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Discussion Starter #1
I was looking over the design of the TA mechanism on the Spica. I don't have one, as I'm running webers, but I was curious if anyone had ever measured the amount of force that the TA applies to the Spica pump? I strikes me that an electronic version (powered by an IC costing less than $3) would not be too difficult to make if I knew two things,
1) the force applied by the TA as it warms up
2) the extension in mm of the TA as a function of temperature
 

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Hmm, That might be interesting. Seems like there are a lot of failing SPICA TA's… If swapped out the purists would have greater inventory to draw from and the high tech aftermarket replacement could do things more precisely and adaptable than the preset temperature/pressure functionality originally used.
:sorcerer:

How do you imagine the mechanical actuation? Could it's extension as a function of temperature "map" be end user reworked via a simple apt driven software interface? But, is there any real need for this functionality? Kind of doubt it because its just a "switch" from cold to warmed up mode without much needed functionality wrapped up in this degree of control. I guess if somebody knows the required force, one could speculate about the required mechanics…
:confused1:

I'm thinking of removing and checking my TA for extension… Hmm, hydraulic, no? My guess it's force far exceeds the effort required to move the little bits inside the pump…just a guess.
:sweatdrop:

But then again, the little monster's rather crude lack of anything even slightly smelling like a computer is one of its greatest charms! I like that.:thumbup1:
 

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Discussion Starter #3
Hmm, That might be interesting. Seems like there are a lot of failing SPICA TA's….
Expensive replacements too.

Could it's extension as a function of temperature "map" be end user reworked via a simple apt driven software interface?
Sure, like the electronic distributors with their selectable curves. You can install a switch to select different profiles or even have USB capability

But, is there any real need for this functionality?
I'm not sure, perhaps a Spica pro can speak up and tell us if anyone ever needs this?

I guess if somebody knows the required force, one could speculate about the required mechanics…
Pretty much.. The mechanical aspect depends mainly on this.

But then again, the little monster's rather crude lack of anything even slightly smelling like a computer is one of its greatest charms! I like that.:thumbup1:
This is true, but it could be more like electronic ignition - a small addition that makes life easier?
 

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I think there is a real need for this. A rebuilt TA is north of $300 and has a finite life. I have looked into this occasionally but it's not my area of expertise. In my ignorance i figure anything is possible:

Use the signal from the temp sending unit as an input to some signal processor that would translate it to an output that would control some linear extension devise.

The force and extension are readily determined. I can do that when I get back in town next week. I think the extension is 6 mm [edited from my original guess of 11 mm]. A pot of water heating on the stove, a good TA, calipers, temp sending unit and a volt meter should do the of mapping the curve which I'm guessing is linear. The force is not insignificant but I'm sure there is something out there that can do the job. Anybody out there a controls engineer?

I am confident there is a market for such a thing. I really like Spica but $300 for a choke is obscene. Make one for $50, sell it for $150 and you could have a nice little cottage industry. Should be able to pay for a Spica rebuild anyway...

Kickstarter.com?
 

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Discussion Starter #5
The force and extension are readily determined. I can do that when I get back in town next week. I think the extension is 11mm. A pot of water heating on the stove, a good TA, calipers, temp sending unit and a volt meter should do the of mapping the curve which I'm guessing is linear. The force is not insignificant but I'm sure there is something out there that can do the job.
Definitely. These parameters need to be quantized before designing a replacement. For force measurement (rudimentary) you can use a scale. For the extension calculation, you'll need to know the water temperature so we can create a proper extension vs temp curve.
 

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I took apart a digital bathroom scale and there are four little force transducers (1 per corner). I used one (and the digital readout) to make a digital valve spring tester and was pleased how well it works.

I can use one of the three extra transducers to read the force needed to move the Spica mechanism .
 

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Not the force exerted by the T/A piston BUT Alfa specs that the T/A extension length be tested with a 4kg resistance on the piston. I'll post a temp/extension graph shortly...
 

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So, according to the chart, going from room temperature (68 F) to operating temp (176 F) (20 C to 80 C) the plunger should move 6 mm (from 23 mm to 29 mm). [I will edit my early guess so as not to spread misinformation.]

This is done with a pre-load of 4 kg or 8.8 lbs. It stands to reason that the plunger force would need to be greater than that at full extension. I can measure that on a few SPICAs and report results later this week.

Papajam, any chance you have a curve of water temperature verse resistance for the temperature sending unit?
 

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Discussion Starter #12
I can measure that on a few SPICAs and report results later this week.
gprocket, if you can publish the exact dimensions here, I can make a model of the TA in solidworks. From there we can work on the necessary form mechanics for an electric version.
 

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This TB has me thinking: It has long been recognized that testing a TA can be done by heating water and measuring the extension. But without the preload me thinks we can get a false reading... I assume the preload is there to eliminate any air in the system from expanding on its own and adding to the extension which would not occur during actual operation. (The magic potion in the TA is a liquid I believe...)
 

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Papajam, any chance you have a curve of water temperature verse resistance for the temperature sending unit?
I don't recall ever seeing any for the temp gauge sensor (either Jaeger or Borletti). But there are specs for the NTC temp sensors for the Bosch L-Jetronic and Motronics EFI systems. Would that do?
 

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The electronic Thermostatic Actuator was made years ago, I believe the product was called the "Alfa Cat" or something like that.

Look through old issues of the Alfa Owner for the ads.

This is not to say that it couldn't be done again but I would want to see:

1) Whether the design was patented and

2) WHY did the company making the old version not have success with the product, sell a bunch, and become rich?
 

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I've thought of this at times in the past as well. I don't think force is an issue, only the length of extension mapped to the temperature gradient and controlled by some sort of stepper. So long as the motor was capable of actuating the pump mechanism.

The only reason I never followed up on it is because I put a new rebuilt T/A on when I last overhauled my engine and that was over 10 years ago. I haven't had any problems with the T/A in that time. I think the rebuilt ones you get nowadays are much better and more robust than the factory ones back in the 70's & 80's.

Probably the same reason no one ever made a killing on an electronic replacement. Just not that much demand for the product.
 

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The electronic Thermostatic Actuator was made years ago, I believe the product was called the "Alfa Cat" or something like that.

Look through old issues of the Alfa Owner for the ads.

This is not to say that it couldn't be done again but I would want to see:

1) Whether the design was patented and

2) WHY did the company making the old version not have success with the product, sell a bunch, and become rich?

This:

Elektromechanischer TA.jpg
 

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For Tinkering’s Amusement

I certainly would not claim to be a SPICA pump expert but my understanding is that the TA acts on a set of mechanical gadgets to modify position of a moving rack, which then changes the amount of gas sprayed into the combustion process. A bit like a choke but rather than restricting air to enrich the mixture, the setup sprays more gas during that phase of the engine warm-up cycle. Key point… it modifies position. As such, the mechanical functional needed of the TA subsystem is extension (not force). That said, the extension must be within a minimum force or it cannot move said internal SPICA gadgetry. All well represented by the graph above.

1mm extension per 10 degrees C
As tested with a 4kg load

Again guessing, the test load is not related to a force/temperature requirement but rather to ensure a minimum force as an indication of TA functionality. I suppose that one could also interpret the 4kg as a minimum force to drive the SPICA pump gadgetry but I doubt that was its intension. Perhaps sticking a cylindrical probe in the TA hole is desirable… maybe a modified fish scale… to measure how much force it takes to excite the mysteries within!

I’m thinking the TA is simply a bulb then long thin tube then an extension piston filled with some sort of hydraulic oil. Heat the bulb, the oil expands, the thin tube amplifies the resultant expansion to move the piston as per the specified graph. Expansion of fluid is notoriously forceful, capable of dramatics like crushing rock when trapped in cracks and hence my earlier hypothesis that achieving minimum force for the TA is not really much of a problem…as long as the system doesn’t leak! Really quite an elegant design solution on Alfa’s part although typically places a significant burden on the required manufacturing processes and so yes maybe charming but not very business savvy.

Assuming my above B.S. is true, let’s return to the entrepreneurial challenge of an electromechanical actuator. What is the need?

1mm per 10 deg C
12mm of travel (to cover the illustrated temperature range)
Minimum force of TBD (but let’s go with 4kg)
Ability to set an origin for the extension (datum)
SMALL PACKAGE SPACE

Small electromechanical actuators are generally poor at creating force.

So, how do you imagine the mechanical actuation?

How about a small stepper motor with worm gear acting on a rack? The rack is connected to a long flexible sleeved rod, which penetrates that mysterious hole in the pump. This way the bulk of the drive motor can be a bit remote from the tight package space around the pump. And I can start to visualize a threaded joint in the flexible rod allowing adjustment to set datum for the actuation...

And, a cheap IC with controls electronics to map overly complex curves into my darlings rather charming… “Pump”.

I’d buy one for tinkering's amusement but not yet convinced that I’d invest in the operations…
 
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