Lets talk about motors
#31
People speak (or type) of smooth motor or ESC combinations. im trying to understand smooth. Or in this case ROUGH.
is it low RPM bumpiness or cogging?
is it a hot spot or a dead spot where acceleration doesnt feel linear with the slope before or after the bump?
Is it the transition from 1 velocity to another with the trigger?
is it low RPM bumpiness or cogging?
is it a hot spot or a dead spot where acceleration doesnt feel linear with the slope before or after the bump?
Is it the transition from 1 velocity to another with the trigger?
Many also talk about smoothness in a much more subjective sense. The subjectivity is difficult to articulate because it cannot be described by symptoms. In order to fully grasp "smooth" versus "really smooth" you need to try piloting a 12th scale mod that can backflip at will or a mod TC that can spin all four tires an entire 100' straight.
#32
Tech Champion
iTrader: (33)
At the club in my area, the owner decided to allow the Trinity Punisher which is not ROAR approved, it's a cheap stock spec motor that costs half as much as most "team edition" motors and goes just as fast, if not faster than most "team motors" that are not available to the public. This helped level the playing field and reduce costs for spec racing. Fortunately, the turf track in my area is technical enough that the lap times between stock and mod are comparable enough that driver skill trumps motor in most cases.
#33
When people talk of sensorless combos cogging is the most common word thrown around. This can describe stuttering when starting from a stop, or jumping backwards briefly, as well as hestation and/or surging when trying to work fine throttle inputs. I only race so I can't really comment on how much this is still an issue with modern sensorless setups.
Many also talk about smoothness in a much more subjective sense. The subjectivity is difficult to articulate because it cannot be described by symptoms. In order to fully grasp "smooth" versus "really smooth" you need to try piloting a 12th scale mod that can backflip at will or a mod TC that can spin all four tires an entire 100' straight.
Many also talk about smoothness in a much more subjective sense. The subjectivity is difficult to articulate because it cannot be described by symptoms. In order to fully grasp "smooth" versus "really smooth" you need to try piloting a 12th scale mod that can backflip at will or a mod TC that can spin all four tires an entire 100' straight.
I should calculate inertia mismatch and see where i sit.
does one type of rotor tend to have more mid to max rpm roughness? Or looking at it down wind from the motor a high or low FDR? Or heavy light vehicle?
#34
Did Bert get a new handle?
#36
R/C Tech Elite Member
iTrader: (7)
I may move to 12th. i said I wouldnt buy more than 1 TC or 1 motor or...
I should calculate inertia mismatch and see where i sit.
does one type of rotor tend to have more mid to max rpm roughness? Or looking at it down wind from the motor a high or low FDR? Or heavy light vehicle?
#37
great analogy.
Maybe I can provide some brain juice.
If you have a big motor in a tiny car it will accelerate like a bat out of hell from 0 to 30000 rpm. If its linear across the entire rpm it probably an inertia thing to fix with mass or gearing. The opposite is true as well but still linear.
I would say that rotor inertia, gearing, and mass can resolve 80% of smoothness.
timing efficiency at each specific rpm takes care of most of the rest.
you can have both problems and they compound.
Maybe I can provide some brain juice.
If you have a big motor in a tiny car it will accelerate like a bat out of hell from 0 to 30000 rpm. If its linear across the entire rpm it probably an inertia thing to fix with mass or gearing. The opposite is true as well but still linear.
I would say that rotor inertia, gearing, and mass can resolve 80% of smoothness.
timing efficiency at each specific rpm takes care of most of the rest.
you can have both problems and they compound.
#39
Do you think the manufacturing process is held tight enough to keep the physics close enough? These rotors are probably somewhere around 30 gmcm^2. If you want punchy I would think you want 10:1 mismatch and closer to 30:1 for ultra glide smooth.
#40
i just got this. stumbled on a post and then looked further in. I’m pretty sure im not Bert. From what i read he is describing something that is extremely described already if you know where to look. I dont know his history or background but he is describing in pieces and parts inertia mismatch without the math and support, Im not here to pick a side but if you or he were looking for a google search I would try something like “servo positioning inertia mismatch ratio”. even the search string probably feels a little alien but it applies to any electric motor performing torque,velocity, or positioning which is really at the core of all of the motion control of an RC vehicle. i have found it impossible to find the suggested ratios after understanding the science but 60:1,30:1, and 10:1 in that order has worked on at least a few 1000 I have sized.
#41
Tech Champion
iTrader: (1)
Im guessing someone thought about rotor mass. im just convinced they had to assume it was going to be driving a system that had mass and friction limits. A small change in inertia is a massive difference in feel. Acceleration takes 2, 3, 4 times the continuous current capability of a motor so acceleration and deceleration is where all the physics are at.
Do you think the manufacturing process is held tight enough to keep the physics close enough? These rotors are probably somewhere around 30 gmcm^2. If you want punchy I would think you want 10:1 mismatch and closer to 30:1 for ultra glide smooth.
Boutique motor manufacturers put that much thought into their motor design (skewed winding slots, optimized winding patterns, skewed magnetization of the rotors, tuned air gaps, etc.), but the big brands don't. That level of optimization is not cost-effective. Unlike commodity products like washing machines or water pumps or HVAC blowers, which are manufactured by the tens of thousands and all held to the same specifications, RC cars are made in small numbers and every owner wants slightly different performance.
The big RC brands just buy motors in bulk from the same factories that make motors for all other types of small devices, with generic "good enough" specifications. Energy-efficiency is not a primary concern in RC, except in some especially-competitive racing niches. Most people just deal with laggy motors by using higher-voltage batteries to shove more amps through their motors. Even people who pay attention to torque curves and throttle response just tweak the settings in the ESC to get the motor to run the way they want, rather than hunting around for a motor perfectly-optimized for their needs. It's simply easier to deal with the concerns you're mentioning by adjusting software settings rather than replacing hardware, even though it's less energy-efficient.
The big RC brands just buy motors in bulk from the same factories that make motors for all other types of small devices, with generic "good enough" specifications. Energy-efficiency is not a primary concern in RC, except in some especially-competitive racing niches. Most people just deal with laggy motors by using higher-voltage batteries to shove more amps through their motors. Even people who pay attention to torque curves and throttle response just tweak the settings in the ESC to get the motor to run the way they want, rather than hunting around for a motor perfectly-optimized for their needs. It's simply easier to deal with the concerns you're mentioning by adjusting software settings rather than replacing hardware, even though it's less energy-efficient.
Of course, this is a hobby, so if you want to track down the perfect 36mm-diameter motor for a car you're building, you can and should do so -- and then you should show-off the result of your hard work.
#43
looks like cool stuff but it would probably take a phone call. Allot of marketing stuff on the website.