Wednesday, July 01, 2020

A new RC car adventure!

Well I am quite excited!  I've just received a WAF of 1.0 (Wife Approval Factor) for a new RC rig :) and I have been busily watching videos trying to work out what to get.  There are SO many choices.  I thought I'd best document what I am actually looking for so that I can make the best decision optimizing for fun:
  1. A "Hobby Grade" vehicle; ie standard replaceable parts etc.
  2. One that I build up from kit; it's fun and I learn more.
  3. I prefer the leisurely stroll to a fast blast, and I am not interested in high speed accidents; I want something that does slowly well.
  4. Not all that fussed by scale look perfection; prefer form over function.
  5. I'd like to take it up the trail by myself; I have a the 12428 for use with Reuben.
So, what kind of kit?  They seem to come in two kinds:
  • RAW (only half of the parts, you spec and source the rest) I am not sure exactly which electronics, wheels, tyres, body etc I'd need for a raw kit. 
  • RTR (Ready To Run): Has everything I need for now, and because this is a hobby vehicle, I can replace them later on if i want to.
Not sure about yet:
  1. Where to get it from; parts availability
  2. If I want an RTR kit or if i want to build it up from a "raw" kit.
Top contenders, prices are indicative and in $AUD.
  1. Axial Capra AXI03004 1.9 Unlimited Trail Buggy Builders Kit
  2. Something based on the Axial SXC10.2 chassis:
    1. The Unimog :) AXI90075 SCX10 II™ UMG10 4WD Kit
    2. The AXI90104 SCX10 II™ Raw Builders Kit
  3. SXC10.3??
Also, to be fair, I'm currently starting to suffer from analysis paralysis!
 will however now try to pick apart the contenders based on my criteria:

 Name     Kind Cost Pros Cons
 Capra     RTR kit    
  Ultra maneuverable, portal axles

.... zzzZZZ

UPDATE 1: I visited the local hobby shop for some cabling and while I was there I ended up chatting to the fellow and ended up choosing the HPI Venture SBK.

Front axle built; the quality of this product is unreal.

Tuesday, June 16, 2020

Wltoys 12428b (part 27: 4600 mah LiPo upgrade ;))

Party time! :)

Can you tell I'm excited!?  What we have here is the Turnigy nano-tech Ultimate 4600mah 2S2P 90C Hardcase Lipo Short Pack, which I intend to install in the 12428.  My research indicated that should fit with some modification of the battery tray.  Most important are the dimensions, advertised and actual; the actual battery I measured was slightly smaller than advertised:

  • Length: 96mm advertised vs 95.47 measured
  • Width: 47 advertised vs 46.9 measured
  • Depth: 25.1 advertised vs 24.9 measured.
So! I intended to sit it vertically in the battery tray and a little cutting of the battery tray was in order:

Tight clearance between battery and strut towers

Note shiny new motor heatsink.

Yes, this is quite high, and very far back.  As high and as backwards as possible.. Now I'm thinking of CG and it's not really ideal.. :) However, it fits!! I don't really care if it wheel-stands too much, these are all about the fun :)

UPDATE 1: Well.. It works ;) it's extremely punchy!  my wife says it sounds beastly! Characteristics are:
  1. At 8.4v the car will easily lift a front wheel under hard acceleration.
  2. Can't speak to playtime as I only reduced it down to storage voltage today.
  3. I'm running a locked diff, so it doesn't turn well at speed.  So that probably means a reduced tendency to roll, which is a good thing.  Although it still happens and the battery impacted the ground..
Hmm.. More engineering required.

UPDATE 2:  With the intent of allowing the battery to move forwards further I removed the battery tray and removed part of the front with some side-cutters; I only removed enough so the battery would fit through.

Battery tray with half the front removed.

I also had to remove about 30mm from the driver insert so it would clear the battery.  All this allowed the battery to move about 25mm forwards where it is nestled and protected inside the rear roll bars. 

Can you see the battery terminal on the top right?

I also made an aluminum tray for the battery to slide along and with just the right amount of bend, it holds the battery nicely without the need for a retaining strap.

The battery is held captive in all dimensions

Finally I shortened up the power cables, and reduced the thickness from 10 gauge to 14 gauge:

New power cable & connectors, reused balance bits.

Combined, these changes made all the difference :) I went for a long play up the bush the other day (uphill, damp earth, rocks).  Characteristics now are:
  1. Extremely long run time :) I charged both batteries but only used one.
  2. A motor heat-sink is now a must, it cut out a couple of times regardless.
  3. Pretty good weight distribution: ~52/48 front to rear ;)

     Weight (g)
    Distribution (%)
    Front Left
     430 24.6
    Rear Left
     425 24.3
    Front Right  471   26.9
    Rear Right 422   24.1
Who'd have thought there would be so much potential for fun in these little cars.  I actually bumped into some Tamiya owners who claimed their 90's cars were brittle and tiring to own.. After a little demo I may have converted him ;)

I'm still loving this thing .. :)

Show Hope fundraiser for International Students in Hobart

Here I am looking at new RC cars whilst others nearby are having trouble buying food.  It was not all that long ago when I myself didn't have a job, and I began to see how it might be for some people.  So I'm assuaging my guilt by donating $50 to the Show Hope fundraiser here in Hobart, Tasmania:
During this Covid 19 season, international students are doing it tough. Casual jobs have dried up. Parents and family at home are facing tough economic times and financial support is hard.  Some students have $0.  Others have a few weeks before their money runs out.  Students are studying,  feeling alone, and anxious about meeting weekly bills.  Show Hope we have provided hot meals, supermarket vouchers, and fresh produce every Tuesday and Thursday.

Wednesday, June 10, 2020

Wltoys 12428b (part 26: Two bent drive shafts)

So we've been having a bit of fun lately, and so this morning I was doing a little proactive maintenance on my boys car; his always seems more .. agricultural .. than mine and I wanted to have a closer look.  Among the general increase in wear and tear (he's a kid) I noticed that both drive shafts (front and rear) on the right hand side of the car were bent.  And during disassembly I then broke the screw holding the pinion to the shaft (as has happened elsewhere on these cars).

Figure 1: Bent and broken

Ignoring how the bent shafts might have happened I was able to get his car working smoothly by replacing the whole rear diff assembly and also a front CV shaft from the spare parts car.  The specific replacements of the parts are below, and I ordered them from Bangood.
The rest of this article discusses how to repair the bent shafts, and replace the broken screw.  It does assume you have seen inside the rear diff of a 12428b ;)

After rolling it on a flat surface, I found the high side of the rear axle, I held the axle in a vice and tapped the high side with a light hammer.  After repeating this a few times it came good.  Or so I thought; I then put it in a drill and it's still out of round by half a mm or so.. hmm..

Harder was the repairing the broken screw which had to be drilled out to 2.5mm and tapped at 3mm (I've also had to do similar previously).

Figure 2: After drilling out the broken screw

In Figure 1 the parts are lined up screw, spider gear, axle housing and axle shaft, with the (now broken) screw fixing the spider gear to the shaft.  During reassembly I didn't have a m3 screw with a small enough head to clear the spider gears, so I had to phone my friend Randal who specializes in such things :)

And finally, the front CV shaft was also quickly fixed with a couple of gentle taps of the ball pein hammer. 

Sorted :) .. hmmm but now what .. ;)

Monday, October 28, 2019

planet earth, time, mind

planet earth, time, mind 
their infinite profound complexity
neatly summarized in words

Saturday, September 21, 2019

Wltoys 12428b (part 25: Fixing slop in steering)

Setting less terrible toe angles seemed a bit pointless when the wheels kind just point wherever they want anyhow.  So that's the next order of business.

I needed a very thin shim, and after looking at the cost of stock at the hobby shop, i very carefully cut down an aluminum can.  I cut this little strip with a steel straight edge and 4 or 5 passes with a Stanley knife. 

0.16mm thick and ~1.89mm high.
Curiously, a can is about 0.25mm thick at the bottom and 0.12mm thick at the top.  So not only is it free, but we can make shims of different thicknesses!

The idea was to remove the play in this part of the steering mechanism.  I'm hoping a picture tells a thousand words, because i'm not sure i can explain it..

Craft knife points to the shim being inserted from the right.
It took a little fettling to get it to fit, and in the end instead of pushing the shim in, i ended up holding it in place with long nose pliers and moving the normally stationary part onto it (if that makes any sense).  

When it was inserted, I tightly folded the ends over so hopefully it stays in place.

Wltoys 12428b (part 24: Fixing front toe out)

From standard these cars come with a toe out that's quite visible.  When i measured it (I am not an engineer..) it seems about three degrees each side (with the standard fixed, equal length 61mm steering arms).  I did this by:
  1. Placing the car on a piece of paper, aligning it perpendicular.
  2. Place a straight edge along the front wheels, draw a line (the outside ones)
  3. Then rule progressive parallel lines towards the centre until they cross.
  4. At the crossing point, use a protractor to measure the angle.
  5. Halve that number to indicate the toe out for each wheel.
Such science!
Then we need to make up some adjustable steering arms so we can alter the toe.

Attempt 1: I cut the heads off some random bolts and screwed in the spare piston ends from the CVA shocks.  This would have worked, however, they're non adjustable.  Worse, I cut down the only bolts I had, and they were too short.. I really could have gone and got some more, cut them to the exact length.

Attempt 2: Buy some adjustable steering arms.  Ended up getting the Tamiya 54539 Full Turnbuckle Set. I fitted them in the following combination to yield an adjustable arm of nominal length 61mm:

Top: The new parts  Below: The standard 61mm arm.
Long story short, after a bit of mucking around I was able to produce 3 degrees toe in with equal length steering arms of 60.60mm.  That's about as good as I am willing to attempt right now, mainly because there will be wild variations in actual steering because of the play in the plastic steering mechanism.

Friday, September 20, 2019

Wltoys 12428b (part 23: RWD with locked rear diff)

So the rear wheel drive conversion has been very interesting.  Not only has it allowed me to isolate and then optimise the rear end, it's unlocked an entirely different vehicle from the AWD one.

However, one thing was immediately obvious, rear wheel traction was sorely lacking.  Hence, locking the rear diff with BlueTac :)

I kept another diff open, hence labeling.

I did this rather hastily and didn't bother taking any in-progress pictures.  However the process is pretty straight forward:
  1. Remove the wheels and rear differential cover etc.
  2. Remove the differential and axle assembly.
  3. Carefully open the differential by removing the 4 screws.
  4. Carefully note the arrangement of the spider gears.
  5. Carefully remove the spider gears onto a sheet of white paper.
  6. De-grease and clean the spider gears and inside their housing.
  7. Take a wad of BlueTac and shove it into the housing..
  8. Reinstall the spider gears, embedding them in the BlueTac.
  9. Shove more BlueTac on top of the spider gears.  Aim to fill it with only the smallest amount coming out of the screw holes upon re-assembly.
  10. Reassemble the differential, carefully tightening screws.  Don't force it.  If you have not enough then the spider gears will still move.  Too much and it won't go back together properly.  
  11. ..fettle until it works ;)
  12. Reinstall in the reverse order of disassembly.

Road Test:

OMFG.  The thing is a beast. Totally different animal..
  1. It feels more agile, nimble, responsive.  And powerful.
  2. Will readily lift a front wheel under acceleration.
  3. Brake application causes rear wheel lock, done carelessly induces spinout.
  4. Turning circle doesn't seem to be badly impacted.
  5. Can now easily do doughnuts.. ;)

Offroad Test:

Hmmmm... something isn't quite right.  It's nearly uncontrollable on full throttle.. I think it's torque steer?

  1. Whenever the car is at full throttle it will steer to the right (clockwise).
  2. From a standing start it will just do a doughnut, always the same direction.
  3. Trim the steering to the left, under full throttle it will travel straight, and then off throttle will travel to the left.  So i don't think a steering or even a toe issue.
  4. It only appeared to happen when the diff was locked.  RWD with open diff didn't have this issue.
Some interesting information.  Fixes? I'll try adjusting the front toe, that needs doing already.  Failing that I don't mind going back to AWD.  I feel like the rear is solid now which is how this all started in the first place.. ;)

UPDATE 1: Fixed the issues with toe out and steering play, but even on tarmac it still very readily wants to steer to the right.