Wednesday, September 13, 2017

Tamiya M05 - Last weeks news, but still an interesting platform.

Being a gearhead, and a RC person brings up some conflicts from time to time.  The Tamiya M-chassis cars exemplify this.  With a boot.  On your toe.  

I enjoy driving in a spirited manner.  I enjoy feeling a car sliding around as the limits of traction are found, exceeded, and reeled back in.  Logic indicates, if you’re accelerating, you want the power going to the rear wheels.  In a world where your derriere is attached to that chassis, it works out pretty well.  

R/C cars are tiny, have lots of traction, and very low polar moments of inertia  Put those in a tumbler and shake, what comes out the other end is a recipe for difficult driving.  By managing front end traction, you can get a car that’s very consistent to drive.  That’s where FWD chassis and the modern touring car chassis come into play.  And, you get really good braking as a nice side effect.  

Where did the Mini Chassis Come from?

Another goal in our hobby is to have something that’s scale.  Usually, the more so, the better.  Big 4wd trucks have 4wd.  Sports cars have Rwd.  Well, Tamiya thought if they were going to bring an Austin Mini to market, it should have Fwd.  And…. In 1994 that’s where the M01 was born.  

Tamiya went all out on the M01.  The car they released, was a classic Tamiya Tub, with four wheel independent suspension, and a clever setup to get the weight spread nicely between the ends of the car.  

They pulled tricks out of their back catalog.  The hairpin coil springs, and monoshocks at both ends.  It’s hard to get a lower CG than with that.  The steering servo is at the back, and it’s all housed in a classic Tamiya tub style chassis.  The M01 was good.  It was enough to spawn racing classes.  And a huge aftermarket.  

A huge aftermarket is a sign of two things.  First, popularity, and second, there’s things that need fixing.  

If there’s a lesson to be learned, is that big open tubs aren’t magic when you go racing.  And the monoshock has always gotten replaced with upright shocks whenever tamiya updates a chassis to perform better.  I wonder why they don’t work harder to eliminate bumpsteer.  

Somewhere around then, Tamiya also released the RWD version of the M class chassis.  They never really caught on with racers.  On a single lap basis, a RWD M chassis could turn a faster lap time.  But for the duration of a race, the FWD chassis would turn in more consistent lap times, and almost always beat out it’s RWD cousin.  Thankfully Tamiya hasn’t given up on the RWD mini chassis, but they’re still not exactly popular.  

The M03 is the next FWD chassis.  Predictably, Tamiya shoved the laydown shared shocks in the bin, and went to some super short vertical shocks.  In an effort to improve weight on the front end, the steering servo was moved on top of the gearbox.  The chassis was changed to a tubular girder of sorts.  And now most of the driving gear was directly attached to the gearbox.  

Happily, this arrangement eliminated a whole bunch of steering linkages.  And the separate shocks now allow for easy corner weight adjustment, and stops the sides of the suspension from affecting each other.   But it also brought the CG up.  In a chassis that didn’t need a higher CG.  How bad was that? Well we’ll get to the rolling tendencies in a bit.

The high mounted steering servo took out a whole lot of slop in the steering department, but the high mount also left the servo linkages in an awkward shape, so again, the chassis is haunted by bumpsteer.

The whole “machinery section” of the car, was screwed to the “drags behind” section with 4 screws, loaded in shear.  I think this was a mistake, putting the whole load of the car on 4 screws like that.  It seems that so did Tamiya.  Because they definitely did something about it in the next revision.  

What about the M05?

In 2009 Tamiya released the M05. As a Mini Cooper.  The M05 chassis is quite a demonstration of cheap plastic engineering.  Without needing a pile of other parts, it provides 3 wheelbase options.  It’s very stiff.  The battery mount allows for easy, quick, pack changes.  The electronics all mount as low as practical in the chassis.  This includes the motor, ESC, receiver, and steering servo.

The M05 went back towards a more balanced chassis, like the M01.  Instead of packing everything on the gearbox, the M05 has trays to mount the receiver and ESC back near the rear axle.  And the Steering servo is in a pocket down low in the rear of the chassis.

The high points:
  • A Sealed Gearbox
  • Bellcrank Steering
  • 4 wheel independant suspension.
  • A stiff chassis to let that suspension do it’s job.
  • Integrated gearbox and chassis.
  • Dizzying array of upgrade and option parts
  • Easily changed wheelbase options
  • Radio trays and integrated transponder mount.
  • Still uses the same body mount post positions as the rest of the M series.  
  • Includes a Motor
  • Includes a Brushless Capable ESC
The low points:
  • The suspension arms are soft.
  • Most models come with friction dampers.
  • Limited gearing options.
  • Lots of steering slop.
  • A bad case of bump steer.  (at least it’s symmetrical..)
  • Designed for Stick Packs (Excepting the M05r)
  • Questionable motor cooling.
  • Requires two sizes of bearing.  

Criticism of the M05

The M05 still has the typical Tamiya problems.  Namely, gearing choice, bump steer, steering slop, and battery compatability.  That said, steering is a big deal, figure in at least the cost of an aftermarket bellcrank setup when buying your car, you’ll have a much better time if you do.
The M05r takes care of every criticism, straight from the factory.  The price reflects that.  I paid $99 for the MX-5 model I bought.  The M05r is currently $190, but it was closer to $300 when I built my car.  

And if you buy a normal M05, parts to address the bits that bug you the most, are pretty cheap.  For example, the version 2 chassis set is $9, and allows the use of modern square LiPo packs.  Stiff suspension arms are $8.50 for the set.  And a set of shocks is $40.  

I ended up going the “buy the base M05, and the parts I want” path.  Four months down the line, i’m not sure I made the right choice, but I’m still very happy with what I have built.  

Building the M05

Building the M05 is a little tricky.  Typical of Tamiya, the process is straightforward, and very well detailed in the manual.  The gearbox is buried in the middle of the front chassis halves, the shock tower, and steering gear all attach to that gearbox.  That’s to say, if you lunch a gear in the transmission, or you want to do diff work, you’re going to be turning a lot of screws, for a while.  

That layering, is where the strength of the chassis comes from.  The rear tub, attaches to the gearbox through wedges, ensuring the screws that pin in in place, aren’t taking the load, and the chassis always assembles exactly the same.  

Sadly, most revisions of the M05 come with the recent, and darned near hateful friction dampers.  While the old friction dampers had a rubber tube, some grease, and a metal piston to get some damping, these new ones are just a clip together shaft that guides the springs.  

I bought the MX-5 model, because it was the best looking, and happily, the cheapest,  When I placed the order, I also ordered some Mini CVA shocks, a 17.5 brushless motor, the Version 2 chassis parts, bearings, and Yeah Racing’s aluminum steering gear.  

That’s a long list of parts to order off the bat, and a significant chunk of money.  The shocks being about $20, the bearings another $15, chassis parts $10 and the steering kit $15.  In the end, it was a 160 car instead of the $100 I picked up the “kit” for.  

Building the car takes some time.  There’s bits you wouldn’t expect to need to build.  For instance, the rear loopy chassis braces aren’t part of the rear tub.  And the rear suspension arms are actually two piece assemblies.  

It’s a pleasing job, for the most part.  Just be sure not to get ahead of the manual.  It does things in a specific order, to deal with that layering thing.   

This isn’t the first M05 I’ve owned.  But it is the first I built from scratch.  The one I owned before, had the aluminum steering rod, and some aluminum bits in the steering.  In the interest of seeing what the stock setup was, I did build my car with the stock plastic steering assembly.  At least for bench testing.  

I was not happy, at all, with how things went with the plastic rig.  The bearings around the steering rack, and the bushings they ride on, really do need to be metal.  Any slack in there ends up being exaggerated by the rest of the steering assembly.  All of the aftermarket bits end up coming with a set of bearings for the bellcrank to run on.

There’s a lot to be said about the steering.  It’s still got that obnoxious Tamiya bump steer.  Between a properly set ride height, and some shims on the tie rods, you can dial most of it out.  While we’re on the subject of ride height, that ends up being something of a problem.

In the US, there’s several sizes of CVA shock available.  None of them are “super mini”.  When you look for recommendations on what to put on your M chassis, they all indicate the mini shocks.  Installing the mini shocks with their biggest internal spacers, sets the fully compressed ride height at something like 7mm.   

Racing setup guides, tell you to set the normal ride height to 5 or 6mm.  Not, fully compressed…  So that sent me to find shocks that were proper.  The M05r comes with the proper shocks.  And, if you do some digging, pairs of super mini shocks are on the market. (Tamiya part: 507046)  Those are what you’ll need.  Unless you’re in the market for the metal bodied shocks, which retail for nearly $90.  (Tamiya part: 54000)

Since that was a “straight from Tokyo” order, to get the super mini CVA shocks I got to drive the M05 on the tall setup for a while.  
My M05

My M05, was built up with a smattering of upgrade parts.  That is, the aluminum steering kit, aluminum outdrives and constant velocity joints, aluminum rear axles, super mini CVA shocks, a short steering servo, and the version 2 rear chassis parts.  

I also went about 90% of the way on doing the body right.  Tamiya is a serious model making company, and their bodies reflect that.  Take your time, and understand what should, and should not be trimmed on your bodies.  With Tamiya’s mold making skill, sometimes the edges that “look” like body trim lines, are not body trim lines.  
The MX-5 body, is two color.  So you need to do a fair amount of masking.  With clear bodies, you start with the dark colors, and work your way to the light colors.  The MX-5 needed all of the red areas masked off, before the black was sprayed.  When you do the masking, it’s best to do lots of small bits of tape.  Also, to Tamiya’s credit, if you don’t get the masking lines perfect, they provide decals for the outside of the body that cover most masking sins.  

I made the mistake of using rustoleum paint to paint my body.  It absolutely does not bond to lexan.  It looked really good on the initial application.  Then I made several more mistakes.  First, I sprayed the red to soon after the black, and ended up with a little crazing of the black paint.  Then I went to do a backing coat of white paint behind the red, to make the body look more solid.  I layed that on to thick, and several places the paint peeled up from the lexan.  

Don’t do what I did.  Buy lexan/polycarbonate specific paint.  Use really thin coats.  Give 3-10 minutes between coats.  And keep using thin coats.  

What this lead to, was paint flaking off the car every time it hit something.  I came home from one trip to the track with a clear bumper and quarter panel Later, to repair the paint, I used polycarbonate paint.  So now the body has what I find to be a pleasing mottled effect where the paint was repaired.  

Driving the M05

On most surfaces, the M05 is a perfectly well behaved machine.  That is until you get on a high traction surface.  In my case, that means carpet.  But lets talk about FWD driving first.  

Rear wheel drive is “the thing” for going fast.  This is because in a corner, you’re constantly needing to add energy to redirect your cars momentum.  This means you need to apply forward force at the drive wheels, as well as deal with side force on those tires.  

To turn the car, you need to apply ~more~ side force, to the tires steering the car.  For a reasonably well balanced car, (either through tire area, or carefully choosing the placement of mass on the chassis) rear wheel drive will let you stress the tires at the front, and back the same.  Potentially leading to the fastest cornering speeds.  However, this sort of force balance is fleeting, and has two breakdown paths.  First, you apply to much force to the driving tires, and you run out of traction in the back, and the car starts to step sideways.  Second, you apply to much steering input, and your front tires can’t keep up, and the car pushes out of the corner.  

Pushing is usually stable, and easily handled.  The back end stepping out, is a much more complex task to manage.  

The big advantage of FWD, is that over driving the car, all ends up with the same outcome.  The car pushes.  This is a stable, predictable, and easy to handle outcome.  

And now we come to MY front wheel drive car.  I bought the car, and installed the big pinion, and a 17.5 brushless motor.  The car was quite quick.  Much quicker than my VTA setup TC4.  Without a lot of care, the front tires would spin all the time.  The narrow chassis and sticky tires lead to a lot of weight transfer.  Mid corner it would spin up the inside tire, if it didn’t just roll over.  

On pavement, the M05 is entertaining, just like a high powered FWD car.  Stab the throttle, and it goes mostly straight, until the tires stop spinning.  Throw it into a corner, it’ll push, to varying degrees, and you can drive mostly on the throttle.  That was great, until I got to carpet.  

The local track has CRC black carpet.  This is some very sticky stuff.  Even without tire sauce, the car just wants to play turtle.  Thankfully, the MX-5 body really tends to roll to the tires.  

Rolling over is still a problem I haven’t entirely solved.  Mostly due to being stubborn I suppose, as if I have traction, I want to preserve it.  The prevailing wisdom, is that you should limit the steering input, to reduce the amount of early turn tire loading, and use tricks to reduce traction as the car loads the outside tires.  Namely, supergluing the sidewalls of at least the front tires, if not both the front and rear tires.  

In spite of not taking time to really deal with the handling (rolling) issue, I find the car very fun to drive, even on the carpet.  Provided I get the corner entry right, weight transfer and the differential limit the applied power, mid corner, preventing rollover once the turn is initiated.  …  On carpet.  

Running around on pavement, the story is quite different.  The car just behaves.  In fact, it’s almost boring with how well it behaves.  For a race car, that’s a great thing.  It’s the car i’m most comfortable handing over to people to try out.  

What needs fixing
Even in it’s factory stock form, the M05 is pretty competent.  And very low maintenance.  

For a car I’m going to drive, I want at least functional oil filled shocks.  The next thing, is to get the steering slop reduced.  

Stiffening the differential would be beneficial as well.  As long as the car isn’t tipping over mid corner, being able to apply more power in a turn is useful.

As usual, you can go a long ways with Tamiya by shimming much of the slop out.  I was able to put shims around both the front and rear axles, the steering knuckles, and the suspension pivots.  $2 in shims made the car much more stable in a straight line, and took the wiggle out of the car when it transitioned from left to right.  

Now, there are serious racers that use this platform.  And to that end, everything could be fixed.  Well almost everything.  Amusingly, there seem to be no chassis stiffening components.  There are high end shocks, glass reinforced suspension arms, adjustable camber links, aluminum knuckles and hub carriers, balance weights, heatsinks, cooling fans, CVD drives, ball diffs, spring kits, and sway bars.  

They are all worth something, but as usual, it’s the world of diminishing returns with upgrade parts.  If you really want to go racing, with the recent price reduction of the M05r, that would be the way to go.  

How can I buy a M05, whats the best to buy?

If you’re going racing, buy a M05r.  It’s a great deal, and comes with the right shocks, tons of aluminum parts, the stiff suspension arms, and is ready for hard case lipo packs from the factory.  It’s hard to beat.  

The next best choice, is one of the special edition chassis kits, that comes with some basic parts.  

The M05 chassis is sold mostly as kits, with a few ready to run sets on the market as well.  It’s still sold mostly as a basic kit, so you won’t be finding many M05’s with oil filled shocks and other parts from the factory.  That really means buy the one with the body you like.  Tamiya body sets are not cheap, so getting the right one with your kit, is a big selling point.  

The following all do not include bodies, but do include at least oil filled shocks, and various other upgrade parts.  Generally speaking they are more desireable, but you’ll need to check them out on an individual basis.  Depending on release date, their prices vary wildly.  

58593 M-05 Ver.II PRO Chassis Kit
84424 M-05 Ver.II R chassis Kit

These have oil filled shocks, and a few other upgrade parts.
58443 M05 PRO Chassis Kit
84131 M-05 PRO chassis kit (Blue-plated version)
84204 M-05 S-spec chassis kit
92228 M05 S chassis kit

And this is just a bare special chassis.
84359 M-05 chassis kit Gold Edition

The rest are all basic cars with bodies.  They come with Motors, ESCs, and friction dampers.

58438 Mini Cooper Racing - M05
58444 Abarth 500 Assetto Corse
92213 Datsun 280ZX Sports Version
58454 Honda S800 Racing
58453 Alfa Romeo MiTo
58465 Fiat Abarth 1000 TCR Berlina Corse
58483 Mini Cooper '94 Monte Carlo
84183 Mini Cooper Racing (Finished body)
58503 Honda Ballade Sports Mugen
58520 MINI JCW Coupe
84316 Volkswagen Golf Mk.1 Racing Gr.2
58581 GoPro Monster Sport Super Swift
58624 Mazda Roadster
47308 Volkswagen Golf Mk.1 Racing Gr.2
58640 Mazda Demio / Mazda 2

Ready to Run:
84134 Alfa Romeo MiTo, yellow
84135 Alfa Romeo MiTo, black
84136 Alfa Romeo MiTo, silver

The M05 starts at $100, and they typically sell for $160.  The RTR models are closer to $300.  If your plan is to build a beautifully scale car, and drive in your driveway, or up and down your street, maybe your basement.  Just a plain M05 is a great place to go.  

If you want to go racing, I’d seek out a M05r.  And carefully compare the prices with the parts you think you’d really need to enjoy racing.  

Edit: At the time this was written, the M07 hadn’t been released.  If you’re giong racing, buy a M07.   My Car Today My M05 has seen a lot of hard track time. I've gone through a few sets of front knuckles, and rear hub carriers. I've even shattered some bearings.

That was a funny thing to discover.  I had the car on the work stand, and one wheel would just wobble.  Sadly, that was the end of the car for the day, I hadn't started stocking spare bearings yet.

I really recommend following Tamiya's directions to the letter when doing your body.  Don't cheap out on paint.  Don't mess around when you do the masking.  You'll end up with this:

Instead of this:

The new paint is metallic, and looks like the real car.  I backed mine with silver to make it opaque.  The top has Testors Flattening enamel.  It takes more time to dry than you might think, so give it a few hours before you start doing decals.

Don't be shy with that masking tape.  I do most of mine with cheap blue painters tape.

And you will be rewarded with nice sharp paint lines.

When I had decided that my old body was to messed up to save, I bought a second M05 kit.  A friend of mine was itching to build ~anything~, so she got to build the second (third) M05.

Her first build, took about four hours to do.

She was very proud of the car at the end.  ... and wanted to keep it.

That..... wasn't to be.  The car was ment to be resold.  Assembled, the M05 brought in $65.  Which means after the cost of buying a body kit, we got to build the car for free.

And to hint at what's coming soon, here's a picture of my trunk:

I really like this car.  There will be a tuning article coming up eventually here.  But this car will be taking a back seat to the M07 I just built.  

As usual, here's a few pictures that didn't make it into the article.