Saturday, August 8, 2020

Exotek F1Ultra front end

I was changing my car over to the long wheelbase setting, and it just occurred to me there are some interesting aspects of the front end which might not be readily apparent.

Owing to the fact that there are two positions for the steering arm post, you can actually get quite a bit of adjustment in the Ackermann for the front end.  Setting the car to the long wheelbase and leaving the post in the short wheelbase position will make the steering rods much straighter.  This should promote more corner speed, but be less aggressive entering the corner.  Likewise, the short wheelbase with the post forward would put quite a bit of angle into the rods, which would be pretty aggressive on corner entry.

Long wheelbase with steering post back (short w.b. position)

One other aspect to think about is the caster link on the upper arm.  This is something that may or may not make a hug difference.  Theoretically, a shorter link would have more change in caster as it moves through it's travel than a long link.  This really only comes into play if there is a big difference in the heights of the inside of the camber link and the height of the caster link at it's rear - essentially the dynamic caster effect.

These are just a few things to think about or try on your car.  If I have time I'm going to see what they do myself next time at the track. 

Sunday, August 2, 2020

Exotek F1Ultra Performance

After getting the car together, I brought it out to the club parking lot race not far from my house.  The lot the race is held at is pretty bumpy, though traction is good due to a generous application of grape soda pop.  This is actually a perfect test for the car.  The rear suspension is designed for exactly this sort of less than perfect surface.

My thinking was to take the tires directly off my TRF 103, as it has been fantastic everwhere I take it.  The last race I used it at was at a very small but smooth track in central Illinois.  Traction was excellent, and we raced a night, so conditions were relatively cool.

We did not have enough cars for an F1 class, so I was running the car in practice and between rounds.  Time was a little limited to get too much done as far as setting the car.

I had Pit Shimizu 575 rears and 571 fronts on the TRF car. As it turns out, the 575 rears may have been a little too soft for the hot conditions on the day, though not horrible.  571 was too aggressive in hindsight.  The car would sort of wander on the straight, and was really sensitive to corrections.  I had the same problem with the TRF 103 when I visited the small track downstate, and reduced droop via shortening the center shock.  Figuring that might help here, I shortened the shock on the F1Ultra.

That change seemed to help some, but now the car was getting on the nose going into the corner.  That was a little strange considering shortening the shock tends to take away entry steering in my experience.  The other problem was now the car occasionally wanted to snap the rear end in the middle of the sweeper if I got overly aggressive with the wheel.  At this point, I changed the fronts to F104 kit fronts, which are less aggressive.  The F104 front is reliable for most parking lot situations to balance the car to stability.

Unfortunately, there really didn't seem to be much difference between the two tires.  I was having virtually the same problems.  At this point, I just put a bunch of droop back into the car, not knowing exactly what to do, and running out of track time.  That did make things better, but not by a huge margin.

The whole experience made me think I had done something wrong setting the droop on the car.  It's a little different that the cars I have run in the past, so I thought my normal tricks might not be what were needed.  I contacted Mike from Exotek to get some advice.

Mike recommended that I run the droop as noted in the manual, and ensure that the ride heights were correct. He also suggested that I look to tire selection, as he felt I was on the wrong rear and had too aggressive of a front tire.  I took Mike's suggestions and went over the chassis to ensure everything was correct (this is also where I developed my alternative micro shock droop check).

As an aside, here are Mike's tire recommendations for asphalt:

"Personally I'm really liking the Volante front tires due to the different compound choices. I tend to have the softest spring settings all around and just tune the balance of the car by changing the front tire;
Medium Soft for more steering
Medium for medium steering
Medium Hard if the car/track is loose

For rear tires I use;
Volante white dots if the track is fast or grippy
Shimizu 72 if the track is small or low grip
Yokomo Soft rears (looks like Shimizu) if it's a bit cold outside."

My qualifier starts at 1:29, it's the white car (Brawn livery)

The next time at the track we had a group of 10 F1 cars (!).  This worked out great, since I was just able to concentrate on working on the F1 car all day.  After getting the info from Mike, and also consulting his setup sheet for asphalt I made a few changes.  Foremost was putting Pardus fronts and Pit Shimizu 572 rears on the car.  I wasn't able to find the recommended Volantes quick enough, but I knew that the Pardus tires were a hard compound.  I also know that 3x UF1 champ Lee Passehl used them extensively in the past, so I thought it would be a good choice.

Beyond that, I also noted in the setup sheet that the shorter of the two camber link positions was used.  I had initially built the car with the link long, so that was changed as well.  I also widened the rear end at the axle.  The wheelbase remained the same, short.

The changes were apparently the right ones, as the car was now excellent straight off the setup board.  The only things I really looked at changing were the front tires and the upper links on the front end.

I did try a pair of Pit 573 fronts in a practice run, just to see what they might do.  They are a harder compound, but even so, they were a little to much in the steering department.  The Pardus tires were actually perfect for the track.  This car develops a lot of steering in the short wheelbase setting, and the Pardus fronts were fine.  In case you are wondering, Pardus tires are discontinued.  You might be able to find them somewhere online new, or even used since they last forever.  Tamiya F104 option hard fronts (54198) would be the closest thing that is available.  Otherwise, I would just follow Mike's suggestions and buy some Volantes.

Changing the upper link did give me some insight to why my car was hard to drive the week before.  While the tire was a big part of my troubles, the long upper link did not help anything.  Once I changed from a short link to a long link, the car began stepping the rear end out in the sweeper again.  The car rolls the front end so hard it whips the rear out when it bites.  So, that was at least a good bit of information even if it was a bad change.

I had changed the upper link looking for just a bit more steering in the center of the corner.  Plan B was to dial in some more caster, which was the correct option.  I made the caster link's gap about 0.75 mm smaller, winding up with a 7.5 mm gap.  Since the last time I raced, Mike has published a new asphalt setup recommending 12* caster (I think his link gap was 6.6 mm!).  I have the car short right now, but I think for the next race I'll take a stab at the long wheelbase to see what that is like.

In closing, I think the main points are correct tire selection is critical (duh), and you may have to look at how you tune an F1 in a new light since this car is a little different.  Once I got things straightened out, the car did the fast lap of the day, TQ and I won the first main.  We had a second main, but my battery connector pulled out in an incident, so I lost too much time, but I was leading at that point.  The car works.  One guy said it looked like a slot car, so it can't be all bad.  You can drive it easy, and it will do super fast laps.  It was pretty composed in most of the rough parts of the track as well.  Not bad, since it helped me get on the throttle a little earlier than most.  

Friday, July 31, 2020

Exotek F1Ultra Build

The new Exotek F1 car has been a source of intrigue for a few months now, having secured the ROAR national championship at the carpet nats.  The car was kept under wraps for quite some time actually.  It has been developed over several years' time.  I saw an early prototype at a race in California a few summers ago, and I have heard about multiple iterations being tested out there.

One of the main design departures from typical F1 cars is the 3 shock pod arrangement, controlled by a panhard rod similar to a NASCAR or sprint car rear axle.  This allows massive travel in comparison to a t-bar or link car with a center pivot.  The entire pod can move up and down, without restraint from the center pivot.  I like this concentration on maximizing travel, as I have felt that most pan car based designs don't have enough travel in the car.  Rubber tires are heavier, and larger than foams.  Greater travel, and also rear traction, should be a strength for a rubber tired F1 car.  Counterintuitive to what you might think, this should be a huge asset for carpet racing.  The dreaded traction roll, and it's little brother, the light inner rear tire, rear their heads when the car runs out of travel.  Once the car can no longer roll in the suspension travel, it will hinge over and flip or at least pick up an inside tire.

The chassis is also different from almost every other car in that the main chassis is a 2 piece hybrid of carbon and aluminum. Different, but I can understand why this was chosen.  I have had an aluminum chassis before, which I felt was too stiff.  It seemed to kill the mid corner steering.  Here the front of the car is allowed some flex without sacrificing too much rigidity in the rear.

The packaging of the kit has tremendous appeal visually, and everything fits nicely in the medium sized box.  Beyond the chassis parts, a front and rear wing are included, leaving only the choice of a body, tires and electronics to the builder.  Note that wing mounting is the standard Tamiya hole pattern, so nearly anything will fit.  Bodies may be a little more restrictive as the links require some clearance.  Most bodies introduced in the last few years should fit, and I think most Tamiya bodies could even work, though the "cut and fit" realistic side pods would probably have to be omitted in most cases.  I chose a Bitty Design body, which fit just fine.

Assembly starts with the front end.  As with any F1 kit, remember thread lock is essential, as the rubber tires will vibrate all the screws loose eventually.  A sparing dab is all that's needed.

I included a picture of my trusty CRC pivot ball tool, which is a must have for any pan car owner.  There are several different brands out there, but this prevents damage to the pivots during assembly.  Using a pliers pretty much guarantees you will smush something eventually.

The pivots are secured in the arms with a large plastic C clip.  It's recommended to add a dab of shoe goo to secure them, and that's wise.  I also much prefer this arrangement to the o-ring securement which seems to be popular with other manufacturers.  I've had the o-rings pop off before which at a minimum makes the suspension get sloppy during the run, if not fail.  This seems very robust.

You may have to hold the grub screw in the bulkhead with a 1.5 mm driver while you spin the ball end down, as pictured.  The grub screw wanted to rotate with the ball end unless I held it in place like this. You can snug it with a nut driver once it's in place.

Once you have the bulkhead and arms set up, the assembly is mounted to the chassis.  You have the option here of two wheelbases.  Long is recommended for large and high speed tracks.  Short for smaller tracks and indoor.  I went with a shorter car.

Just a tip, you can use a hex driver to hold the rear suspension mount as you tighten it...that's what the hole is for...

After you get all the suspension mounts and post for the steering on, the rear link mounts and chassis connections go on.  It did seem like a lot of parts for this part of the car.  

With the chassis bolted together, everything does seem solid.  I was a little concerned there might be some tolerance once everything was built up, but the two parts came together nicely, matching up flush. Also pictured are the turnbuckles and  ball cups, including a molded version of the now famous Exotek front end for full  adjustability of caster and camber.  

Again, the pivot ball tool comes in handy for the upper arm. It turns out the good old Tamiya cross wrench has the perfect size drive for the hex adjusters on the turnbuckles, making threading the ball cups a snap.

When securing the knuckle on the kingpin, be sure to squeeze the assembly together as you tighten the set screw.  This will ensure even ride height and minimal slop.

Both Tuning Haus and Tamiya sell the same style of circlip which I prefer to e-clips for the kingpin.  There is just more surface area and it's easier to pop them off for spring changes and maintenance.

I added some Tamiya hard grease on the kingpins for some dampening.  Adding the grease above and below the arm, then working it in seems to be the best way to ensure it covers the whole area of travel on the kingpin.  You can use any number of silicone lubes for gear diffs, greases, Tamiya Anti Wear grease (THICK) to slow down the action on the front end.  This stuff has been working pretty well for me lately.  Just remember, it has to be redone fairly regularly to be effective.  Once a race day is the minimum in my book. 

This is the front end finished with bellcrank steering.  I found over time that leaving the screw in the upper arm connecting the caster control turnbuckle loose enough that it will still pivot ensures there's no binding.  It's not hanging loose, but it's not locked down.

The rear pod is a little different from most cars, in that the lower plate is a single machined piece of aluminum.  To me, it appears to serve to purposes.  One, the rigidity is much better than most cars, and I hope this means there will be less bent left side pod plates.  Two, it adds weight down low on the rear end, for an increase in traction.  This is a rubber tire car, and it's never bad too have too much rear traction.  "You can't fire a cannon from a canoe..."

This is the assembled pod, sans axle. 51.9 g, which is certainly heftier than the typical carbon lower type pod.  Again, the weight is down low, so I feel it will be beneficial.

You can see the huge amount of travel afforded by the panhard rod arrangement when the shocks are off the car.  Obviously, the car will have much less movement when the shocks limit things, but this is far more than anything I am aware of that out right now.  You could go rock crawling with this setup...

Here's the center shock, which includes an internal limiting spring.  I have never tried anything like this before, but the manual states using a softer spring improves rear traction.  I can only assume that as the shock extends, it keeps an abrupt stop from disrupting the rear end of the car, versus solid shims more typically used to limit shock length.  

The shock goes together pretty easily, and is designed in the Tamiya style.  One thing I did do was to slightly sand the non shouldered guide, as it seemed to be overly compressing the o-ring once the bottom of the shock was assembled.  The guide sands easily with something like 1200 grit paper, and you don't need to take much off.  You might need to test it a couple times, but it's better to go slow and not remove too much material.

I punched a small hole in the top of the shock with a tiny drill bit.  I have run a "dead" shock on my F1 cars for a long time, with almost no rebound.  I think it makes the car more stable.

The rear end has a lot of well thought out features.  The oversize bearings are nice to prevent wall shots from destroying the typical thin 1/4" I.D. bearings used in pan cars.  Some might want an axle carrier that uses shims to set ride height instead of the cam adjusters on this car.  I personally like shim adjustment, but I see the value in an easy to set and strong axle carrier.  With rubber tires it's not as critical to have super fine adjustment, but I do like being able to dial in ride height more precisely when switching brands of tires.  

The wing mount is the best out there in my opinion.  The over the motor design is much better than the perimeter style mounts in that the parts count is vastly reduced, resulting in less weight.  It also allows the body to rest on top, ensuring the body will never interfere with the pod.

A fan can be attached to the left side pod plate, again moving weight down on the pod since most other cars wind up with the fan above the motor.

One thing you may want to do is replace the upper ball studs for the micro shocks with something like Tamiya 42231 Damper Ball Connectors (that's what I used).  There is an internal hex, making it easy to remove the shock without having to pop the top off the ball stud.  This will be important when you set the droop on  the micro shocks, which must be adjusted by shaft length.

Tamiya 42231

That's the main part of assembly.  I chose to use an Xray gear diff in my car instead of the ball diff.  I have not put my ball diff together, but I'm not worried about how it will build, having used Exotek diff parts on Tamiya cars in the past.  

I just wanted to add a tip on wings.  The car does come with what appears to be a Montech front wing, and a rear wing that is a copy of the old Ferrari wing that Tamiya first made, then copied by HPI for the old Super F1, and many others followed suit.  I personally don't like how the Montech looks, but I know a lot of people use it.  One reason it is a good wing is that it is far enough off the ground that it has far less "touch downs" where it contacts the track and disrupts the suspension.  

The Tamiya 2017 wing set looks great and can be made to have a much better ride height very simply.  With a lighter or butane torch, you can carefully heat the inner portion of the wing and make a Z bend with a needle nose pliers.  Once allowed to cool while bent to shape, the wing will hold its form.  The touch down problem is greatly reduced or eliminated.

Here's the car with electronics mounted.  Admittedly, space is tight for the receiver and speed control.  I used a Tekin RS Pro and a Futaba receiver.  Tekin has one of the smaller ESCs out there, and you do need to stick with a small footprint to fit everything in.  The servo is a low profile 9551 Futaba.  Something full size might fit, but low profile is really what the car was designed for.

Setting Caster:  I have found the easiest way to measure caster is just to keep track of the gap on the caster turnbuckle from side to side.  So if your calipers measures 7.5 mm between the plastic rod ends, and both sides are the same, the caster is even.  If you want a rough idea of the amount in degrees, you can line up a camber gauge next to the kingpin to estimate caster, and note it corresponding to the gap measurement.  I just prefer the gap number, since it is much more accurate to track adjustments than eyeballing a camber gauge, and requires no special tools or setup gear.  Caster and camber work together on this car, since adjusting either can change the other adjustment, especially if you make a big change.  Generally, looking at the turnbuckle gap will keep you in the ballpark.

I wanted to show how I measured the micro shock droop on the car.  The manual shows the use of a ride height gauge on the bottom of the chassis to check micro shock droop.  This does work.  I just felt that it was awkward to do the measurement in that way.  I initially set it in that fashion and to ensure the shocks were drooping out, I was holding the car above me.  I guess I could have simply flipped the car over, but I wasn't sure if that would correctly estimate the droop, especially seeing it should be 0.5 - 1 mm total. 

I used a set of sedan droop gauge and droop blocks.  The blocks can be set transverse across the main chassis.  As you can see, the droop gauge can enter under the pod from the side, right where the link attaches.  I repeated the measurement process many times once I found the best spot to ensure it corresponded with the measurement I got using the method recommended in the manual.  This produces the same measurement, but I feel it's much easier to do, and it is consistent.  

I think it's important as just setting the micro shock droop via shock length may cause a different setting side to side if you make both shocks the same length.  I noticed I needed to be 0.3 mm different side to side on length to make droop even.  That may sound miniscule, but the car has no center pivot, so droop imbalance side to side is exaggerated.  Without the difference in shock length, droop was close to 1 mm off side to side.  This is also where the Tamiya ball studs come in on the upper end of the shock.  It's super easy to remove the upper ball still attached to the shock, and just pop the bottom off the pod.  A ball end wrench is the easiest way to get the top off.

Pod droop as most refer to it is separate from the micro shocks.  The center shock length sets the angle of the pod plate as seen from the side of the car as it unweights.  Since there is no pivot, this acts different than a center pivot car (link or t-bar). To be honest, I'm not sure how all this interacts, as the microshock droop sets how far the pod can move down vertically.  Hmmm....

That's the build up on the car.  I'm going to do another post on the car's performance.  This has been pretty long and I'd like to address  what happened the track on it's own.

Part 2:Exotek F1Ultra Performance

Tuesday, March 3, 2020

Toe in for tires

Recently I was racing at a series race on carpet where we had to use the Gravity RC F1 tire.  Normally, with the Pit Shimizu tire (CRC, TCS) I keep front toe out at about 2*.  I have run much more in the past, but I discovered on carpet, the Pit tire can overheat with a large amount of front toe out.  That being the case, I have become a little more conservative with toe out on carpet.

As the day went on, I was getting a bit frustrated with the lack of steering on my car.  There was not a good amount of turn in, among the many bad habits my car displayed.  I went to local CRC driver Mark Sweeney, who mentioned he had been running quite a bit of front toe out on his car.  He gave me several tips which were excellent in getting my car competitive on the Gravity tire, but the toe out was interesting in that he felt that the extra heat generated by the toe out was a plus.  I think he is probably correct, seeing  that the Gravity tire is harder than the Pit.  There is not the same amount of steering with the Gravity tire. 

Adding extra toe out to the front of the car worked out.  I suppose the lesson is to consider the trade offs of the front end set up overall (less vs. more toe), but also to realize you can manipulate tire temps with toe. 

Wednesday, January 15, 2020

Simplicity in a chassis mounted wing

So in the last year a bunch of companies have come up with a way to directly mount the rear wing to the chassis.  This is something the paved oval racing crowd did like 20 years ago, although they mounted directly to the body.  The same effect was achieved.

Some cars, like the Tamiya TRF103, have not had a commercial solution for this style of wing mounting.  I have seen on RcTech a few people re purpose Xray mounts to the Tamiya car.

Last week, I had a sudden revelation while watching tv - why not mount the wing the way the oval guys did? Piano wire and some wing buttons had to be much lighter than the extra fasteners, carbon, and aluminum bits that made up the typical ready made setup.  Wire wire is also cheap and universal.

This was the first try:

So the wing mounted straight to the body, but that was less than solid. After a day or two of thinking and looking, it turned out I could use a wing mount post on the cross brace of the chassis.  There was already a hole there.  All I needed to do was grind a flat onto the wing post to fit into the area allowed by the hole placement.

The wing is mounted to the wire by wing buttons in the side of the wing.  It's very snug, but I may drill a small hole in the plane of the wing to allow the wire to just engage and ensure the wing alignment is good during crashes and other hijinx.

This style mount could be adapted to most cars if you can find a spot for the wing mounting posts.  The posts and buttons should be less than $20 at any hobby retailer who deals with the oval crowd, and .063" piano wire is like $1.50 for 3 feet.

Example of parts for around $12:

Good luck and happy wire bending.

Ran this yesterday at the track, and it worked without a problem.  A more refined solution to the mounting of the wing to the wire would be nice, but it does the job as is.

Saturday, June 15, 2019

Access Hobbies 2019 TCS Race

Finals video

So the thing about Access Hobbies this year was the tight, 1/12 style layout they presented the Tamiya TCS racers with.  Before the closing of my local track, I was running my TRF103 with a peg diff tightened into a spool, and the battery lengthwise in the chassis.  This worked really well at home.

Despite the number of cars on the track, traction was not overwhelming.  The spool was hard to drive, especially off the corner.  Reverting to a slowed down ball diff was the way back to stability.  I am beginning to find that the spool must have a massive amount of traction to really be effective.  When the condition is correct, it is unbelievable, but I would say that most track conditions favor a combination peg/ball diff, or even a slightly loose peg only diff (non-TCS races you could use a gear diff as well).

The lengthwise battery did not work as well as a transverse battery, period. I have always favored the transverse battery in almost all situations, but the TRF103 really seems to like the battery lengthwise most of the time.  Not here, the car seemed a bit more planted and rotated better with a transverse set up.  I have to say it was just the tight nature of the layout.

The other factor was the track surface itself.  The traction peaked off on Saturday evening.  Leading up to this, I had shortened the wheelbase on the car, and steering was plentiful.  The last qualifier on Saturday was the fastest for me, and my car did the  fast lap of the weekend as far as I know.  Unfortunately, I had an accident that zipped off most of the spur gear, so the best time to qualify was wasted.  Sunday morning, the track had reverted to a state where the short wheelbase hurt more than it helped, and I returned to the long wheelbase.  I lost some steering, and to be honest, I think that the link setup might have been better at this point, as the link 103 cars looked to have a bit more steering in the lower traction.  Odd, in that most times T bar setups have more traction, and would be better when traction is down.  It may just be that the T bar in high traction allows the short wheelbase to work, and the improvement in corner speed is only available with the T bar's superior traction.  In any case, the car worked well enough on Sunday.  I feel like the other cars might have been a little better in the main, but I had a very good start and built up enough of a lead that I didn't have to push too much.

Other than those big changes, I was able to raise the upper arms at the kingpin, which tells me traction was not too great.  Normally, I run the upper arm pretty flat to avoid traction roll, but I was able to get away with maxing out the spacers under the arm.  I also ran 0.5 or 1 mm under the rear ballstud of the upper arm, just to take away any chance of lifting a tire.  Sometimes in the tight turns, if I had to get on the brakes, it could be hairy without the spacer.