Turbo Ultima steering bellcrank upgrade

After installing the Ultima RB5 front axles and carriers and replacing the tie rod ball ends, there was still a lot of steering play from the hubs all the way to the steering servo, a Futaba S132H.  The original Turbo Ultima steering design was rather sloppy to begin with due to the use of bent wire and oversize holes in the steering bell crank assembly.   Even when new I was not happy with the design of the bent steering rod that went from the servo horn to the bell crank, but it worked so I left it alone, even for the restoration in 2010.  Well, no more.  I wanted that steering slop eliminated as much as possible.

Earlier this year I was searching for vintage parts on the net and discovered that A&L parts were being produced again from the original designs.  If you were into RC back in the late 80's and early 90's you'll recognize the A&L name.  Well, Daryl Lane (the 'L' in A&L) is operating Factory Works (http://www.factoryworks.com) and also selling reproduction A&L parts at http://vintageteamaandl.com.

One of the parts A&L has re-released is the steering bell crank assembly for various vehicles including the Associated RC10, Kyosho Ultima, Kyosho Optima Mid, and more.  According to the web site, the original plastic molds are the same, but the color of the plastic is now a darker yellow in order to differentiate from the original parts.  I never owned the original parts, so I cannot say if this is true or not.  The new parts are, at least to me, fairly bright yellow, so the originals must have been day-glow or something if they were even brighter.

I ordered part #2180 from A&L which is the Ultima bell crank assembly with ball bearings since I did not have any bearings of the correct size in my stock.  I also ordered a Tamiya servo saver assembly from another online hobby shop because my Turbo Ultima never had one installed.  Why Tamiya?  Well, I didn't know of any part numbers for Kyosho servo savers and I knew the general design of the Tamiya was exactly what I wanted.

Here are the parts cards for the servo saver and ball ends:

Unfortunately I did not take a picture of the A&L steering bell crank kit in its packaging before I opened it and started assembly, but it was a simple plastic heat-sealed bag with no header card separated into three different compartments.

Installing the steering bell crank kit took a fair amount of time because I had four inter-related and connected things to consider:

1. Which bell crank parts to use (it comes with a left and right so you can decide the best orientation for your particular vehicle).
2. How to position the steering servo.
3. Which parts of the servo saver I was going to use (it comes with a short and long servo horn).
4. I had to design a new steering tie rod that goes between the servo saver horn and the new bell crank assembly.  I wanted to use a Tecnacraft rod if possible.

I ultimately positioned the servo in the chassis so that the back of the servo was hitting the side wall of the aluminum frame, and flipped the servo mounts backwards so the holes at the bottom of the frame lined up with the servo mount holes and the servo mounting tabs.  The servo output shaft is positioned toward the front of the vehicle in order to allow the use of the large servo saver horn supplied with the Tamiya servo saver kit (part Q 2).  The large horn protrudes above the upper deck of the chassis, but the upper deck FRP plate has a factory cutout that allows complete freedom of movement for the horn.  It works so well it's like it was designed that way.

I should mention that the only reason this mounting design works is because of the Futaba S132H's short body.  A regular sized servo would not work as nicely.  The angle of the steering rod to the bell crank would be even worse from the ideal 90 degrees than this.  Secondly, I had to reduce the steering dual rates on the transmitter to somewhere around 67% in order to limit servo travel in both directions and prevent binding at the steering extremes where the cranks hit the frame.  It can't steer any more than that, so maximum steering is achieved.  I do not know if it is possible to use the shorter servo saver horn because the extra travel required by the horn and the fact that the steering tie rod is connected to the inside may cause binding when the servo pulls back because the tie rod ball end would hit the servo saver body itself.

 
I used one 10mm and one 15mm Kyosho ball end with a Tecnacraft tie rod to form the steering tie rod linkage.  It just worked out that way due to the limited selection of tie rod lengths I had to choose from.  The ball stud and nut came with the Tamiya servo saver assembly kit. The same style ball stud was used on the other end mounted to the bell crank but no nut was needed.  I drilled the mounting hole a little wider in the bell crank before screwing in the ball stud because it seemed like it was designed for a 2.6mm screw, while the stud was 3mm and I didn't want the bell crank to split.

Two yellow combination mounting nut and bearing posts hold the steering assembly to the main chassis frame using long flat head screws pushed up from the bottom frame.  The bell cranks, with bearings installed, fit over the mounting posts.  White plastic nuts are used to hold the bell cranks in place so they don't "lift" up and off the posts during use.

The black fiberglass steering plate comes with the A&L steering bellcrank kit.  Two screws and shims connect the steering plate to the bell cranks.  No bearings or bushings are used for these pivot points, which is a little disappointing.  I hope the screw threads don't chew through the steering plate over time.

Perhaps some structural rigidity is lost because the A&L bell crank mounting screws do not reach the top chassis plate.  I think with some work the screws and bearing posts could be replaced with aluminum posts of the appropriate width and length.  A stepped design to the post could be used to keep the bell cranks at the bottom where they belong.  Then the original kit machine screws that held the original bell crank posts could hold the new posts in place, keeping the structural rigidity the same as the original design.  If I had the resources, I'd try it, so for now it is just a dream.

I had to switch to shorter Tecnacraft steering tie rods again due to the change in geometry created by the new steering assembly.

So, after all of that, did it work?  In a word, yes.  The steering slop is completely gone.  In fact there is now more play in the outer hinge pin/steering hub than in the whole steering system.  The A&L steering bell crank kit is very highly recommended.