30 replies to this topic

[dalek]

I'm posting a rollout chart in a format that I recently saw that seems to be easier to use than the previous layout that I had made for myself.

 

That previous layout had rollouts in the LH column whereas the layout attached below has pinions and spurs in the LH columns and has tire diameters as the top row.

 

The attached chart is what I feel is appropriate for flexis and running 64 pitch gears.

Edit:  Added a chart for Retro gearing and tire diameters.

 

If anyone wants a chart with different variables (pinions, spurs/crowns, tire diameters) you can download and modify the attached xls file or I can make the chart for you.

 

Note:  It isn't a lot of work for me to modify the chart b/c all I have to do is change the variables (the two LH columns and/or the top row).  All of the other cells in the chart update automatically.

 

 GEARING--TIRE DIAM. Rollout Chart, Flexi 64p, 10-15,32-39,680-800-010.pdf   439.49KB   73 downloads

 GEARING--TIRE DIAM. Rollout Chart, Flexi 64p, 10-15,32-39,680-800-010.xls   39KB   54 downloads

 

 

______________________________________________________________________

 

The following chart was requested for typical retro 48 pitch gearing and tire diameters:  

 GEARING--TIRE DIAM. Rollout Chart, Retro 48p, 08-14,26-29,790-850-005.pdf   426.78KB   46 downloads

 GEARING--TIRE DIAM. Rollout Chart, Retro 48p, 08-14,26-29,790-850-005.xls   35KB   28 downloads

 

 

[Jay Guard]

Hey Dale:

Great looking charts but how about making one for us Retro guys?  48P Pinion gear sizes would be between 8 and 14, Crown gears between 26 and 29.   Maybe make the tire sizes from .790" to .850" in .005" increments.

[dalek]

 

Hey Dale:

Great looking charts but how about making one for us Retro guys?  48P Pinion gear sizes would be between 8 and 14, Crown gears between 26 and 29.   Maybe make the tire sizes from .790" to .850" in .005" increments.

 

 

I posted the chart in post #1. 

Note:  For simplicity, I didn't change "spur" to "crown"

[Jay Guard]

Dale: Looks great, thanks!

[Mark Onofri]

Can't thank you enough! You save me countless hours and a lot of (my limited) mental capacity! Are 72 & 80 pitch coming in the future?

[dalek]

Can't thank you enough! You save me countless hours and a lot of (my limited) mental capacity! Are 72 & 80 pitch coming in the future?

 

In regard to 72 pitch, the pinions with 2.0 mm bore (typical flexi motor shafts), listed on Eagle Distributing, run from 7 to 15 teeth.  Spur gears run from 37 to 44 teeth.

 

However, the pinions from 10 to 15T give rollouts typical for flexis with .680 to .800 tires so that's the chart that seems to make the most sense (image below).

 

Before I post the PDF and XLS files, does anyone feel that the chart gears and/or tire diameters should be modified in order to better fit actual usage that I'm not aware of?

[Mark Onofri]

Not a complaint but a suggestion. We're running 15/35-36 with.775-.790. The chart stops just short.

[Jay Guard]

Mark, the runout you are asking for is in the first chart in this thread.

[dalek]

Here are the chart PDF and XLS files for gears available in 72 pitch.

 

Note:  Also see the charts in post #1 if this chart doesn't have the pinion, spur and tire diameter that you're looking for.

 

 GEARING--TIRE DIAM. Rollout Chart, Flexi 72p, 10-15,37-44,680-800-010r1.pdf   440.77KB   8 downloads

 GEARING--TIRE DIAM. Rollout Chart, Flexi 72p, 10-15,37-44,680-800-010r1.xls   39.5KB   6 downloads

 

[dalek]

Not a complaint but a suggestion. We're running 15/35-36 with.775-.790. The chart stops just short.

 

Hi Mark,

 

As Jay posted, it might be best if you just used the first chart in post #1 rather than me adding four more lines (for spurs 35, 36, 37 and 38) for the 15T pinion.  The chart would print out smaller.

 

FWIW, I'm not totally surprised that there are 35 and 36T 72P spurs out there but I didn't put them anywhere on the 72P chart because when I checked Eagle Distributing to see what 72P gears are available, they didn't list anything smaller than 37.

[Shruska55]

Thanks for the great tool. My phone calculator practically burns up when I get to figuring rollouts. This At-s-Glance is really helpful!

 

Scott

[Mark Onofri]

Jay,Dalek,just saw it, I mistakenly thought it was for 48p.
And, ALL the charts are very much appreciated. I've been waiting for years to prove or disprove what another very fast racer told me years ago. I believe it was " for every .00 you decrease in diameter, you add a tooth to the spur" I think that was it, well,it should be easy enough to figure out now,I hope?
Don't you wish you had the time to do everything you want/wanted to? If your lucky enough to get the time, it's a 50/50 shot of remembering it or , still wanting to do it!!!

[Mark Onofri]

48P 10/35/.800
64P 8/28/.800.
72P 12/48/.800
All will give you a
4:38 final drive ratio. However, they will not all preform the same. I hope that with these charts in front of people, they can see the difference. It makes me laugh and also, want to race people who think that the higher the pitch, the smooter they'll run. Of the numerous reasons for gears, these are the ones, IMO, that are important:
1) convert the given input to the desired output
2) maximize the life/productivity of the machine
3) attain the desired TIME per unit of output with the available amount of input and also,refer to the first three (3)

[Mark Onofri]

Jay, it kinda pales in comparison to the magnet explanation on the Slick 7 site but, I don't want to get beat up and my lunch money taken away by getting into it any deeper.

[MSwiss]

You must of meant 12-42.

And your post should read;

48P 8/28/.800
64P 10/35/.800
72P 12/42/.800

I doubt you'll find a 64P 28 tooth gear

[Dave Crevie]

Actually, gear ratios have nothing to do with gear pitch. A 10/30 pinion to spur/crown in 48 pitch is the same as 10/30 in 64 pitch, 3 to 1. Where pitch matters is when you want fractional gear ratios. i.e., ratios that have decimals in them. You can get 3.16 to 1 with 64 pitch gears, you can only get 3.10 or 3.2 in 48 pitch. (not without going with a bigger crown/spur than the rear tire diameter.)

[team burrito]

speaking about rollouts, i've been having this argument about same size gears. the argument is a company makes 8, 9,10, 11, 12 tooth pinions that fit the spur gear without moving the motor. i said it doesn't change anything because the circumpolar ratio remains the same - am i correct?

[MSwiss]

No.

[team burrito]

if the diameter remains the same for both gears, nothing really changes, does it?

somebody posted an example of those gears; all of them are 5.5mm diameter.

[Eddie Fleming]

if the diameter remains the same for both gears, nothing really changes, does it?

That is not the way it works.

 

Mike's post above explained it perfectly. 

 

If they were friction drive you would be correct.

[Dave Crevie]

The photos of those pinions (probably Slot-it) show exactly how they get away from changing arm shaft to axle distance to change ratios. They cheat on the gear tooth profile. While the pinion at the left appears to have true tooth profiles, you can see that the manufacturer of the three pinions to the right have different tooth profiles. The teeth are "scrunched" together so that they can get more teeth inside the same outside diameter. The gear mesh is not correct, but just like the Parma crown gears don't have a proper tooth profile, they sorta work so everyone keeps using them. 

 

Those of you old enough to have raced Cox sidewinders should remember that to change gear ratios, you had to change both the pinion and the spur.

[Mark Onofri]

Dave, I'm willing to bet you have a copy of "The Machinest Handbook" in almost every room of your house! Good eye on the root depth.
Mike, it's dyslexia.
I'm going to stay out of the pitch debating, it seems to get heated.

[Dave Crevie]

Mark; I do have most of the updated printings of the "Handbook", but actually I relied more on the Society of Manufacturing Engineers publications for my work. They cover every single aspect of designing, making and theory of producing stuff. Plus, as part of my work, I often had to design and build gear drives, so I have a fair amount of gear knowledge. You might find some of the SME publications useful. Just Google SME-books. If you don't want to spend the money on "the Big Book" , each of the chapters are available as individual books, and even E-books if you are trying to save a few bucks. I suggest you try;

 

                               Manufacturing Processes and Materials. (the Big Book) I think I payed around $500.00 for my second edition about 30

                                                                                                 years ago.

 

                               Manufacturing Processes and Fundimentals. Essentially the first several chapters of the big book. 

 

                               Geometric Dementioning and Tolerancing. Addendum to the big book.

                          

                               Gear Hobbing, Shaping and Shaving. How to make metal gears.

 

                               Plastic Injection Molding Processes and Fundimentals. How to mold plastic gears.

 

The SME invests a lot of time and money on educating aspiring manufacturing engineers, and particularly machining processes for up and coming machinists. They are very detail oriented. 

[Mark Onofri]

Thanks Dave, I can never have enough books on the subject.
Did I misinterpret the basic theory ? The higher the torque/load , the larger the tooth? For example,if you have a high torque motor,48p. High rpm, 64+ pitch.

[Dave Crevie]

It actually depends on the diameter of the gears. For slot racing, with small gears, you want finer teeth so you have more in contact with one another. And for two basic reasons. You like to spread the tooth loading over more teeth. Plus you have better entrance and exit angles on the teeth. 

 

In this drawing, you can see there is minimal contact between the teeth where they mesh;

 

 

in this drawing of a finer gear pitch you can see that there is more contact between the teeth where they mesh;

 

 

As part of this improved total contact, as the gears turn, the angle between the first point of contact between the teeth and the last point of contact increases with the finer gear pitch. In the two drawings, the pressure angle has also changed from 27 degrees to 31 degrees. The wider the pressure angle, the duration the teeth are in contact and bearing load, the more load the gears can handle.

 

Anyway, that is as simple as I can explain it. Maybe it helps.