25 replies to this topic

[Shruska55]

To expand the question stated in the title of this post: When I buy a new motor, the manufacturer generally provides the RPM of the motor, but little else. How to I determine a starting point gear ratio for any given motor I wish to install?

 

I understand how to calculate the gear ratio: Crown/Spur / Pinion Size. Rollout is Ratio / Tire Diameter. e.g. 38/11=3.455 Gear Ratio. 3.455/.790=4.37 Rollout.  My issue is how to choose where to start?

 

Like many, many racers, I do not have a local track. The closest raceway is 2 hours away and the programs run there are limited to several commonly used motors throughout the slot world. The JK Hawk 7 and Retro 7, MA 605 Eagle and 606 Retro Eagle the the retired ProSlot PS4002FK. It's a good crew and when I ask the other racers for help, they gladly provide it. However, when stepping outside of the gear options run at the raceway,  blank stares are my answers. Most focus on setting up cars for the classes raced there.

 

Because I'm approaching this not just as a racer, but as a hobbyist, I want to build one-off cars to experiment (read play) with and possibly promote as a class at the raceway. I do not have a track in my backyard (yet!) on which to have unlimited time to experiment using trial and error methods. As I've said, the platform is currently 2 hours away which limits my available options. Even assuming a limited number of common gear/pinion size choice options, there are still lots of combinations to choose from given a pinion range off 6-16 and Crown/Spurs from 26-45T.

 

With the assumption that T&E may be the only way in the end, is there a reasonable method for determining a starting point gear ratio for any given random motor? I guess, perhaps my question is how to baseline a motor without a bunch of expensive tools.

 

Thanks,

Scott

[slotcarone]

My suggestion is to use a motor that is already being used at that track and gear accordingly.

[Phil Smith]

Yes, just ask someone at you track. That's what I always did.

[MSwiss]

For running odd cars, you either have to use info on the particular motor, if it is already used on that track, and compensate for the weight, downforce, and tire size of the "new" car.

 

I don't see how you can just pull a ratio out of a hat.

 

Tracks have different voltages, wiring, traction level, etc.

 

Slot car racing is testing.

 

Guys ask me all the time on gear ratio's for drag cars.

 

There is so many variables, it's impossible to give them a concrete answer.

 

Guys want to slot race, but it seems like they always want a short cut.

[Bill Seitz]

Scott's not asking for "THE" ratio to race with, but something in the ballpark to start testing with and at least not blow it up. I don't know of any magic formula, just years of experience and a calculating mind to fill in between the data points.

[MSwiss]

I explained how (if you know something about the motor)

If you don't, you have to guess.(4-1, 3-1, whatever)

There is no at home or bench method.

Unless it's some oddball motor, you can post the question on Slotblog or Facebook and somebody will give you some sort of idea.

[Shruska55]

Mike,

 

I explained how (if you know something about the motor)

If you don't, you have to guess.

There is no at home or bench method.

Unless it's some oddball motor, you can post the question on Slotblog or Facebook and somebody will give you some sort of idea.

Mike,

 

My premise was that I don't know anything about a specific motor and that I wanted to buy one and experiment (read Play) with it in a one off project car.Whatever that motor might be, it would be one that I nor anyone at my distant raceway has experience with.  I happen to have a bit of disposable income that allows me to take a flyer on some gear to build an experimental car from which I can learn more about this wonderful hobby I've found again after 50 years.

 

ProSlot has a nice gear and rollout range for the PS-4002FK on the package. It gives a starting point to test. It would be helpful if all manufacturers were to put a starting point gear ratio range, if not a rollout as well, on their labels such as the 4002r had.. 

 

I understand that there are an extraordinary number of variables compounded by just the voltage level run at each King in the country. The motor will respond differently at each just on that point alone. As I also said, I'm trying to fill a 50 year gap in knowledge. I perhaps naively thought that the collective 10,000 years of experience here on Slotblog might be able to point me in a direction. That's all, I was looking for, Mike.

 

My premise also stated I wanted to experiment (read play) with an unknown motor. We don't use the CR-106 in Texas. However, thanks to you and all the others using that item, there is a ton of information available as a starting point for it if I should want to use it in a project car that doesn't have the word Retro prefacing it.

 

Further, I have zero experience with current 16D motors and no where in my local/regional slot world does anyone race hard body stock cars or have an interest in doing so that I know of. That doesn't preclude me from building and running laps with a project car in the off chance I may be traveling on holiday to an area which does race that class.

 

It's a hobby for goodness sakes. Hobbies are about exploring and the joy of discovery. At least to me.

 

So, I thank Bill S for his comments about trying to discover a starting point from which to experiment and test. He got what I was asking.

 

All the best for a wonderful and peaceful Thanksgiving.

 

Stay Healthy everyone!

 

[MSwiss]

What am I missing here?

 

"Hobbies are about exploring and the joy of discovery."

You want to experiment, but you don't want to experiment.

If you don't want to pose the question to a large audience, where the chances are probably 99%, someone can give you a general starting point, just start conservative and keep going to a bigger pinion until the motor starts running hot.

[Mike Patterson]

Since nobody asked me, I'll throw in my 2 cents worth:

 

Start with the largest crown/spur gear that will pass tech. Use an 8 tooth pinion on the motor. Run the car. On a King track, I like the motor to peak just entering the bank. If your motor is peaking sooner than that, go to a 9 tooth pinion, later, a 10. Since King tracks are very similar, whatever gear combo you end up with should work anywhere. Similar tracks, like a hillclimb or King Cobra, should work out about the same. Simplistic? Sure, but I'm a simple person, and lazy, too.

[Shruska55]

Mike,

 

Thanks for the input. I don't have access to a King or Hillclimb near me, but the road course I usually run on over in Dallas, while flatter, has similar length straights. I can use your suggestions to develop my own baselining procedure.

 

I appreciate it.

[Shruska55]

Since nobody asked me, I'll throw in my 2 cents worth:

 

Start with the largest crown/spur gear that will pass tech. Use an 8 tooth pinion on the motor. Run the car. On a King track, I like the motor to peak just entering the bank. If your motor is peaking sooner than that, go to a 9 tooth pinion, later, a 10. Since King tracks are very similar, whatever gear combo you end up with should work anywhere. Similar tracks, like a hillclimb or King Cobra, should work out about the same. Simplistic? Sure, but I'm a simple person, and lazy, too.

 

Mike,

 

Let me ask some additional questions. I know you are an experienced slot racer. If I may ask then, what do you base those gear suggestions on? Motor RPM or some other motor spec or just your experiences?

 

Say I wanted to use a Mid-America Condor 16D motor. The link to MA's page shows no RPM or any specs for that matter. Nor does the printed catalog. Is there a general rule of thumb for motor types or is it based on your experiences with King and HIllclimb tracks and your years of experience? Or do I just have to know all about the Condor? which as a newbie, I don't. It it's based on experience, you may see my conundrum.I don't have your experiences and need a starting point. I have disposable income and can eat a few bent parts, but not everyone can. 

 

I just picked a motor with no specs. (My MA catalog was on my bench and I grabbed it so, this mea culpa, Roger, if you read this.) I'm certain there are others, though perhaps not many. I'd have a multi-day project with four hours travel round trip to my 'local' raceway to do the testing you suggest. I'm game. It's all part of the hobby.

 

I'm thinking of this as a prototyping exercise. I want to randomly pick a motor and build something around it. Not for competition, but for my own personal education. Also for fun, Who knows what might come of it. Create something new and exciting for the slot ecosystem to race around a track.

 

Thanks again!

 

Scott

[Pablo]

Maybe this will help, maybe not. When I make a custom car where the gearing is uncharted territory I always use the online Pro Slot gear chart. It calculates final drive ratio (FDR) in a format where you can see your pinion and spur/crown choices. The math is dirt simple and the formula is simply spur/crown teeth divided by pinion teeth, and that result (gear ratio) is then divided by wheel OD.

 

https://proslot.com/gear-chart/

 

I am currently building a vintage Ferrari 330 P4 car I will use as an example. I'm putting a Phoenix flexi motor into an inline Dynamic chassis. Why? Because it fits. The period correct motors that would be proper are almost all gone. The cans survived but the endbells were all ruined by cracking them with self-tapping mounting screws and hot rewound arms with weak magnets. Guilty as charged, just like the rest of us.

 

The locals in my area gear the Phoenix 13/33 with .720" OD rears on King tracks at up to 13+ volts with modern flexi chassis. So I use that info as a starting point. But my old style car is probably going to run on tighter tracks. 

 

So I compensate (guess) 12/33 vis. 13/33. Then I go to the chart. 33/12 = 2.75 gear ratio. 2.75/.72 = 3.8 FDR.

 

Now I change the OD setting to my desired wheel size which is 7/8" (.875"). The largest crown gear my car can use without extending below the chassis is about a 30t 48P. So I look at what pinion I need to duplicate my desired approx. FDR of 3.8, and a 9T will give me almost exactly that.

 

30/9 = 3.3. 3.3/.875 = 3.78 FDR. Close enough for a good smart starting point. The math is no mystery - the chart simply lays it out for you to visualize.

[Shruska55]

Pablo,

 

That helps quick a bit actually. I've used the PS chart for the PS product and have used it to adjust for OD and quick glance gear ratios on known motors. It also sounds like you are doing what I am trying to do: Build one off project cars. Your mission sounds like it's more for the fun of it given your experience and time in slots. That's the point where I wish to get to, but that lost 50 years weights heavily against me unless they invent a immortality serum.

 

Thanks for that tip.

 

All the best,

Scott

[Jay Guard]

[Pablo]

Funny but very true. Let's not forget a couple things Batman didn't mention:

1. That is for disposable motors only

2. After you cook one, back off one tooth on the pinion 

 

  

[Pablo]

Or maybe I should say, after you find the point where it runs too warm, back off one tooth.

[Mike Patterson]

Scott, listen to Jay. He's way more knowledgable about slot racing than I am!

[Shruska55]

Scott, listen to Jay. He's way more knowledgable about slot racing than I am!

Good advice, Mike. I certainly don't want to run afoul of the Black Knight!

[Mark Onofri]

But wait, there's more

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[Mark Onofri]

Wait for it

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[Mark Onofri]

I could get into a loooong lecture on the physical limitations and, the design criteria for gearing but, I don't think you would appreciate or, agree with that.

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[Mark Onofri]

Oh, credit where credit is due. The 1st obviously is from Front Line
The second one is from
Sonic.

[Mark Onofri]

Because I'm a big Slick 7 fan, I also agree with Jay. But, only if you're using Slick 7 gears. Hopefully, you'll also hear a Earth shattering kaboom (if you did it right)

[Shruska55]

Mark, there is certainly wealth of information above. I must say I'm both non-plussed and non-minued.

 

Non-Plussed:Your Post #19 - I love the information there. Plus, I bought a fiddle stick a couple of months ago. I wasn't quite sure what the tool was for, but it seemed cool just by the name and I'm a sucker for tools. That Front Line document explained what it for to me. So...That answered an unasked question! Cool!

 

Non-Minused: 1 From my OP - Like many, many racers, I do not have a local track. The closest raceway is 2 hours away and the programs run there are limited to several commonly used motors throughout the slot world. The JK Hawk 7 and Retro 7, MA 605 Eagle and 606 Retro Eagle the the retired ProSlot PS4002FK.

 

Non-Minused 2: From my Post #7: My premise was that I don't know anything about a specific motor and that I wanted to buy one and experiment (read Play) with it in a one off project car. Whatever that motor might be, it would be one that I nor anyone at my distant raceway has experience with.

 

I would give my left Almond to have the ability to use the advice in the first paragraph of your post #20. I've solved the mystery of the remainder of #20 and what's in Post #21. It's that dang starting point for when an Orphaned Motor is left on My Door Step. I don't know it's parentage. I'm not certain how tightly wound it might be. I want to nurture it and help it grow swift and daring. Achieve all it can in life. I don't want it to burn out early and sit, alone all day in a cold dark place or worse, be thrown on the ash pile of history. I want it to realize it's full potential! Be a winner, by golly! If only I knew where to start.....

 

The Non-Minused part(s) above are meant in jest.  Mark. I've seen some of your other posts and I believe you have a sense of humor, yes? I hope I don't hear an earth shattering boom of a different kind.

 

BTW: I'm serious about the fiddle stick. I've have had one on my tool wall and I stare at it daily figuring I'll Google its use one day. Now I don't have too. Thank you.

 

All the best,

Scott

[Bill from NH]

Scott, Fiddle Stick use has been controversial, depending on who you talk to. I've used one since the early 70s without concerns & they are useful when re-tensioning springs. These were first available from John Thorp when he sold brass ones. If you end up with more than one Fiddle Stick, expect each to give its own reading. I'll have to look at Mark's Frontline sheet.