Speedy's RM01 Lancia Stratos Build Thread

[ALEXKYRIAK 1046]

^^^^^^ This is why I’m on Tamiya Club.  Awesome mate. Loving this.  

[speedy_w_beans 4272]

Well, it was a happy day today as the postal service delivered my M2.6x12 screws.  This gave me a good reason to try out those axle spacers I printed earlier!

So I just removed the original screws and put them back in Bag B, and as you can see the spacers and new screws work just fine.  I checked for any additional radial play at the ends of the axle, but everything is still running true.

One small detail I hadn't considered earlier is the 5 mm feature near the face of the hex.  The axle stub itself is 4 mm like any regular touring car or M-chassis axle stub, but this extra little feature means an unmodified wheel doesn't sit flat against the hex.

The easy answer is to drill out the rear wheels with a 5 mm drill bit, and use that extra feature on the axle stub as the way to locate/center the wheel on the axle.  Then clamp the wheel down with a nut as you would normally.  Anyhow, not a big deal to have a dedicated rear wheel vs. a front wheel.

This is the first time I've had all the wheels installed with a hex adapters, spacers, and the front end with F103GT knuckles.  It feels really good to see the ground clearance, feel the smoothness of the ball diff, and play with the suspension movements!

When my final batch of parts come in, I see a few tweaks on the horizon.  The rear axle spacers will likely grow from 5 mm thick to 6 mm thick so the width will increase from 170 mm to 172 mm, about 3 mm less than the rear of the shell in total.  The front wheel hexes will shrink from 7 mm thick to 6 mm thick so the width will decrease from 165 mm to 163 mm, about 3 mm less than the front of the shell in total.  That'll be my baseline for fitting the shell.

It weighs so little!

[Juls1 1661]

Be interesting to see how this drives, that is if your intending to drive it? 

[speedy_w_beans 4272]

On 11/2/2018 at 10:22 AM, Juls1 said:

Be interesting to see how this drives, that is if your intending to drive it? 

Yeah, I'll drive it a little just to get a sense of how it behaves.

Still waiting on parts, so I updated the rear axle spacers to 6 mm.  Then I replaced the 7 mm front hexes with 5 mm hexes, and printed a 1 mm spacer for the time being.  Anyhow, the wheelbase and intended widths are spot-on at 172 mm rear and 163 mm front, so today I trimmed the shell and did some test fitting to see how it looks.

Seems reasonable.  The front wheels steer without binding on the body.

So while I'm waiting on parts I'll probably sand the trim lines a little and work on rear fitment some more.

[_oliK 108]

This looks sick! And going with the RM-01 that has all of it's little weight in the center is a great choice!

[Kingfisher 1171]

On 11/1/2018 at 6:24 PM, speedy_w_beans said:

 

 

Will you be selling these adapters on shapeways or anywhere? I have a pair of RM-01's and have been curious on how they would do with rubber tires. 

[speedy_w_beans 4272]

1 hour ago, Kingfisher said:

Will you be selling these adapters on shapeways or anywhere? I have a pair of RM-01's and have been curious on how they would do with rubber tires. 

Kingfisher, I'm happy to make you some and drop them in the mail.  Just let me know how many you need and where to send them.  Also let me know if you need rear axle spacers of a certain thickness.  If you want the CAD files I can email them to you, too.  The rear axle height inserts just need to be flipped to lower the axle/raise the chassis to make it level with the front end.

For the front end you'll need a set of F103GT "T" parts, M05/M06 axle stubs, four 850 bearings, and cross pins/hexes to suit.  The wheelbase will be wrong at <200 mm with the kit front end, but if you want to just try it then this is the minimal-effort way to go.

I'm using the Mini Cooper Racing tires because they have a tread pattern, which would be accurate to a typical road tire (slicks are illegal for 1:1 road use, usually).  However, for best performance you might find Tamiya's hop-up slick tires a better option.  They make both 60D Type A (lower temperature) and 60D Type B (higher temperature).

[Kingfisher 1171]

1 hour ago, speedy_w_beans said:

Kingfisher, I'm happy to make you some and drop them in the mail.  Just let me know how many you need and where to send them.  Also let me know if you need rear axle spacers of a certain thickness.  If you want the CAD files I can email them to you, too.  The rear axle height inserts just need to be flipped to lower the axle/raise the chassis to make it level with the front end.

For the front end you'll need a set of F103GT "T" parts, M05/M06 axle stubs, four 850 bearings, and cross pins/hexes to suit.  The wheelbase will be wrong at <200 mm with the kit front end, but if you want to just try it then this is the minimal-effort way to go.

I'm using the Mini Cooper Racing tires because they have a tread pattern, which would be accurate to a typical road tire (slicks are illegal for 1:1 road use, usually).  However, for best performance you might find Tamiya's hop-up slick tires a better option.  They make both 60D Type A (lower temperature) and 60D Type B (higher temperature).

Thanks. I think just the wheel hexes would be all I need. I wouldn't know what to do with the cad file.  I have all of the other parts you listed. I can make the wheelbase work with one of the extra bodies I have. I've collected a few reproduced bolink 1/12 pan car bodies that don't have wheel wells down the sides. 

I don't race them on a track. My girlfriend and I just use the RM-01's to chase each other around a parking lot. 

[speedy_w_beans 4272]

A little more work to share...

First, I did spend some more time trimming and sanding the shell.  Most of the cut lines are smooth now, and I was able to get the rear end to fit together better.  It's impossible to tell until there is paint on it, but I feel like the rear end of the shell will come together reasonably well.

Some parts came in this past week.  A few more might show up today.

Originally I had 3Racing front axle stubs installed, but the anodizing wasn't the same as the rear axle.  I ordered some Yeah Racing axle stubs since their 5 mm thick wheel hexes seemed to more closely match Tamiya's color.  It's hard to tell from this photo, but the Yeah Racing stubs are on the left and the 3Racing stubs are on the right.  Looking at them directly, the 3Racing color is more blue-green.

I opted to keep the printed wheel spacer instead of opening the pack of blue anodized wheel spacers.  In the end, the front axle is now consistent with the rear axle in terms of color and usage of printed parts.

Next up were some foam inserts.  I prefer one-piece foams instead of gluing the foam strips together Tamiya provides.

I had been waiting on the 3Racing servo saver and Tamiya 42 mm blue turnbuckles to work on the front end, so I gave it a try knowing the Ackermann is probably wrong.  I just wanted to see how wrong it is.  Plenty of servo parts...

The 42 mm turnbuckles were too long, so I went back to the kit 32 mm turnbuckles.  Anyhow, the front end looks like this at the moment.  I tried rolling the chassis around the garage floor in different arcs, and I could see the inside tire was scrubbing at higher steering angles.  So, the geometry of the front end will need to be revisited.

I turned my attention to the rear motor pod next, and installed the kit 380 motor.  Raw power and speed runs are not the goal here; adequate power is good enough for some casual driving in the street.  I'm using the 380/540 adapter plate that comes with the kit for now.

Pinion and adapter for the smaller motor shaft...

Positioned and meshed.

So here's where I'm at today.  The rear pod and motor seem ok to me.  The battery tray will be reworked as soon as I get an actual battery in front of me.  I ordered a 2S LiPo from Hobbyking that measures 69 mm x 43 mm x 16 mm, so it should fit within the battery tray mounting screws, pitch damper mount, and under the pitch damper itself.  There's room for a receiver and ESC.  Probably the big question at the moment is whether I can improve the steering angle relationship between inner and outer wheels.

More to come...

[speedy_w_beans 4272]

The postman showed up and brought some more goodies later in the day!

In particular I was interested in the battery.  Tamiya's 6.6V LiFe pack (55105) measures 70 mm x 38 mm x 20 mm, and I picked this LiPo pack because it was advertised as 69 mm x 43 mm x 16 mm.

A quick check looks good...

One interesting part is L4; it's not used per the RM01 kit instructions, but the same sprue is provided in the F104V2 PRO kit.  It turns out L4 is used as a battery stopper when a hard case LiPo is used in that chassis.  As luck would have it, there are two extra holes in the RM01 chassis that just happen to be spaced properly for L4.

Then I designed some very simple battery clips to complement L4...

Printed...

... and installed!  I used some extra M3x8 button head screws as rubber band / hair band posts to keep the battery in place.  I might install some padding later to reduce any side-to-side movement, but for now the concept seems like it will work just fine.

Side shot...

 

[yogi-bear 2321]

thats a tiny battery! what sort of run times do you think you'll get?

[speedy_w_beans 4272]

12 minutes ago, yogi-bear said:

thats a tiny battery! what sort of run times do you think you'll get?

Great question.  Tamiya's 55105 LiFe battery is spec'd at 6.6V, 1100 mAh.  Anecdotally one person on RCTech claims the LiFe battery and 380 motor combination will provide over 15 minutes of runtime.  My pack is 7.4V, 1600 mAh, so I'd guess somewhere in the 20 minute range.

The 380 motor is pretty thrifty compared to the regular 540 motor; it takes about half the current in all conditions (no load, max efficiency, stall):

380 Motor

540 Motor

 I just weighed my chassis with all the electronics stacked on it, and it comes in at 637 grams.  That's a little under half the weight of a competitive 4WD touring car.  Also, there's very little friction with very few moving parts.  I'm guessing it will run longer than my attention span! 

[Grastens 2795]

A fantastic build of a fantastic subject done in a really interesting way! Your attention to detail, both in the design stages and in the finishing, are in keeping with the excellence of the very project itself

I am looking forward to hearing how the motor-battery combination fares in such a lightweight car.

[IBIFTKH 1369]

Great build, your attention to detail is amazing.

Regarding run times, I've got a couple of 1300mah lipos for my T3-01 which has a 370 motor. Run times are 20 minutes or more so I would think yours would be similar or better.

[speedy_w_beans 4272]

I mentioned earlier that I wasn't happy with the steering; the Ackermann was so extreme the inner tire was clearly scrubbing on the garage floor while trying different arc paths.  A lot of this comes from the F103GT knuckles, which inherently have about 19 degrees of angular offset from the kingpin to the turnbuckle ball connector.  The RM01 knuckle, in comparison, only has about 9 degrees of offset.  The result is for a given steering angle the inner knuckle turns at a much higher rate than it used to.  I wanted to compensate this, and the idea with a single servo was to push the turnbuckles forward.  It just wasn't enough.

So, I had this thought about using a pair of slim servos and orienting the horns so the inner knuckle would see slowing rates of change right away, and the outer knuckle would see increasing rates of change. This would compensate against the inner knuckle's tendency to change more quickly than the outer knuckle.  The idea for this comes from some engine control work I used to do; we would apply governors to generator sets.  Many of them had throttle bodies for gasoline or natural gas.  The air flow relationship (and therefore torque/power made at speed) was very nonlinear.  The first few degrees of throttle tip-in would change air flow dramatically, and the last 20-30 degrees of throttle made very little difference.  To compensate, or somewhat linearize, the relationship between our governor's shaft rotation and the air flow / torque / power the engine made, we'd come up with nonlinear linkage geometries where a lot of initial governor movement would just start to crack the throttle open, and later a little governor movement would effect the last 20-30 degrees of throttle movement.  It wasn't perfect linearization, but it did work well enough for a standard PID control to stay stable under all load conditions.

Anyhow, that's a side story talking about nonlinear linkages, but the same concept can be applied to affect steering rates for both inner and outer knuckles.  The challenge is to swap where the turnbuckles connect on a servo horn and keep them in the same plane.  That's not possible, so separate servo horns offset to reflect the angle swap works the same way.

Design work on some servo mounts...

Printed part...

Servos mounted...

Front view...

And in the car!

Here's the result at the moment.  I'm using a LiPo to power a BEC, which in turn goes through a servo power analyzer, then to the receiver, where channel 1 is split to feed both servos at the same time.

If you watch closely, you'll see the outer wheel now moves more than the inner wheel!  So that's a little too much.  However, this is a good thing because I can easily move the servo horns one spline position each, change which hole is used on each horn, and even change which hole is used on the knuckle.  I'm pretty confident I can dial the steering in with this setup.

[Fabia130vRS 2098]

This is amazingly pleasant to watch

[ThunderDragonCy 7881]

1 hour ago, speedy_w_beans said:

 

Amazing work. Loving this. Bravo! 

[_oliK 108]

I've only ever seen two servos on Drift cars. And an interesting choice of battery for sure!

 

[speedy_w_beans 4272]

I finished the electronics installation today.  It started with placing the receiver and ESC, then trying to decide what to do with the BEC and servo signal splitter.  Ultimately I decided to make a small box for the BEC and place it under the ESC, and make a splitter cable from two small extension leads instead of using the block of connectors.  It's easier to tuck the splitter in with the wiring than to find a location for a splitter block.

The battery's balancing lead is tucked under the hair band, and the XT60 has been replaced with a Dean's connector.  The ESC's mini Molex connector and the BEC input are soldered to a mating Dean's.  The BEC output goes to the battery input of the receiver, and the ESC's input lead goes to the receiver's channel 2.  The ESC's input lead has the BEC wire removed from the connector shell, insulated with heat shrink, and folded back into the main bundle of wiring so there's no conflict between the external BEC and the ESC's internal BEC (two servos overload the Quicrun's BEC so I needed a stronger external one).  The receiver's channel 1 goes to the splitter lead, and the servos connect to the splitter.  There are a few zip ties securing all the wiring.  I generally don't like to shorten wiring as the electronics may move to a different car in the future.

Most everything is nice and low in the chassis...  The only exception is the ESC which is stuck on top of the external BEC box.  The current weight as shown is 650 grams.

I took it for a gentle test drive in the kitchen and was pleased to see the turning radius is about half a meter, and the wheel angles are about right.  I could kick out the rear end of the car at will in a tight turn, and straight line acceleration was scary in such a confined location.  It's easy to imagine wedging the car under the freezer or oven!  It rolls very well with very little friction to slow it down.  I'm really eager now to take it outside and test it in the street, but the forecast is calling for rain for another day and a half.

[Jason1145 3986]

This is bordering on the obsessive, my daughter would accidentally step on this car and all the fine little details would be wasted in 14KG clumbsy instance... this is why I can’t do attention to detail 😂 but I like that you can, and very generous of you to help out another member with the printed parts too  

It’ll soon be the best part, painting the body!

[_oliK 108]

650 grams? 

 

[speedy_w_beans 4272]

3 hours ago, _oliK said:

650 grams? 

Yep!  Comparing weights for 1/12 pan car electronics vs. typical weights for 1/10 touring car electronics:

• About 75 grams for a RS380 vs. 160 grams for a RS540
• About 92 grams for the small LiPo pack vs. 189 grams for a shorty LiPo, 313 grams for a standard LiPo, and 417 grams for a NiMH 4200 stick pack
• About 5 grams for a receiver, no difference
• About 23 grams for the 1625 ESC vs. 39 grams for a 1060 ESC
• About 51 grams for the dual servo setup vs. 47 grams for a standard Futaba S3003 w/ hardware
• Plus you can see the simplicity of a pan car chassis plate, two gears, a ball diff, and pivot ball suspension vs. all the moving parts and structural parts of a touring car.

[Grotty Otty 868]

Top work, the twin servo solution for the steering is genius. 

[speedy_w_beans 4272]

Worked on the front bumper today.

I started with Tamiya's 54819 Urethane Bumper XL, traced the outline on card stock, and started test fitting the chassis and body with the card stock.  What I found was I needed to trim nearly 32 mm off the bumper; essentially I was going to trim an XL bumper down to standard size!  So I dug around the parts bin and found an old TT01D standard bumper, and discovered it was a very good fit between the front wheels and the inside of the body shell.

There was no way I would be able to measure all of the lines and radii of the foam bumper to design a bracket, so I took the easy way out and put both the RM01 front bumper and the TT01D foam bumper in a flat bed scanner to get some images with all the curves captured.

And...

From there I was able to pull the images into the CAD tool itself and trace the features using the drafting tool.  Several splines, fills, cuts, Tamiya font searches, and finishing touches, and I had this:

Parts were printed, and it all went together just fine.  I used a silver paint marker to make the lettering stand out more.

The bottom of the bracket is sloped so the front end of the FRP chassis plate won't take a direct hit.

I'd like to do something about protecting the diff and gears more from debris, then it's on to body mounts.

[Kevin_Mc 411]

Simply amazing.