Iso-elastic Basson arm

[Pascal]

Well, I think I'm going to try this out. With some simple modifications the arm can be transformed into something that resembles an iso-elastic arm.
I'm going to take out one of the springs and have a cable acting as the diagonal one, attached to the top axis of the upper bone. The pully has to go, I will have a pully/drum combination machined in a workshop. The drum will have a smaller diameter than the pully. This way, when you boom from the most upper position to the lower, the diagonal cable(spring) might stretch 5 cm, but because of the pully/drum the spring in the lower bone will only stretch half that amount resulting in a larger force helping you to boom up....
The steadicam provid and ultra arms use this type of assembly and call it iso-elsatic: less stretching of the spring so that when the arm holds 20 lbs at equilibrium, hanging perpendicular to the ground, it will hold close to 20 when you've boomed up. This way the arm could, in theory, hold itself in position... quite ambitious, but I think I can pull this off:cool:
Feel free to post any comments you like!

[charles]

Sounds interesting. Post some pics of the new pully drum mounted when you're done, okay?

[Pascal]

Here it is.
I'm not changing anything on the arm-chassis, just adding a couple of things, and taking some things off!

[Pascal]

And a close-up of the pully/drum

[Jason]

Good luck and let me know how it goes

[charles]

Pascal. What is the distance from the spring connected to the wire to the drum and what is the length of the spring in it's relax position?
BTW, when you replace the hand knob with the Alan screw you did yourseld a big favor. The knob was big and cumbersome. With the Alan screw it looks much better. I think you gonna give this arm a better appearance than how it looked before. A major improvement Pascal. I'm impressed

[Pascal]

Hi Charles,

The arm has two different sized springs, I need to figure out which one would be best for this modification. But it's save to say neither of the springs will be stretched beyond its limits because of the pully/drum. Only downside is that the spring has to be pre-streched to a point that it will hold 20lbs. This might compromise the arm chassis after a while... On the other hand: it's made of steel, so it should be able to handle quite some stress.

Yes, that tensioning knob really is cumbersome; it limits the boom range because it bumps into the vest bridge/connector, so it comes to a sudden stop when you boom down... Furthermore: the entire adjustment range isn't available with the way the sping is fixed to this knob adjuster, can't turn the knob any further than half-way through the adjustment range. With the Allen bolt modification I can use the entire range!

I still need to sort out a couple more details. Will keep you posted!

[Pascal]

Ok, a detailed drawing of the pully. I've send the drawings to my machinist for evaluation; stress points, weak spots etc. The pully has a ratio of 2:1 which means the spring should hold twice as much at maximum elevation than it did before. Which is a good thing!

[Pascal]

and side view

The two gaps are for the cables to be fixed onto the pully. There will be a tensioning block fixed to the spring to make sure both cables running from the spring will be of the same lenght when they reach the pully, that way the force exerted by the spring will be devided across the two cables.

[charles]

I'm impress Pascal. Nicely drawn. I might add but I'm having difficulty in understanding how you're going to attached the two spring cable. I see the notches but how are they going to be connected?

[Pascal]

The idea is to have ball fittings or studs on the end of the cables, like the kind you find on bycicle hand brake cables. These then will be hooked around these notches and the cable winded once around the pully. For extra security the fittings are held in place by some steel screws

[Pascal]

Finally got a decent program running on my computer, so here's my first sketch :p
I also renamed the thing to tripple pully.

[charles]

Nicely generated Pascal.

[charles]

"Only downside is that the spring has to be pre-streched to a point that it will hold 20lbs."

I was wondering if the 20lbs or 9kg, you are talking about, is the total weight of the combined sled and maximum camera weight, you will be flying?

BTW, did you know that the new steadicam flyer uses no pullies or wires but it functions as an iso-elastic arm. I was looking at the it's design and noticed that this may have been accomplished by the slanted slots in the side walls. As the spring is adjusted vertically it pulls back while still keeping remaining linear.


So, did you finally complete the arm to function as you wanted?

[optonica]

Hi

I've had a quick go of the flyer (very quick) and it isn't completly iso-elastic like the master, provid etc but it's as near as you can get on the older type design!

It requires a small amount of force to hold it in place, no where near as much as the basson or most others you could easily hold it with one finger for example! where as with the master and it's brothers you can actually let go and it stays!!!

Also a true iso-elastic will also do the funky step movement as jason found out when you step up a step it actually wants to stay (could be fun a flight of stairs) as opposed to trying to rise with you like the older arms and the flyer. However the flyer does rise a lot slower from this type of shot! Hence why I can work the flyer as I'm pants with an iso-elastic arm.

One thing I do want to say is that on the one I got a go of the gimble was crap loads of play and friction and this is based against my basson not a high end rig! it could be that it was a well used demo/prototype but this better not be on the production model or some people will be pissed!!!

Ant

[charles]

Tanks Ant for that short review. I heard the same thing about the flyer from one of the Glidecam members, who had also tried it. Oh well....



Hi

I've had a quick go of the flyer (very quick) and it isn't completly iso-elastic like the master, provid etc but it's as near as you can get on the older type design!

It requires a small amount of force to hold it in place, no where near as much as the basson or most others you could easily hold it with one finger for example! where as with the master and it's brothers you can actually let go and it stays!!!

Also a true iso-elastic will also do the funky step movement as jason found out when you step up a step it actually wants to stay (could be fun a flight of stairs) as opposed to trying to rise with you like the older arms and the flyer. However the flyer does rise a lot slower from this type of shot! Hence why I can work the flyer as I'm pants with an iso-elastic arm.

One thing I do want to say is that on the one I got a go of the gimble was crap loads of play and friction and this is based against my basson not a high end rig! it could be that it was a well used demo/prototype but this better not be on the production model or some people will be pissed!!!

Ant

[optonica]

Hi

Charles I believe the reason the spring guide slots angle back towards the bottom is because, if it was going straight down when the spring was at the bottom it would start to get slacker as moved down as the distance wouldn't be as far as reaching to the top (if that doesn't make sense let me know)

For example draw a rectangle now measure from the bottom left corner to the top right one now measure from the bottom left again to half way up the right hand wall! there is a difference in the distance. This isn't how the flyer (and the master for that) changes it's strength it is actually changing the amount of leverage the spring can get over the pull of the sled i.e. changing the 3:1 ratio to 4:1 which would make it able to carry less weight (again any questions let me know and i'll try to explain more)!

I'm not saying it would't work if it wasn't angled back in the slot but with the ratio changing and the spring getting slacker the adjustment would be very difficult to get right the tinnest of turn would throw off the arm balance and would really start to get annoying when setting up the rig!

From reading my earlier post there is something I must make clear I do like the flyer a lot and would love to own one if it took the weight of camera I would fly on it. It is great for it's weight range and lovely and smooth and a well designed and balanced arm but the gimble really let it down for me. I just hope it was down to the fact it was a demo model and had well abused!!!

Ant

[Pascal]

Hi,

I've been making some drawings to see what exactly happens when you adjust the tension in the Flyer arm. To me it seems that the stronger the tension the less iso-elastic the arm will become, because the lifting triangle gets larger and larger. So you go from a PRO based arm to a Glidecam based arm. I know what a PRO arm feels like, and I know what a Glidecam arm feels like, and the Glidecam arm really looses a lot of lifting force when you boom up, unlike the PRO that keeps that lifting force. The angled slots are IMO only angled back because of the extra adjustmentrange you get from moving up and back.
I just realized what you mean by the slacker, Ant (had something mixed up in the translation). The diagonal gets a lot smaller when fully adjusted and boomed up than with the lowest adjustment and boomed up. So the force inside the spring is a lot lower when fully adjusted and boomed up. The angled slot keeps the spring from loosing too much power when booming up. This also means that booming down gets harder. So in now way can this arm be iso-elastic. The arm being so smooth is accomplished by removing the pullys and cables from the design as you mentioned, Charles.

When I tried out the Ultra arm it didn't stay where I put it, unlike the Provid that did hold the weight at any given hight. But the Provid I tried really had a lot of "sticktion" which made it very weird to handle, and it actually feels like friction because you don't have to apply any force to boom. I gues the amount of stretch of the Provid springs is very small. I placed the sled in a position and moved the elbow up and down, and no matter what position the elbow was in the arm held the sled at the position I had it set in. Jason has experienced this with the apple box training: you going up and down and the arm lets the sled stay at the height it was in at the beginning.

"So, did you finally complete the arm to function as you wanted?"

No.... To be honest, I haven't done any of the things I talked about. Lack of time and money. And if I were to change the arm it would make more sence to build an entirely new arm, which I would love to do. A structural stronger design than the Basson's arm, NO WELDING, and probably a no pully system. However I'd like to try out the differential pully to get near iso-elasticity...

Pascal

[charles]

Thanks for th eexplaination Pascal.

One thing I've noticed using the pro arm design is that I would need very strong springs if I was to use an extention spring setup. I feel this is the compromise in choosing this design. I also feel it would be more preferable. I guess the angle has a big part to play and thus getting the right spring to function in that scenerio takes some calculating.

I've attached a photo of the spring setup in my old arm. The springs in that setup were 4mm x 30mm x 110mm. While adding weight to the arm it deflected with ease without any resistence. Yet, when the same springs were placed across the diagonal it produced some resistence.

I'm going to try 5mm x 36mm x 120mm using the pro design to see if that will do the trick.

[optonica]

Hi

Pascal what camera where you flying on the ultra? if it was something lighter like a beta (i know it's not light but for the ultra it is) then it would struggle to hold it's height like the provid even though it is supposed to not care what weight it's flying all the systems work best near there maximum weight and the ultra is really for film cameras! the broadcast master was better for beta stuff! with the ultra and cine Put something heavy on it like a panaflex millenium plus mag 45mm prime and film and it works perfectly but that silly sticktion feel returns!

For the record I love the Pro arm it's without a doubt the best arm out there as it is nearly iso-elastic in feel but still has the right amount of spring in it (I have no idea how to discribe it)! closely followed by the 3a!! I need to start saving!

Also charles I'm sure you probably know this but the pro arm springs are not that strong really or heavy gauge springs but they are stupidly long about 3-4 times the length of the arm when out of the canister which is how they keep the lifting force so well when boomed up because they are still nowhere near there full extended length! with such a short and heavy gauge spring you may struggle to get that Pro feel!! but I'm guessing your trying to get away without the canister which on the pro stops such a long spring deflecting out to the side in the middle of the spring.

Ant

[charles]

Also charles I'm sure you probably know this but the pro arm springs are not that strong really or heavy gauge springs but they are stupidly long about 3-4 times the length of the arm when out of the canister...

...but I'm guessing your trying to get away without the canister which on the pro stops such a long spring deflecting out to the side in the middle of the spring.

Ant

I knew the springs were longer than the arm itself. Can you imagine the forced used to compress the springs into those canisters? Yikes! That's why I'm trying out this approach as the cannister method is completely out of the question but not entirely impossible.

By me using the very strong springs I think it might just work. After all Ant. the springs in the Pro arm are compression compare to the extention springs I will be using for this setup. Therefore the springs has to be stronger for extension springs in this setup than compression springs.

BTW Ant, how are you enjoying Jasons rig? Any new changes?

[optonica]

Hi

I hadn't realised you were using extension springs I thought you were doin a Pro style arm (compression)! now I understand your twist on Pro style to be with the extension springs housed in the arm is that correct? In which case i'll let you off with the beefy springs! just so you know the Pro springs are put into a long tube with the canister at the end then pushed down into the canister with a ram!

I had bought my rig from basson about 1 week before jason got his new steadicam rig so it isn't jasons old rig. Which i'm glad about as basson have made massive improvements over there design of jason's rig!

I'm currently in the middle of making loads of changes. for example top and bottom j-box and d-box electrical connectors compatable with steadicam ones, steadicam compatable monitor sockets, adjustable monitor bracket, adjustable batt mount bracket, laser guide (for following pre marked lines or marks on the floor), power level meter. Hopefully this will be finished in the next week or two! HOPEFULLY!!!

I'm also making many other toys to go with it. Like a steadicam weight autocue (wireless), mattbox, radio focus and wireless video link. These are in different stages at the moment either in design or like the video link near completion.

I look forward to seeing more of your rig as it proves great inspiration to myself and others!

Ant

[charles]

Hi

I hadn't realised you were using extension springs I thought you were doin a Pro style arm (compression)! now I understand your twist on Pro style to be with the extension springs housed in the arm is that correct? In which case i'll let you off with the beefy springs! just so you know the Pro springs are put into a long tube with the canister at the end then pushed down into the canister with a ram!

I had bought my rig from basson about 1 week before jason got his new steadicam rig so it isn't jasons old rig. Which i'm glad about as basson have made massive improvements over there design of jason's rig!

I'm currently in the middle of making loads of changes. for example top and bottom j-box and d-box electrical connectors compatable with steadicam ones, steadicam compatable monitor sockets, adjustable monitor bracket, adjustable batt mount bracket, laser guide (for following pre marked lines or marks on the floor), power level meter. Hopefully this will be finished in the next week or two! HOPEFULLY!!!

I'm also making many other toys to go with it. Like a steadicam weight autocue (wireless), mattbox, radio focus and wireless video link. These are in different stages at the moment either in design or like the video link near completion.

I look forward to seeing more of your rig as it proves great inspiration to myself and others!

Ant

Yep, extention springs it is. glad you concur with me on using the beefy springs.

So they used a Ram eh? Wow! Can you imagine the force if ever that thing would decide to sprooooong outta there(obviously that is not going to happen) but think of the force.

Ant, I would love to see some pics of any improvements you have done with your rig. Especially all those interconnection. :)

Here are some pics of my creation:

1. The first pic is one of the alternative base module

2. The second pic is the second, more linear and compact base modules

3. The third is my vest with ratchets and an adjustable fore & aft device to adjust the pitch of the arm. I will be buying a steadicam adjustable block soon but so far this construction works pretty well, not perfect but at least I can decide where I want the arm to be.

4. On the back of the vest I've placed cross straps. This helps the vest from pulling or rolling forward when the arm is loaded. It kinda makes the vest more sturdy.

[optonica]

Hi

Yeah those Pro springs are under some load! There is one op somewhere (they won't name names) that got a bit nosey about how one worked and opened it :-s I bet that gave him a bit of a shock. A bit like a jack in the box! :p

Ant

[charles]

Ouch! That must have hurt?! :'( Nosey bugger. Aah well. :A: