sedan system

[bigenginltlman]

Hi, I'm new to BL, but not R/C, and I have a few questions...

I'm looking to build up a sedan, and I was wanting to know, what would be the best brushless system for a sedan? If it matters, I really haven't decided what chassis to build it on, but probably a TC4. Anyway, I wanted something that has the power of or close to the power of a hacker system without the cost. If that can't be done, I'll just buy a Novak system and get on my way...

Also, is LiPo the best way to go with these? I'm going to buy the Triton charger if I do this project or not, so the cost wouldn't be too far off from a good NiMh pack. Also, what's a good high power battery to go with?

TIA for any help!

Oh, and sorry if this is a repost, but I did do a search first.

[OptimaMan]

A Lehner Basic with an MGM Compro 80 amp controller is a good combo for a TC4. It'll allow you to go up to 4s lipos (14.8 volts!!!) and has BEC. A Basic 3600 is a good starting point. If you want more speed, get the 4200. If you want more run time get the 3100. With 4s lipo, it'll take you to 50+ mph easily and geared lower, it'll let you run for almost 30 minutes with the right lipo pack. MGM Compro is 165 bucks and the Basic is like 120 bucks. That's not too much more than a Novak but with the potential for a LOT more voltage (and power). For batteries, a Polyquest 4s3500 mah will fit just fine in the TC4. If you want to go with only 11.1 volts, get the 3s3200 mah from Kokam at Tower. Both packs will set you back like 130-150 but they can deliver over 600 watts CONTINUOUS power! (that's 3x more than the Novak can handle!)

[bigenginltlman]

Cool, thanks for the info. I was looking at that combo on the rc-monster site - is that a good place to buy from? Also, what makes the other ESC's (warrior's?) so much more expensive than the MGM's?

I really want this car to fly, so if I can't go fast without buying the better ESC's, I might have to forget the whole idea...

[joostin421]

just personal opinion, but the Novak SS5800 is great system for the money - especially for a newb to brushless and even the masters.

justin

[SpEEdyBL]

If lipos and a charger are too expensive, get the lehner basic 5300 along with the mgm compro and run 6-7 cells.

[bigenginltlman]

I think lipo's can be an option.

But without spending $400, is optima's combo the most power I can get when using lipo's? What about Feigao motors (just a question)?

Also, should I use the compro 80 or the new compro 120 people are talking about when it comes out?

Thanks for the responses.

[OptimaMan]

The most power you can get will be limited by your batteries and not the motors. A GOOD 20C 3200 Kokam 11.1 volt pack can only deliver 600 or so watts continouos and peaks of about 1000 watts. The 4s3500 Polyquest also fits the TC4 and even that battery at 12C can delivery about 600 watts too. So, for a "stock 7 cell" battery tray, you can only expect aobut 600 watts continuous (that's 3x more than the Novak SS5800 can even handle though).

Feigao motors will run fine in the TC4, but you can expect slightly sluggish acceleration when compared to the Basic series due to heavier rotors. The basic is slightly sluggish compared to the Hacker C40 or Kontronik Twist series. Actually, my recommendation is really the C40 or Twist series for the TC4. It's only like 30 bucks more (I don't mean to be snobby here, but 30 bucks isn't THAT much more) and you'll get better acceleration and better heat dissipation. Those motors will take you well beyond 60mph if you want it to also.

If you plan on going 4s, a Twist 42 is about as fast you want to go. If you go with 3s, a Twist 55 is about as fast as you want to go. If you go with 7.2 volts, get a motor that spins as fast as possible. :) If you want the extra power handling, you can go for the 120 amps instead of the 80 (I've thermalled 80 amp controllers before).

[bigenginltlman]

Can I run the twist 55 with 4 cells, or are you saying it would be too fast? Would the c40 be faster than the twist 55?

What battery would you run with this setup? Are polyquests the best lipo's?

Thanks again.

[Dan-o]

Are any of these other companies systems sensored? I know the Novak systems are. Does it matter very much whether they are or not?

[tcolesen]

With sensorless technology as good as it is today, sensored just isn't necessary to get a smooth setup. Craps seems to swear by the U-Force/Plettenburg Extreme's sensorless smoothness.

[bigenginltlman]

Sure is fun bringing back old threads, huh? :D I haven't forgotten this project quite yet!

Anyway, I was posting because I saw that polyquest's new batteries are 20C (almost all of them), and I wanted to know: can I use the polyquest 3300mAh 4 cell battery with the new 120 MGM compro and a hacker c40? I just wanted to know if the ESC could handle the power. If it could work, that could get me some pretty high speeds.

TIA

[havy]

Where can you get the polyquest 20C packs at? Thinking of going w/ a Twist 55 and that battery pack and the U-force.

Is this a safe combo w/ the U-froce?

Where can I find the twist motor.

Running on 6 cells for racing I'm happy w/ the shadow, but I want to try a fast set-up w/ good runtime, so was thinking the Polyquest and the twist is a good option.

havy

[bigenginltlman]

Just do a search for polyquest on yahoo. You'll see quite a bit of links.

I was looking at www.maxamps.com though.

[Muck]

The Polyquest 20C are too large to fit in most 7 cell spaces. Look to Kokam 3200 20C or polyquest 15C.

[bigenginltlman]

Not even the 2100mAh? I wanted a 4 cell 20C battery...

[Muck]

Yes, I believe up to 2500mah Polyquest 20C will fit. Sorry, I thought you were looking for something in the 3300mah range.

[bigenginltlman]

To fit in that stock battery tray, I'm going to have to compromise something. I could get two batteries for decent runtime, but I'd really rather not. :confused:

[bigenginltlman]

Okay, I'm back! I'm selling my savage to pay for this thing, so this time I'm really going to buy the car. Currently, I'm looking at the following setup:

TC4 (not factory)
20C Polyquest 2100mah 4s
MGM Compro 80 or 120amp ESC

Which MGM ESC would be best for this car? Will the 80 amp be enough, or should I be on the safe side and go with the 120 (or even the 160)?

Also, is the TC4 the best platform, or should I use a different one?

TIA!

[Rtsbasic]

Damn, this threads older than I've been visiting here :) Get a Mtroniks Pro ESC instead of the MGM. Its fully sealed/waterproof and just as smooth if not smoother, and does upto 4s lipo w/built in cut off.

There are new motors around as well..Feigao 380C motors. Imagine a Hacker C40 for a fraction of the cost. Check out www.starluckrc.com for the motors, and Mtroniks controllers. See here for his Xmas combo prices:

http://www.ultimaterc.com/forums/showthread.php?t=57779

The TC4 is still a good car, although at the min the new Xray seems to be the fastest thing. I personally would rather go with a 3s Kokam 3200 20C pack, and Polyquest cells are I think a bit harder to get now. You can get the Kokam cells for a good price. 3s with a 380C 9t would be a very fast combo, its fast even on 2s or 6 NIMH cells, and safe upto 3s.

[bigenginltlman]

Thanks for the response. Is the Mtroniks just as fast as an MGM, and which controller should I get?

Will that combo really be as fast as a MGM/Hacker or MGM/Kontroniks combo?

One last thing: does anyone know how large a lipo pack can be to still fit in the battery tray of one of these?

[tcolesen]

You can't really measure a controller by how "fast" it is, but the Mtroniks controllers are excellent. Their service is also excellent, unlike MGM's, which I have been waiting about 5 1/2 months from to hear anything about my MGM Compro 120amp controller that I sent in for service (mid June).

The Feigao 380C motors will be just as good as the Hacker C40 motors, and the other Feigao motors will perform like Hacker motors, at a fraction of the cost. I believe the Kontroniks motors are 4-pole, so they don't compare directly with the Feigao 380C motors, but for the price, I would take a 380C.

6 NiMh cells are: 48-50mm wide x 138mm long x 23mm tall. If you are looking for a Lipo battery to fit into a TC4, look for something with something near these dimensions.

[Rtsbasic]

As an example of Mtroniks service, I recieved a faulty unit 2 weeks ago (it blown up in my car!!), I returned it to them last week (didn't post it for a week - no time). They're sending out a new one tomorrow, along with a brand spanking new replacement for my old Pro that I sold to a friend (it stopped powering the reciever..reasons unknown, so I sent it back with my blown one) They're controllers are as fast as any other sensorless one I've driven, and my old Pro was from the first production run in May, and still ran brilliant up to last week.

I don't have a 380c - just a couple of regular 380's (too cheap to buy the 380c versions yet :) ) but my 8t and 9t "normal" ones are very fast, the C ones will be even better because the built in heatsink. I would take a Mtroniks Pro/Feigao 380C combo over almost every other combo any day.

[Muck]

I have a 9t 380c uforce 75 and 3s 3200mah Kokam that I run in my tc3. It's pretty crazy fast. The 3s fits in with the screws adjusted outward and a little foam padding in the front or rear of the pack. If your going to race on a track I would stick with 2s or a 6 cell packs because you'll have alot more controll in racing conditions. If you want to drag race then go with 4s.

[bigenginltlman]

Thanks people, you saved me a bunch of money!

So the "pro" ESC would be the one to go with? That will handle a 20c 4s lipo, right?

[tcolesen]

Yes, it will handle 4s Lipo, and even has a low-voltage cutoff for it in the programming.

[OptimaMan]

Yeah, the Mtroniks PRO is much better than the MGM 80!! Got them all... So, as update, get the Mtroniks Pro, get the Feigao 380Cxx motor and go 4s lipo - just try those 4s3500 mah polyquest from starluck - you WON'T be disappointed. They're on sale for only 120 right now.

Heck, the pro and 380Cxx motor combo is only 200 (last I read) and the battery is 120. So, that's only 320!!!

[Rtsbasic]

Yay I no longer look like a fanboy when I recommend Mtroniks. LOL.

Just had a look on starluck's website as that sounds like a cracking deal, but the biggest one they have is a 3s 4400mah 12C for $120. I'm fairly certain this would fit into them 7 cell trays on the TC4, and in a touring car I honestly cannot see why you need more than 3s, espically when it might get hard to fit them in, and unnecessarily raises the cost.

[havy]

Yay I no longer look like a fanboy when I recommend Mtroniks. LOL.

Just had a look on starluck's website as that sounds like a cracking deal, but the biggest one they have is a 3s 4400mah 12C for $120. I'm fairly certain this would fit into them 7 cell trays on the TC4, and in a touring car I honestly cannot see why you need more than 3s, espically when it might get hard to fit them in, and unnecessarily raises the cost.

Yes the pack fits very well in the TC4. I use this pack w/ a hacker 9t in my TC4 and the car has amazing performance... quicker than a nitro off the line and faster than most or just as fast on the straight. This ads up to toying w/ the nitros in the infield and frustrating them when they try to catch up or get away on the straights :D

havy

[OptimaMan]

I guess they no longer have the 4s3500 pack... The 3s4400 is just as good though - just slightly lower voltages. I would use a motor around 4000 kV if I were to go 11.1 volt. I have used the Twist 42 and the 1520 10 turn. Very fast in my tc4. You need to get the steel outdrives. The factory team tc4 has the steel outdrives.

[Rtsbasic]

The 380C 9t has a kv of around 4400, so will be well suited to 11.1v. My ideal setup would be the 3s4400, 380c 9t and a Mtroniks Pro in a TC4 (well, in my case a TC3 with BMI chassis, but you get the idea).

[bigenginltlman]

Anyone ever tried www.maxamps.com? They have a great selection. I was looking at some 4s batteries, and I was trying to guess exactly how many mm tall I can get away with. I guess I could always remove the batt. strap and use fuel tubing with a wire run through the center to secure the battery. That should work...

[bigenginltlman]

The FT chassis can't do that though, because of the top plate of the chassis.

[Rtsbasic]

With the standard tub chassis's you can just use some longer screws to secure the battery down..Dunno about the FT TC4 chassis, but with my BMI one I could have the battery raised quite a bit before it hits the upper deck.

[bigenginltlman]

Looking at the pic, if the box at the end of the battery (where a seventh cell would be) is just a spacer, I could go longer too...

[Rtsbasic]

In the first pic, its a peice of foam, to reduce chances of the battery moving around.

[havy]

Looking at the pic, if the box at the end of the battery (where a seventh cell would be) is just a spacer, I could go longer too...

The Polyquest 4400 3s battery fits the length of the whole tray nicely on the TC4. You could put it on the FTTC4 maybe using double sided tape.

havy

[starluckrc]

I could probably drop ship you a pack from my distributor. 3S4400 and 4S3500 are both a great fit.

[bigenginltlman]

Is the 4s 20C, and is it still $120?

[SpEEdyBL]

It's 12c.

[starluckrc]

Update.......I do have a couple of 4S3500mah packs I pulled out for testing that have only 2 cycles on them. Actual discharge was to 3.7V or higher each time. Email if interested in a deal.

[DrMotor]

Feigao motors will run fine in the TC4, but you can expect slightly sluggish acceleration when compared to the Basic series due to heavier rotors.

The statement about sluggish acceleration is wrong. The equivalent linear mass of the Feigao rotor is only approx 38+25 gram.

Rotor mass: 25 gram (approx value for 380S)
Feigao rotor inertia: 600 gram mm2 (approx value for 380S)
Gear ratio: 25 mm drive / motor rev (value may change depending on track)
Calculation of linear mass: 600/(25/2pi)^2 = 38 gram

[SpEEdyBL]

How can you say that without even testing this for yourself? The 540 rotor has more than twice the moment of inertia of the 380 rotor, thus requiring twice the amperage to accelerate at the same rate as long their kv's are the same. Most batteries aren't up to the task. Remember, moment of inertia goes up by the 5th power every time the mass and radius increase proportionally.

[DrMotor]

How can you say that without even testing this for yourself? The 540 rotor has more than twice the moment of inertia of the 380 rotor, thus requiring twice the amperage to accelerate at the same rate as long their kv's are the same. Most batteries aren't up to the task. Remember, moment of inertia goes up by the 4th power every time the mass and radius increase proportionally.

How I can say that without testing:
1) You don't know what I have tested.
2) Physics and formulae.

Repeating the calculation for 540 motor, assuming that one selects a different gear ratio for the 540 than one would for the 380:

Rotor mass: 50 gram (approx value for 540S)
Rotor inertia: 2600 gram mm2 (approx value for 540S)
Gear ratio: 35 mm drive / motor rev (value may change depending on track)
Calculation of linear mass: 2600/(35/2pi)^2 = 84 gram

Does the change from 38 to 84 gram make the battery suffer or acceleration sluggish? No, it does not. More important is the (almost 100 gram) additional weight of a 540 motor compared to a 380 motor.

[SpEEdyBL]

It's true that 35 mm roll-out is the correct gearing for a 540, but people don't gear them high enough because of misconception. A 4,000 kv 540 brushed motor may not seem so appealing, especially if the buyer wants something that would match their old 9 turn brushed motor in performance. So then they end up buying a low turn 540 motor with 6,000 kv. Bad choice. The motor would have to be geared with a small pinion gear to keep the amps down and then it would take a lot more time to accelerate the heavier rotor to the top of its rpm. Actually, the 4,000 kv motor would be the best choice because when geared properly, it would draw about the same current as the the brushed 9t and reach the same top speed. The rotor itself would not need to accelerate to such high rpm. It's needing a 30 tooth pinion instead of a 20 tooth that seems odd.

Even though acceleration of a 540 is not as bad at second thought, the acceleration of a 380 is still better. Bigger things in general will always take more time to accelerate. It's alot easier to make an r/c car accelerate faster than a real car.

[bigenginltlman]

Will a 380's top end be as fast as a 540's?

[OptimaMan]

DrMotor: I was referring to the old 540 sized and not the 380C when saying that Feigao motors are slower than the basic series.

FYI, the 380 sized rotors DEFINITELY are quicker than the Basic which is DEFINITELY quicker than the 540 sized.

Your formulas and calculations might show negligible differences... but I can feel the difference and see the difference!

I can't seem to follow your formula, but from I remember from HS physics oh 15 years ago:

Assuming equal top speed and same kV and same efficiency:
Energy to reach that top speed is the translational energy + rotational energy.
Rotational energy of a larger rotor spinning at 40,000 rpm vs. rotational energy of the smaller rotor spinning at 40,000 rpm. is the difference in energy to reach that same speed.

Do you know the rotational energy formula for spinning masses. The mass is a solid cylinder?

If you know, please respond and let's figure it out.

Thanx for having this good discussion!

[OptimaMan]

okay, doing research... rotational energy = 1/2 moment of inertia x angular velocity^2
The angular velocity of the 540 rotor is higher than the 380 motor. 19mm vs. 15 mm. Angular velocity differences is roughly 1.6x higher in the 540 motor than 380 motor.

Next, the difference in moment of inertia is roughly is (MOI is 1/2 MR^2 for solid cylinders) using mass as 50 vs 25 and r as 19 and 15, we're looking at a difference of 50x9.5^2 vs. 20x7.5^2 which is approx: ratio is approx 3.2x higher for the 540 motor than the 380 motor.

Figuring this out, the 540 motor will need approx 3.2 x 1.6 = 5x the energy to reach the same RPM as the 380 motor!!!!!!

next thing to figure out is how much energy is actually needed to spin a 380 rotor to say 40,000 rpm?

I'll let somebody else figure that out. Somebody can figure it out in joules... any takers here?

[tcolesen]

I'll take a stab at it:

1/2 x [1/2 x 0.0025kg x (0.0075)m^2] x [(2 x pi x 666.67revs/sec.)^2]
The energy required for a 380 rotor (15mm diameter, 25g weight) to spin at 40,000RPM comes out to be 0.619 Joules.

Now for a 540 rotor, with 19mm diameter and 50g weight at 40,000RPM.
1/2 x [1/2 x 0.0050kg x (0.0095m^2)] x [(2 x pi x 666.67revs/sec.)^2]
This comes out to be 1.98 Joules. That's 3.2 times more energy for the 540 rotor over the 380, assuming all measured quantities are correct.

This is of course only calculating theoretical energy of a spinning rotor in a frictionless environment without a load. As I see it (and theoretically), with the addition of the rotating and non-rotating mass of a vehicle, the MOI increase between the different size rotors woudln't be that much. But, as the vehicle gets lighter, the rotor's mass (comparatively) will become more noticeable.

BTW, Optimaman, I looked around, and I found that angular velocity has nothing to do with the radius of the rotating object, so the angular velocity for each object is the same (assuming both are spinning at 40,000RPM). If the radius were factored into the angular velocity, then the units for rotational energy would be (kg x m^4/s^2), but the unit for energy (Joule) is (kg x m^2/sec^2).

Now, how's that for some head-spinning math! Being in AP physics right now sure does help (for me, at least).

[SpEEdyBL]

Actually, I think the masses of the rotors are off. Lets say the mass of the 380 motor is 1. Assuming each rotor has the same density, you can find the relative mass of the 540 vs. the 380. The 380 rotor is 15x25 and the 540 is 19x21. Volume for a cylinder is hight x pi x radius^2. (21 x 19^2)/(25 x 15^2) = 1.35 relative to the 380. Moment of inertia for a cylinder is 1/2 Mass x Radius^2. (1.35 x 19^2)/(1 x 15^2) = 2.16. The 540 rotor takes 2.16 times the energy to accelerate at the same rate as the 380 rotor. (If you noticed that I didn't exactly follow the equations for volume and moment of inertia it's because some values canceled out).

However if you gear each motor appropriately, the 540 wont need as much rpm to achieve identical power. A 380 motor has about 1.39 times the kv of a 540 motor of the same resistance. Each geared properly, both motors will pull the same amps, have the same power output and reach the same top speed. For example, the 380 may need 50,000 rpm to reach a certain speed, but the 540 motor will only need to rev a 36,000 rpm. Since the 380 has a 2.16 advantage in moment of inertia and the 540 has a 1.39 advantage in rpm, 2.16/1.39 = 1.55. That's the number comparing the total amount of energy needed to accelerate each motor to its own rpm in the same time. Remember, the resistance of each motor should be the same to get equally powerful motors at a given voltage. Also, gearing has to choosen according to kv of each motor to get the same speeds. Plus the slower motor will have more torque so the gearing also compensates for that. And just for reference, if you were to use an 8 turn 380 motor, a 10 turn 540 would be the correct motor to match it with.

[OptimaMan]

Another variable is the RPM the motor is running at. I notice that it is easier to drive, less cogging, more natural drag brake when the motor is running higher RPM. Another reason I like the 380C over the 540 in my 1/10 vehicles.

[DrMotor]

540 motor will only need to rev a 36,000 rpm. Since the 380 has a 2.16 advantage in moment of inertia and the 540 has a 1.39 advantage in rpm, 2.16/1.39 = 1.55.
The speed should be squared so that the formula is 2.16/1.39^2=1.12
Note that the inertia of the rotor is only one or two % of the car's total inertia --- increasing next to nothing by 12% is still tiny like this... :)

I calculated in earlier post (using slightly different values for the inertia) that changing from size 380 to size 540, while maintaining good (not same) Kv and gear ratio, adds approx 46 gram to the car's inertia because of rotor inertia and another 80 to 100 gram because of increased weight of the motor.

The best motor size is normally the smallest one that does not fry itself. Both my 1:10 scale cars run with 380 size BL.

[SpEEdyBL]

How could it be 2.16/1.39^2? I put down 2.16/1.39 because 1.39 times the force results in 1.39 times the rpm in a given amount of time (two indentical rotors). Also, force is a direct correlation to acceleration. Why woundn't 1.39 times the force equal 1.39 times the acceleration? I still like my first answer. Otherwise, please explain if I'm wrong.

[DrMotor]

How could it be 2.16/1.39^2? I put down 2.16/1.39 because 1.39 times the force results in 1.39 times the rpm in a given amount of time (two indentical rotors). Also, force is a direct correlation to acceleration. Why woundn't 1.39 times the force equal 1.39 times the acceleration? I still like my first answer. Otherwise, please explain if I'm wrong.
Kinetic energy of rotor is proportional to speed^2.

(Alternative explanation: 1.39 times the acceleration and it needs to reach 1.39 times the speed. Total is 1.39^2)

Confusing?

[RcWebel]

Yeah, the Mtroniks PRO is much better than the MGM 80!! Got them all... So, as update, get the Mtroniks Pro, get the Feigao 380Cxx motor and go 4s lipo - just try those 4s3500 mah polyquest from starluck - you WON'T be disappointed. They're on sale for only 120 right now.

Heck, the pro and 380Cxx motor combo is only 200 (last I read) and the battery is 120. So, that's only 320!!!


Will Starluck be offering the 4s3500mah Polyquest any time soon??
I don't see it in their website...also bring the combo back..............
please Starluck....I don't want to miss out on the fun....

[tcolesen]

Starluck RC has a couple of 4s 3500mah batteries left the last time I heard. Polyquest no longer is a company, so if you go to any other website, you will see really good deals on Polyqest, if there is anything there.

EDIT:
Go here:
http://rclipos.com/
Click on Polyquest on the left.
Scroll down under narrow packs.
Find "PQ4S-3600N". That's what you want (the size is correct).

[SpEEdyBL]

Kinetic energy of rotor is proportional to speed^2.

(Alternative explanation: 1.39 times the acceleration and it needs to reach 1.39 times the speed. Total is 1.39^2)

Confusing?

First were talking abou the necessary force to get the rotor to accelerate at a certain rate, and now it's the kenetic energy of that the rotor has? Remember, this is the time it takes for the rotor to spool up to a certain rpm, not the distance, so there is no squared value. And a motor moving 1.39 times as fast has 1.39 times the momentum. Sorry maybe I'm having too much fun.

[DrMotor]

...this is the time it takes for the rotor to spool up to a certain rpm
Yes, but the "certain rpm" is a factor 1.39 lower for the larger motor than for the smaller, right?