2012-08-28

RC10 Gold Pan Renovation: Part 2, wheels

After getting my RC10 back in service, it became apparent that I would need new tires some day.  The rear tires had very little tread or traction left, and the ground clearance was barely sufficient to run it on short grass.

Unfortunately, the original RC10 wheels are a small obsolete size, and modern tires aren't available to fit them. My options seemed to be:
  • find vintage wheels and tires on ebay or other sources
  • buy JC Racing wheels that use standard buggy tires but allegedly fit on the original RC10
  • rebuild the rear end to fit modern buggy wheels
The JC Racing wheels look really nice, but they take a long time to ship from the UK, they're expensive, and I'd need to salvage the wheels every time I replaced the tires since they cost so much.  Also, there isn't nearly as much challenge involved in slapping new wheels on the car as there is with rebuilding the entire rear end.

There are many threads on various RC forums regarding the various ways you can adapt your gold pan RC10 to run modern 1/10 scale buggy wheels.  Unfortunately they tend to skimp on the details and expect you to figure stuff out yourself.  Truthfully, there are so many minor differences in early RC10 buggies that this might be the best bet.  But hopefully the story of what I did will help others who have the same problem.

I'll deal with the front and rear wheels separately, because the front is much easier than the rear.

Front Wheels

Currently, RC10B4 wheels are still available, and they fit just fine on my original 3/16" axles.  I started with DE Racing "Borrego" wheels for the B4 buggy, with 3/16"x3/8" bearings to fit them.  I bought JConcepts Barcode front tires.
DE Racing Borrego front wheel, and original RC10 wheel

Overall, this setup mostly works, but it isn't perfect.  The larger diameter wheel fits just fine, but the wheels are also wider. This causes the tire to rub on the front A-arm at full steering. This can be adjusted with servo travel on the transmitter, but it must increase your turning radius somewhat.

The Barcode tires were completely useless on grass, I may as well have been driving slicks.  Since my options were either to drive them for a few days and buy replacements, or save them for indoor driving and buy replacements, I opted to save the bar codes and buy even more wheels and tires.

I got Associated B4 wheels all around, hoping they might work slightly better than the DE Racing wheels.  For the front, I got Pro-Line 4 rib tires, a modern version of the original tires on the car.  Overall these worked very similarly to the bar codes: they're a bit too wide, but otherwise they work fine.  They also don't have great traction on the grass, but they have a heck of a lot more tread.

Rear Wheels

When I say "rear wheels" here, I really mean the entire rear end of the car.

There are two basic problems with using the original RC10 with newer wheels.  First, the old RC10 axle is weird. Instead of being a constant diameter 3/16" axle as in the front, it has a fat section near the center of the car, tapering down to a narrower part where the wheel mounts.  The taper keeps the wheel from rubbing on the hub, but modern setups use a thick conical washer for this instead.  The second problem is the wheel offset: the old hubs don't stick out as far, so modern wheels end up rubbing on the rear arms.

The basic solution to both of these problems is to replace the original hubs and axles with RC10B4 hubs and axles.  Unfortunately since you're changing the hub location, this has a bit of a cascading effect and requires replacing quite a few parts.  For reference, I've found it useful to refer to the RC10B4 manual pdf (Google it if the link ends up broken), to find modern part numbers for the required replacement parts.

I opted to stick with the RC10B4 pin drive on the rear wheels for now, but it should be easy to use hex drive wheels with a hex adapter if the B4 wheels become unavailable.

I'll try to detail everything I ended up actually using, without any of the extra parts I didn't use; but I may forget something.  Most of these parts are shown on page 10 of the manual referenced above.
  • Associated 9584 rear hub carrier
  • (4) 3/16" x 3/8" bearings
  • Associated 9670 rear axle RTR
  • Associated 7368 3/16" axle shims
  • (2) Associated 9671 B4 RTR dogbone
  • Associated 7377 axle spacers
  • Associated 7369 universal roll pins
  • Associated 5407 O-rings
  • Associated 9608/9608B wheel spacer
  • 4/40 threaded rod, for longer camber links
  • 8/32 wheel locknuts
RC10 gold pan with RC10B4 rear hubs
The assembly is mostly straightforward.  Remove the old wheels, hub carriers, and camber links.  Save the ball link parts for use with the new hub carriers and camber links, and reassemble the hubs as shown in the manual above.

The B4 hub carriers have a narrower hinge pin hole, so open them up with a 1/8" drill bit.  As long as your hinge pin is loose in the old A-arm, it doesn't matter if it's a bit tight in the new hub carrier.

Since the new hubs are offset farther out than the old ones, you need longer dog bones to compensate, or they will fall out when your suspension is fully extended.  Some people have replaced their dog bone linkage with CVD links, but I was not willing to risk getting the wrong part since it cost so much more than the dog bones.

On the original RC10, the rear dog bones are held in place using springs in the hubs with small nylon spacers on the differential side.  In modern cars, O-rings are used at both ends of the linkage. The B4 RTR dog bones are just at the limit of maximum workable length using a reasonable camber angle.  The important part to get these to fit correctly is to remove the nylon washer from the differential side of the link, before replacing it with a rubber O-ring.  When you're finished, you should be able to bottom out the shocks before the dog bones bind up, but they won't fall out going over jumps.

The wider hub offset also affects your camber settings.  You need longer camber links in order to maintain the original camber setting.  On my car, I had to increase the distance between the ball link ends to about 0.75" in order to maintain a good camber setting.  This was enough of a change that I bought a long piece of threaded rod to build new camber links, rather than risking stripping the original plastic ball link ends by using them when they're too loose.
RC10 with B4 wheels and Traxxas/Pro-Line tires

I started with DE Racing Borrego wheels and Barcodes tires, just like in the front, but these tires don't have any more traction when you put them on the rear wheels.

For my second attempt, I used Traxxas step pin tires and Associated B4 rear wheels.  These have a lot more traction on the grass than any of the other tires I've used on this buggy.  On the grass, the buggy used to oversteer a lot on corners, but now it pushes like crazy.  I like the overall look of the car with these tires.  The combination of pin and rib tires mirrors the car's original look.

I may want to install a slightly smaller pinion to compensate for the larger wheel size, but otherwise I'm happy with these modifications. I should still be able to use the old wheels, so I can compare the handling to see if it's any better now.

My original buggy had bushings throughout instead of bearings.  This project replaced almost half of the bushings with bearings, so I now have reduced friction as well as more modern wheels.

RC10 Gold Pan Renovation: Part 1

As I mentioned before, I had an Associated RC10 remote control buggy as a kid. It was a high quality car at the time, and took the hobby by storm when it was first released.  I wanted to get my car back into service after many years in storage, so here's what I did.

RC10 gold pan, first release
This is an original "gold pan" model RC10, predating any stamps on the bottom of the chassis.  This dates it at about 1984 when the car was first released.

The first step in getting the car back into service was just to see if it even worked.  This was easier said than done, due to the state of the car's electronics. The original radio was a wide-band aircraft radio (oops!), using frequencies that are no longer usable, so that had to be thrown out before it was even turned on.  The speed controller was a rheostat, and was mostly broken, so it also needed replacement.

The obsolete NiCd battery was so destroyed my dad didn't even give it to me.  Unfortunately the original crosswise battery box mounting didn't leave enough space for modern NiMh batteries.  In retrospect, I think I could've found a LiPo battery that would have fit, but instead I decided to remount the battery box lengthwise.

After a few attempts to make an adapter to mount the battery holder without drilling the chassis, I gave up and made a critical decision in the evolution of this car: I was not going to attempt to preserve the original buggy, but instead I would just make it work well using modern parts where necessary.

I'm keeping all the old parts, so it could be returned to close to its original state, but truthfully most of the parts I'm replacing for a reason, not just on a whim. The RC10 was a wicked good car in its day (see what I did there?), but mine was the very first version of the kit.  Changes were made to critical systems early in its life, and even when this car was original, people routinely replaced parts with better alternatives when possible.

So: To heck with it! I drilled and tapped 2 holes in the chassis to mount the battery holder.  Done!  One end of the battery now sticks in where the throttle servo used to be mounted, and the other end is held down by one of the two original battery holders.  A 6-cell NiMH pack fits perfectly, and I could probably run 7 cells if I found a hump pack instead of a long pack.  I haven't made the switch to LiPo, but I'm sure something would fit here.

For the other parts, I got a Spektrum receiver and a brushed ESC.  I ripped out the throttle servo, speed controller, receiver, and receiver battery pack, and replaced them with the new parts.  The old Futaba servo needed a new connector, so I rewired it.  I also needed new bullet connectors on the motor, to replace the original Tamiya connector. I powered everything up, and... it worked!  Of course it did, why wouldn't it work after replacing most of the electronics?

In the following weeks a few other problems cropped up.  The steering servo was slow and weak, so I replaced it with the Hitec seen above.  The motor ended up dying a slow death, probably because of worn brushes like my Losi motor (but after 28 years instead of 28 days). I replaced that with an Axial 27 turn motor to keep it at "stock" speed.

In the end, it's more important for me to get enjoyment out of this buggy than to maintain its original state.  I get more enjoyment out of repairing and improving the buggy than from driving it when it's in crappy condition.




2012-08-12

Tamiya Honda S800

Before I got back into driving RC cars, I had spent a lot of time playing Forza 3 and Forza 4, on-road circuit racing games on the Xbox 360.  Although I had only ever driven off-road RC cars previously, my experience with Forza made me interested in on-road RC cars as well.  I'm interested almost exclusively in smaller vintage cars (old cars that aren't muscle cars).  I also had fond memories of kit building, and my purchase of the ready-to-run Losi buggy made me wish I had purchased a kit instead.

So, put it all together and I ended up with an obvious conclusion: just before vacation last month, I ordered a Tamiya 1/10 scale RC Honda S800 kit, which uses Tamiya's M-05 FWD on-road chassis (unlike the original's RWD drivetrain).

The kit went together quickly; almost too quickly to be satisfying.  I had the mechanics and electronics done in a few evenings, and didn't run into any problems with the build.  I wanted to keep things simple and inexpensive the first time around, so the only hop-up part I used during the initial build was a bearing kit. I remember how much of a pain in the butt it is to add bearings after the car is complete.

The decal sheet that comes with the car allows you to reconstruct the S800's most famous racing livery: #25, currently on display at the Honda Collection Hall at the Twin Ring Motegi circuit.  I painted it using Tamiya Yellow polycarbonate paint, with a coat of Pactra white behind it.  The white really helped the yellow shine through, and the result is almost too bright compared to the historical car it's patterned after.

There are a lot of decals (really just stickers), and they took a long time to apply.  Each one needed to be cut out individually before being applied appropriately.  It ended up being tedious, but not as difficult as I feared to get the decals in the right place without any bubbles.  The end result was definitely worth the work!  This is a really beautiful car.

Comparing the car to pictures of the original, the only places where the decals are at all different is where the original car has holes in the body, but the model has decals.  Specifically, in the rear lower corners there are round decals with an odd shape that doesn't make much sense, which correspond to holes in the body on the original car.  It's almost as if the decal designer looked at one picture of the car and made a decal of what could be seen through the hole from his vantage point.

The only complaint I have about the decals is with the ones that are supposed to go over curved surfaces, such as the chromed fender lines and the trunk hinges.  These don't stick well enough to stay on the car (as seen in the image above, if you know what to look for).  Since they're simple single-colored decals, I will probably take them off and paint the lines instead.

I had one problem with the car after it was assembled with the body in place.  The rear end of the front fender was very close to the front wheel, and it would catch on the wheel during turns.  This suboptimal body position can be seen in these images. I fixed this by raising the rear body clips so the body was higher in the rear, and angled away from the front tire, and I haven't had any problems since. It looks a bit better than the "low rider"look the rear has with the stock body position.

The Honda S800 is a really interesting car. It looks to me like it's basically a clone of a contemporary MG roadster, similar to Honda's N600 clone of the Mini.

Today I had my first chance to really drive the car instead of just puttering around in the alley.  It's so nice looking that I've been afraid to scratch it up. But I built an RC model and not a plastic display kit for a reason, so to heck with it.  The kids wanted to ride bikes and scooters in the flat walkway in front of the church across the street, so I brought my car as well.

Not surprisingly, this car handles extremely differently than the buggies I'm used to driving off-road.  On the flat, with no obstacles to run into (and using the stock motor and a 6 cell NiMH pack) I was 100% unable to roll the car over in a corner.  It pushed into corners at speed, which is expected for a front wheel drive, but the rear end cut loose long before the car felt likely to roll.  This FWD chassis is extremely stable, with a very low center of gravity.

The stock M-05 chassis comes with friction dampers instead of oil-filled shocks.  I didn't want to replace these until I experienced driving without them, but it was quickly obvious why oil dampers are necessary.  The body bounced around a lot when cornering, in a very unnatural and unpredictable way.  

After a bit of driving around aimlessly, I set up cones and Ezra rode his bike while I raced him with the RC car.  Flat-out, he was no match for the stock motor, but around the corners his massive size made him very hard to pass safely.  On 3 occasions, I ended up in front of him and he ran over the car.  Oops!  It survived with only scratches (on the inside of the body), so no harm done. I also hit his rear tire a couple of times, which instantly flipped the car due to the tire's upforce.

At this point, I've gotten over my fear of scratching the car; but I'll probably touch up the paint and apply electrical tape where it's most likely to hit the chassis. I'm also a lot more interested in driving it than I was before.  I've ordered some 3Racing dampers, which are far cheaper than the Tamiya hop-up part.  Other than that, I plan to leave it stock until something breaks or wears out, just as I'm doing with my other cars.

2012-08-02

Miniature Cars: Losi XXX-SCB

To anybody who thought this was only a miniature wargaming blog: sorry! It's a blog about whatever interesting things I'm doing at the time, and that has meant miniatures for a long time, but it is not exclusively about gaming.
"And now, for something completely different." -- Monty Python's Flying Circus
A while back, my parents brought me my old RC10 gold pan remote control buggy, almost 30 years old.  I stuck it in the basement and forgot about it for a while.  But in June, I decided to go to a local hobby store to get some parts to put it back into action.

Losi XXX-SCB
After a bit of discussion with the local RC car expert, I decide it made more sense to get a new car instead of fixing the old one, at least until I had more clue.  I settled on a Losi XXX-SCB short course buggy, ready to run. My decision was based primarily on what it looked like: many of the modern RC offroad cars look pretty horrible, but this one reminds me of a 1930's open-wheel racer.

Out of the box, this is a really fast car compared to my antique RC10.   I really like it, and highly recommend it, with one caveat: don't expect the motor to last very long.  It has a cheap but fast brushed motor with a built in fan, that sucks dust into the brushes and wears them down very quickly.  The motor isn't serviceable, so it needs to be replaced quickly if you drive outdoors.

In my case, my replacement motor was defective and blew up the speed controller as well, so now I have a new Duratrax Element (by Castle) brushless motor system.  It is completely sealed against the environment, and it has already lasted a lot longer than the original motor did.

With such a nice offroad car, where do you drive it?  It quickly became apparent that in order to maintain interest, I needed to have goals.  Simply driving around aimlessly to see how fast it is didn't stay fun for long.  I started by convincing Frank he also needed one, so at least we could drive together.
Backyard RC track, first layout

But the real keep to keeping things interesting was driving it on a track, so I could try for incremental improvements in performance.

I got a bunch of flexible 4" irrigation pipe and 60d nails, cut the pipe in half the long way, and laid out a track in the back yard.  It's very small: the whole yard is as wide as a single lane of a ROAR compliant off-road track.  But it's a lot more fun to drive with the track than without it.

We've been changing up the layout, and encroaching onto the neighbor's yard as well.  More recently we added a jump to the long straight.

There is a nearby indoor carpet track, but I don't think they're doing any off-road racing in the summer.  That will be a good way to drive in the winter, though I may want to try it out when the population is lower.

After playing with these cars for a while, my interest has increased instead of decreasing, so expect more posts soon.