Hello wise board of SMA!

I am planing to make simple moco unit with Arduino system. I got great help from previous post about the subject and from Simon Tytherleighs comments.Things have developped plesant ways since last time I looked to this subject. Seems that it is possible to do system with ~400€!

One thing what puzzles me is bearings of pan and tilt head. I am planning to make U shaped one.
Have you used some axial ball bearing for Pan? Maybe something like this:
https://www.vxb.com/ProductDetails.asp?ProductCode=Kit7852

Or do you have it without any bearings, just wax or something?
How about Tilt?

Thank you,

-Tatu

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Hi there. The bearings are quite a challenge, and what I did was to use ball bearings available from Servocity. They are really neat and come with a surround that can be bolted onto a flat surface.

https://www.servocity.com/1-000-bore-quad-pillow-block

I used the 1" size as I also used Servocity tubing shafts and gears, and reckoned that bigger was better. They are beautifully made, so I don't regret the choice. You need 2 bearings to hold the shaft. I was able to mount them inside a section of 1 1/2" square alloy for a vertical support (i.e. pan) and on either side of  1 1/2" X 1" section for the tilt mech. Doing it again I would mount either side of the rectangular section for both.

I will post some pics for you as writing it down is often confusing.

Hope your rig is going well. It is such a thrill to finally get it all going!

OK, here are the pictures with some captions to help. NB There is another spacer washer at the back end of the tilt bearing, just inside the clamp. I made them out of some old plastic bearings I had.

And a few more, showing that the whole camera mount can be adapted from commercially available brackets and sliding mounts. It's really important that you can adjust the position of your camera and the focus motor, hence the use of the Fotomate. I just took the second slider off another one that I had.

This moco rig setup has been used quite a few times, and once it is set up with minimum backlash, it does work well. The minimoco I made does not have a jib arm, and I think this limits its versatility, so I would recommend making a jib arm if possible.

The rotation bearing I used for Maximoco was completely different to these. I did start with a shaft and a thrust bearing like you showed, but ended up with a 350mm dia bearing, comprising two pieces of hard plastic, 20 14mm ball bearings and a bearing 'cage', just a bit of MDF with generous holes in it, to retain the bearings. The whole thing uses a 6mm central shaft just to hold it in place.

Around the edge of this I used a piece of flexible gear rack, and mounted the motor at one corner. It works very well and is extremely stable.

Rise and fall for the jib arm is using a 12mm dia ballscrew, with the motor mounted at the bottom. There is no backlash on this arrangement.

Thank you Simon. Your system looks really solid!

I am trying to keep my head small and movable. I was thinking to put 2 trust bearings to midle 10mm shaft. One below the fork and one to top of it. Inner forks bearings would be basic 8mm/22mm ball bearings attached to external fork.The rig is made from aluminium and pulleys 3d printed. Now the camera heads height is ~22 cm + 1x trust bearing. I was hoping that teflon bearing could be enought. those height is less than 2 mm.

My palan is to use GT2 belt and meke it tense with extra idle pulley. Stepper motor for pan is now laying in between the forks, witch is litle bit limiting for camera. But idea is to rig camera to Smallrig15mm aluminium rods so I can move it in depth. That makes system more flexiple. Those 2 paralel rods will hold allso a focus puller. For axial movements I will propably get planetary gear steppers. Whole thing should be attacheable to camera rails, tripod or jib arm.

Is your focus system exact enought? The motor for it is 200 steps per round? Then the minimal movement with that kind of gear is >0.5mm? In macro shooting that feels heavy. Geared steppers arent so cheep, so i dont want to by one for focus, if its not needed.

Now I am looking for 0.4A per phase 12V steppers. If my system would use 4 of those, 24v 4A power suply would be enought for sure. But is half of it enought (24v 2A)? Some people count the wats and others dont?

Your design looks OK. The weak point is the pan bearing, which has to hold everything. So you need to make that good and strong. I don't think your system will work out much smaller or lighter than mine.

Smaller bearings for the tilt will be fine, I am sure, especially as you are dividing the load equally. But they should really be ball bearings to work smoothly without play. I like the 15mm rod idea as it is quite versatile, but it will be a bit more bulky than my system.

Belt transmission is a good choice, but you must pay attention to tensioning, as the success of the whole system depends on minimising any play or backlash. I think I would mount the tilt motor on the outside of the arm so as to get the height of the bracket lower, but that's a personal choice.

My focus system works well with the big plastic rings you can buy for camera lenses. I might also put another gear in between to reduce the speed further. But you can control the speed within Dragonframe Arcmoco. It is called Jog Speed, and you should start slow and increase it until you are happy. Don't forget that the 0.5mm step is reduced by the gear ratio to something like 0.1mm. And you can set limits so you don't break the lens ring.

The steppers I use come from stepperonline, who have given me good service. I have opted for steppers with about 1.6A draw at 24V, so have used a 15A power supply for 6 axes. The NEMA 17 geared steppers need to be the high precision type otherwise the backlash is too great. Or you use NEMA 24 motors without a gearbox, like Edu Puertas, although he used a worm drive for reduction. I don't know where you would find motors with the low current draw you describe.

I also use the metal aviation type connectors, 4 pin for the leads, and have a large loom for the big rig. Must make up a smaller one for Minimoco.

Pan bearing can be weak point. I have to tight the shaft so that pan axis is steady, but same time there will be more pressure for bearings. Propably pressure will cause more friction. That + shafts friction will make connection a bit stiff I think, but it wont be wobly. Or it will be loos and wobly. Is it possible to adjust the pressure so that system will work nicely?  Sadly I am not able to calculate it. Geared Motor can give torgue more than 3Nm, so small friction around shaft is acceptable. I will seek what solutions Servocity has. It seems to be good place for parts. pillowblocks and clamps might be safer choice.

Stepperonline has good selection of steppers. 0.4A 12V seems to be usual for nema 17 link

I think this is where your thrust bearing comes in, although it would not be necessary if you use similar bearings to mine, which are wide and stable. You want to avoid friction, or you get 'stick-tion' where something does not move when activated , then suddenly unsticks and moves a lot. Not so good.

I had a look at the NEMA motor you linked to, and you need the 30:1 gearbox to make it slow and torquey  enough. This is rated at 1.68A per coil. It just means getting a bigger power supply unit, but I found I could get a whole range of motors with similar rating, so the drivers were interchangeable.

I think that I will go for one thrust bearing and put pillow bearing as top part (maybe this). Then I have bearings for both surfaces (vertical & horisontal). 10 mm rod should be steady enought. The thrust bearings width is 3 cm witch will be facing the base directly. Pan pulley wil be attached to base so that it is not holding any weight of camera.

With my pulleys and 10:1 gear a get 14 000 steps for 360'. That sounds a lot. But when I divide it to circle witch is 2m from camera, 1 step is nearly 0.9cm! Damn distace! I declaire war against time and space! (- by bying bigger gear)

This is all sounding pretty good. Just make it as accurately as possible.

For the stepper motors, I have found that the slower gearboxes, 30:1 and up are what is needed to slow things down. When you think about it the pan and tilt will not be travelling great distances, so do not need anything faster.

Check that your 15mm rail system will clear the frame when you rotate up and down. Make sure that you never allow the machine to crunch anything as it will just keep in in travelling until you tell it to stop!

One last thing. The brackets sold for NEMA 17 motors with gearboxes fit the smaller size, and I could not find any for the larger gearboxes online, so I bought some alloy brackets and re drilled them.

I hope that system could be usable. One thing is motors backlash. 30:1 gears has Backlash at No-load: <=25 arcmin -  which would mean 7 hole steps! With this accuraty bigger gear would be pointles? And is there any use of microstepping? Are those accurate enought?

If you use geared steppers there will be some backlash. The ordinary geared steppers seem to vary in their backlash quite a lot, and I found them unacceptable. The high precision ones are made much better, and their backlash is much smaller. 

With the tilt you can have the camera a little off the centre of gravity, so it always has the backlash in one direction. This works unless you tilt the camera far enough to tip it the other way! And Dragonframe has a rollback facility, where the motor goes a bit further than zero when resetting, so it approaches the first move with backlash already taken care of.

I am using the black box type of driver, and these offer micro-stepping. I use 1/16 micro-stepping. This works well, and as you say something like this is needed so movements can be precise. I have no evidence on their accuracy or inaccuracy, but have not heard of any problems so I think it is fine.

Incidentally I am also using mega 2560 Arduino boards. They offer the 8 channels. 

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