Reds Racing 21.5T Spec Motor for Stock Touring

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B.C.Ninja
Posts: 696
Joined: Thu Nov 05, 2009 8:51 am

Tue Feb 13, 2018 10:55 am

So as some of ou are aware in the beginning I was against a spec motor for Stock Touring for various reasons, love it or hate it, it's what we have in the rules at the moment so I thought I'd utilise my time instead of bagging it out but rather sharing some of my knowledge on the current spec motor as to help those a little unsure of how to get the most out of the mtor. I have used the motor at a couple of events now and just this weekend as able to get the motor on an analyser and see what I could get out of it, and to also check some of te finer details of the motor. Now this is my findings so there may be variances in findings to what other people run, but for a newbie running these motors this should give you some insight on how to set up your motor.

So.... Here Goes.....

1, construction: Now I found the motor to have a rather solid construction, there are a few drawbacks that I have found that I will discuss here along with the positives also, firstly the can is well engineered and dissipates heat very nicely, you really have to have the motor fully tweaked to get anywhere near a danger point temp wise, it has a separate stator so that in the event of a meltdown the stator can be replaced(if available), although this three piece design can make it tricky to reassemble the motor after a teardown. The sensor board is a very rigid design and upon testing the sensors were nicely aligned, my current motor was only 2 deg between my two outlying angles, now the one drawback to having a rigid sensor board is that I wasn't able to tweak the board to reposition the sensors to achieve a balanced board, not a bigie as they were good enough for me. However the motor is shimmed poorly from factory, the rotor is positioned too far away from the sensor board, in my findings I removed the large brass washer and shimmed the rotor much much closer to the board with standard motor shims, I then had to reshim the pinion end to eliminate excess float, for this I required larger shims as the shaft is stepped, I luckily had some old nitro clutch shims that did the job, from a fellow racers motor we were able to improve his sensor accuracy by two degrees simply by shimming, so although not required it does have its benefits, the sensor accuracy allows the esc to fire the stator coils more accurately leading to a more efficient running motor. Another construction issue I noticed was that some motors have an extremely tight timing ring, my motor needs to be removed from the chassis to allow me to use a pair of pliers to adjust the timing, whilst others are as free as a bird, again not a biggie, more of an annoyance if I wanted to slightly tweak my timing whilst mounted.

2, Timing Sweet Spot: Now contrary to common belief setting a motor to a determined amp draw is not how to set up a motor, I constantly hear 6 amps being flogged around, where this magic 6 amps came from I do not know, now current is inversely proportional to tourque, the more torque the less current, the less torque the more current, so a motor that has less torque is going to draw more current for the same RPM, so setting motor x to the same current draw as motor y is just daft as they both have differing electro-mechanical properties, so where to set your motor? well with the reds I found that nothing really happened untill you wound the timing ring past that 40deg mark, from there you could start extrapolating your data to find your sweet spot, now my sweet spot may differ to others but I found that there is a little compromise that needs to come into play, I ended up finding that around 51deg was where I had the best bang for buck, good KV and hence RPM with not to high a current draw, I had the best KV to Amps ratio, but was that where I set my timing, no, I found that if I increased my timing by another couple of degrees my efficiency did drop but not by enough to offset the greater production of RPM, my current was still low enough to not cause any over heating issues (8.1amp) and was certainly lower than what I normally ran on my Team Powers motor of 10.7 amp (although rpm was much greater), this was my trade off, a slightly lesser efficiency but a much greater yield in RPM, now some may say that set to efficiency and then gear to track, but to gear for the same results,you would need to increase pinion size by quite a few teeth. Now the reds motor actually doesen't have timing marks this high, you can actually turn the ring past the markings, so mine is just a few notches past the last mark, and on the track she was pretty sweet.

3:Gearing: Well like most 21.5's around the 3 FDR seems to work, depending on track layout, chch I run under 3 and at HB this weekend I ran a smidge over 3, and cmr I would most likely run lower again due to the technical aspect of the track, now for the newbies you need to remember that power is no good unless you can transfer it to the ground, so for starting out gear slightly lower, this will allow you to pull a bit harder out of the corners and make up for any loss of traction due to driver skill and setup, setup makes a massive difference, I improved my laptimes in HB this weekend by 0.7sec by putting a better setup on the car, thats more of an improvement than any motor choice would allow.

Overall, well she aint a bad wee motor, there is a few minor issues I have with it mainly regarding the rotor shimming and the tight timing ring, but all in all she's not to shabby, I was mostly impressed with the close sensor position, not perfect but for a non certed motor pretty tight, so hopefully this helps a few cats out in setting up their motor, like I mentioned earlier some peoples methods and thoughts may differ, and this is just my breakdown of what I have found using my understanding and knowledge of motor theory, at the end of the day I can't outdrive this motor and these settings and as a base setup it's a bloody good starting point, so turn up your timing, gear around 3 and go cut some laps, too easy :mrgreen: (y)

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Dirt Racer
Posts: 710
Joined: Wed Oct 29, 2008 8:40 pm
Location: Hawkes Bay

Tue Feb 13, 2018 11:31 am

I found that with the tight timing ring it helps to also loosen the 3 main motor screws that keep the can together. Once they're loose, the timing ring can be adjusted without taking the motor out of the car.

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Conemaster
Posts: 193
Joined: Fri Nov 23, 2012 2:59 pm
Location: Auckland

Tue Feb 13, 2018 12:57 pm

nice work there nick, (y)

good to see a bit of knowledge sharing as really the whole idea of the stock motor is to make the class a bit more of a level playing field
TAMIYA - Serpent - PBD - LRP - R1 WURKS - Futaba - Team Associated

Jonathon
Posts: 36
Joined: Fri Nov 11, 2016 9:17 pm

Tue Feb 13, 2018 6:17 pm

Thanks for sharing, thats really helpful.

When is the spec motor announced for the next nats? Will it be the reds motor for the forseeable future or will it be tendered every so often?

Mishy
Posts: 10
Joined: Fri Aug 07, 2015 9:56 am

Tue Feb 13, 2018 9:40 pm

Wow ...... over 50 deg timing? I'll have to put some testing in on mine, aye. We all seemed to get topped out at just over 40 deg before heat becomes an issue. I guess the taller gearing many of us have been running has an effect there though ...... Time to pull the gearing back, start adding timing, and see what the lap times look like!
Thanks for your thoughts on this!

Zarathrustra
Posts: 101
Joined: Thu Dec 17, 2015 9:46 pm
Location: Napier (HBRC)

Sat Feb 17, 2018 4:23 pm

Dirt Racer wrote:
Tue Feb 13, 2018 11:31 am
I found that with the tight timing ring it helps to also loosen the 3 main motor screws that keep the can together. Once they're loose, the timing ring can be adjusted without taking the motor out of the car.
A fair few of the earlier ones we got last year had this issue (the new one I got in December was fine). They used red loctite on the main screws in the factory, and it seeped on to the the sensor board ring. Pulling them apart and cleaning it off allows the board to spin nice and free. (y)

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B.C.Ninja
Posts: 696
Joined: Thu Nov 05, 2009 8:51 am

Mon Feb 19, 2018 8:05 pm

So I'm a tad bored sitting at DB Breweries waiting for something to break down, so thought I'd waste some time by dishin out some info for some turkeys so they can increase their knowledge on the ole brushless motor, so I'm going to talk a little on Heat and Timing, and their effects on performance, so again, not a bible but at least a little insight, for those that don't know I have a Dip Eng in Electrtonics as well as being a qualified sparkie in the industrial sector and am also in the process of nailing out my IMC Lvl 4 ticket aswell, so have a little formal training in the area, so here goes.

Heat: So we all know heat is bad, but few know how much is bad, now there are two main things that happen with heat, the first is an increase in the resistivity of the windings of the motor, now coppers temperature coefficient isn't too bad at all as far as conductors is concerned, hence why it is used as a main conductor in many areas of the electrical trade, did you know that the conductivity of copper is better than that of gold???? so anyway as heat increases so does the windings resistance, but by how much, well coppers resistance will increase by 0.393% per degree over its resting resistance at 20deg, so what does this mean, well actually stuff all, if you crunch the numbers you'll notice that your increase in resistance is rather small in the scheme of things when you take into account the very small resistance of stator windings, crunch that with a little ohms law and then use that to determine drop in rpm by using KV values and you'll notice that it has less effect than a well timed fart. Now the second thing to come into play heat wise is the effect heat plays on the magnetic strength of the Rotor, now this is the one to take note of, once you hit a certain temp, the once aligned magnetic particles (not the right term but makes it easier to understand) start to go a bit rogue, and thus the magnetic field strength is reduced, now for the ole neodymium rotors we use, this value is up around the mid to late 80deg C mark (don't quote me on this, also differs to new Hi-Temp Rotors), the reduction in magnetic field strength of the rotor causes large increases in current draw to maintain the same rotation, more current means more heat, more heat means less rotor strength, therefore more current and so on, you get my drift and you'll end up with thermal runaway, also you can end up with a permanent reduction in rotor strength and permanent damage to your motor, so all in all, Temps keep em under 80deg C, this will give you a little head room if things go a little pearshaped, at the end of the day the enamel coating on the stator windings is spec'd for well over that so that in the odd occasion that you get above the magic number of around 86deg you won't go thermal nuclear.

Timing: Now this is an interesting one with a shit tonne of strange voodoo surrounding it, so I'm going to try and tailor this to us "Toy Car Racers" (sorry Selwyn I'm sure you'll give me a clip for saying that one :mrgreen: (y) ) So for starters really there is only 3 things we need to concern ourselves with as far as timing goes, the first doesn't really matter too us too much but is food for thought and that is miss-alignment of the magnetic field (simplified description here), so what happens is that the magnetic field becomes skewed by the rotation of the rotor, by a certain angle at a given RPM, optimal power is generated when these lines line up, advancing the timing will allow the lines to line up at a certain RPM and Timing Deg, now this is very handy when you are setting up a motor that runs at a given RPM for long periods of time, like in a factory, or a fan or the likes, you can tune the timing to counteract the skewing of the lines of flux and therefore find a point of max efficiency and therefore power, now for us this is not the case, we are all over the show when it comes to RPM, we stop and start and are somewhere in the middle of the RPM range all the time, now that doesn't mean we should disregard it as it can be used as a tuning tool. For instance, if you were on a track where you gathered a great advantage from a long straight away, like Chch for instance, by tuning the timing to counteract the skewing at a high RPM you would be giving yourself an advantage, although your tradeoff would be a lower efficiency at the lower end of the rev range, now for a tight track if you ran a lower timing value you would gain back some of that lost efficiency and be operating the motor in a more favourable powerband for a greater proportion of the track, so if you were at the likes of CMR dropping by a few degrees would be beneficial, confused yet :? it's pretty simple really, find a good timing mark on the ole Motor Analyser, have this as a base setup, if you run a tight track drop by a few deg if you run more open hi speed increase by a few deg, easy.
Now the main effect timing has on a motor is an effect called "Field Weakening" so pretty much what happens is that you weaken the magnetic field of the stator by energising it before the rotor is at is intersection point, thus increasing RPM but reducing torque, but considering modern BS motors have oodles of torque this isn't to much of a trade off, to add to that you also reduce the effect of Back EMF that is acting upon the non "active" pole of the rotor, so as the rotor spins passed its energised coil, the other pole of the rotor is spinning passed a non energised coil creating back emf to flow within that coil, kinda acting like a generator, by advancing the timing this stator pole will still have a little magnetic field present, therefore reducing the Back EMF generated by the passing rotor, allowing the rotor to spin more freely, the way I like to try and explain it is by looking back to the ole playground merry go round, the one you see on the likes of the Scooter Spin youtube vid, now if you tried to spin it by grabbing onto every rung you wouldn't be able to spin nearly as fast as just kinda slapping it around, you loosen your grip and it will spin faster, see where this is going, kinda the same principle, well very loosely lol hahahahahahahah it is very similar in effect as running a smaller Rotor, a smaller Rotor creates a greater "air gap" between the rotor and stator, therefore less magnetic strength, therefore higher RPM but less Torque, easy hahahahahahahahaha
Now Finally the 3rd effect, pretty much this one has to do with time, now a stator winding is an Inductor, it wants to oppose change, so as it is energised it takes some time to generate the full magnetic field, at low RPM there is little effect, but at higher RPM this effect could be negative to the performance of the motor as the rotor may have already passed the energising coil before full field creation, so if you energised the stator prematurely you could negate the time it takes to create the magnetic field, therefore improving efficiency, this is very similar to the first effect regarding the skewed field and is also very well related to rotor shimming.

So what does all this timing whoohaa mean, well what it means is throw the 6amp idea out the window, borrow someones motor analyser and have a play, then go with my few degrees more for open track and few degrees less for tight track ideology and cut some laps and see how she goes, well its smoko time now so better look busy :mrgreen: (y)

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