Gorden Group venture - Gimbal Review

[Jake Danilchik]

Charles and Chuck,

Charles , I wasn't aware that the gimbal clamp bolt issue had been discussed elsewhere as I have not gone to any other steadicam websites.    Chuck, as usual, thanks for sharing your solution to the problem, hopefully Gordon will be able to implement it on the next run.     So on to address one of the *other* issues.

Once the Gimbal tube assembly is symetrical it allows a person to start adjusting the gimbal's side to side position.

The diameter of the spacer(s) ( see picture below ) that define the side to side position of the gimbal tube assembly needs to be smaller to allow the spacer to touch the inner race of the bearing rather than rubbing against the yoke.  Thus, when the bolt(s) are tightened it won't cause excessive friction.   Also the width of the spacers need to be accurate ( and likely custom for each gimbal "off the assembly line ").  I turned some aluminum tubing down and made a variety of widths.  Then I spent an entire evenning repeatedly filing away at spacers to make minute adjustments to the side to side spacing.  ( If you have to make one shorter then other side has to be longer and thus I suggest making many many spacers of varying length to get close to the right combination ~ then file them to fine tune ).    This was the solution I used to fix Wing's first problem and on my own gimbal that is very similar to the Cody/Gordon gimbal.    Again,  I hope this is addressed in future group ventures based on this design.   Overall, it is a beautiful .... just some kinks that are critical to proper functionality. They are fixable and necessary ! As we all know the gimbal is the one thing that has to be close to perfect or all is for not !
Again, a plea for further thoughts on this :-)

Cheers,

Jake

[chuck colburn]

Hello Jake,

That's exactaly the right thing to do with the gimbal tilt bearings, it's called setting up the end play of the bearing. If you don't do this and tighten down the screw you are going to do one of two thins, either score the inner and or outer races of the bearing or dimple (brinelling) them. In either case you can kiss the bearing goodby. You can make the adjustment of the end play easier by using a spacer that is close to the right length but not quite and using steel shims in combination to find that sweet spot where the bearing turns smoothly.
Here is one source for such spacers.
http://www.sdp-si.com/D790/HTML2/D790C10039_1.html

Another idea that comes to mind is to not use ball or roller type bearings at all. Since there is no rotational speed to speak of, I would think that a properly fitted teflon coated bronze bearing would serve quite well in this application. There are precision made shoulder screws that would be perfect for ths use. One would still need to set up end play but not to such a degree of precision as would be required with a ball type of bearing. Either way the use of a self aligning type of bearing would ease the accuracy requirerments of the assembly.
Here is one type of teflon bronze bearing.
http://www.spyraflo.com/specifications/teflon_bronze/index.html

Chuck Colburn

[trung dau]

Hi Jake,
Something I don't understand. Why do u need a balance weight clamp on the gimbal? do u afraid it make the whole rig out of balance? The top stage itself is imbalance, the camera it self is imbalance, the cable inside the post make the rig imbalance, the monitor is imbalance so we need to adjusting balance the rig before operating.

the most important of the gimbal is how the bearings work. is the pan bearing in the centerline of the gimbal and the post? R the centers of tilt bearings exactly in the midle os the gimbal and the pan bearing?

[Jake Danilchik]

Hi Trung,

I agree that the most important aspect of the gimbal is centering of the CG on every axis of the bearings. In order to find and adjust to that center I decided to take as many variables out of the equation.    The short answer is that *if* the gimbal clamp wouldn't rotate it wouldn't be any different than having to adjust for batteries , monitor position the camera having a different lens... etc using the top or bottom sled adjustments.

However, I think it is best to take as many variables out of the equation in order to find the gimbal's true center.  If a cable was inside the tube flopping around I centered it with foam insulation ( for copper water pipes ). YET, I didn't even want the wires to get in the way of perfection so I removed the top stage, bottom stage, etc before I tried to find the gimbal's perfect center.  I knew the carbon fiber tube was probably the most symmetrical piece in the sled assembly that wouldn't require a counterweight.  If you go to this extreme you'll find that if you don't counterweight the bolt you'll have a tilt issue when trying to determine whether your gimbal is centered.   If the clamping mechanism is not symmetrical and you use the top or bottom sled to adjust for the weight of the clamp assembly you will always need to note the orientation of the bolt clamp.    Basically, in Cody's design if you loosen the bolt to change the gimbal position you are at risk to rotate the gimbal clamp as there is currently no way to stop this from happening other than taking extra care not to rotate it.

At the very least it needs to be pinned so it cannot rotate but I found it easier to find the true center of the gimbal by reducing all variables.  If you reduce the variables this "sore thumb" becomes very apparent and needs to be addressed before going further ( by using a counterweight on the clamp itself ).

I think we all agree ( Job and Charles said it best earlier in the thread ) how important the gimbal is so why not go the extra mile to redesign this so the clamp isn't an issue.    I was able to get nearly a 6 second drop time that resulted ( after the pendulum action stopped ) in a perfect repeatable horizon.  I doubt I could have done this without putting counterweights on the gimbal clamp and also removing all the other variables while adjusting the gimbal.  In use I don't think I'll ever be able to maintain a usable horizon with a 6 second drop but regardless it pays off when you are flying with a 3 second drop.   I'll  never stop refining the gimbal. 

cheers,

Jake

[Jake Danilchik]

Chuck,

I am going to try those teflon bearings out.  Thanks !

p.s. re:   "end play".   I used to race slot cars and know that term very well but forgot it until you mentioned it.    I would adjust the end play in the motors so the brushes and armature commutator would wear nicely and the gears wouldn't vibrate... etc.. anything for that competitive edge !  :-)

Jake

[trung dau]

i have find a way to stop the clamp rotating while we do adjusting. It's very simple, i will show u all when my gimbal is ready.

IS there any way to check the is the tilt bearings are in alignment? And Check if the pan bearing in the center of the gimbal?

I wonder which one the best pan bearings are for 1.5 inch gimbal and 2 inch gimbal?

Thanks

[Joe Sanders]

Has anyone tried porcelain bearings?

[trung dau]

what is porcelain bearings?

[chuck colburn]

Chuck,

I am going to try those teflon bearings out.  Thanks !

p.s. re:   "end play".   I used to race slot cars and know that term very well but forgot it until you mentioned it.    I would adjust the end play in the motors so the brushes and armature commutator would wear nicely and the gears wouldn't vibrate... etc.. anything for that competitive edge !  :-)

Jake

Good morning Jake,

Ahhh slot car racing. I grew up in southern California which had to be the slot car capital of the world so I know of what you speak.
Anyhow if you are going to use those or any type of plain bearing, (bronze etc.) be sure that the axle be it a custom piece or a precision ground shoulder screw is the proper matching fit, finish and hardness for the application. As odd as it sounds a harden steel shaft fitted to a properly lubricated oillite bush will wear out before the bearing will.
Most catalog sites for plain bearings will have specs. for the fitting of the axle to the bearings. Also since plain bearings have so much more working surface area, you can use a smaller size unit if you wish. Since there is no rotational speed to speak of I would think that a properly fitted bearing and axle shaft would have a longer service life than the operator using it. LOL
Here's to a happy new year to all,

Chuck

[chuck colburn]

Has anyone tried porcelain bearings?

Hey Joe,

Never used porcelain type bearings but I've read they're good for extreme enviroments. Might come in handy for that moon walk (not the kind Michael Jackson does) shot.
What I have used are sapphire bearings. Every bearing in the movement of the CP-65 (aka Showscan) camera was of this type. As I recall they were not all that exspensive albeit they weren't very big either. They were kinda of a pain to work with as you had to pick a matched pair for size and/or centerless grind the rotating or sliding shaft to fit the bearings.
If your done loafing around for the holidays we are all waiting with baited (or is that eggnog) breath for new info on the building or cranes and jib arms !

Have a good one,

Chuck

[Jake Danilchik]

Here is the fore / aft  adjustment mod that I came up with for my Cody gimbal.
-Jake

[Charles King]

Nicely done Jake. I guess it works perfectly now.

[Cody Deegan]

I used to think having the clamp on the bottom would throw off dynamic balance as well.  And to some extent maybe it does.  I did a lot of tests and even had a brief discussion about it with Elliot years ago.  But I was able to achieve dynamic balance with my rig all the time.  I don't know if it has something to do with having 10 pounds of weight on top and 6 pounds below counteracting each other, making the gimbal clamp seem insignifigant, but it just never seemed a relevant enough factor to spend time fretting over.  I never bothered with centering my cables inside either.  But perhaps addressing all these issues does make for a far superior system.

[Jake Danilchik]

Cody,

yeah, I have to admit that my little rant regarding the gimbal clamp was a bit over the top :-)  I guess I was striving to be a purist , contrary to my usual self !

Jake

[Lucas Adamson]

So, how are people getting on with these gimbals now?

Has everybody got theirs set up now?

Mine needs some tiny tubes between the yolk tilt bearings and the pan bearing case to act as spacers, and I will be set. McMaster Carr do a 3/8 OD .245 ID tube. Item no. 89965K243, which is perfect.

I also had to replace the 1/4" 20 bolts for the yolk with longer ones, and file them to precisely the right length, to get maximum thread coverage.
Also, as mentioned earlier, I cleaned out the pan bearing after taking off the covers and discarding them, and replaced the grease with teflon lubricant.

It is silky smooth in all directions now though.

How about everybody else?
Lucas