Friday, April 24, 2009

Maiden Voyage

Indeed, today was the day for the maiden voyage of this rebuilt Hybrid Optima Mid. But first the preparations to get to there.

Remember I said that the ESC needed rewiring for the receiver? I used a 1x3 .025 square pin terminal strip to connect the two units. Neatly finished off with some clear shrink tubing and now we have a simple rewired ESC control connector.

This is how it dressed out in the car; a bit of a service loop, cable draped over the battery holder, and a bit of double sticky tape on the backside of the connector.

Overall, a pretty tidy wiring solution if I do say so myself. Here you see an ancient NiCD 6-cell battery pack which a friend brought by a few days ago. To my surprise, all the cells warmed up fairly evenly and peaked just fine after two false starts.

Remember my complaining about the radio battery connection being glitchy? Well! Look what I found in an old cable bin in the cabinets! An extension cord from game system of some sort. Having ohm'd out the wires and determining I wasn't going to melt my battery pack, or zap the controller, I plugged the two ends of the cable to their respective sockets and it worked! This makes me a very happy camper.

I also said the car weighed in at below ROAR legal weight of 3-1/2 lbs in this Stock Class configuration... here it the proof [you'll have to take my word on the zeroing of the scale though]

After a cold run on the scale to check for serious flaws, I was confident enough to push some power through the car. Here you get the same first look at performance as I did. Thanks to my wonderful wife and her extra-ordinary skill in following fast moving objects with the camera.


I am indeed pleased with the performance. I'll do some more video analysis but I can swear that the front end was nearly off the ground, and if traction was improved, they would have been. I was well impressed with the cornering stability as the car actually pulled into the corners under power.

It has been a great adventure to bring this hidden treasure back to life. I am also glad to have documented the intricacies that make up this absolutely unique manifestation of Kyosho's finest machines. I hope you too have found a gem or two of wisdom from these pages.

Please feel free to add comments or question and if and when I see them, I will do my best to reply.

Peace; Out!

Thursday, April 23, 2009

Final Assembly

"The end is near!" the morbid and the doomsayers say. But also those on a quest... being left with mixed emotions of gladness and sadness all at the same time.

The facts are clear; all the prep-work pays off in the assembly process. First we used medical fabric tape to close up the hole on the front differential case: Great stuff!

Next, push in the shafts holding the a-arms in place and tighten the set screws. Remember that the front shock was air free? Well, it seems pretty good for now.

Same for the rear suspension; add pins, and washer shims as required, and bolt on the shock and control arm plate. Note that the shock mount is not per the original Optima Mid design as it is now one large plate. Oh, I also made a wing in the meantime... you'll see more of it in a minute but I did install it once the plate was installed to the differential case.

A cursory check of the control arm lengths, front and rear, show them to be in a reasonable starting position. When we dial in the car we'll see what needs changing.

Next is the battery hold down. This is one of the stock Optima zip ties for the battery holder. One end is routed through the chassis and held just in front of the steering servo...

...The other end too is routed through the chassis and then the screw and post are inserted to hold the battery in place. The recess in the chassis keeps the battery from sliding forward into the front side brackets.

The orientation of the battery in such a fashion is great from a high-center CG point of view. It makes body roll much more consistent in high speed off-road cornering. A trick I learned from another custom Optima project.

The rear shocks were not quite as nice to me and really screamed "Rebuild Me!". So here you have a unique look at some rare shocks. These too came from the mystery 4WD kit. These feature a removable seal end, shoulder washers (2), and o-ring seals (2). In the top of the shock is the common bladder for pressure relief for the shaft volume. One feature I remember putting into this car was a beveled split washer below the piston. There is no free play between the shaft and piston.

Not having any shock oil, and not even knowing what weight I'm going to need, I opted for household oil for the time being. It felt pretty good for getting a few rides in. Notice that I moved the shocks bottom pivots back to the a-arms. If I do move them to the knuckle, I'll need to lengthen the shock bolts on top.

Then comes the true button up... adding the motor. I picked my green Rev Tech(?). I have an old motor plate that is meant to let air flow through the motor but not blow chunks into the gear cover. The o-ring closes all openings. I also picked a relatively small pinion because I suspect this is a pretty low wind motor, like 14 or 15 turn.

After letting the double sticky tape cure overnight on both the chassis and the ESC, the two came together for a very tight bond. This was pretty simple. Remember that I picked the location pretty carefully so it won't interfere with the motor as the pinion or spur gear gets larger. The motor wiring came out sweet and simple!

Here is a shot of the car with wing and wheels. The wing has some plastic wing mounts and some thick piano wire. The wing itself is aluminum with a single bend. This is a very solid solution. The tires have barely been run but I suppose that they will wear into slicks pretty quickly.

I still need to make a 7.2v pack and modify the ESC control connector. In short, this car is just about ready to roll. The end -IS- near :)

Wednesday, April 22, 2009

Assembly - day 2

One of the challenges of 4WD systems is keeping the dirt out. Dirt tends to pack into belt cogs and grit shortens the life of your main bearings. Sacrificial plastic gears don't stand a chance. Well, fabricating custom drive train covers is simpler than one may think. As with the lower chain cover, the top chain cover is a simple plastic tube. Ever wanted to know what to do with used overhead projector "foils"? Here is the perfect fate for those otherwise useless spent plastic sheets. First things first; optimize! This is the front of the tube...

...and this is the back of the tube. Note they are different depths.

A overhead transparency foil, a straight edge, an X-Acto knife, and some tape is all that is needed to make a very effective dirt blocker. These are the number I used: The sheet is 8.5" wide... and on each end I scribed a small mark at the distances noted: this is the front case opening...

...and this is the rear case opening:

With the scribe lines in place, I now connect the two marks with the straight edge. This is important! ...scribe along the straight edge using the -backside- of the blade. This provides for a very nice scoreline without going through the plastic. I trimmed about 1/8" off one end to make the length correct. I also put a strip of tape on either end to keep it from splitting. Now trim away the extra plastic beyond the score lines and fold the remainder into a tube.

I will be the first to admit that I should have done this before the side plates and steering were added. The heat sink too got in the way a little bit but that is not to say that it cannot be done in this order. Obviously, I got it on there, and I did not do any disassembly.

The final step is to put 4 pieces of tape equally spaced along the length of the tube to hold it closed. Here is a closeup with what you should have ended up with:

...and in the back:

The overlap is on top with the opening toward the left side of the car.

I had a little time left over to look at the ESC. This unit is definitely larger than the previous Novak I had in this car. Making room for the motor, ESC, and battery has become a bit more tricky. I am looking forward to using tat torque feature, though. I mounted the switch on the controller with double sided thick tape. Usually, I don't use no stinkin' switch, but what the heck, live a little. And then I taped the wire to the back of the ESC to manage this switch wire loop.

When all is said and done, the ESC will be living in the approximate position shown:

It took a while to get the chain cover just right but I am confident that this will serve its purpose quite well. Other materials I can suggest include a 5-mil Mylar. Even stiff plastic sheeting will work. The trick is to be able to score the material without having it split. Here is where we stand so far with the assembly.

Looks like the suspension will be next!

Tuesday, April 21, 2009

Assembly Begins - day 1

This happened faster than I thought. The chore was to enclose the lower drive chain. Goal; not to separate the chain. First things first... I put the two a-arm pins into the chassis. I had notched the rods so that the set screws, seen here, keep the pins from backing out. There are actually 3 set screw but the one at the top of the screen is only for making sure they are parallel. Originally, I had the back a-arms somewhat canted inward. I'm going for parallel now. The difference is using a different end plate. I have a carbon fiber end plate that has the two holes for the pins set further apart. Since I want good high speed tracking in a straight line, this will work best for the on-road setup.

I had a piece of clear plastic sheeting laying around which I cut to 20mm wide. I then took some sharp small hobby scissors and trimmed in the ends. These two pictures show well the conditions I was after.

The tab into the plastic on the front is only about 1/8" long. Being relatively stiff, there is no reason to worry about the tab getting caught by the chain.

Next, I put double sticky cellophane tape on the chassis where the plastic sheet will be adhered. Since the chain length was already correct, I just placed the front and rear case assemblies in the chassis so the chain would lay in the slot. Next, I simply started to lay down the plastic strip as it adhered to the double sticky tape. Had I thought ahead a bit further, I would have left the front brace on the rear gear housing assembly off. The front brace, the H-bracket, can be removed at any time if more finger space is required. Remember that at this point, the gear cases are just sitting there.

In case off-road dirt tracking is anticipated, one could consider a much more substantial covering of the additional grooves in the chassis. I consider this optional as only the chain needs to be protected form the elements that might find their way into the gearboxes.

After careful inspection of the chain cover, it is time to consider committing the gear cases tot he chassis. I spent some time selecting appropriate screws form the handy hardware box and found everything I needed.

Once the chain is set for tension, which in this case is fully retracted, a few pieces of packing tape seal off the last few crevices at the chain cover. You have to look pretty close to see this piece.

And a piece in the back about 10mm x 20mm:

It is amazing how effective this simple solution is. And even after 15 years, the previous tape came right off without a fuss. If the car will always be run in a clean environment, like carpet tracks, I'd say the chain cover is completely optional.

Now we are ready to put the steering back; add the side plates;...

...and have our first close look at the front bumper which protects that mono-shock.

Notice that the upper control arm keeper has a hole drilled in it right next to the metal brace. The looped .090" diameter piano wire has spring tension holding it to the very front metal bracket. Overall, this is a very stiff system although I did back this up with fabric tape so I wouldn't loose a piece on the track somewhere due to an "incident".

So this is where I finished yesterday. I will post the next steps soon.

Monday, April 20, 2009


Seems everyone has at least one task, feature, or design that just fights you every step of the way... mine is wing stays!

After going through the trouble of making new wing stays, I just couldn't get the screws short enough to keep them from interfering with the wing wire. I got there eventually, but gheeze... what does it take!

This is what I ended up with: SAE 6-32 hardware and the aluminum posts that have a shoulder which have a nice tight fit in the carbon fiber holes.

..and the set screws will keep things nice and tight... right?

Now to figure out what I want to do for a wing. The one I have is pretty beat up. I might just fold one up from an alloy sheet. I like those best.

I got a lot more done today as I began the re-assembly. It is a little late for me to blog this effort tonight so please stay tuned. Here is a sneak peak:

The gear cases are installed and the bottom chain guide is now sealed. I'll take you through this tomorrow.

Sunday, April 19, 2009

Parts Prep - day 5

Having concentrated on the main chassis long enough... and not having any epoxy on hand... I decided to do some work on the business end of the car: the suspension.
These things look so simple when they are in one piece. Funny just how much makes up the driving end of the typical RC car. Here is a shot before disassembling the suspension...

...and after

Much of the magic in this car is in the front suspension. The carbon fiber mono-shock adapter plates just begged to be mounted to the Maxxum long a-arms. The wing-mounts on the back are for hard stops at full sag.

And the steering knuckles were reversed [L<->R] so the steering arm allows for maximum steering angle, or in other words, smallest turning radius.

The a-arms and the pivot are completely stock. No carving or tapping. They are completely independent with regard lo left and right. Not so for the steering knuckles. These are ground for maximum clearance both at the universal joints and at the a-arm. This is so that the full motion of the a-arms can be maximized for the mono-shock arrangement. For the most part, it is a pretty simple modification on the surface, but as you have already seen, the front gear case had to be modified for the shock, and you will see how the gear case bottom plate is reinforced for the rigors of racing in a few more days.

By the way, I failed to mention my ball bearing lube of choice: I've been using ProGold Lubricant's ProLink chain lubricant for bicycle chains. In the cycling world, this is the "go back to" lube of choice when the new fad fades. I've found this lube to be quite effective.

Back to the car. On the rear suspension, there is often quite a bit of play between the a-arm and the knuckle. This is where a handful of 3mm washers can be quite useful to take up some extra slop in the system.

In this case too, the rear a-arms are fully stock, unmolested Turbo Optima a-arms. I did decide to move the shock balls to the knuckle for better cornering. In general, I will be lowering the car's stance to make it more stable in high traction cornering. If I'm not mistaken, I think I have a short-shock carbon fiber shock mount that would allow for the Kyosho Gold short shocks to be installed in the back. If I'm not careful, I'll be searching for an on-road body soon! For now, I have the custom carbon fiber shock mount and control rod stay. There are plenty of options for dialing in the wheel's attitude.

As for those shocks in the image, these too were from the mystery 4WD. Notice that both ends can be removed. I've put Kyosho's Gold shock plastics and springs on these shocks as well as new red rod ends from the original Optima's red shocks. These shocks still need to be rebuilt once I figure out what to use for shock oil. Here is the same shock on the front suspension...

Funny thing is, the front shock is still air-free/leak-free. I have a feeling the oil's viscosity is just a little too heavy for on-road use. I'll probably save the shock work for last.

If you look carefully at the image, you can see the grinding done on the steering knuckles.

I went through the hunt for good rod ends. I seem to have plenty of usable rod ends in the bone pile. I also found the left & right handed turn buckles for the back.

One of the wheel bearing needed replacing and the universals were still in pretty good shape. That is one item I haven't seen show up on eBay... dog-bones and universal shafts for Optima. Does anyone know if later Kyosho models use compatible universal joints that are readily available? I may just have to learn how to re-join the ends of the shafts I have in the bone-box.

Next I need to commence with completing the chassis. We are not far from the assembly process. Stay tuned!

Saturday, April 18, 2009

Parts Prep - day 4

Today was a productive day. Having decided on the drivetrain made the next step pretty simply; overhaul the gearbox and differentials. I began with the front. Much to my surprise, I fully neglected putting any type of grease in the front diff. This is not like me so there must have been a reason I did this. This front diff had very smooth action and was still perfectly good for continued service. I decided that cleaning the bearings and changing out the casing for new was a worthwhile effort. I do remember all the deflashing that the bevel gears required in the past. The effort of filing the gear teeth clean makes the diff performance 10-fold improved. Notice that I use shield washers on the outside for the bearing to help keep the bearings clean. The bearings barely had a film on them.

During re-assembly, I used my favorite hobby grease: Parma Silicone Lube #7900. This lube applies thick but tends to ooze into all the crevices over time. This lube is safe for plastics and is tenacious about minimizing friction. In the long run, it will ooze out of wherever you put it so you want to use it sparingly. One bottle will likely last a pervasive hobbyist a lifetime.

Here is a shot of the assembled front differential. I reversed the drivers so the wear surface is virtually new. I try to take out all the sideplay when tightening the drivers on. I also use a hard hex wrench and make sure these are tightened very well. If you've been collecting Optimas for a while, you will notice that the setscrews used here are quite rare in your parts boxes.

Next, apart comes the custom dual chaindrive ball-diff. The unit was a bit raspy and definitely a bit dusty. If you've never worked on one of these, this section will be one for you to pay much attention to if you ever plan to install one.

I could easily have put a normal bevel gear style rear diff in this Mid. The shear beauty and performance of these units makes this little adventure well worthwhile. These can be set up as slippers [not recommended on 4WD] or simply dial in the drive you want to push onto the outside wheel. I set mine up to where the plates would slip only in case of a hard shock. I replaced the plates as the ones I removed were pretty rough. The bevel washers were still in good shape, and the small thrust bearing was in pretty good condition. The screw still had some thread lock on it, and the foam washer also was in good shape. Overall, this was simpler than I had anticipated. Please note the error in the photo... you cannot use a shim washer on the left side bearing! Doing so would keep the driver from engaging properly with the disk.

This is where the two shim washers should go in order to keep the bearing clean. Also notice the orientation of the bevel washers: <><><> ...followed by 2 special washers for the thrust bearing. The foam plug has a hole in it to make adjustments without removing it.

Here again, the Parma grease did its usual perfect works by holding the 8 balls in the thrust bearing. This was just what Doc ordered to slide this sub-assembly into the driver.

Always check the function of your ball diff after your first run when you've rebuilt the unit. These tend to require a little break-in period. One other word of warning about this ball diff... the part were the balls are installed must be on the drive side! Reversing this will diminish performance.

So here you have them, a virtually new set of differential. Sweet!

Next comes a perplexity that comes to light only after you try something new and have never really had to, or had the chance to correct the little mechanical nuances. In this case, the slack side of the drive chain is wearing the boss for the case screw. If I recall correctly, I had one track-side repair to replace the power side drive chain. I can imagine that slapping the chain against the case had something to do with that. The wear area is the "I I" on the right gear case.

This was my determined correction to the shortcoming. I ground away the plastic to make room for a hard rod end ball. It is not meant to spin, but it is there to make sure that the chain can glide past it and maintain its dimensional shape. A screw is used to keep the ball in place through assembly when you push the right screw through exchanging the ball's holding shaft.

When all is said and done, nothing has been changed except the expected lifetime of both chain and case. This setup has a near perfect fit for this chain-pitch. Backlash is quite minimal. Do notice that one of the case mods is removing one of the back screw bosses.

With a 7-18, or 2.57:1 ratio, this is pretty much the same as stock 14-37, or 2.64:1 ratio.

Here is a quick video of how efficient this drivetrain really is.


Now for a second shortcoming of my original build. Obviously, I never checked the spacing of the two pinions as compared to the differential itself. Turned out I needed to remove almost .050" from the idler pinion to have the two match up properly. I seem to have had the chain biased quite heavily to the right in operation. This might have been the second reason for the broken power drive chain. Today I put the idler on the lathe and matched it all up.

I have no excuse for this oversight other than sloppy work. I am glad I had the opportunity to fix this as this car will see a whole lot more power run through it than it was originally designed for. Remember, this was a car dedicated to ROAR 4WD Stock Class racing. I fully anticipate putting my Rev Tech Red on this car. This car has never flown as fast as this motor can take it.

Here is another piece of the how-to puzzle. This mystery car that sacrificed the needed technology to make this modification possible also had a simple and clean solution for the spur gear... a flange that the gear simply screwed onto. The flange has 2 setscrews the same size as your everyday pinions. The reason this flange is key is that the drive shaft is 4mm vs the 5mm of the Mid. Even the bearings have a spacer in it to make them 4x10's. I'm also happy with the fact that this is a 48-pitch gear... since I have a nice collections of 48-pitch pinions.

The next image is to preserve the knowledge of the sequence of all the spacers and shims to allow for minimal side play. I left out one of the shims, the second one to the left from the idler. Even though the idler is free-floating, it will rotate at the same speed as the drive pinion. If you look carefully at the 7T idler, you will see I had to cut into the setscrew holes.

Again, be sure the diff is installed correctly!

The next step is pretty straight forward... add bolts, motor plate and battery holder [H-bracket]. One bolt through the wing mount serves to replace the hacked case screw; and the new ball in the case is in place. Again, push the screw out holding the ball with the screw that goes through the case. That way you know it hasn't fallen free.

I played with the chain a bit to make sure it rolled freely over the 7T cog. The chain did have a rough spot where it was joined. Working with it a bit made it behave as I would expect it to.

Here is a shot of the diff cases on the chassis. Notice I also marked the connector signals for the ESC on the receiver.

I think I am pretty close to buttoning up the chassis and drivetrain. I have a little epoxy work to do on the chassis first. I also need to make new chainguards from Mylar sheets. Do you think I can put all the pieces together without breaking the chain and threading it through the chassis? We'll see!