New LiPo – fits perfectly!

Just received my new LiPo for the TOP Scythe – it’s a BRCA-legal Team Torke 6500/70C from www.rcracinguk.com.

Funnily enough, it fits the car as well as the old NiMH cells it was designed for! Because this LiPo is about 40gm heavier than the old one, by running it up against the centre bulkhead it gives perfect left/right weight distribution straight away (the old LiPo had to be mounted much further out and had bumps on the bottom). And since the LiPo is further in, I can use the original tape mounting positions without covering the plugs, so the LiPo is now held in even more securely.

A nice detail on this LiPo is the labels. At first I couldn’t understand why they run them along the side of the pack – but now I see that it stops the tape from covering them and eventually damaging them. Neat.

I also took the opportunity to make a few LiPo stoppers from 2mm plasticard, held on by servo tape. Makes the fit accurate and repeatable.

Dave

I love the smell of tarmac in the morning…

Considering my passion for RC, it’s surprising how rarely I actually go for a practice and a practice alone. Today was one of those days.

We’ve had wonderful week of early-spring weather, and the Cotswold Model Car Club track at Kemble was in great condition, clean and dry. Ambient temperature was in the high teens.

I was joined for the day by my 3-year-old son Elijah. His first visit to a track. The long-ish drive meant he started the session by sleeping, but was quite keen to be technical director by the end of the day, telling Daddy when it was time to stop driving, finding lost tools and rearranging the power cables…

Anyway, onto the practise itself. My intention was to get a better setup on the motor and speed controller. I’ve usually been hugely dissatisfied with the feel and performance of my 13.5 boosted setup, and the rare occasions when I’ve been happy have only left me even more confused. My latest hunch that I have been dramatically under-gearing the car and wasting the natural torque of an electric motor, smothering the car’s punch out of slower corners and giving a “two-speed” effect where you are waiting for the boost and turbo to kick in.

My motor is a Speed Passion V3 with the timing on the 10deg mark. My ESC is a Hobbywing Xtreme Stock. To get a good baseline for the gearing I started in “blinky” mode (508_no_timing). At 4.86:1 (the highest I could go with the available pinions) the car felt surprisingly quick around the big Cotswold track, with a lot of punch. I could have even gone a tooth or two bigger on the pinion. The laptimes don’t lie though – slow 22’s are nearly 4 seconds off my best with boost.

I tried the car at 5.35:1 next. A smoother feel all around the track (in part due to a better gear mesh), but the laptimes were in the mid-23’s. A further change to 5.94:1 resulted in a car that was simply slow, revving out before it had even reached the exit kerb of some corners. I didn’t want to sacrifice any more bottom-end performance, so I decided that this ratio would be a good basis to start boosting from.

So, a return to the pits, a charge of the batteries, a re-application of the tyre additive and a lift of the lid of the laptop. I updated the ESC software to the latest stock profile (930STOCK) and left the settings at their defaults. Put the car on the track, and straight away I was running laps in the slow-19’s and quick 20’s. The boost alone was worth nearly 3 seconds a lap. And the car felt good, really good. A quick increase of the braking strength to 75% gave me a car that was very driveable indeed, a slight dullness in the lower midrange but barely worth worrying about – perhaps gearing up again would be the answer. Motor temps were quite high, but the car coped with about seven minutes of intermittent running without problems.

And then the LiPo swelled.

Coming to the end of a short run, I felt the car slow down as if it was about to dump. I brought it to the end of the lap and pulled in. Took the car back to the pits, started to brush it down, and untaped the battery pack. Which promptly expanded to what seemed like twice its usual height, splitting the hard-case wide open. I quickly moved it to the other side of the pit area, just in case something dramatic happened.

In the end, nothing did – in fact, after half-an-hour of waiting for the YouTube-style fireball I put the LiPo back in its protective sack and drove back home, dropping it off at the council dump on the way.

I’m surprised that the LiPo swelled so dramatically. Even though it is almost three years old, and is only rated at 30C-ish (it’s an older Intellect 5000) I would have still expected it to be up to the demands of a 60a rated speed controller. I don’t think it was over-discharged as the ESC’s low voltage protection was at 3.2V per cell and hadn’t kicked in on the track, and the LiPo’s resting voltage once out of the car was closer to 3.5V per cell. Hopefully just one of those things.

So with the rebuilt TOP Scythe out of action for the day, I grabbed the Tamiya M-05L for a quick run. With no additive on the tyres and its club-night carpet setup it was a real joy to drive, a bit flighty at the back end perhaps but such an addictive flow through the corners. These front-wheel-drive Mini’s are so much fun around almost any track that I’m debating whether to bother with the touring car at all this summer. It needs a LiPo now, and BRCA legal ones are not that cheap.

I’ll just sign off with another note about the day. Despite the good conditions, the tyres (used Sorex 32RYs) did not generate any heat in themselves at any point in the day. This probably contributed the Scythe’s at-times awkward combination of understeer and tail-happiness. There’s usually a lot more grip when you have had 100+ cars running on the track over a big race weekend.

Dave

Dabbling with drift

For the past month or so I’ve been trying my hand at RC drifting. It’s pretty simple to get started if you already have a touring car, the biggest change is to fit some drift tyres and there are a few other tweaks you can make to make the car hold a more spectacular drift. It’s pretty tricky to get a precise drifting rhythm going though, and I am a long way from mastering it.

In fact it will be some time before I get any more practice because I am rebuilding my touring car to “grip” specifications for the coming outdoor season!

I should give some props to HPI Europe for their very good introduction to drifting.

My drift conversion was very simple. First step was to fit a set of the pre-mounted HPI T-drift slicks (#4739) – I’m glad I chose the pre-mounts because the tyres are very stiff and it would have taken a lot of coaxing to get them onto any other wheels (apparently soaking in hot water helps). I ended up adjusting the camber to almost zero to get the tyre “wearing” in the middle.

Next big change is to the drivetrain. I tried the car with diffs front and rear, and although you could get a drift going, the car would snap out of it quite quickly if the rear diff found some traction. Switching to the spool in the rear end seems to make the drifts a lot longer. I’ve also tried a one-way in the front and although it is quite good in the house, it seemed to initiate the drift a bit too aggressively when I tried it at my local carpet track. A front diff might be a good compromise.

Final thing to comment on is the motor and ESC combo. This is the same Speed Passion 13.5 and Hobbywing Xtreme Stock that I run in blinky mode for club “grip” racing, but it feels a lot slower in the drift car, I don’t think I would want any less power otherwise it would be hard to get the car sideways with a dab of throttle. The Hobbywing is a great forward-only ESC for racing but it is not very good with reverse enabled, there is a stubborn delay between reverse and forwards.

As I’m sure you’ve noticed, the detailing of the body is a big part of a drift car, and this one is no exception, with an exclusive Lexus IS convertible… or rather an old Protoform LTC-R with the roof cut off!

Video of my limited skills…

And video of some awesome skills from Japan… this car uses a counter-steer setup (overdriving the rear end to make it hang out wide in the corners) which isn’t easy to acheive with the Scythe. I’d love to try it out one day though. You should really watch all of the Drift 44 videos – they are jaw-droppingly good…

Dave

Basic touring car setup tips

Just thought I would share my approach to setting up a touring car, specifically for the small club track at Chippenham (www.cmcc.org.uk).

The build

I can’t emphasise enough how important it is to build the car well. None of these adjustments will make any difference if a bearing is binding or if the steering isn’t able to reach full lock. So take the time to make sure everything on your car is aligned correctly, that ever moving part moves freely, and that every stationary part stays put.

Weighing in

Once you have built the car up, you have to get it up to race weight – and get it balanced. BRCA regulations are 1350gm, and you want to get that weight even from left to right. The corner-weighting scales pictured above are a bit of an extravagance (most cars have holes in the shock tower so you can balance the car on a piece of string), but they demonstrate how well balanced my TOP Scythe is with just a little lead down the middle and the LiPo offset over the side of the chassis. Front/rear weight distribution is best left at factory settings to start with.

Bear in mind that different components have different weights. For that reason I always recommend running the same type of battery in your car throughout the race meeting. Throwing in an older pack for one race that is 50gms lighter will not only fail scrutineering, it will also make the car handle very differently – and a consistent car is essential if you are trying to understand setup changes or developing track conditions.

The setup

Generally, I would start out with the kit settings in terms of linkage positions and shock components, you may wish to tweak these one at a time but you have to be pretty confident/foolish to throw a completely different setup on a car and expect it to work.

Once you’ve got the car on the setup board at race weight, the first job is to set the ride height. Everything else follows from this. Bear in mind that different brands of tyres may have slightly different diameters, so the setup for one may not work for another.

I always set my car up with a 5mm front ride height and a 5.5mm rear ride height.

Next step is droop. This is the downtravel of the suspension beyond ride height. There are many ways of measuring it – choose the one that is consistent for you. I prefer the gauge method – but there are a few things you need to take into account. Most of them are numbered in such a way that a bigger number on the gauge is actually less droop. They are also only useful for measuring the position of the suspension arm relative to the bottom of the chassis – they don’t take into account ride height or tyre size or anything like that. So you need to do a bit of trial and error.

I usually start off by setting the rear droop at the point where the spring just starts to come off its collar when you lift the car off the ground. With my current car and the Sorex 28R tyres that works out at 5 on the gauge. I then set the front to have 1mm less droop (6 on the gauge in this case). I always check to make sure that the suspension is not pre-loaded – ie that the shocks extend a little when you lift the car off the ground. Pre-loaded suspension is edgy to drive and bad over the bumps. Never use the droop screws to adjust ride height.

The last basic job is the camber. I always set the car up with 2deg negative at the rear and 1.5deg negative at the front. This tends to give even tyre wear with a slight understeer balance. Take the measurement at a few points around the wheel to compensate for any warping. Don’t waste your time and money on a setup station, the only worthwhile measurements you will get are ones taken with the racing wheels on the car. A good quality camber gauge, ride-height gauge and flat board is all you need, although a droop gauge and a toe gauge can be handy.

Adjustments

Most modern touring cars have more adjustments than you could realistically make use of. I’ve had this Scythe for over 4 years now and there are settings I have never tried out – and I am one of those people that will change something on the car between every race if I have to! There are a few key adjustments that make a big difference when you are trying to get an ill-handling car close to what the track needs…

Tyres – most of us race on control tyres these days, but tyre prep (and the overall condition of your tyres) is a massive part of the cars performance. Check the gluing around the edge of the tyres regularly and re-glue if necessary. Have a consistent additive routine – for carpet on club nights, I clean with lighter fluid, and apply Nosram Carpet to the whole width of the tyres for about 5 minutes. You can try narrowing the application on the front tyres, or re-apply the additive, for different effects. A new set can do wonders.

Front drivetrain – Spools are very common outdoors, heavily-filled gear diffs are gaining in popularity, but on a tight indoor track, a medium-action diff makes the car a lot easier to get around and often quicker as a result. I currently have a tight ball diff in the front of the Scythe. The rear should always have a free-but-not-free-spinning diff in it.

Springs – probably the quickest way to get a big change in handling. Stiffer springs give less feeling of grip but more responsiveness.

Dampers – I generally keep the damping in harmony with the springs for a similar plush feel all round. Heavier damping will make the car feel smoother.

Radio settings – Something I find myself using a lot. Just one click of steering rates during a race can turn an understeering car into one with perfect balance. Resist the temptation to dial out too much steering to make the car easy to drive – you might not have enough to navigate the corners! My car is usually on 85-90% lock indoors.

There are a few more advanced adjustments on the cars, like roll centres and steering ackermann, but these are rarely quick fixes and need to be thought through. Best to leave them on kit settings unless there is a serious handling problem that springs and dampers can’t solve. I can recommend Elvo’s setup guide if you want to read about them in greater depth.

Electrics

I briefly mentioned the radio, I should also mention the motor and speedo. Chippenham club nights now run to 13.5 “blinky” rules. For those that don’t know, “blinky” is a mode which stops the ESC adding timing to the motor electronically. It slows the cars down and makes the throttle feel more progressive – it is how brushless should have stayed all along. I run the Speed Passion v3 13.5 at a 5.5:1 ratio and could possibly go a little higher. Brushless motors have ample torque and can pull big gear ratios even on a small track. As far as ESC settings go, there is hardly anything to change. The Hobbywing Xtreme Stock I use has a “punch” setting which they call DDRS, and the only other thing you may want to change is the drag brake setting – the less you can get away with the better.

Driving

Let’s just say that “smooth is fast” and leave it at that!

Dave

CWIC Rounds 1&2 – 23/10/11

Winter is here again and time to go back indoors for a racing fix. And there is no doubt that the Chippenham Winter Indoor Championship is one of the best events in the UK at which to get it.

With some 120 entries across 6 classes there was a full day of great racing on the 30mx16m carpet track laid out at the Christie Miller Sports Centre in Melksham.

I decided to run in two classes – Mini Formula and 13.5 Touring. Mini Formula is new for this season and is basically Tamiya front-wheel-drive Minis with HPI Saturn 20 motors and Sweep tyres. 13.5 Touring is unchanged from last year.

Mini Formula

Overall a very enjoyable day. These front wheel drive Minis are so much fun to drive, you get a real sense of controlling the machine.

The first two rounds of qualifying went well, and I was second overall in both. The only noticeable issue with the handling was the amount of diffing-out on corner exit, so for the final round of qualifying I re-fitted the 3Racing gear diff with #5K oil. After a few mistakes in the first couple of minutes while me and the diff got re-acquainted, I set some decent individual laptimes, but ended up slower over 5 minutes. My Round 2 time was good enough to just stay ahead of Andy Travis who took third overall. Joe Keaveney was in a class of his own and would start the finals from pole.

In the first final, Joe started slowly and I tried to nip down the inside. We touched; he span;  I waited; and by the time he had got going again I was right back in the traffic. After a couple of laps I was on the tail of Steve Bendrey and John Ridding who were fighting for 3rd place. I managed to get ahead of John and then had several laps of really close racing with Steve, who was running a super-neat line which meant I just couldn’t get past. Eventually I got a sniff of the inside as we went through traffic and just managed to get ahead through Turns 2,3 &4. I set about chasing down Andy but just as I was getting close I clipped a marker and rolled, landing on the wheels. I started the chase again but ran out of laps and finished just under a second behind. Joe meanwhile had re-taken the lead after the first corner incident and drove away from the field, finishing a lap up, which is quite amazing considering the cars are all very similar and running a handout motor.

The second final started in a similar fashion. Joe was slow through the first corner, I took a look down the inside on the exit of turn 2, but there wasn’t room to pull a move and I clipped the flappy marker, rolling onto my wheels but ending up well back in the traffic and 9th at the end of the first lap. Fortunately I managed to find a clean route through the field and after a few laps was back up to third and chasing down Andy Travis. This time I managed to catch him a few laps before the finish, and used the gear diffs excellent traction out of the final corner to glide by on the straight. As far as I was concerned I had sealed second place, but unbeknown to me, Joe’s switch had come loose mid-way through the race and he finished a few laps down. So a win! Unexpected by me and unlucky for Joe, but I’ll take any luck that comes my way. This leaves me in the lead of the championship after the first two rounds, a nice bonus.

13.5 Touring

I wasn’t even sure I would bother with touring this year, because I’ve had a few odd problems with the car over the past year, and I don’t really enjoy the feel of “boosted” stock racing. Nevertheless, I thought it would be a waste to leave a usable car at home, so I freshened up a few parts on the TOP Scythe and gave it a run.

The car was terrible in the first round of qualifying, with no rear-end grip or balance, but I knew that the traction would come up as the day progressed so I left the car exactly the same for round 2. This was an OK run, and although the car’s balance was acceptable, it just felt slow in both power and cornerspeed. Third round was a disaster, a bump in the early laps popped a bodyclip off, and when the body lifted up for the third time I pulled over (thanks to Rob Long for patiently sorting the body the first two times). The car also revisited its habit of loosening rear wheel nuts, despite me changing wheel bearings and diff internals during the week. This issue only started when I fitted aluminum diff halves – so they’re staying in the pitbox from now on.

Qualifying result was 6th in the B final, which probably reflected my pace. The car was slow off the line in the first final (which left me wondering what powertrain setups the other cars were running), and by the time I had got to the first corner there was already a car on the apex facing the wrong way, which I hit and ended up close to last. After four minutes of just trying to get some laps in and moving up the order as others made mistakes, we ended up with 5 cars on the same bit of track fighting for second place. It all got a bit messy at times but somehow I ended up leading that pack at the finish. The winner was long gone.

The second final’s start was a carbon copy of the first, as I once again collected a car facing the wrong way at the first corner apex and found myself close to the back of the field. Ultimately it was a slightly less dramatic race as I crept up through the field to finish 4th, a lap down on the winner.

To sum up, the minor disappointment of 13.5 was more than made up for by the pleasure of Mini Formula, and of course the trackside banter. Looking forward to the next meeting!

Some pics of my cars post-race follow.

Dave


Diff balls under the microscope…

Got the Intel QX3+ microscope out of the cupboard to satisfy my curiousity about how rough diff balls get when they wear out.

The results are in…

New diff ball
A new steel diff ball. Some surface imperfections but smooth enough to see the reflection of the microscope lens in it.

 

Bad diff ball
A failed diff ball. Look at the gouges in it!

To add a little context, these are “no-name” steel diff balls that let go after just two runs in the car. So the quality is probably not that great in the first place. The gouges and grooves in the failed balls are quite surprising to see though. This is 60x magnification, and some of the fine white lines are lint from paper tissue.

TOP “Scyton” – update…

I am less pleased 😦

What seemed like stability on the club track turned into diabolical understeer on the big track at the CWIC.

There is a chance it was tyre related because they are a few meetings old, and I reglued them as they were starting to tear away from the wheel, but I think it is fundamentally the suspension changes.

Farewell Scyton, welcome back Scythe and Photon!