Brushless Motor and ESC Combo?

[hamz9561]

I am in the process of building an electric 1/8th scale truggy. Any ideas for a good b/l motor and ESC for this beast?

 

[sweetdiesel]

Some more details please. Which vehicle? Which batteries do you plan on using (nimh or lipo) and how many cells? If you plan on using lipos, do you have a charger and balancer for the cells you plan on using? Bashing or racing? And most importantly how much is your budget?

 

[hamz9561]

Looking at about $500 for ESC and motor. Planning on initially running NiMH stick packs (12 cells) with at least 3500mAh capacity. Does this help?

 

[sweetdiesel]

As suggested before, the Novak HV Maxx is a good start that will keep you under budget and still run well with 12 cells. The limiting factor with the Novak is that you can only run a max of 14 cells.

Personally I would go with a Quark 125B ESC and either a Neu 1515 1.5d motor (2700KV) or a Lehner 1940/6 (2613KV) for use with 12 cells. This would put you right at about $600 for both. You can substitute a Feigao XL can motor instead of one of the high end motors listed to stay under budget. The Feigao’s run about $90 each are very good motors for the money.

The Quark ESC gives you the flexibility of running a higher cell count later if you choose (up to 18 cells nimh or 6S lipo). Another ESC option is the Mamba Max. Many folks are using the Mamba Max ESC and have successfully run up to a 4S lipo with the BEC disabled. If you plan on sticking with 12-14 cells only, then the Mamba Max ESC would be the best bang for your buck. Not sure if you are in a rush to get this project completed, but Castle Creations will be releasing a Mamba Monster Max system in a few months. The motor will have a larger can than the 540 size units in the current Mamba Max system.

Here is something to think about with brushless motors in a heavy vehicle such as a truggy. It is preferable to run a lower KV rated motor with higher voltage packs rather than a high KV rated motors with less voltage. The low KV motor/high voltage set-up will run more efficiently, and will tax the ESC and batteries less than a high KV/less voltage set-up.

Batteries will also play a very important part in your brushless set-up. Be sure to budget for them and buy the best you can afford.

 

[hamz9561]

Okay, that answers my questions on this subject. I've got the Revo roller that I purchased from another member and starting to transform this pumpkin into a slick coach. It just takes time and money.

 

[godale03]

Hey SweetD.....

Could you explain the Motor voltage vs the battery voltage a little more? I am curious as to how this all works together, as I am going with the HV Maxx setup and 14 cells. Some good info to be learned here. Thanks

Tom

 

[hamz9561]

From what I understand, the kV rating of a brushless motor is how many RPMs you get per volt. If you have an 8000 kV motor and are running you get 80,000 rpms. That's the good news. The bad news is that the higher the kV rating the less torque that a motor has.

 

[godale03]

Ah.... it is starting to make a bit more since to me now. I am also guessing that the higher the KV the harder the drain on the battery.... I think LOL


Tom

 

[sweetdiesel]

To help explain how the low KV rating/high voltage vs high KV/low voltage scenario we will need to establish a couple constants. First, we can only use motors that are within the same series/can size from the same manufacturer. So you can’t compare a Neu motor to a Novak motor, nor can you compare a motor that has a XL can with a motor that has an L can. We will also make the assumption that the ESC used can handle both the voltage and amp draw of either scenario.

Assume you have a car that requires the motor to spin 30,000 rpm to attain a desired speed of 30 mph. To get to 30,000 rpm, let’s say that the required power output is 1000 watts. Here is how different motors/voltages would effect the amp draw. A higher amp draw would require more work from both the ESC and batteries. For sake of discussion, we will exclude voltage drop under load and motor/ESC efficiency in our equations.

Ex.1

Neu 1515 1.5d 2700KV rating

To get to 30,000 RPM, we would require 11.11 volts. (30,000 rpm/2200KV) To get amp draw, we take the power output of 1000 watts and divide that by the voltage. 1000/11.11 volts = 90.01 amps.

Ex.2

Neu 1515 2.5d 1700KV rating

To get to 30,000 RPM, we would require 17.65 volts. (30,000 rpm/1700KV) To get amp draw, we take the power output of 1000 watts and divide that by the voltage. 1000/17.65 volts = 56.66 amps.

As you can see the difference in amp draw is quite a bit. The lower the amp draw, the cooler the esc will run, and the batteries will also stay cooler.

The bad news is that the higher the kV rating the less torque that a motor has.

Not true. Within the same can size of the same manufacturer, the motors will have the same maximum torque output regardless of KV rating.

 

[godale03]

Damn math again! Hey sweet D... thanks for the explanation. It does help. My question though... is if a lower KV motor is better for the overall "Health" why do they make so many KV variations? Do you know what the KV rating of the HV Maxx 6.5 is? Thanks again.

Tom

 

[sweetdiesel]

Different applications require different KV ratings. You have a higher KV rated motor for low voltage applications or where weight and space for more cells is an issue. There are also design limitations of the ESC to handle amp draw and voltage, and rpm limits of the motor bearings.

The HV6.5 system uses a 3100KV rated motor. Novak rates their motors unloaded, so under load it is slightly lower.

 

[godale03]

Different applications require different KV ratings. You have a higher KV rated motor for low voltage applications or where weight and space for more cells is an issue. There are also design limitations of the ESC to handle amp draw and voltage, and rpm limits of the motor bearings.

The HV6.5 system uses a 3100KV rated motor. Novak rates their motors unloaded, so under load it is slightly lower.

So is this a good thing? Thanks

Tom

 

[sweetdiesel]

It's neither good or bad, it's just a number to use as a reference to compare motors. The HV6.5 system you have is a very nice set-up Tom. If you are wondering if you should go with something else, I can say you are right at the point of diminishing returns.

You can spend A LOT more money for a little more performance.

 

[godale03]

Thanks for the Info SweetD. I was begining to rethink my decision to go with the Novak system. In my limited experience it helps to have people like yourself validate a purchase like this. I spent alot of money on a product I did the research on, but still didn't have all the answers. Novak is a great company.... maybe not cutting edge, but it sounds like the HV Maxx will get the job done! Thanks again.

Tom