Lotus 23 SALT - Printable Version

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Lotus 23 SALT - Ecurie Martini - 12th-Apr-20

SALT? – Scandinavian/American Lotus Tribute. Okay, that doesn’t help much so, expanding a little: in Carver’s Lotus IX thread on the SFI forum, the Lotus 23 was mentioned as a particularly challenging subject due to its diminutive size. I contributed to the wandering of the thread by suggesting a possible answer to that challenge and identifying a few additional challenges. Evidently, in some sort of time zone and distance insensitive fashion the same idea occurred to both Carver and me. After some further discussions we have agreed to embark on a joint project wherein I will look to the ironmongery and he will employ his artistry in creating the coach work. This thread will chronicle the outcomes of that collaboration on a completely unpredictable schedule.


I would point out that this sort of dual origin is a well-established tradition in the automobile world. It was very common in the 1930s and earlier for a manufacturer to build a chassis and then ship it off to a coach works house for a bespoke body. (I may have even partaken of some of this myself. Years ago I owned, in sequence, two Sunbeam Talbot Mark IIs. I seem to recall a note to the effect that the bodies of those cars were built by Thrup and Mayberly.)


Enough introductory blather. Having committed to the project I made a list of the questions, problems, decisions etc. to be addressed. Some, like “13 inch wheels?” were solved forthwith – RS slot racing does them. Others fell into the category of “there is probably something that I’ve done before it will work here” but one issue stood out – the gearing.


And why is this a problem? Because of the numbers. (This is a foreshadowing of what is coming so, if numbers bore you, you are advised to go to the next thread on the forum)


There are 3 numbers here that matter: the gear ratio – obviously; the center to center distance of opinion and spur – the build is envisioned as a sidewinder, probably with the axle carrier soldered to the motor so this is important and finally, the diameter of the spur gear. for most builds the latter is a major concern but given the small wheels and tires that the model will carry it turns out to be the most critical number. As measured from a scale drawing, the rear tires and 19 mm in diameter. While off-the-shelf tire availability might bump that by a millimeter, it is nevertheless, for build purposes, the target. While typical rules exempt gears from a ground clearance specification, we are, after all, talking about use on a racetrack and not a cog railway. Starting with a not overly generous 2 mm of ground clearance. this dictates in maximum diameter for the spur gear of 15 mm.


Looking at 64, 72 and 80 DP spur gears we find the following with a diameter of 15 mm +/- 0.2 mm:


64 DP:36 tooth, 72 DP :40 tooth and 80 DP: 45 tooth


The next step is to look at the gear ratios. One of the objectives here will be to build a light chassis. One can always add weight but incremental lightness is a rare commodity. Based on observations from recent builds and behavior in both proxies and on my local tracks, my goal would be ratios between 2.2 and 2.8 : 1. For planning purposes let’s choose a ratio of 2.5:1. This would call for pinions of 14, 16, and 18 tooth for the 64, 72, and 80 DP spurs. (The numbers, of course, do not come out exactly but they are close)


With this information in hand we can generate the 3rd set of numbers, the center to center distance of the gear sets. To do this we add the pitch diameter of the spur to the pitch diameter of the pinion and divide by 2. At the results are:


64 DP gearset :9.92mm
72 DP gearset: 9.88mm
80DP gearset: 10.00mm


Will this work? A few more numbers – an FF 050 motor is 15.3 mm wide. The diameter of an axle carrier will vary depending on construction but, given bearing dimensions etc. 4mm is probably a good working number so


(15.3+4)/2 = 9.65 mm. It should work but with little margin for error in the dimensions of the axle carrier. A note in passing: there are alternatives that might yield a little more flexibility in both gear ratios and build style – the obvious one is in anglewinder (and Slot It does a 15mm angleinder gear) but there is also the option of turning the motor on its side. There are pluses and minuses to both of these approaches but they will certainly get a look.


A final note on gear ratios – there is some flexibility here without the necessity of rebuilding the motor/axle carrier assembly. One of the things that comes out of the numbers is that the center to center distance does not change if the total number of teeth on the pinion + spur does not change. In other words the dimension we calculated for a 36+14 64 DP gearset will hold for any combination that adds up to 50 e.g. 37+13, 35+15 etc.


WAKE UP! Class is over.


EM

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RE: Lotus 23 SALT - munter - 13th-Apr-20

A very worthy project of this ignored but iconic sports car.


A few thoughts in no particular order.

Consider the 030 Solarbotics standard motor.....a short ff050. Increases possibilities for full sidewinder or low degree anglewinder.
1.5mm motor shaft and a 64pitch pinion bore? I have seen them but only 7 tooth at the highest tooth count
Some of the higher pitch pinions used a small bore but still low tooth count.
Parma and some others do make a 64pitch spur gear slightly less than 15mm with a 3/32 bore
Putting the motor on its side could compromise body clearance, as you said this is a small and low car.
Dont solder anything to the motor....use a plate and 4mm m2 motor screws....these small motors would lose some of there magnetism with that heat blast....plus being able to dismantle everything can help a lot.
Gear ratio on the 050 motors can be tall (as you already know), taller than 2.5:1 but the 030 motors like to rev so 3:1 is a good starting point for them.

aahh....that is about it for now except if you need some Lotus wobbly inserts in small diameters I could probably help.

Regards
John

Ps get out your jewellers loupe

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RE: Lotus 23 SALT - chrisguyw - 13th-Apr-20

I have several  MRSlotcar sidewinder motor pods that utilize an 050 motor, and use a MrSlotcar 15.5mm spur and a MRslotcar 4.5mm pinion, and still have ample clearance between the backside of the can and rear axle. The motors in these cars are fairly hi revving 30K, so need ratios in the 4:1 + range, and mine are geared with a 7T pinion (MrSlotcar) makes these with a 1.5mm bore, and, a 31T 15.5 mm spur.

If you are looking at gear ratios in the mid 2:1 range (I personally think that something in the 3:1 range will be much more suitable) you could use a 10 or 11T pinion (6.5mm) and a 28/29/30/31 T 15.5 mm spur and have a ton of clearance between the can and the rear axle.

You should not have really much of an issue with the sidewinder configuration, as the 050 motors are no longer than a typical "S" can, and if you use appropriately "skinny" wheels and tires you should be OK....it will be snug but more than likely manageable....if not, try the 030's as John mentioned, and, they will also be much happier geared in the 3:1 range

Cheers
Chris Walker

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RE: Lotus 23 SALT - chrisguyw - 13th-Apr-20

Hi Al, In the above post, I said that I was using a 15.5mm spur in conjunction with a 4.5mm pinion, and was able to achieve adequate clearance when using an 050 motor in a sidewinder configuration..........I just checked, and I was mistaken......

I in fact used a 4.5mm pinion with a 16.5mm spur (both form MRSlotcar) sorry for my error !!

That said, you can see in the attached pic. that there is ample clearance (even with a 4.5mm pinion).....so, if you utliized a 10/11T 6.5mm pinion, coupled with a 29/30T 15.5mm spur, or a 30/31T 16.5mm spur you would have plenty of motor/axle clearance, which would negate the need to solder the axle tube to the back of the can (not a great idea with these motors).  All of these gears/sizes are available from MRslotcar......and all are made by Sonic, one of the premier slotcar gear manufacturers in the world, so, they are outstanding quality.

Cheers
Chris Walker

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RE: Lotus 23 SALT - munter - 13th-Apr-20

Quote:and all are made by Sonic, 

Thanks Chris, I didn't know that. I have limited experience with those gears so I guess I should dive in and see what I can make, learn, find out.

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RE: Lotus 23 SALT - Ecurie Martini - 14th-Apr-20

John and Chris:


Thanks for your comments – food for thought and a little more discussion:

I think there is just enough width considering the narrow wheels and tires to be fitted to accommodate an FF 050 motor. The 030 could be a fallback – my reservation is some reports I’ve read suggesting that reliability could be an issue.

Certainly in the days of the open motors with alnico magnets, the idea of soldering to the motor would never have occurred. I’m not certain how current ceramic magnets react to heat. I know that soldering in is a routine method of motor installation in some of the hot “thingy” classes often with motors costing 10 to 20 times will we pay for our little Chinese cans. I have used this approach in a couple of chassis. A pre-and post installation check a few simple parameters, current draw, unloaded speed and speed with a fixed load (a small propeller) has not revealed any differences. I use a large iron, a low melting solder (TI X) and an in and out very quickly. I hold the motor down on the soldering pad with a bare finger without discomfort.

On gears – a couple of points and a question: for planning purposes I looked only at conventional 64, 72 and 80 DP gears. My prejudices that a better mesh, i.e. smoother, quieter and lower energy loss can be obtained with these gear sets then with gears such as Slot It that use a modified tooth shape to achieve an approximate diametrical pitch in gears with a constant diameter and varying tooth count. Here is a chart that I drew up listing a theoretical diametrical pitch for a range of Slot It gears. My observation is that reasonably good performance is obtained with gears sets where the calculated number for each gear is close. As the spread becomes wider, noise, a good surrogate for poor mesh and power loss, increases. Looking at the website, I assume that the Mossetti gear sets are similar in design to the Slot It gears. Chris: what has been your experience with their performance?

The “regular” pinions are available in a wide range of tooth number. Bore size is not important. I’ve had good success with using metric tubing to bring the motor shafts of slimline motors up to 2 mm.

I will typically try to use gears with the highest tooth count possible. I believe they run smoother (after all, a 4 tooth pinion would be essentially square)The downside is of course that as the DP increases, the teeth are more fragile and mesh more critical.

Back to the sketchpad and drawing board.

Al

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RE: Lotus 23 SALT - munter - 14th-Apr-20

That sounds good, Al. 
I will leave you to get on with it.

The reliability issue with the 030 motors is unfounded in my opinion.
As far as I can tell the initial concerns came from Tasmania and on further questioning I found that the failing motor occured when the motor failed after tires were trued on the car that the motor was fitted to. ie held onto sandpaper on the track....probably by a heavy hand.

I have used them in a few builds and have had no reliability issues. I do gear them using an eight tooth pinion though.

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RE: Lotus 23 SALT - chrisguyw - 14th-Apr-20

Hi Al, Firstly all of the MrSlotcar gears are cut by a very well respected/trusted  manufacturer of high end  commercial slot car gears, one that has been around for years, and , their quality is second to none . I (as have thousands) have used gears from this manufacturer for years (including the MrSlotcar offerings) with no issues whatsoever.

As with all the fixed dia./different tooth count .5 module pinion and spur gears on the market, it is important to use ones that do not deviate too much from "perfect"

The following is one of those handy dandy conversion thingies you can use to find the "perfect" tooth count for any .5 module pinion/spur. (When I say "perfect" I mean very close), as all these conversion thingies only get you close, but, close enough that only a blind man will know the difference  

To calculate the "perfect" tooth count for  any fixed dia. 5. module pitch. gear (pinions/spurs) ...do this

Take the gear dia. and multiply by 2.......subtract 2 from this total

Eg, (A 6.5mm pinion)...........6.5 x 2 = 13.....subtract 2  = 11........."perfect" tooth count (closest to .5 module)  for a 6.5mm .5 module pinion is 11T.

In my experience you can deviate about 10% either way  from "perfect" on any gear without issue......so.... for a 6.5mm pinion (11T "perfect"),...you can use either a 10T or a 12T.......any more/less and there are mesh issues.

Cheers
Chris Walker

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RE: Lotus 23 SALT - Ecurie Martini - 14th-Apr-20

(14th-Apr-20, 03:33 PM)chrisguyw Wrote:  Hi Al, Firstly all of the MrSlotcar gears are cut by a very well respected/trusted  manufacturer of high end  commercial slot car gears, one that has been around for years, and , their quality is second to none . I (as have thousands) have used gears from this manufacturer for years (including the MrSlotcar offerings) with no issues whatsoever.

As with all the fixed dia./different tooth count .5 module pinion and spur gears on the market, it is important to use ones that do not deviate too much from "perfect"

The following is one of those handy dandy conversion thingies you can use to find the "perfect" tooth count for any .5 module pinion/spur. (When I say "perfect" I mean very close), as all these conversion thingies only get you close, but, close enough that only a blind man will know the difference  

To calculate the "perfect" tooth count for  any fixed dia. 5. module pitch. gear (pinions/spurs) ...do this

Take the gear dia. and multiply by 2.......subtract 2 from this total

Eg, (A 6.5mm pinion)...........6.5 x 2 = 13.....subtract 2  = 11........."perfect" tooth count (closest to .5 module)  for a 6.5mm .5 module pinion is 11T.

In my experience you can deviate about 10% either way  from "perfect" on any gear without issue......so.... for a 6.5mm pinion (11T "perfect"),...you can use either a 10T or a 12T.......any more/less and there are mesh issues.

Cheers
Chris Walker

Excellent information - and a lot simpler to use than my spread sheet.  Thanks
BTW - I am well aware of the quality of Sonic gears - the discontinuance of their 31T crowns has left me scrambling.

A

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RE: Lotus 23 SALT - Anthony B - 15th-Apr-20

Ok - I put my hand up - what is the Lotus 23 SALT.

Googled it, looked in Sportsracingcars online - could not see a car with that specific ownership or sponsorship..

Fandangled way of saying would love to see pics of the car.


LOOOOOOLLL  - thanks Leo for the answer - a combination build between 2 slot constructors  

Ok then - slight different tack - a pic maybe of the end-game form that you are shooting for? 23, 23B, 23C?

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