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#21
14-10-2012
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Quote:
A decent ESC will improve the situation slightly, (when you run it in sensorless mode, but not all can do this) but to fix the problem properly, a complete sensored system (motor, esc, sensor wire) will be needed. As there is no way of converting a sensorless motor to sensored. My first car had a sensorless system (actually a pretty good one, as these things go), and by mucking around with settings and pinions you could get it pretty smooth on take off, but on going to sensored, it was actually quite a struggle to have it NOT start smoothly! If you are going to change both the spec of the motor (less turns) and a new ESC, it's probably worth dropping a few quid on 2 or 3 new pinions, if the current car runs a 21 (for instance, get yourself a 20 and a 19 and maybe 18 (?) to start with. Or if you are at the club, tap up one of the friendly guys and trial a few different sizes one evening, we seem to chop and change fairly regularly in our club. (i'm currently experimenting with a smaller spur that i borrowed off a club mate, and i've had a pinion or two off him as well!) FWIW, i have run a 6.5, 8.5 and 10.5 (all sensored) in the same car. 20 or 21 for the 6.5, 23 or 24 on the 8.5 and a 26 on the 10.5 (biggest pinion i can fit!) so a fair range. 
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#22
15-10-2012
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I run a reedy sensorless that comes with the b4.1 rtr. The only time i get juddering is pulling up to the start line slowly.
Ive had 2 different motors in it And its the same on both. Dont think its a sensorless issue, probably just a set up thing but i prefer to keep things simple. Less wires less hassle! Before shelling out for another combo i would borrow someone elses sensorless speedo to make sure you dont just need another esc
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#23
15-10-2012
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A sensorless ESC will ALWAYS 'cog' to a certain degree... better sensorless speed controls however will cog less but a sensored speed controller will always be better off the line (so long as its working correctly)
All brushless speed controllers need to know where the rota inside is in relation to the three coils inside the motor in order to maintain control of it. A sensored motor does this with (ahem) a sensor - from pretty much standing still the ESC knows where the rota is inside hence a smooth pull-away - a sensorless ESC on the other hand uses the 'back EMF' from the coils inside created by the rota (permanent magnet) spinning to know where it is... to get the motor spinning from a standstill the ESC fires the coils in a set sequence to 'force' the motor to spin - it takes a little while for the speedo to work out where it is (hence the 'cogging') - once its up & running the control should be smooth.... there is an argument that a sensorless motor/esc combo has the potential to be faster... but at the expense of off-the-line smoothness.
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#24
15-10-2012
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Thanks for all of the advice guys. So it looks like a reasonably decent sensored combo would be a worthwhile investment! Liking the look of the new Speed Passion Revention ESC and motor. Anyone have and suggestions for alternatives? No more than say £100 - £120 ish.
Thanks again.....
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#25
16-10-2012
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The Reventon combos look alright. Go for one of the milder motor options at first as the ESC has a 9.5T limit but seems to be sold with faster motors than the limit in some places. It also has the backing of a proper UK distributor.
I had a Reventon Club Stock for a little while myself, couldn't complain about it at all, although I did blow it up (my mistake).
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Linear Mode
