Brushless HPI Pro 4

[OptimaMan]

Here's a pic of my new brushless HPI Pro 4. It's got a Basic 3100 which geared 9.0:1 gives it a top speed of around 18 mph with 7.4 volt lipoly pack at 2100 mah. With this setting, nothing gets even warm. Check out the total weight w/o body though - 2 pounds and 4.8 ounces!!!

http://home.comcast.net/~youngsongdmd/pro4.jpg

[Signats]

Wow! less than 2.5 lbs RTR, better not run it on a windy day it might not stick to the ground:D

What is next for your RC feather, a bigger pinion or more voltage?

[OptimaMan]

More VOLTAGE. With the 7.4 volt with that gearing, I drove it around for at leat 5 minutes and the battery only used up 800 mah.

I'm going to put 11.1 volts on it next with a 1900 mah pack. I should get about 24 mph top speed (which is good for the local track - small carpet track) and I'm thinking I should easily get 5 minutes run time w/o anything getting hot.

Then... I'll go up to 18.5 volts and 22.2 volts!!!!

[DaFF]

:eek: :eek: :eek: less than 2.5 lbs RTR :eek: :eek: :eek:

I guess you must spank the competition with a car that light !

Very nice ride...

DFF

[Signats]

Originally posted by OptimaMan
More VOLTAGE. With the 7.4 volt with that gearing, I drove it around for at leat 5 minutes and the battery only used up 800 mah.

I'm going to put 11.1 volts on it next with a 1900 mah pack. I should get about 24 mph top speed (which is good for the local track - small carpet track) and I'm thinking I should easily get 5 minutes run time w/o anything getting hot.

Then... I'll go up to 18.5 volts and 22.2 volts!!!!

Is there a limit on the voltage that the motor can handle?

My basic 3100/18.61 combo pushes a (4+ lb.) 1/10 stadium truck into the low 30mph range on 6 GP 3300s and gets about 18 min. of run time (on a track). This is a very efficient and powerful set up.:) After 18 min. the hottest component is the motor at about 130* F.

Do you have any idea how much heat is too much for the magnets in a BL motor?

[OptimaMan]

When the motor is too hot to hold in your hand, then it's too hot. :) I've heard 200 degrees F once. The limit of the voltage is the limit of the RPM of the motor. 3100 rpm/volt with a max rpm of 65000 means roughly 22 or so volts....

[OptimaMan]

hey guys - that's NOT 2.5 pounds, it's 2 pounds 4.8 ounces!!!! So, that's more like 2 and a 1/4 pound!

[NIC]

Really cool car OptimaMan :) ! It´s fun to see different approaches to car set-ups. Here you have found a REALLY light set-up for tight tracks. And if you want you can make this car really fast also for larger tracks just by raising the voltage on that motor. Really smart !

Nice project you have there :) !

One question:
Will the esc fit between the motor and a standard-sized servo ? Or would it take the low-profile Futaba 9550 digital-one to make room for the esc ?

NIC

[DaFF]

Yeah, it sure is an awesome project :)

Anyway, is you car running good the way it is setup ?

Because it does seems to me that the balance of the car would not be optimal, given the fact the weight of the batteries would not be equal to the combined weight of all electronics + motor (balance btw right and left ??)

DFF

[OptimaMan]

DaFF, the speed control is right in the center. The motor is a Lehner Basic which is realllly light (about 4 ounces). The battery is about 3-4 ounces depending on whether I use a 2 or 3 cell. So, the difference between right and left is a mere 2 ounce or less (the weight of a receiver and low profile servo). If I take it racing, I'll just put the transponder on the battery side. If I decide to add another pack to the battery side, then the transponder will go on the electronic side.

As it is, it runs fine - as far as I could tell. It has the same amount of steering right and left.

Racing? Well, I'll be the first to admit, I'm not the best driver so even if I have a total weight and handling advantage, I'll still probably won't win. Besides, all they run in our track is stock and anybody with anything else and they'll all start whining. BTW, at the local track, they have about 5-6 heats of stock TC of 5-6 cars each heat so there is a A, B, C, D, E, and F main!!!! As you can guess, it gets pretty competitive.

[OptimaMan]

The Schulze controller should fit right on the chassis in between the servo and motor w/o any modifications. If you use a standard sized servo, it would be very close - you would have to have 90 degree solder joints to the Schulze controller. The fact that I'm using a Basic motor helps because it is so short too.

Either way, I just mounted on the top because it's easier access and performance difference of having an ounce of weight higher on the chassis is negligible to me.

[OptimaMan]

NIC:

yup, you got it. Keeping the 9.14:1 ratio (really easy on the motor), and using very efficient motor (basic 3100), the amp draw is very low and the overall system is generally over 80% efficient.

The "no resistance" speed is:

7.4 volts 18.66 mph
11.1 volts 27.99 mph
14.8 volts 37.33 mph
18.5 volts 46.66 mph
22.2 volts 55.99 mph

Of course, this is "no resistance" speeds. But generally with a good brushless setup, and Lehner's motors are rated with load, and without gearing too tall, you'll notice that it's only slightly less mph than theoretical. I'm not claiming these, but this is what I actually am expecting:

7.4 volts 2100 or 4200 mah 17-18 mph
11.1 volts 3000 mah 35 mph
14.8 volts 2000 mah 42 mph
22.2 volts 1900 or 3000 or 3800 mah 50-52 mph depending on which combination of lipolys.

I want you to understand one thing here. The 3100 rpm/volt motor produces a LOT of torque. By putting 22.2 volts to the motor, you are at the maximum power output of the motor before it blows up. At this power, and gearing taller, 70 mph is very very easy to achieve. With a 6:1 ratio, "no load" speed is 85 mph, wit h a 5.22:1, "no load" speed is 97.99 mph. Of course, it'll probably more like 70 and 80 mph respectively... and if the motor doesn't have enough torque, I have a Basic XL 3100 also. :) If I recall, Cliff Lett used a Basic XL 4200 to get his TC3 to like 95 mph? The Basic XL3100 is MORE efficient than the 4200 and by simply raising the voltage higher, I still get the same RPM, with more efficiency and lower amp draw.

See, the biggest misconception in brushless motors is that "higher Kv is faster". Yes, it's faster given the same voltage, but if you have the ability to mix and match your cells to alter voltage, you can get every motor to rev to the physical limits of the motor (the rotor breaking apart due to centripetal force). So, you can get a slow motor to go the same RPM as a "fast" motor. Generally "slower" motors are more efficient also so you will build up less heat which means higher efficiency - longer battery and magnet life. Now, let's say you get a 6000 rpm/volt motor vs. 3000 rpm/volt motor. You would have to put 2x the voltage on the slow motor to get the same rpm.... but the 6000 rpm motor needs 2x the capacity... and a little more due to the fact it's LESS efficient!!! I'm going to have to post this in another article..

[DaFF]

Thank you optimaMan for the clarification about weight balance of your car.

DFF

[OptimaMan]

Hey guys, some actual measurements. With 11.1 volts with a FDR of 9.14:1, my actual speed was 28 mph. That's up the street and down the street with and against the wind speed. Interestingly enough, that's the same speed as the "theoretical" speed without the motor bogging down. Which means that Lehner motors are rated under load or I'm not loading the motor much at all.

At the local racetrack, the stock speeds are at 23 mph (pretty slow huh?) so now I geared my Pro 4 with 11.42:1 which should give me a top speed of 23 mph so I can race with the stock cars. Total race weight with rubber tires and body and 1900 mah 3 cell pack is 2 pounds 10.4 ounces.

With the car tweaked and setup properly, it handles very evenly both right and left hand turns. The left right balance is perfect and the car is VERY smooth. This car is TOTALLY OUT OF THE BOX STOCK with NO adjustments... I just have to learn to drive now. And, I'm not used to the one way front diffs. Need to dial out some braking.

[DaFF]

Thats interresting...

It tells me that if I use a 4200 instead of your 3100, the speed could be roughly 28 mph / 3100 x 4200 = 38 mph

That with the same 11.1 volt and the same FDR 9.14:1

What run time did you get with the 11.1 volt 1900 mA and 9.14:1 ratio ?

DFF

[Serius Black]

So, what would it take to get your car to run on mod-sedan race pace? 18 mph is dreadfully slow for the money invested. 24 is ok for stock - maybe. Cool experiment, though.
I've yet to look in to Li-Poly cells since they can't handle the draw for mod-class racing, but I see where you're going with this. Isn't a six cell, megavoltage LiPo pack still lighter than a 6 cell NiMh pack? I've been so ingrained in racing for so long, I haven't had a chance to play around with this stuff.

[OptimaMan]

It wouldn't be too difficult to run at mod sedan pace and then some. By simply tripling the number of cells so I have 3 11.1 volt pack at 1900 mah would give me sufficient power to race with any mod guys. FYI, the present 1900 mah is rated at 6 C or almost 12 amps at 11.1 volts. With voltage drop, we're really looking at 100 watts/pack. With 3 packs, I can run 300 watts continuous and closer to 500 watts peak and with a motor efficiency of over 80%, that's over 240 watts of output and 400 watts peak output. If I recall, the basic 3100 is over 80% efficient at 10 amps. Fomr 16 amps to 40 amps, it's 87% efficient!!!! WAY more efficient than a brushed motor.

AND, 3 11.1 volt 1900 mah packs combine to be less than a single 6 cell 3300 mah pack!!!!!!!!!!!!!! (So, yes, 9x3.3 volt 1900 mah cells weigh less than a 6 cell pack)

SO, a 11.1 volt 5700 mah pack weighs less than a 7.2 volt 3300 mah pack. See how all this stacks up? And, a 7.2 volt pack cranking out continuous 300 watts is like 50-60 amps continuous and it would have to have peaks at over 100 amps to be similar in power output.

This isn't even the end of it. Next month, there will be new lipoly cells that can almost DOUBLE the output of the ones I'm using right now!!! So, next month, a 11.1 volt pack at 6000 mah will crank out 500 watts continuous and peak at possibly over 800 watts. Now, we're talking more power output/weight than GP3300's here... with almost 3x the energy density!!!! That's why Craps is going to crazy over these cells.

[DaFF]

Optima,

I was wondering what tire you have on the picture where the scale says 2-4.8 ?

Is that rubber of foam ? 24 or 26 mm wheel ?

(Awaiting my Pro4, should be here soon)

BTW, I saw in a previous post that you said you have a website. Could you pls give us the address ?

Tks

DFF

[DualBL]

http://home.comcast.net/~youngsongdmd/

btw, NICE house! :)
-Nick

[OptimaMan]

Thanks Nick!

Daff - that's rubber and it's 24 mm.

[OptimaMan]

Oh, and I don't really have a website - I just post a bunch of pictures... and I did delete the old "index.html" file cuz it's been a while - maybe I'll work on a new one for all the RC stuff... But that takes a LOT of time and TIME is what I don't have these days. (I suppose if I stop posting, I'd have more time)

Since that picture, my BL pro 4 now weighs 1 ounce more due to 11.1 volts as opposed to 7.4 volts.

[gbone]

Optimaman, your car is impressively light to say the least. I was wondering (depending on gearing ofcourse), can you pop little wheelies with it?

[OptimaMan]

Wheelies would be possible if there were enough traction. Even with sticky foams with traction compound on carpet, the tires will break traction. It's fun though - this TC accelerates out of the turn so fast, the other guys scratch their heads and wonder what the heck I'm running! Imagine that - too much acceleration!! That's what BL is all about.

[NMT_RACER_BOY]

how much is that in grams?

[glassdoctor]

36.8oz= 1043.28 grams

Hey, you could go with a smaller lipo and shorten wires, etc... shave another 2 ounces and get under the one kilo weight. :D

[NMT_RACER_BOY]

wow
that IS freaking lite!

Are you running the front oneway or dual diffs?

[Kden46]

:eek: Damn that's a killer looking PRO-4!!! 24mph on 11.1volts sounds slow but I guess that's your gearing!

I've seen a PRO-4 with a Novak 5800 system and 7.4v li-po pack and it looked alot faster than 24mph!

But your setup seems to be exactly what you need for your track! Nice job!

[DaFF]

Ttt.