Higher pinions = safer MMM's? Or no? Someone's lying....

[snellemin]

Originally Posted by BrianG

I suppose, but it's really no more difficult than wiring up battery connectors and wiring.

You'll be amazed at how many people are incapable of doing such a thing.

[J57ltr]

And judging by the bad solder jobs I see on here I would say that most would be better off buying the premade items.

For the BEC I am building it cost me $7 for 20 TVS's shipped, Didn't have to pay for the fuses since I needed them for a work project. Gotta love Swiss Navy Projects.

Jeff

[lutach]

Wow, Novak. I should start having them made with either 2 or 4 small caps (The last one would make Novak's knee buckle and wouldn't be near what Novak charges).

[snellemin]

Lutach,

those with the 4 caps are still my Fav.

Good lord, whats with all the caps? And about my earlier post, it was about something else which im over now so just nevermind me

[RC-Monster Mike]

It conclusively answers the question - read it again:
The question was weather higher gearing with larger pinions = death to ESC's
The conclusive answer:
In 99% of the cases, that is exactly true. Smaller pinion = less ESC stress.


While your back EMF question may be a point of confusion for you, Freezebyte's questions was conclusively answered. Smaller pinions = less ESC stress.

Regarding the higher rpms with a lower pinion yielding higher back EMF - not sure I buy it. On a given voltage, the rpms of a given kv motor will be the same, regardless of the pinion installed on the motor shaft. If braking from a given vehicle speed - yes, the smaller pinion will have had to be rotating faster(if everything else emains the same) to achieve the speed, but the mechanical advantage of the smaller pinion is still there on decel as it is on accel, so less torque on the motor shaft proportional to the increased speed(less motor current to achieve the higher rpms and vehicle speed and less "reverse current" to slow it). A 10 pound truck requires x amount of braking force to stop in x distance, regardless of how the force is applied(high rpms with high reduction or low rpms and low reduction). Force = force, doesn't it? The higher motor speed would result in a higher voltage spike at a lower current level - force would be the same. That is how i see it anyway. :)

[J57ltr]

Originally Posted by RC-Monster Mike

It conclusively answers the question - read it again:
The question was weather higher gearing with larger pinions = death to ESC's
The conclusive answer:
In 99% of the cases, that is exactly true. Smaller pinion = less ESC stress.


While your back EMF question may be a point of confusion for you, Freezebyte's questions was conclusively answered. Smaller pinions = less ESC stress.

Regarding the higher rpms with a lower pinion yielding higher back EMF - not sure I buy it. On a given voltage, the rpms of a given kv motor will be the same, regardless of the pinion installed on the motor shaft. If braking from a given vehicle speed - yes, the smaller pinion will have had to be rotating faster(if everything else emains the same) to achieve the speed, but the mechanical advantage of the smaller pinion is still there on decel as it is on accel, so less "force" on the motor shaft proportional to the increased speed(less motor current to achieve the higher rpms and vehicle speed and less "reverse current" to slow it). A 10 pound truck requires x amount of braking force to stop in x distance, regardless of how the force is applied(high rpms with high reduction or low rpms and low reduction). Force = force, doesn't it?

"the mechanical advantage of the smaller pinion is still there on decel as it is on accel, so less "force" on the motor shaft proportional to the increased speed"

The mechanical advantage is higher on the motor during braking with a smaller pinion so there is more force (energy) being generated during a stop. Think about this, I don't know if you have ever push started a manual transmission but you don't do it in first gear you do in in second. the reason is that in first this has the numerically highest gear ratio and is very hard to get started. Why? Because the load is super high when you pop the clutch (slam on the brakes in RC). You are basically swapping the gear ratio when you are braking, this is what I am asking. Could this be a part of the problem (ya, ya the batteries).

We are not talking about controlled enviroments here these things are being handled (put under stress) by a lot of people that don't have a clue, they are in every hobby, it's just the way it is. No one is doing a test where they are topping the truck out and comming to a marker, applying maximum (impending lockup)breaking force recording the results and doing the same for the other pinion and calculating what they need to stop in the same difference. I haven't put the math to but I see your point. But I also see that there a difference, a force over time difference.

Besides as I see it since Patrick quoted me it was a response to me and not Freezebyte.

Jeff

Very nice discussion guys! Some of you are definently more in the know about circuitry design then I ever was, hence why I had to drop out of electronics design in college, my brain hurted

[JThiessen]

Originally Posted by Freezebyte

Very nice discussion guys! Some of you are definently more in the know about circuitry design then I ever was, hence why I had to drop out of electronics design in college, my brain hurted

They have an electrical class there? I thought all ya had was painting, basket weaving, and wool fashion design.....
[IMG][/IMG]

Originally Posted by JThiessen

They have an electrical class there? I thought all ya had was painting, basket weaving, and wool fashion design.....

Smart ass....

[JThiessen]

Originally Posted by Freezebyte

Smart ass....

Yuk....yuk....! I've got another pic for ya, but they have Photobucket blocked at work.....I'll post it up tonight.

Edit....I think I'm gonna save my other pic for Nov 21st...just in case....

[RC-Monster Mike]

I think your push start analogy is not proper(you are mixing up the motor and the load here). The gear ratio does not reverse when braking - only the direction of the force reverses.
A better analogy or perhaps more clear idea of how this is working is using a 10 speed bike. If you had superior balance, you could roll the bike backwards in 10th gear and try to stop it by pedaling forward(this would simulate a large pinion or low reduction). Then try again with the bike in 1st gear(to simulate a small pinion). At a given vehicle speed, the pedals will be moving faster in 1st gear(voltage), but will require less torque(current) to stop the bike and vise versa. The mechanical advantage or gearing does not change or reverse - only the direction of the force. The mechanical advantage that exists on acceleration also exists on deceleration.

And while Patrick was responding to you...he happened to answer Freezebyte's question - the question was still answered, though. :)

[J57ltr]

I don't know how my description is wrong other than not specifing any gear other than 1st.


Well going from say a 14:1 to a 1:14,is a big difference, because you are spinning the motor with the wheels instead of spinning the wheels with the motor, so the motor spins faster with a smaller pinion with all other things being equal. This produces higher voltages that could possibly damage the ESC. The motor is acting as a generator at this time, and it's voltage is proprotional to it's RPM.

The question was:Higher pinions = safer MMM's? Or no? Someone's lying....

Jeff

I think I worded my title poorly, it probably should have been someones "misinformed" instead of lying

[RC-Monster Mike]

Originally Posted by J57ltr

I don't know how my description is wrong other than not specifing any gear other than 1st.


Well going from say a 14:1 to a 1:14,is a big difference, because you are spinning the motor with the wheels instead of spinning the wheels with the motor, so the motor spins faster with a smaller pinion with all other things being equal. This produces higher voltages that could possibly damage the ESC. The motor is acting as a generator at this time, and it's voltage is proprotional to it's RPM.

The question was:Higher pinions = safer MMM's? Or no? Someone's lying....

Jeff

OK. Lets try this again. In your push start analogy, your scenario proves my point rather than yours. The gear ratio doesn't work in reverse as you are trying to illustrate. In your example, the engine compression represents a constant braking force if you will(force used to slow the vehicle). This braking force is STRONGER in 1st gear due to the mechanical advantage. At the SAME BRAKING FORCE represented by the engine compression, the lower gear(more reduction or smaller pinion if you will) more easily slows the vehicle - this is why you select a higher gear to start the car(higher pinion if you will). The car engine represents the motor in this case - not you trying to push the vehicle(this represents the inertia we are trying to slow). The engine (which is simulating the motor)has the mechanical advantage.

Now, I think I see what you are trying to say - higher motor rpms will deliver higher voltage . You could take the stance that a higher voltage can damage a component, which is later destroyed by current, which has been mentioned in this thread. While this statement is true, it simply is not applicable in this scenario. The motor rpm doesn't change simply by installing a different pinion.
Your very theory is an impossibility in actual practical use. If using a 2200Kv motor on 6s, the motor rpms will be the same when driven by the end user regardless of the pinion selected. Therefore, the motor speed when brakes are applied will also be the same. Yes, the truck speed will be different, but that isn't the point. The motor Kv is a constant. 2200Kv at 22 volts yields 48400 motor rpms with any pinion or no pinion at all. Unless you are suggesting that it is dangerous to quickly change to a smaller pinion immediately before you try to slow the vehicle? Nobody would argue the dangers of this actvity, but how do you do this?!
The motor does not know what gear is installed onto it. At any given voltage, the motor rpm does not change with the pinion. For this reason, the very premise of your theory is an impossibility. With a given battery and a given motor, the gearing does not impact the motor speed(aside from loading that may lower input voltage and therefore motor rpms, but this is another discussion altogether). The 'force' required to stop the vehicle is different with different gearing(ratios, mass, etc. all come into play), but at a given voltage in practical use, the motor rpms do not change by simply installing a different pinion, which is the very premise of your thought.
I think you may be too smart for your own good.

Lets all just walk away with the knowledge that better batteries and lower gearing most often leads to successful funtime with our brushless cars and trucks. :)