Motor/ESC suggestions

[trailranger]

I am gathering parts for my car and before I commit to a final motor pod design I was thinking what Motor/ESC combo should I pick.

Requirements
1. Size, Motor must not be longer than 75mm, wires not included
2. Power will be a 4S to 8S A123 battery pack. 5S or 6S Perfered (Charger is a 6S)
3. Price
4. Availablilty
5. Rebuildable motor design (I would like to inspect the rotor for signs of failure)
6. .125" shaft size, will be using 48P gearing.
7. RPM...how high can we go!

My initial thoughts was using a Novak 4.5 HVMAXX system. I would do pratice runs with a 4S pack and then work up to a 6S pack. I would Disable the BEC and use a 6.0V RX pack.

I would like to try the Phoenix 180A 25V ESC since I am worried about the Novak crapping out with 6S A123 pack. I know last year Team Novak Pushed a 5S LiPO pask and it survived but with a 6S A123 pack I would be 1.2V higher than what they were pushing.

Should I try the Phoenix with a 4.5 HVMAXX motor?

[ajlovering12345]

Hi

The mistake people make is to select a motor and then design the car and then figure out what speed it will go. You should be looking at what speed you want then see what design will get you there.

If you car is around 3Kg, about standard for an electric car, and you aim for 140 mph it will take 11 seconds to get there and you will need 2.5 to 3 hp. (B4maz spreadsheet!)

Motors usually rev to around 50,000 rpm. A 6S pack puts out 23 volts so you need a motor of KV around 2200. If the motor you have is higher KV you need lower volts and more amps to get same HP

3hp is 2238 watts so with 23 volts you need 97 amps. The 2200mah LiPos are usually 90 amp burst so ensure cells are at least 2200 mah.

The ESC has to be able to handle 90 amps so go for a Quark or the MGM or the CC HV110.

So result is

2200 Kv Motor at 23 volts
90 amp min esc
2200 mah 6 cell Lipo

[trailranger]

The car's target weight is under 1500grams and I really doubt I will draw over 60amps unless I gear it to 300mph. I'll start my gearing for 100mph and go from there.

What would be wrong with running the Phoenix 180 25V? More amps and in the voltage range I will be using

[ajlovering12345]

The Novak HV 4.5 is rated to 750 watts and 17V so max 44 amps. This is for 6 mins so thought you can get away with possibly 70 amps burst. Thats a max of 1200 watts and 1.6hp. This power will get a 1.5kg car up to 130 mph but you will need 1.7 hp for a 1.8kg car.

If your looking at more speed try a better motor

[Hard Case]

Josh
Based on your criteria ,there is nothing on the market that meets all of your requirements (as far as I know). However, Inspecting the armature is not that important. Either it's together--or not. If this requirement is removed, there is no doubt what will meet your criteria.

***The Mamba Max system from Castle (http://www.castlecreations.com/products/mamba_max.html)***

I have used these motors & speed controls in drag racing.
They are very impressive. Plenty of power & easy to use.

The ESC can handle up 6s ---
Less than 75mm long --
1/8" shaft ---
Readily available -- (great customer service- in the USA)
Affordable System -- `$210
RPM - as long as you stay under 60k (based on Kv & Voltage) it will run all day

Hope this helps
Nic

BTW
5s / A123's, I'd get the 4600kv system
If you go 4s, you will not need a receiver pack.
A123's have a nominal voltage of 3.3v (who knows what the voltage drop will be?)
4x3.3x4600=60,720 RPM (no load)
In drag racing . we run 4s lipo with a 7700kv and go 100mph in 132'

[trailranger]

The Novak HV 4.5 is rated to 750 watts and 17V so max 44 amps. This is for 6 mins so thought you can get away with possibly 70 amps burst. Thats a max of 1200 watts and 1.6hp. This power will get a 1.5kg car up to 130 mph but you will need 1.7 hp for a 1.8kg car.

If your looking at more speed try a better motor
Novak numbers are hard to interpret. The ESC has like 480amp per phase limits, but quote such low watts based on the 6-min run. Meaning you should be able to run that esc and motor for 6 mins and not worry about thermal.

The MM system seems to be a good deal but when I first got into brushless with a MGM COmpro and fagio motor i was dissapointed in the motor once I killed the bearing. No way to replace the bearing without damaging the motor.

Now that I own three Novak systems and a lrp I am brand loyal due to the customer service Novak offers.

[trailranger]

Nic, I'll look at the MM 5700 package. I plan on starting with 4S and working up from there. Plus the system is for sale at $212.

Are you sure it will handle 6S of A123s? I already expect to disable the BEC and run a RX pack. ESC's do wierd things when under load and over voltage and I dont want a run-a-way missle.

[Hard Case]

The recommendations that Castle makes on the MM system are underrated.
The ESC can handle 100 amps constant and peaks of --- who knows? maybe 300? I've tried to measure it while drag racing, and never got a good measurement. BTW drag cars pull more amps than a speed run car will.

I have run (with my dragster) 4s lipo with a 7700kv motor without a rec pack.
Also - 5s lipo with a 5700kv with a rec pack.

Nominal voltage for an A123 is 3.3v x 6 = 19.8v
Nominal voltage for an lipo is 3.7v x 5 = 18.5v

I think the extra 1.3v wont kill it. It's all about HEAT anyway. As long as you run it as a speed run car,
one run at a time,we are only dealing with a few seconds.
In our dragsters, the motors don't get hot. 180'F---is the "heat limit", but don't worry, it wont get there.

The thing you should be careful of is the RPM. Sure, in drag racing we are "over-voltage-ing" the motors. But the runs are so short they never get up to terminal velocity. So make sure the the RPM does not go above 64k.
And don't rev it up without a load. (I did that once ---LOL--I wont do that again)
It might be a good idea to start out with 4s & a 4600kv motor.(4cells x3.3v x4600kv=60,720 RPM (no load))
Then --- you can measure RPM, figure the load & and add cells accordingly.

N

[trailranger]

Mamba Max with 4600KV motor on its way along with the castle link, CC 10A BEC, Eagle Tree B/L RPM sensor and Magnet RPM sensor.

I did see that tower had the Sidewinder w/ motor for about the same price as the MM w/o motor.

[ajlovering12345]

......
It might be a good idea to start out with 4s & a 4600kv motor.(4cells x3.3v x4600kv=60,720 RPM (no load))
Then --- you can measure RPM, figure the load & and add cells accordingly.....

N

Nic.

RE your comments above. I was thinking along thse line so tell me if this is correct.

I work out the max cells I need for the no load max revs of the motor and this would give me a max MPH say 120. In tests I dont get near this so then add cells to speed the car up until I get the MPH i need. You cant then rev the car with no load. Will that work or will it overheat the motor?

Cheers

[Hard Case]

AJ

You're sort-of on the right track. I'd mess with gearing first.
But the only way to know for certain -- is to measure the Motor RPM & voltage drop with a "data logger". Then the calculations from the spreed sheet should work. For the most part ,it's "voltage drop" that has a big affect.
So, gearing is your first avenue to experiment with.

I think if everything is done right------- It is possible to 120mph with 1 1/2 HP. (4s Mamba Max )

With the MM, heat should not be an issue (for speed runs). The reason I mentioned to stay under 64K RPM is that ---- you don't what the armature (magnet) to explode. The bigger the armature (in physical dimension) the slower the RPM the armature can handle. The "little" Mambas can spin 80k to 100k ! But they can't put out the watts that the Mamba Max can.
No matter what the RPM of the motor--- it can all be made up with gearing.


4cells x 3.7volts per cell = 13.2 volts
13.2 volts x 85 amps = 1122 watts
Watts = HP ( 1 HP = ~745 watts)

Cheers
Nic

[trailranger]

Nic, what about the amp load?

I was working the SpeedCalc and every calculation I made I was trying to get the amps under 100. For my A123S I would like to keep the amps under 60 per cell and I understand that voltage drop would be fairly high at 60amps.

Do you have a magic number to stay away from?

[Hard Case]

Josh
The only way to know for certain -- is to measure the Amperage, Motor RPM & voltage drop with a "data logger".The calculations
from the spreed sheet are just a starting point-- until we have more data. For the most part ,it's "voltage drop" that has the biggest affect. If the voltage drop is so low that RPM is drastically affected--- thats when it would be useful to add another cell. This should lower the amp draw. Hopefully it will be obvious when the data is on a graph.

Once you get a measurement, please share with us -- so all of us can learn from your experimentation.;)

N

[trailranger]

Well since the car is not built, the only thing I can do for testing would be:

Use my data logger: Hook up a 4S A123 battery pack to a 0~500A load tester and crank that baby up.

First test about 10A and for 3 seconds. Let the cell recover (30sec) and bump it by 10A every time till I have reached a point higher than my calculated amp draw on the car. After the test I'll load up my Eagle Tree and post it sometime next week.

[B4Maz]

Josh
The only way to know for certain -- is to measure the Amperage, Motor RPM & voltage drop with a "data logger".The calculations
from the spreed sheet are just a starting point-- until we have more data. For the most part ,it's "voltage drop" that has the biggest affect. If the voltage drop is so low that RPM is drastically affected--- thats when it would be useful to add another cell. This should lower the amp draw. Hopefully it will be obvious when the data is on a graph.

Once you get a measurement, please share with us -- so all of us can learn from your experimentation.;)

NAnother important thing that affects voltage drop that no one mentioned yet is battery capacity. A higher capacity battery will have less voltage drop than a lower capacity battery.

"Battery capacity verses Voltage Drop

One would think two batteries of the same voltage but different capacity would have equal voltage drop under the same load. Not always true. The battery with the larger capacity will have less voltage drop due to having a larger plate surface area. Since the load is essentially spread out over a larger area, the battery chemistry is less affected."

[trailranger]

I may have to go with a LiPO pack. I was messing with the A123 cells and I am having problems with soldering to the Aluminum casing. The tin "stickers" are a pain too. I was looking at the 3000HV packs from MaxAmps. My goal is still keep the work load low and about 60A if possible. For that my target weight of 1500grams is very important.

Yes B4, capacity affects voltage drop. For a while I was using Maxwell's technology excell spreadsheet that would calculate drop under load.

The spreadsheet was designed for capacitors, but you can fudge and make one amp hour = 3300F, plug in the IR and the load and it will output how long before your minimum voltage is reached. Before the advent of 3800's or good LiPO's using ultra capacitors seemed the way to go.

[tcolesen]

Did you remove the A123 cells from a Dewalt 36v drill pack? I've made a total of 5 packs using those cells, and soldering to the tabs, and not one pack has come up with a dead cell.

[trailranger]

Yes they are dewalt A123 cells. Paid $85 shipped for a new pack. Tonight or tommorow I will try Solder-iT paste for aluminum. I only messed with two cells for practice. I am sure they are good, but I didn't want to ruin the cells by excess soldering.

If I switch to LiPO I should shave about 70g's off the car. I feel a lighter car will get to speed faster and use up less batteries doing so. It will be a balance to have the right sized power source. I don't want too small of batteries and the voltage drops too low under load, but I don't want excess weight being the reason the voltage is dropping so low. Also the car only has some much room to get too speed. I wish we had a mile long course or a tether car track. I know a tether car is not radio controlled, but it would usefull for testing out high speed runs