18 replies to this topic

[lucky77]

Hi All, 

 

As many of you are probably well aware, ProSlot suggests an"overall gear ratio of 3.25 to 3.75 or to a "rollout" ratio of 4.25 to 4.50 "on their website for the 4002FK. Am I missing something? These ratios blow my mind. I've been running them with, say, .750 tires, @ 9/29 = 2.42 rollout ratio. To achieve their suggested rollout range with a 4.33, I'd have to run a 9/52 with the same tire size.

 

What gives?

 

Thanks in advance,

CJK

[John Streisguth]

I think you're multiplying by the tire diameter when you should be dividing

[lucky77]

I was using this roll-out ratio chart ... http://www.shoppscr....atio-chart.html

[MSwiss]

Try using this gear ratio/roll out chart.

 

http://proslot.com/g...?tiresize1=.750

 

This one produces results that make sense.

[lucky77]

Thanks, Mike and John -- it appears as though, as John said, the chart I was referencing multiplies by the tire diameter instead of divides. I'm surprised the chart is still linked to their site and in use. Thank you both!

 

CJK

[Fast Freddie]

What Proslot says is a gear ratio "OR" a rollout ratio.  Doing only one or the other might not yield the results your looking for.  I make every attempt to get both ratios within the Proslot parameters.  You might be surprised in the results you get.

[Racer36]

Couldn't find a math teacher at work to help you with that one Chuckles? Lol

[DOCinCanton]

In a recent 1 hour race, I ran a 12 on a 38 with 0.73" dia tires. I think that that works out to be a roll out ratio of 4.22. This is about as agressive as I want to go.

[Zippity]

Should the calculations be any different for angle winders?

 

I run 12/37 with .640" rubber on my Champion Turbo Flex LMP car.

 

According to Swiss' link, that gives me a ratio of 4.82 

 

The car goes better with .625" rubber - a ratio of 4.93

 

Is it just a matter of horses for courses?

[lucky77]

Precisely, Dennis! That's why I'm a school counselor and not a math teacher. :]

[lucky77]

So here's a question:

 

What would you say is a minimum and maximum rollout ratio for all of the classes of cars we race? 3.6 - Zippity's 4.93 (which is the highest I've ever heard of)? I ask because I'm working with an engineer who is building me a motor and chassis dyno, and he needs to know the range for the chassis dyno setup.

 

Thanks!,

CJK

[Samiam]

Track design will dictate the numbers as well as car weight. On a banked track with a light car you can run lower numbers than with heavy cars on flat tracks.

[lucky77]

Thanks Samiam -- yes, I am aware. I'm looking for a range across our hobby (accounting for different classes, different tracks, different power, etc.).

[Racer36]

Chuck,
I was at 3.73 at Fantasy and the car was pretty darn good.

[Les Boyd]

So here's a question:
 
What would you say is a minimum and maximum rollout ratio for all of the classes of cars we race? 3.6 - Zippity's 4.93 (which is the highest I've ever heard of)? I ask because I'm working with an engineer who is building me a motor and chassis dyno, and he needs to know the range for the chassis dyno setup.
 
Thanks!,
CJK

They already have this where the track or class only allow one pinion, one crown or spur, and a minimum tire size. Like the FCR classes.

[lucky77]

They already have this where the track or class only allow one pinion, one crown or spur, and a minimum tire size. Like the FCR classes.

Thanks, Les -- I think I'm probably not being as clear as I should be. I'm looking for what we think is the total actual range of rollout ratio across our entire hobby ... not specific to one class or one track. Like, if were were take every 1/24 scale car in the US and look for the low and high-end extreme of rollout ratio, what would they be?

[MSwiss]

If I understand this right, you are hoping this dyno will measure and give you useful results for every slot car application.

 

I don't see how that is realistic, especially when racers will tell you a motor in one type of car, will run great, but will be mediocre in another.

 

Or a motor at one track will run great, but will be mediocre at another.

 

I spent 19 years at Koford Eng., a fair amount of them, watching Stu get frustrated by dyno results and finally giving up on it for slot car applications.

 

I know that won't deter you or your engineer friend, but I think something more realistic would be to be able to tell with 98% certainty, how a certain type of SKU will run in a certain car at a certain track.

 

IOW, take 10-4002FK's, try them in the same car at the same time at the same track, get results, grade them 1-10, and have the engineer build a dyno that will garner the same 1-10 order.

[lucky77]

If I understand this right, you are hoping this dyno will measure and give you useful results for every slot car application.

 

I don't see how that is realistic, especially when racers will tell you a motor in one type of car, will run great, but will be mediocre in another.

 

Or a motor at one track will run great, but will be mediocre at another.

 

I spent 19 years at Koford Eng., a fair amount of them, watching Stu get frustrated by dyno results and finally giving up on it for slot car applications.

 

I know that won't deter you or your engineer friend, but I think something more realistic would be to be able to tell with 98% certainty, how a certain type of SKU will run in a certain car at a certain track.

 

IOW, take 10-4002FK's, try them in the same car at the same time at the same track, get results, grade them 1-10, and have the engineer build a dyno that will garner the same 1-10 order.

 

Hi Mike,

 

No, not necessarily every slot car application. Just a highly refined instrument to help take some of the guess work out of the process. This particular dyno uses a hysteresis brake (similar to the $27,500 one sold by Magtrol) and will acurately measure 5 points of data across the full RPM range (exclusing any RPMs near stall to prevent overheating) including: 1) Motor Efficiency, 2) Mechanical power, 3) Electrical power, 4) RPM, and 5) Torque. My hope is that, like I said, it will take some guess work out of the process (and prevent a lot of soldering and unsoldering to find out) -- especially when you have two motors that are almost identical. And, hopefully, with some use, I can get good enough to use the motor efficiency data to help predict how a motor might perform on one track versus another. 

[MSwiss]

One the problems is you have the below scenario, recounted by top racer Will Brinkley , in a recent thread about breaking in motors.

"Here is the kicker though. My slowest motor at the Fall Brawl (lower voltage track I think) was the absolute best motor at the R4 (higher voltage track). It was a screamer too."

Each time you go to a new track, you'll still have to try every motor, if it's important to you that you have the absolute fastest motor, that you own, in your car that particular day.

As far as avoiding soldering motors in and out, I suggested to another racer, who trying to avoid applying heat to them, as much as possible, make a test car with a screw in motor bracket.

While I wouldn't race a 64p/72p gear/anglewinder style car,without soldering the motor in, for testing motors, it's probably fine.