17.5 “blinky” – first impressions

Let’s be blunt – on a big track like Cotswold, it’s slow.

But the pleasure of blinky racing is not the speed, it’s the superior throttle feel. And slow cars mean much closer racing for those of us with average driving skills.

Here is the motor I have chosen…

At £65 RRP and widely available for closer to £55, these seem to be a bit of a bargain for a BRCA legal motor with full UK distributor support. It has a sintered 12.5mm rotor (the largest allowed in the rules) and adjustable endbell timing from 7 to 27 degrees – the essentials for a good stock motor. Whisper it, but it is made by Dualsky and is basically the same as their Z5 motors. And for once, I have no reason to doubt the accuracy of the timing measurement!

Fitted into my new ARC R10 touring car for the Cotswold club meeting on 19th August, I was starting from a completely clean sheet. No prior chassis knowledge, no prior motor knowledge, and nobody else at the club running a legal blinky combo to compare to – all I had to aim for was a laptime of 19.8s which was apparently run earlier in the season. At least I knew the settings for the “blinky” software on my Hobbywing Xtreme Stock – they are very simple.

I put the car down for practice with the timing at 7 degrees and the gear ratio at 4.06:1 – the manual recommends 4.0:1 as the starting point for a big track. No surprise to find that the car was way undergeared, topping out 1/3rd of the way down the ~60m main straight, and not even needing the brakes for the hairpins! Changing these big pinions on the ARC is a topdeck-off job, so I only had time to test 3.82:1 before practice ended, and that was still undergeared. Laps were just sneaking into the slow 22s, but the track was cool and green and I didn’t have the adrenaline of a clock to beat.

For the first timed race of the day, I ran 3.62:1. The car felt better, and I could feel myself pushing harder. The reward was a best lap of 21.7s, with motor temps at 60C. For round 2, I left the gearing alone but advanced the motor timing to 17 degrees (the middle mark). The car felt quicker, and the laptimes were quicker too, with a best of 21.2 – but the motor was a lot hotter at 80C, right on HPI’s recommended limit, although it hadn’t gone soft on the track.

In round 3 I changed the motor back to 7 degrees timing, but geared it up to 3.43:1. The car felt less punchy on the track, but the laptimes were almost identical, with a best of 21.3 and a total race time within a couple of tenths (14/304)! Motor temps were healthier though, at 70C.

Round 4 saw a small setup change to the car (going to a gear diff with 500K oil in the front, rather than a spool, which felt smoother), and also a further increase in the gearing, to 3.26:1 at 7 degrees timing. I got my best lap down to a 21.1, running a 14/302. The motor was at 75C with no signs of softness. For reference, the track was at 39C during this race and the ambient at 25C – pretty warm for the UK.

I qualified for the B final – unsurprisingly I was slower than all the 13.5 boosted runners, but just managed to get ahead of the sole Tamiya Mini! The first leg of the final was good fun – I managed to get in between the two boosted cars in the early laps, and managed to hold one of them off for a few more, partly because I was a little quicker through the corners, and partly because the boosted car was waiting for a clean opportunity to get past. At one point he did get past but I managed to nip down the inside again for a short-lived advantage, however my luck was running out and the next time he got alongside he blasted away into the distance. Towards the end of the race, the leader made a couple of mistakes and I actually managed to finish ahead of him, just breaking to a 15-lapper (but with a short first lap due to the starting grid). As far as the motor went, I ran it at 7 degrees timing again with a ratio of 3.11:1, but it was too high and the motor went soft in the last few laps, with no brakes left by the end. Temps of 90C showed that HPI’s advised limit is pretty close to the mark. The best lap was 21.0 before the fade.

For the second leg of the final I went back to the 17deg/3.62:1 combination, just to confirm my findings. The car felt zippy but the laptimes were down, back to 21.3 again with the motor at 75C.

After the racing had finished I did a couple more practice runs. First of all I tried maximum timing (27deg) at 3.62:1. The first thing I noticed was a strange throbbing sound from the car; the second thing I noticed was that the car started to go soft after only three minutes; and the third thing I noticed was that the laptimes were weak, ranging from 21.4 to 21.9 (timed on my transmitter, so not 100% accurate). My feeling is that this is simply too much timing, and that the motor is almost “cogging” as it accelerates.

I used my final practice of the day to run in some tyres for the BRCA Clubman’s meeting on 9th September. I put the car back on the best setting of the day (7deg/3.26:1), and it felt good, with laps ranging from 20.8 to 21.4 (transmitter timed again). So a couple of tenths gained from the fresh tyres, but still some way short of my 19.8s target.

So, to sum up…

Timing – Compared to gearing up, increasing the timing seems to add more motor temperature for an equal improvement in performance. I’ll do some more tests in the range between 7 and 17 degrees (although it is hard to accurately set the motor at the 2 degree intervals marked on the can). 27deg seems to be too much and the motor may be “cogging”.

Gearing – 3.26:1 (@7deg) seemed the best balance on the big Cotswold track, bearing in mind that it was a warm day by UK standards. I need to try some of the finer ratios (pinions have been ordered for 3.19:1), and perhaps 3.11:1 wouldn’t go soft on a cooler day.

Car – I haven’t written much about the car – basically it was very good in all the timed runs. But it is a bit heavy at 1440gms (BRCA limit is 1350gms). A shorty Lipo has been ordered, this should get the car down to the minimum weight, and hopefully that will be reflected in the laptimes.

MORE…TESTING…NEEDED!

Dave

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