disc will be rotated by an AC motor/gearbox and ride on heavy-duty casters. Speed control will be achieved using a small variable frequency drive unit. I'm interested to see how your's turns out after you power the rotation.
Ruzzzx9 9 years ago
I love this idea
I have a Cubify sense and I'm going to build a variation on this.
The sense needs to do this for scanning because the software needs the background to move :D
ProfFreddie 9 years ago
If that was so, then you could not scan anything with a plain background, which I hope is not the case because I'm just about to buy a Sense.