21.5 2S rollout?

[f888fhw]

Just wondering what is a good starting point.

At the minute im at (3.142x50x16)/48=52.3mm / rev

[Chequered Flag Racing]

read on it may help,

search rollout & mmpr here
http://rcracechat.com/vb/showthread....12-Circuit-Car

Thought I would post a bit about my experience of running 1s verses 2s in my mardave. I’ve been running 1s 13.5 with a nosram x11 13.5 for a long time and found it to be very boring to drive as I was having to push high rollouts to gain any sort of top end to compete with the mardave brushless systems at my local clubs. I was using rollouts in the region of 62-67mmpr and was always on a fine line with motor temps. I much preferred my 10.5 which had a more comparable drive to the mardave system.

I decided to try 21.5 and the micro 1800mah batteries. The only motor I could get my hands on second hand was a LRP X12 21.5. I kept the 2 dot insert so 37.5 degrees of timing and a rollout of 53mmpr at a club with a 12*21m track. Car was really quick and required a softer rear tyre as I was spinning the rear tyres and the car was waggling its tale whenever I put the power down. However I had real problems with heat and the motor was far too hot after a run. I then fitted the 0 dot insert and retarded the timing to 27.5 and dropped down to 48.5 mmpr and the car was now awesome. Heat no longer a problem as the motor was coming off at 50 degrees. The car has loads of lift out the corners which you really miss with 1s and I was definitely matching the mardave system. Interestingly top speed was also similar so it seems the 21.5 punches hard but then runs out of puff.

I also got a new Thunder Power Z3 13.5 to replace my old nosram and what a difference. The thunder power revs a lot more so gives a lot more feel when driving. I advanced the timing on this to 30 degrees and on the same track I was running 56mmpr. My fastest lap time was 0.5 seconds faster in the 21.5 favour.

At a smaller track I reduced the 21.5 rollout to 46mmpr and the 13.5 to 53mmpr. Both motors ran cool and were good to drive. Fastest lap was 0.2s in the 21.5 favour. I TQ’d using the 21.5 and then ran the 13.5 in the final, taking the win to show I was not gaining an advantage using the 21.5.

Recently ran at ardent against a 1s powered Schumacher. I would say both cars were on a par and the advantage of the better lift was lessened due to the more open nature of the track. I was quicker but more so because my car carried more corner speed than due to the motor setup. I was running a rollout of 62mmpr and temps were still acceptable at the end of 5 mins. Wouldn’t have liked to have run a higher rollout.

Rollout seems to be a 6-7mmpr rev difference between the two motors. The 21.5 is running similar gearing to the X12 10.5 I was running for a while. However I was deliberately gearing it down to be on par with the other cars as I was running the 10.5 while waiting on a new 13.5.

[f888fhw]

Thanks for the reply. I ran @ Teesside last Sat night and to me the previous roll out was too low.

I have a diff on its way and i'm going to give it a go at aprox 58mm / rev.

I have seen the new track and it looks very technical and twisty so i dont think a high roll out would be good.

[Chequered Flag Racing]

Originally Posted by f888fhw

I have seen the new track and it looks very technical and twisty so i dont think a high roll out would be good.

I was at at Barley Mow on Sunday gone and asked Jewitt if I should drop a pinion for the smaller track although it was open & flowing, he said not, he was right, so stayed on 68/69mmpr on 13.5.

[f888fhw]

So if my maths are correct you are running a 29 - 30 T 48dp pinion?

(51*3.142*X)/70=68mm rev

X= 68*70/51*3.142=29T pinion

51 = standard sort of rear tyre dia

70 = Standard mardave 48 DP diff spur

[Chequered Flag Racing]

48dp, 31/68

foams size 49ish I think

I'll just gear to keep close to current mmpr for the motor. After some running I think it needs to go 70t / 72t spur