ARC R10 – build and race!

This could be a long one – bear with me!

After nearly five years of running the TOP Scythe (apart from a brief flirtation with the TOP Photon), I’ve finally decided to get up to date. And the touring car I’ve chosen is the ARC R10, which I got from RC Racing UK.

Why change? A few reasons.

  • I wanted to be able to run a front gear diff, and getting one into the Scythe would be a journey into uncharted territory and discontinued parts.
  • A few of my favourite Scythe parts were getting hard to find.
  • The Scythe is not built for LiPo and there is only so much you can do with plasticard and UHU glue.
  • It was showing its age and was prone to “senior moments” with reliability and handling.

It will live on as a spare car though – it’s basically worthless, so no point in selling it.

Onto the ARC…

The car is proudly “Made in Taiwan” and comes from the same people who are behind the “Blitz” range of bodies and “Titan” range of tools.

The parts are all bagged up. Silicone oils for the rear diff and shocks are included, but no other tools or lubricants. You will need the usual assortment of metric hex drivers from 1.5mm to 3mm, a 3mm turnbuckle wrench and long-nose pliers. I have a few other tools that I like to keep handy, including an M3 thread tap, flush-cutters, and an emery board. I also sparingly use  Tamiya’s “Anaerobic Gel” threadlock and an old tube of extremely thick Mugen “Super Grease”.

You also get this nicely printed manual, a base setup sheet and some stickers. You may notice a few similarities between this car and others on the market already – it’s obviously been heavily inspired by some of the more popular designs, but it has a few unique details, and the quality is exceptional.

ARC R10 option parts

I also ordered a few option parts. Naturally a front gear diff, as that was one of the main reasons for changing, and also the flex chassis set. Chassis flex has become a significant tuning option in recent years, and I want to give it a try.

ARC R10 chassis weave showing 2 layers of glassfibre within the carbon

One interesting detail about the R10 is the chassis material. This is a shot of the kit chassis, and you should just be able to see two white rings in the countersinking. Those are two layers of glass fibre within the carbon fibre, intended to generate more flex. My kit chassis also has holes for a shorty LiPo (mounted rearward), which seems to be a change from the prototype.

Bag 1

ARC R10 spool showing where burr has been removed

First job of the build is the front spool. It’s an alloy hub with a moulded pulley and steel outdrives. Although not clear in the instructions, the pulley fence is directional and will only fit easily if the lip on the inside is orientated towards the 38T pulley itself. Threadlock the screws otherwise they will almost certainly come loose. You can see from this pic where I had to rub down a burr on the steel outdrive to make it fit the bearing properly – I only noticed this later in the build when the shock tower wouldn’t fit. An emery board (just a cheap one from the supermarket) is a great tool for this job, far more accurate than a Dremel. This was one of two parts faults I had with the build – the other was that a number of the stainless steel screws had mis-formed hexes and needed replacing.

ARC R10 diff internals

The gear diff is a simple and effective design. Compared to the 3Racing gear diff in my M-05, the outdrive o-rings actually fit, which makes a huge difference! The gears are all plastic, as is the one-piece cross-pin. The assembly is sealed with a single o-ring. It’s worth cleaning up the moulding around the edge of the gears, but there is no need to mess about with anything else, this diff is smooth from the outset. I always lubricate the seals with a little of the #1000 silicone oil. It’s worth rebuilding the diff after the first few runs, as the oil always finds hidden nooks and crannies inside the case, and is sure to need topping up. I built up the front diff with #500,000 oil, which is more like molten glass!

Bag 2

Onto the second bag, and the first job is the shocks. These are nicely finished, with aluminium bodies and machined pistons (3×1.0mm) and spacers. The bottom is sealed by a single o-ring, but the top has a design that is new to me, albeit very effective. The bladder needs to be seated in the top of the cap (tweezers made this job less fiddly), and then when it is screwed on, the excess oil automatically bleeds out of a small hole in the side of the cap. The result is a very consistent shock build, albeit one with a rather strong rebound because of the unvented air chamber above the diaphragm.

Now, I have noticed a few comments about these shocks on RC Tech. Personally, I have no problem whatsoever with the feel of the damping with the kit pistons and the suggested #500 oil. In my opinion, the fashion for trying to set a shock to 25% rebound or whatever is a complete waste of time – take the shocks off the car after a run and you’ll see that the rebound is already completely different. Just build the shocks in the natural way, with the piston pulled down, the chamber full of oil, and the diaphragm seated correctly. If you really want a softer rebound, drill a hole in the top of the shock to remove the air pressure. Whatever rebound you run, the pressure is very small compared to the pressure of the springs. Mini rant over.

Bag 3

The spur gear (which I am sure is supplied by RW Racing in the UK) is attached to an alloy layshaft (I used a little threadlock), and the moulded 19T pulleys are pressed onto pins and held in place by big E-clips. Changing spur is a rather tricky job.

With most of the drivetrain and the shocks completed, it’s time for the car itself to take shape. ARC suggest running a bead of superglue around the chassis edges – I didn’t, never have done, and never had a chassis issue as a result. I’d rather the edges of my parts remained CNC accurate for the best fit. You might have notice how slim the car’s chassis is, you might also be able to see that the undercut beneath the motor is a lot shallower than on many other cars. This retains the chassis strength, and stops the end of the motor from grinding on the track. The design seems to work, because there were no signs of rubbing on the bottom of the chassis after the first race meeting (more on that later). The aluminium bulkheads are identical front and rear and very nicely finished in 7075 alloy.

The rearward front suspension mount is fitted upside down to clear the belt (an assembly grease comes in handy here to stop all the spacers falling of the screws). I also use a little threadlock on the steel steering posts. Finally, although you can’t see it in this picture, the eccentric mounts for the diffs have a little recess in them, which I mark with a silver paint marker. I also mark the top of the eccentrics with a silver line, which makes it a lot easier to get both in the same position when setting belt tension.

Bag 4

The car is really beginning to take shape now. At this point you should refer to the setup sheet, as the manual is a little bit vague about the spacing required. The dual bellcrank steering is well designed, with everything symmetrical. The wishbones have different holes on each side – use the side with the ridge for the shock mountings if you are following the kit setup.

Bag 5

The driveshafts are another example of the thought that has gone into the car. They are all steel as standard, so durability will not be an issue, and they use clips to hold the joint pins in place rather than a grub screw, which makes the action smoother.

The car is very nearly finished now. I forgot to take any photos of the suspension parts close up, or any photos of the car with the top deck and shocks on, but I have a few more pictures of the completed car to come. The suspension goes together very precisely, and drops under its own weight, I have been unable to find anywhere that needs a shim (very unusual for me), the only place that might take a fine shim on the whole car is behind the wheel hexes. Make sure the anti-roll bars drop under their own weight too, with minimal lateral or vertical movement.

A word of warning at  this stage – the manual suggests screwing the suspension balls into the ball end to prevent damage – I made the mistake of screwing it into the inner camber link position. The long screw went through to the steel spool outdrive, which wrecked the tip of the thread (albeit barely scratching the spool), and then as I unscrewed the damaged screw, there was a small amount of damage to the aluminium upper bulkhead. But, testifying to the quality of the car, the bulkhead survived, even though the screw was junk. Fortunately ARC supply a small bag of spare hardware.

Bag 6

Lets just skip to the finished car! A few final build notes…

  • The servo mount precludes the use of a servo saver, the manual recommends using rubber grommets.
  • Spend some time on getting the servo travel even, the manual setting of 10 degrees offset is in the right range, and although my steering EPA ended up at 90% in one direction and 120% in the other, the steering is correct.

  • The jaws for the LiPo have a small range of adjustment and mean that no tape goes under the chassis.
  • The usable range for the pinion and spur gear is between 99 and 111 teeth in total with 48dp.

  • The body post protectors are very neat in that they use a straight pin rather than a body pin.

  • Kit belt tension was much too tight on the rear for me. After a few runs I have settled on three notches loose for the rear and standard for the front, using gear diffs at both ends.
  • The shock mounting balls take a 3mm hex wrench.
  • I had to take a small amount of material off the top deck to move my motor all the way back. I also needed to take some material away when fitting a very large (43T) pinion.

  • Consider gluing the nuts that hold the front bumper into place, they fall out rather easily.
  • The Blitz XFR shell has dimples in the correct place for the body posts, which makes it an easy choice. It’s not the best looking shell in the world though!

Setup

I built the car according to the kit setup. I chose the following electrics…

  • Futaba S9550 low profile servo
  • Futaba R133F receiver
  • Hobbywing Xtreme Stock ESC
  • HPI Flux Pro 17.5 motor
  • Team Torke 6500mAh LiPO

All these items fitted in very neatly, with everything on the lower deck. But despite these being average-sized electrics, the car seems a little heavy…

ARC R10 running weight - 1444gm

1444gm is some way above the BRCA limit of 1350gm. Time for another opinion – the BRCA limit is too low. 1350gm was chosen when the average LiPo was closer to 250gm – now they are over 300gm. Nonetheless rules is rules, and 90gm over the limit is too much (for comparison, the Scythe in a similar spec was about 1380gm). A shorty LiPo has been ordered.

Having said that, the car is exceptionally well balanced at that weight. As you can see from the scales, it is more or less balanced left to right, with a slight rearward weight bias (about 49/51). A good basis for a 4wd touring car.

Race

I’ve written about the car’s race debut at length already – but there wasn’t much to say about the car itself. Put simply, it was very, very good. At the start of the day, on a cold and green track, the back end was a bit loose – but that wasn’t unexpected. Once the track got some sun and rubber on it, the car was virtually perfect, with a very neutral balance and plenty of grip – so much so that I had no desire to try the flex chassis. I did try the front gear diff though – and I liked it. It took some of the snappiness away from the cars steering, and helped it roll through the apexes more smoothly, with no loss of corner exit speed. Any time gained would be measured in a couple of tenths, but it was more confidence inspiring. And that is where I have left it!

Dave

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