Control column problem and solution

[Delta Whisky]

I came across an issue when installing my control column and thought I'd share it as I haven't seen, via a search of this site, that anyone else has documented this problem.

I noticed an excessive force was required to move the control stick fore and aft after installing it in the frame. The problem turned out to be the outside end of the bushing welded in the right end of the control column - the surface wasn't flat and not normal to the axis of rotation. The solution was a jig set up to ensure a little (or, a lot) of filing didn't make the situation worse.

The picture shows that situation about half way through the filing process. A few more details and pictures can be seen on my build log.

[Airfoil]

I am having a similar problem because the -4 bolt hole is misaligned a degree or two. When you tighten everything down is binds.

[Mesteve]

I am having this same issue. I am staring with the outer end of the bushing to see if squaring that up will remedy the issue.

If that doesn't free it up, I guess it's off to figure out a jig of some sort to ream the inside of the welded bushing to square it up to the axis of rotation. has anyone already tackled that to square up the inside of that bushing?

[Jerrytex]

I had a similar issue and it turned out that the mounting points on the frame where not all equally on the same plane if that makes sense. I ended up having to add washers to varying degrees between the aluminum column end brackets and the airframe to adjust the brackets so the bushings didn't bind.

[Mesteve]

That is certainly something I didn't contemplate; however, on the bench, when rotating the stick fore/aft, the aluminum bracket moves left to right a visible amount.

[jiott]

I had the same problem and fixed it like Jerrytex, with washers.

[efwd]

fixed mine with washers as well

[Jerrytex]

"however, on the bench, when rotating the stick fore/aft, the aluminum bracket moves left to right a visible amount."


Yes, I experienced that too, and it looks like others have as well. I think what also might be happening is the the bushing might not be totally perpendicular to the control tube. The control tube is only required to rotate a small amount so the bushing only has to be perfectly lined up for maybe 30-40 degrees. The washers are accounting for any unevenness in the mounting tabs as well as aligning the bushing in the mount to the column for that 30-40 degrees of movement. If that makes sense? Just my 2 cents.

I set the mount in place loosely on top of the tabs and added washers, tightened, and tested. I kept doing it until i had the mount at just the perfect angle or position, that it moved nice and smooth.

[Mesteve]

I was able to get the movement cleaned up by taking the bolt out and setting the ream through both the control stick and fixed bushing, turning it slowly while moving the stick through its full range of motion. Worked like a champ!

[cpdutch]

OK. After trying multiple combinations and variations of every solution in this thread over a 3 day period I thought I had it licked, and then... I torqued the bolts/nuts that hold the plastic/nylon bearing to the recommended 20-25 in-lbs. Only used 20, which is very little, but I noticed right away that it was more than I had been tightening with regular wrenches. It bound right up, so it was time to rethink this whole approach. The washers under the bolt heads were clearly leaving a deep impression in the nylon bearing/block which seemed like a poor use of the material. Essentially it was cold-flowing under pressure, and since the bearing needs to be held in place by a torqued bolt/nut combination I came up with another approach. I got a piece of 3/16' I.D. stainless steel tube and cut sleeves that would slip over the bolts. Opened up the holes in the bearing block and set them in-place. Their length was such that the clamping force would compress against the sleeve before overly compressing the bearing block against the control column. A little fine adjustment in trimming the sleeves to the right length was a lot easier than sanding more of the bearing block. (I noticed that the shape of the bearing opening was becoming slightly oblong, so I really didn't want to sand any more.) Result - I was able to get a positive contact between the control column and the bearing, and the bearing was held more firmly in place as the sleeves were positively clamped against the tab. It's a variation of the proper approach to design an O-ring seal. The metal-to-metal contact should occur before O-ring channel compresses the O-ring more than a certain % of the O-ring thickness.

Using all the prior suggestions yielded decent movement only if i didn't get a decent torque on the bearing, so this approach solved that issue.

Am interested in other's thoughts on this approach.

[Geek]

OK. After trying multiple combinations and variations of every solution in this thread over a 3 day period I thought I had it licked, and then... I torqued the bolts/nuts that hold the plastic/nylon bearing to the recommended 20-25 in-lbs. Only used 20, which is very little, but I noticed right away that it was more than I had been tightening with regular wrenches. It bound right up, so it was time to rethink this whole approach. The washers under the bolt heads were clearly leaving a deep impression in the nylon bearing/block which seemed like a poor use of the material. Essentially it was cold-flowing under pressure, and since the bearing needs to be held in place by a torqued bolt/nut combination I came up with another approach. I got a piece of 3/16' I.D. stainless steel tube and cut sleeves that would slip over the bolts. Opened up the holes in the bearing block and set them in-place. Their length was such that the clamping force would compress against the sleeve before overly compressing the bearing block against the control column. A little fine adjustment in trimming the sleeves to the right length was a lot easier than sanding more of the bearing block. (I noticed that the shape of the bearing opening was becoming slightly oblong, so I really didn't want to sand any more.) Result - I was able to get a positive contact between the control column and the bearing, and the bearing was held more firmly in place as the sleeves were positively clamped against the tab. It's a variation of the proper approach to design an O-ring seal. The metal-to-metal contact should occur before O-ring channel compresses the O-ring more than a certain % of the O-ring thickness.

Using all the prior suggestions yielded decent movement only if i didn't get a decent torque on the bearing, so this approach solved that issue.

Am interested in other's thoughts on this approach.

Dan Yocum (One Lucky Fox) had a solution for bearing block that was perfect. Go to the Build Logs section and look at One Lucky Fox build, post #35. I did this and it worked perfectly. No deformation of the block, torqued the bolts up and the stick was smooth fore and aft. Also took a LOT less sanding to get it right.

Gary

[LetMeFly]

I decided to replace the bolts provided with bolts drilled for cotter pins. Then I torqued it to snug using a castellated nut, but still allowed easy stick movement, and secured it with a cotter pin.

[cpdutch]

Dan Yocum (One Lucky Fox) had a solution for bearing block that was perfect. Go to the Build Logs section and look at One Lucky Fox build, post #35. I did this and it worked perfectly. No deformation of the block, torqued the bolts up and the stick was smooth fore and aft. Also took a LOT less sanding to get it right.

Gary

The picture One Lucky Fox posted of his solution is exactly what I did as well. The only thing I did differently was I sourced my stainless steel tube from a local RC hobby store at about half the price and I got it the day I needed it.