Seesaw Arms w/out bearings, P50

Also available are the optional PDR0085, a bolt-on replacement, which CNC machined from a solid billet of 6061 aluminum.

We've had reports of blades occasionally going out of track and have learned it's usually related to excessive play in one of the Seesaw Arms. Check for excess play before flying your model because the resulting flutter can easily be strong enough to lead to a Spindle Shaft bending. Fortunately, the shaft is a sacrificial part and is hence, inexpensive and easy to replace.

The cause is usually either the button head bolt(s) securing the AUD0048-2 Seesaw to the AUD0005-2 Aluminum Center Hub have come loose (remove, clean with acetone, and use threadlocker before snugging them back into place), which is easy to find, or the M3x15 Allen head bolts, which pass through the steel hat section (or shaft), upon which the seesaw arm bearings piviot has backed out of the AUD0048-2 Seesaw.  Be careful tightening this bolt as it bottoms on the steel hat section and is threaded into the polymer seesaw and can be easily stripped out.  However, alternatively, there's excessive play, caused by a ganging of tolerances, which is a fancy way of saying one of the hat sections is slightly too long.

Checking for the latter condition is actually pretty easy.  First, grasp the Seesaw Arm between your thumb and forefinger and give it a side-to-side wiggle. Next, rotate the head around and check the other Seesaw Arm the same way. If you've experienced blades going out of track, then dollars to donuts there's more play in one Seesaw Arm vs. the other!

You may be asking yourself, "What's ganging of tolerances?" Simply this . . . it's surely no surprise that two bearings with the same part number can actually vary slightly in size, right? I.e. measure them using instruments of sufficient precision and you'll almost always discover that one can be slightly thinner than the other. Similarly, the ID and the OD can vary slightly as well. The same holds true for the shaft - such that it might be slightly longer than others in the same parts bin. Ditto with the seesaw arm itself, but nonetheless, these differences are within the +/- tolerances of the design. Then during assembly; thinner bearings, maybe a seesaw arm with a thinner ring gap, or perhaps a longer shaft, when assembled result in slightly too much play in one of the seesaw arms. It doesn't happen often but occasionally parts (each in proper tolerance) when combined may result in an assembly that's out of tolerance - in this case too loose!

First, just try tightening the bolt. Be careful though since this bolt threads into the plastic seesaw. Fortunately, if it's stripped, all's not lost since plastic-type CA used as thread locker will have you back in business because you can pretty much restore the threads using it. If the damage is too bad, happily, seesaws are inexpensive so it's not that big a deal.

If it's not loose, then back the bolt out and look to see if the shaft itself (the one the bearings ride on) isn't just a hair too long (you'll see it sticking out past the inner race of the outer bearing of the seesaw arm - it's pretty easy to discern). If this is the case, then file a few thousanths (or however much is needed to make for a perfect fit) off the end of the shaft.

That's how you remove the extra play and the process is called "blue printing". Top pilots blue print every assembly of a machine. Most of us aren't top pilots, but blue printing an assembly is a simple, easy, and free modification. Best of all, it may result in a tangibly better handling helicopter plus it's fun to do - after all, it's called modeling for a reason! While you're at it, check the mixing arms for excess play and blue print them to perfection also!

We've had reports of blades occasionally going out of track and have learned it's usually related to excessive play in one of the Seesaw Arms. Check for excess play before flying your model because the resulting flutter can easily be strong enough to lead to a Spindle Shaft bending. Fortunately, the shaft is a sacrificial part and is hence, inexpensive and easy to replace.

The cause is usually either the button head bolt(s) securing the AUD0048-2 Seesaw to the AUD0005-2 Aluminum Center Hub have come loose (remove, clean with acetone, and use threadlocker before snugging them back into place), which is easy to find, or the M3x15 Allen head bolts, which pass through the steel hat section (or shaft), upon which the seesaw arm bearings piviot has backed out of the AUD0048-2 Seesaw.  Be careful tightening this bolt as it bottoms on the steel hat section and is threaded into the polymer seesaw and can be easily stripped out.  However, alternatively, there's excessive play, caused by a ganging of tolerances, which is a fancy way of saying one of the hat sections is slightly too long.

Checking for the latter condition is actually pretty easy.  First, grasp the Seesaw Arm between your thumb and forefinger and give it a side-to-side wiggle. Next, rotate the head around and check the other Seesaw Arm the same way. If you've experienced blades going out of track, then dollars to donuts there's more play in one Seesaw Arm vs. the other!

You may be asking yourself, "What's ganging of tolerances?" Simply this . . . it's surely no surprise that two bearings with the same part number can actually vary slightly in size, right? I.e. measure them using instruments of sufficient precision and you'll almost always discover that one can be slightly thinner than the other. Similarly, the ID and the OD can vary slightly as well. The same holds true for the shaft - such that it might be slightly longer than others in the same parts bin. Ditto with the seesaw arm itself, but nonetheless, these differences are within the +/- tolerances of the design. Then during assembly; thinner bearings, maybe a seesaw arm with a thinner ring gap, or perhaps a longer shaft, when assembled result in slightly too much play in one of the seesaw arms. It doesn't happen often but occasionally parts (each in proper tolerance) when combined may result in an assembly that's out of tolerance - in this case too loose!

First, just try tightening the bolt. Be careful though since this bolt threads into the plastic seesaw. Fortunately, if it's stripped, all's not lost since plastic-type CA used as thread locker will have you back in business because you can pretty much restore the threads using it. If the damage is too bad, happily, seesaws are inexpensive so it's not that big a deal.

If it's not loose, then back the bolt out and look to see if the shaft itself (the one the bearings ride on) isn't just a hair too long (you'll see it sticking out past the inner race of the outer bearing of the seesaw arm - it's pretty easy to discern). If this is the case, then file a few thousanths (or however much is needed to make for a perfect fit) off the end of the shaft.

That's how you remove the extra play and the process is called "blue printing". Top pilots blue print every assembly of a machine. Most of us aren't top pilots, but blue printing an assembly is a simple, easy, and free modification. Best of all, it may result in a tangibly better handling helicopter plus it's fun to do - after all, it's called modeling for a reason! While you're at it, check the mixing arms for excess play and blue print them to perfection also!