I need more torque?

[Voodoobrew]

I have changed my heavy axial bomber to MoA with 2.2 tires. 95% of my driving is in the bottom 10% of the throttle range so that's whats important to me. My previous setup was the stock axial 35 turn motor and a gear ratio of 76:1 (hot racing 2spd & 11/64 pinion) (Stock would be 30.3:1)and I was happy with a top speed about 4.2mph and torque when I first hit a steep 70° climb, (speed at 3% didn't change much or stall).

Due to a miscalculation in the origional bombers gear ratio (didnt calculate gear reduction in the transfer case) i set it up to go almost twice as fast as intended.
My new setup is 43.9:1 and can be geared to 51.9:1 with 2 Rc4wd 35t motors. Now its top speed is around 7.2mph and it stalls when I hit that 70° climb so i need to give it more throttle to get up, but then once it starts moving its to fast.

I am looking for 2 quiet motors, probably brushed, I don't like the brushless whine. Just bought 2 HW1080 esc's on a 3s lipo. Motors that will have very low end torque cause i'm usually barely creeping (which I think heats up motors). Nothing longer than a 540 motor, this limits the steering on my Rc4wd bully ll MoA axles.

55t trail masters would give me the same top speed as before (4.14mph) with my 43.9:1 gear ratio, do you think that is a good choice to reduce the stalling ( under load) and increasing the torque. Or a 45t and reduce the gearing to 51.9:1 (4.24mph).

I am curious if the crawlmaster 540 20t expert would have enough torque with 51.9:1 gearing (around 4.8mph 1375kv assumed).

How much more torque to the different 1500kv Holmes Hobbies motors produce.

I don't mind the extra top end, it can be fun, but it needs to have more torque.

And what is the difference between low end control vs. torque?

I do my calculations on this excel thingy, but it wont calculate torque. https://docs.google.com/spreadsheets/d/1qRQxNXzf5-iOVL-J7NEjJFcdtjU4hW5xzKsDp01D0a4/edit?usp=sharing

In this youtue video https://youtu.be/BcuhdkCucGA?t=766 JohnRobHolmes says higher turn motors do not produce more torque, they produce less torque at full throttle, ok i cn see that. But what about torque at 20,000rpm?

 

[JohnRobHolmes]

Low end control and torque aren't directly related, but the feel of a motor with higher torque will be more consistent under load. it won't slow down as much when it hits an object.

I would suggest the Torquemaster or Trailmaster series for torque, as the crawlmaster is not as "strong' feeling. A Pro handwound motor will give you a huge jump in torque, but also a pretty big jump in price. For the same price you could go brushless and have even more torque, but there are downsides in regards to noise and control as you have seen.


Peak torque from a brushed motor depends on your input voltage more than anything else. If you are running 4s or less, a 27t or 30t motor will make peak torque. Running higher voltage will allow a slower motor to produce the same torque. But if you don't need all that wheelspeed, going with a slower motor will still net you "enough" torque to crawl with. We certainly have enough evidence to say that 55t motors make enough torque to crawl with

To your question about torque at 20,000rpm, it will depend on how much RPM overhead you have to spare (within the golden zone of brush saturation, so 27t motors or slower). A motor with enough voltage to spin 30,000 rpm will have the ability to make more torque than a motor with enough voltage to spin 25,000rpm. A motor that cannot spin faster than 20,000 rpm cannot apply any torque at 20,000 rpm. This is the nature of how permanent magnet motors work. If you are trying to compare two motors that top out at the same speed, however, it basically boils down to efficiency and resistance of the motor. So the motor with higher efficiency and typically lower terminal resistance will be the 'stronger' driving motor. This would be Pro handwound vs expert or sport. Or brushless vs brushed.

 

[Voodoobrew]

Is the higher torque on the 27T and 30T throught the full range, I ask because on a 55 turn motor at 500 rpms you are giving the motor more voltage to achieve the 500 rpm then the 27t motor. so at 500 rpms which one has more torque? Since the 80turn has more voltage.

 

[JohnRobHolmes]

Through the full range, yes. Torque is made by amps and not directly tied to voltage input.

 

[Hydrocarbon92]

Peak torque is very misleading because it's power that moves you. Torque is per-turn of the armature, power is force per second. If you can get a higher-rpm motor with a higher watt rating and gear it down enough, it will have the same wheel speed as a high-turn motor but a lot more power.

Here's a pic I made of two low & high turn motors' dyno plots. When geared for the same wheel speed, the "high torque" motor just looks pathetic (pink/red humps). Both are the same physical size & same voltage.

 

[JohnRobHolmes]

Your graph supports the notion that slower motors do not produce more torque, but less in most situations.

 

[Voodoobrew]

Can you please label which motor is which, on the graph, with out proper labeling graphs are not very useful. I would assume since you said low & high turn then (pink/red humps) low turns are the pink humps and high turns are the red humps. So maybe all the lighter ones are the high turn motors?


And I dont think all the power will do a dang bit of good, if you dont have the torque to turn the tire. This will turn all that power into heat instead of rotating force. Which is where I feel I am at.

to me it looks like higher turn motors produce more torque up to 12000rpm and use less power to do it.

 

[Hydrocarbon92]

The brown/orange slanted lines are torque, the higher is the low-rpm motor. The green lines are amps, the line that drops lowest is the low-rpm motor. The two red/pink humps are horsepower (actually Watts), the higher is the high-rpm motor. That's the actual power applied to the dyno's hub.

Your graph supports the notion that slower motors do not produce more torque, but less in most situations.

How so?

The slanted lines that start on the upper left are the torque numbers. The graph shows the slow motor DOES make more - 60% more. Since horsepower is torque created in a unit of time, that 160% figure is divided by 3.

Think of it this way, would you rather have one pint or 3 cans of beer? (It's actually more like 2 pints vs 8 cans)

Torque spins the motor, but power moves the truck.

 

[Hydrocarbon92]

Can you please label which motor is which, on the graph

I didn't originally label them since it was for my own curiosity. The original tests used the same size motor cans and same test voltage. What this does NOT show is how the torque would be multiplied by the gearing. If the high-turn was a 1:1 gearing and the low-turn was 3:1 reduction, the dyno would read the same RPM for both but report 750 N-mm of torque for the low-turn motor. The power figure would remain as-is if we used that gear-reduced RPM figure & tripled torque values.

I don't have photoshop nor the original pics on this PC, so excuse the MSPaint-iness of this.

This lead me to go from a 45T motor to a 27T motor in my Wraith with a much smaller pinion - and gain both max speed AND low-speed power. I will not be using anything higher than 35T ever again, unless I'm severely limited by gearing or can use a crapload of voltage.

 

[Voodoobrew]

OK that's helpful and makes sense.

 

[JohnRobHolmes]

Ah, I had the torque backwards. The telling point of why the low turn motor is not producing more torque is that the amps are not high enough to support it. A motor that has 3x higher Kv needs 3x the phase amps for the same torque at the shaft. Going with such different motors is bound to run into equipment limitations. Assuming the battery and ESC will handle the amps (like it can in a crawler), the faster motor will produce more torque. If we go to something like a 45t and 35t motor, or 2200 and 2700kv motor, the faster motor will produce more torque at the shaft.

Here is what happens when you aren't hitting equipment limitations. Faster motor produces more torque, more power, more RPM, more everything until something saturates. System A is a 7 turn, system B is a 5 turn.

 

[Hydrocarbon92]

Thanks for the graph, I wasn't able to find any decent brushless examples. Mine was 2 brushed motors if anyone is confused. Imagine what torque would look like if you geared the higher-KV brushless down to simulate same wheel speed.

I think the main thing to consider is lower KV is really only better if you can pump more volts thru it for a similar max RPM. Or if you can't gear it down enough for a decent minimum speed.