Monday, July 26, 2021

Review: Turnigy Ultimate 4600mah 2S2P Hardcase Lipo Short Pack

So I decided upon the Turnigy nano-tech Ultimate 4600mah 2S2P 90C Hardcase Lipo Short Pack because I was able to get it to fit inside the WL Toys 12428.

First thing I did was to plug it into my charger and charge it to capacity (at 1C which is 4.6A) and it ingested about ~3500 mAh in ~83 mins.  The charger is a SkyRC iMAX B6AC V2 and is connected to my Ubuntu pc running GNU DataExplorer:

But the real test is discharge.  On paper my battery charger/discharger maxxes out at 2A discharge, but I was only able to get it to discharge at 0.6A .. not sure what's going on there. 

UPDATE 1: Real world test; since I installed these packs (two cars) we've been out for two RC adventures, we kinda played till we'd had enough and came home, and in neither case did we run out of battery ;) I didn't time it, but I'd say we had fun for 90 mins or more.  Very impressed.

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.