Results Motor break-in

[speedfreak]

Hi guys and boff's

As requested not so long ago, the "know how" on breaking in stock motors, i.e. johnsons and mabushi's. Terry.sc, Type49rs and Sammy all suggested similar technics and I now have results.

Motor no. 1 Johnson. silver can. (dyno pulse run in for 30 mins.)

Tested at 7.0 volts

max rpm; 16674

amps: 1.3

max amps 1.48@ 6.94V (16254 rpm)

No. 2 Johnson silver can (water dunking for 4 sec's)

Tested at 7.0 Volts

max rpm; 16101

amps: 1.4

max amps 1.73@ 6.76V (15400 rpm)

No. 3 Mabushi silver (water dunking for 4 sec's)

Tested at 7.0 Volts

max rpm; 16563

amps: 1.3

max amps 1.65@ 6.75V (15889 rpm)

No. 4 Johnson dull silver can (water dunking for 4 sec's)

Tested at 7.0 Volts

max rpm; 16382

amps: 1.2

max amps 1.41@ 6.76V (16198 rpm)

No. 4 Mabushi silver (metal polishing with slave drive)

Tested at 7.0 Volts

max rpm; 16659

amps: 1.61

max amps 1.81@ 6.75V (16382 rpm)

thats all i've done so far, I am quite pleased with the results but still a bit off pace.....compared to most of the guys at the club, but I'm sure will get there. Based on the above data, does anybody know if its possible to calculate the torque?. We have a race this coming weekend, in which I will be particapting. I tend to use 3 different motors for each heat, fastest for the final of course. Would you guys agree to using a rollout not exceeding approx. 43.

Thanks once again...looking forward to your coments!

[sosidge]

Well, I'm afraid there are two reasons why your results are meaningless.

1) You haven't listed the performance figures BEFORE break in, so there is no way of knowing what, if any, improvements there have been.

2) You seem to be using a "motor checker" rather than a "motor dyno". Results from "checkers" are almost meaningless as the motor is under no load. You will never be able to work out a torque figure.

Overall, the track is still a better way of testing the motors than what you have done.

Sorry.

[DJTheo]

Yes, problem is that so small differences are more due to tolearances of motors and experimental uncertainties, so to make safe conclusions more motors of each type are needed and measurements before run in.

Cheers

[RETRO R/C]

It is still great that you went to the effort to catalouge all that for us.

Like the guys pointed out above - the results are not really conclusinve - however it will all tell on the track......not bad results for 540's. 7 volts is a bit high - but still acceptable.

Cheers - and thanks for sharing your results!

Darryn

[Rockenroll]

Yeah thanks for the results least you have contributed something apart from criticising.

Good work

[speedfreak]

Well guys, I have taken them for their real dyno runs....

On average all seem to be above their std's, rpm lowest 15400, highest 16150

torque lowest 80nmm, highest 98 nmm

power, 65, highest 75 watts.

thanks for replies......be it negative or positive...

key thing is to remember...SOME OF uS ARE STILL LEARNING!....

[raemin]

If you want to calculate the torque, you'll need the best efficiency or resistance of the armature at best efficiency, from the on all can be mathematically calculated as the engine power curve and efficiency is an inverted X² curve. I may send my custom xls spreadsheet once I have some times...

[DJTheo]

Problem is that efficiency varies according to load and RPM and its not granted that maximum torque or RPM are at the max efficiency RPM so to calculate torque from current, would be as unsafe as calcualting a real car engines power and torque from its fuel consumption. Much better to look at the manufacturers curves or measure the actual torque with a dyno.

Cheers

[raemin]

That's why we have to use the power ratings at best efficency, the other figures can be deducted fairly easily. A chart is worth thousand words, so here is a motor output chart:

.

Obviously this is a theoretical curve and the real curve is often diverging after the maximum output due to brush arcing. Other than that if you use brand new brushes and a freshly cut com, this curve is prety accurate.

If you're interested here is the excel application I am using to calculate these. It is largely derived from the work of the tekin dyno engineers.

[grizz]

another way is to run in on low volts (up to 2v) for 4 days, watch the contact area brush to comm !

or slave run in for about 2 days runing the slave motor at 12v dam noisy though

i did it, and it realy improved the output

[DJTheo]

Just checked the excel sheet and as I had thought it caclulated the torque from the efficiency. To actually measure the actual efficiency on an individual motor you need to measure also the mechanical power of the motor, so the rpm AND torque, if you use the efficiency from the manufacturer specs you can directly also just use the torque from the manufacturers spec as this isn't different. To really completely theoretically calculate the torque of a motor you need much more complicated equations and infos like magnetic field strengths.

Cheers

[raemin]

My tekin dyno provides me the actual peak curve, plus rpm amps, so yes I can calculate real torque as I plug dyno measured efficiency. However as the tekin GUI is not user friendly I made an excel sheet to make nice graphs. While working on these macro I came to the concluison that similar graphics could be drawn out of manufacturer specs. I just wanted to see if they were cheating... I consequently reworked the excel sheet to produce the same graphs based on manufacturer specs. If you look at the sheet just make a chart comparison between tamiya official specs and my dyno data for the F1 acto power engine. That's scary, and all the more since I took 2 factory prep motors with soldered silver brushes and freshly skimmed comms.

Getting back to the subject: how to get good number without a proper dyno??? When building the graphs I came to the conclusion that the whole idea is that the rpms and amp curve are (theoreticaly at least) straight lines and a good way of starting mathematical calculations on straight line is to find 2 points... If he only has a motor checker a good way of comparing these engines would be to attach a prop on them and measure rpms and amps with and without the prop at 5 volts. To my knowledge a prop is even better than a freewheel for measures. This would allow to calculate the rpm and amp curves and out of that compare these engines prety accurately. He won't get perfect motor data, but at leat he will get exact motor ranking (?). He may also use several props. To crown it all he might buy props with thrust ratings in order have precise torque figures out of RPMs.

It might look complex, but once you understand the logic it is easy to make your own $15 motor benchmark.

Raoul

[DJTheo]

quote:My tekin dyno provides me the actual peak curve, plus rpm amps, so yes I can calculate real torque as I plug dyno measured efficiency.

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You can only calculate it for the highest efficiency RPM, as for this one you only know the efficieny from the manufacturers data sheets, but since you use a given measurement you actually don't measure it but take the manufacturer one so why bother doing that? The only thing it can be usefull when manufacturer gives efficiency but doesn't state torque, but as said you rely on his statements and don't have a figure of the actual torque of your individual motor as also efficiency varies between samples and motor condition.

The method you write with the propeller is much better and can really measure torque and output power (unlike most simple dynos, only the expensive ones that have a load and measure the motor accelaration can) and used since years for nitro engines measurements. [8D] There exist special propelers with calibrated datasheets so you know the power according to the RPM that the motor reaches with each. Only thing is you need several propelers as each one will give you the motor torque only when the motor has reached its maximum RPM with that propeller, so you need for each point in your power or torque curve a different and specific propeler. Proplem is that power and torque curves aren't really lines so 1 or 2 aren't really enough.

Cheers

[speedfreak]

Hi guys, and boff's

Must apologise for not replying, we had a race meeting yesterday, my first, be it. For the record, class entered, open stock, (any johnson or mabushi motor in any chasis. with 4 door shell). 1st heat started 6 out of 6 finished 3rd. 2nd heat started 1 out of 5 finished 2nd. finals 2nd out of 5, finished 4th. Quite disappointed with myself, i.e. the finals, I caught the leader on lap 8, passed him and led for another 6 laps, then was passed by the guy started 3rd, took myself out on the last lap!, damm! but rewarded with driver of the day!. I would have been much happier with 2nd place rather than driver of the day. Guys ...thanks for the imput, your comments and suggestions will be tested. Raemin, DJTheo......great debate...outstanding, I will try various ops and keep you guys posted, for now i need to get more power out of them motors. Raoul, thats 1 very sorted out excel sheet, what a legend! I will try and make use of it. thanks buddy.

[WillyChang]

Dunno what 4s dunking does for motors... usually with new ones

I'd run them under water with a 4c pack for like 5-10 mins!!

(it ain't run-in until the FULL face of the brush touches the comm)

hiya SF, do you specialise in 540 racing? []

If so, there's a few extra things we generally do for 540...

- invest in the HIGHEST VOLTAGE batteries, makes a huge difference.

If they're NiMH we abuse them by jacking up the charge rates

as higher charging rates give even more Vs.

- motor bushings must be well worn in (out?)

- some guys zap the magnets (without opening the can)

- get a shell with the least drag, don't need too much downforce

- build your car so there's minimum drivetrain drag.

Shaftdrivers... blow on the rolling chassis w/o motor & it rolls

TA04/415 belters... belts are so loose they flop around.

- learn to drive smooth! Car has to be setup well so you can take

all the corners without lifting off. Good tyres, good line.

Keeping cornering speed up is the key to 540,

big difference to driving in mod or 27T stock.