Turbo Optima build - Project Barney: Finished

[SAND SUPER STORE]

I had just seen the video,and i found a difference in power

I took the 900w info from here: http://www.hobbypartz.com/96m25-car-3650-3200.html
here is a cut and paste:
code 96m25-car-3650-3200
Net Weight (g) 223
Watts 900
Outer Diameter?mm) 35.8
Length (mm) 50
Stator 21MM
No of cells (lipo) 3
max efficiency (%) 85%-89%
max efficiency current 59
no load current (A)/7.4V 2.1
Internal Resistance (mohm) 0.0129
Shaft Diameter (mm) 3.175
Shaft Length (mm) 16
KV (RPM/VOLT) 3200
Turns (for cars)Poles 11T/2POLES
Max Voltage 12.6
Wire Size 0.34
Bullet Connectors YES
Bullet Connector Size 4.0MM
design for FSD


in the video his telemetry gives a reading of 751w , not 900w ...I did not understood if he had any limitation in esc

anyway is slightly more that one HP (736w)

your formulation is ok, "Watts = Volts x Amps, which in this case would be 7.4V x 60A (max, from the ESC) but about amps, I'm unsure because I'm old school and do not know if a modern progammable esc can limit the amps to a predefined amout like his maximum. if esc does not limit current amps, it will overheat and burn if it has no built-in thermal shutdown
be careful when track testing and check esc temp

*60 amps is the limit that your esc can handle before burn
*59 amps is the current at wich maximun eficiency (89% per datasheet) is reached (eficiency converting electric power in mechanical power (so remaining 11%is loose in things as heat and friction) but it can demand a lot more amps at full speed / power
*about 100 amps is the maximum this motor consumed at video testing (aprox 100 amps x 7,5v= aprox 750w)
*I think it would be better to have a bigger esc not?

I'm more or less novice in brushless , but amps and watts are same thing for any kind of motor

yes, 11t is a reasonable winding, but it can be more or less powerful (watts , torque) by constructing it with bigger or thinner diameter winding wire is as simple as this

at same 11t winding higher power means that motor can handle longer gear ratios ( bigger /taller motor pinion) tha other motors with no motor overheating

hope this can give some light about this

[sgirouard]

That Tacon 3200KV runs equivalent to the Traxxas Velineon motor with a slightly different power band (the Tacon is smoother across the entire powerband and the Traxxas has more low end but tops off quicker).

It's a BEAST of a motor. You can't compare brushless rpms to brushed in determining power, remember that's no load RPMS. The brushless will have TONS more power under load than the brushed. Anyway, should be a fun buggy.

[Coelacanth]

Also don't forget that Turbo Optimas used to run 30,000+ RPM Le Mans 240SB motors on 8.4V, whereas I'll be running the Tacon 3200kV on 7.4V. That was one of my reasons for going with a bit stouter motor, because I wasn't going to be using an 8.4V 7-cell battery anymore. I'm running a 14T brushed motor in my Zebra Optima with 8.4V and I wanted something that would perform equivalently with only 7.4V of juice.

[SAND SUPER STORE]

I'm running a 14T brushed motor in my Zebra Optima with 8.4V and I wanted something that would perform equivalently with only 7.4V of juice.

I think it's going to be much much more than an equivalent, sure

Also don't forget that Turbo Optimas used to run 30,000+ RPM Le Mans 240SB motors on 8.4V, whereas I'll be running the Tacon 3200kV on 7.4V.

yesterday nigth I was asleep and made some mind rough calculations

a kyosho 240sb back in the day was announced for 4 minute races, so it "eats" a 1200mah in 4 minutes , an hour = 4minutes x15 , so to run one full hour it eats 1200 mah x15 = 18000mah =18 amps/h , so at 8,4 volts gives (P==VxI) 8,4 x 18= 151 watts

this are rough calculations based in a battery duration, but we can be sure all LeMAns 240 series were below 200w

take those 150w and compare with the Tacon's 900W...or 750w , no matter , is at least 5 times more powerful than the old 240SB, aproximately same rpm, same sp1eed, but 5 TIMES MORE TORQUE , that's the reason why I warned you about this "beast" , I like the beast motors, and 2 days ago , after warned you , I searched for one of this to buy it and test it, but I was unable to locate one , is always out of stock, a shame.
by the moment, the most powerful I have at home is a 650 watts unsensored one that I tested in my lazer zxr, in asphalt, with vintage 1990's duratrax slicks in optima mid wheels with a 4200mah 40c lipo and was amazed (near frightened) of the torque it had, test ended soon when tires went out of the wheel at every tigth turn (tires unglued)
I discovered that car was capable of drift 4 wheels in straigth line at ANY speed no matter if you push hard from stop or from mid speed. it just go drifting for meters and meters with small or no speed increase, for speed increse I need to release sligthly the trigger and push again with care.

I usually raced this same car, same tires and wheels(never were glued) in 1990 with 14t double , 48000 rpm brushed trinity motor spending more than 100 batteries in 2 years (this tire set was indestructible, lots of rubber in them),with no problem, weekend after weekend, and this tires never went out of the wheel bead, never deform under acceleration, even with car in the air.
perhaps someone here had them, duratrax 1.9 slick tires.
but as soon this tires meet the 600 watt brushless, they found his limits
I feared for the integrity of the whole car , belts, sprockets, swing shafts ...and used the trigger with care. This motor was really a beast , and it have "only" 650 watts

have a nice day

[Coelacanth]

José, respectfully, I'm not sure about your math. The simple calculation of watts is Volts x Amps, and for that, I get 7.4V x 60A (continuous current)...which is 444 watts. I could always downsize to a 30A ESC which would reduce the watts to 222.

What power the motor makes isn't independent of anything else; it depends on how much voltage & current are supplied to it. A 900W motor won't put out 900 watts if you only feed it 6 volts & 10 amps, for example. That's only its max power rating, and where they obtain that number from, only the manufacturer knows.

[sgirouard]

Don't downsize your esc. You'll burn out your esc, not limit your power. I won't talk math, I'll talk my personal experience.

1. Keep in mind a fully charged 7.4 volt lipo usually ends up around 8.4 volts. The lowest Lipo I've ever owned finished at 8.26 volts.
2. I own and run a tacon 3200 and I also own a Cheetah 13x2 mod brushed motor (a tad bit faster than the 240).

There's NO comparison with these two setups. The tacon is faster top speed by a little but what really stands out is the torque. If I roll the Cheetah backwards, I can get a wheely, where as the Tacon will wheely from a standing start like NOTHING.

The Cheetah, you feel the acceleration, while the tacon feels like it's INSTANTLY at top speed.

Dont get me wrong, I think Barney can handle the tacon, BUT I'd really watch your punch settings on your esc.

EDIT: Also remember when you're using power calculations and RPM calculations, those are all no load ratings.

[SAND SUPER STORE]

hi! I think as sgirouard,
You can fry your esc you if hit hard the trigger
A 60 amps esc does not limit current to 60 amps, just can support 60 amps trough his fets with no burning.

If your motor is an Amp eater, it's going to try to eat as much amps as possible, at full throttle the only part "limiting" the current is the C's of your lipo,
Sample , my 4200mah 40c is capable of give a punch (if motor demand it) of 4.2x40=168amps, so surely tacon is going to try to take 100amps trough esc , burning it if it is not capable of hadle that 100 amps.
If this same batt were only 20c , his maximum punch would be 84amps, and that same motor that was eating 100 amps before, will be only eating 84 amps because battery is not capable of give more (this is also bad for batt, suffering and heating a lot), but surely the 60amp esc will be burnt before any damage to batt.

So as thumb rule, to use big motor, use big esc and high C's lipo, that is the safe way.

[Coelacanth]

Thanks for the numbers. To add to the confusion, my batteries (shown on Page 8 ) are 4000 mAh, 25C, so exactly 100 amps. This 60A ESC is supposed to have a 360A burst rating, so I would assume it won't burn up. It *is* an Asian knockoff ESC mind you, so no guarantees.

And of course I'd be limiting the punch level via the program card--and Barney has the torque limiter gear installed as a rudimentary slipper of sorts.

It won't be long before I can do some driving tests, the weather has been looking like spring (finally!) and hopefully all the roads will be clear soon!

[jwscab]

transistors can handle more power than actually rate for small periods of time. Think of the internal structure as a switch with a tiny value resistor. The more current you pump through it, the hotter it gets due to the resistor. The junctions inside can only handle so much heat before they break down.

so if you have an esc rated at 60 amps, the FETs should be able to handle that much current indefinitely. probably not, however, with the real world of over ratings, and misuse through inadequate cooling. Of course, the PCB traces can only handle so much as well, since they are in effect tiny resistors as well.

you can easily spike as much current as you can for a fraction of a second and it won't harm the transistors, but if you violate a breakdown voltage, you will damage the part.

[sgirouard]

A 60 amp esc, 2S 25C lipo and the 3200KV tacon will be just fine across the board.

I've run anywhere from 20C to 40C through a 60amp esc with up to a 10.5-4200KV motor.

[Coelacanth]

Here's a thread revival--I already had the electrics setup for Barney other than the fine-tuning stuff like punch, but with all the changes I made to the car, it wasn't comparable to stock anymore, and I wasn't sure what pinion gear I should be using with the larger tires' diameter. I did a LOT of research into the actual math, and my gawd, there's a buttload of inaccurate, even totally wrong, info out there...and much of it was right on RCTech.net. You wouldn't BELIEVE some of the formulas I encountered that were totally out-to-lunch!

Sure there's gear ratio calculators and such on various sites, one of those was incorrect, too. The ones that were accurate, didn't show the math...the math is crucial to understanding how gear ratios, rollout, and optimal pinion gear/spur gear sizes correlate. Using a web calculator is easy for those who don't want to waste the time to understand, but calculators of any kind just contribute to our society's attitude of lazy ignorance.

I finally dug deep enough in my research and did a WHOLE lot of trial-and-error until I could make my own spreadsheet to calculate the results *I* needed to know. And here's my rather lame method of estimating rollout. Apparently, most sources seem to agree that a rollout of 1"--i.e. your car moves forward 1", plus/minus 10% or so, for one full revolution of the motor--is what you aim for. This is supposedly the most efficient gear ratio for the motor, transmission, spur/pinion and tire diameter.

Here's a screenshot of my spreadsheet. I dialed in Barney's rollout almost perfectly with a 12T pinion, to 1.056". The spreadsheet also shows that I'll need to increase my Zebra and CYANide Optimas' pinion gears by 1T each to get a similar rollout, just a shade over 1". For OptiMutt, a 22T pinion would be optimal.

I think the spreadsheet would work for most other cars as long as you know the important variables. These days, most of those variables are published right on the 'net, but that wasn't the case for the old vintage Optima series. Please disregard the estimated top speed calculations, they're out-of-whack...I haven't sorted that out yet.

Here is how I estimated the actual physical rollout, marking a 1-inch distance on a piece of paper and using a triangle to quite accurately measure the distance Barney rolls with one motor revolution. I just rotated the pinion gear one full turn and checked the distance travelled. It was very close to 1". There's a bit of play in the drivetrain, so I tried to account for that, but at least I know it's fairly close to the math.

[Bormac]

I for one definately appreciate your view on this stuff. Keep me posted will you on how well the car drives with the correct gearing.

[Coelacanth]

I installed a couple wing mounts from some cut-down Axial spacers, chose them mainly because they were green, had wider bases, and 3mm threaded ends. The wing tubes were cut just below the height of the shock tower so they won't get in the way of the body, and are long enough to insert the wing wires, which will be bent a bit at the ends for a tight, secure fit.

I actually didn't think I would be able to install a front stabilizer on this car because of those big front shocks & everything else barely recognizable from a stock Turbo Optima...but I was seeing how low-profile the Optima Mid's stabilizer assembly was, and since Barney uses the same Maxxum front arms as OptiMutt (which are functionally the same dimensions as regular Turbo Optima Mid arms), I had another look. There wouldn't be much room but in the end, it was possible!

I bent some 1.5mm steel piano wire to fit inside the Optima bumper brace and extending through the Mid-style stab ball-ends. It had to be a custom piece because neither an Optima nor the Mid's stabilizer wire would work. Their front ends and arms are totally different as far as stabilizer mounting locations go. Also, to keep the wire position as low as possible, as close to the arm as possible, I flipped the bumper brace upside-down and reinstalled it so the stabilizer wire groove was on the bottom instead of the top. That's a pargu2000 alloy bumper brace by the way, anodized black.

You can see that it's close, but it clears the CVD bones with a little room to spare, and doesn't come close to the CVD throughout the shock compression. Oh, I couldn't find any 4.8mm balls so I used some spare 4.8mm ball nuts, which work just as well. The stabilizer wire just has to protrude through the holes; the balls inside don't really need to move for the stab to work.

[keithrc]

I like the green and purple colour combo, do you know if Pargu still does the Optima chassis plate sets in the different colours?


Keith

[mattxb]

That is a killer Optima! Nice work man!