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3" TOADLOADER Docking Focusers

Manual, DC Servo (analog) & Auto-Focus Stepper (digital) Motor Control

Without Comparison, the most Loadable, Functional & Feature-Packed Focusers on Earth


Mount any VSI Focuser to any Scope - Not just Meade & Celestron

AP, Borg, OGS, RC Optical, Takahashi, TeleVue, TMB, Vixen, etc., etc. - Just Call VSI

3" TOADLOADER Features & Specifications:

Introducing VSI's GIGANTIC 3" TOADLOADER Docking Focuser with huge dual 2.5" diameter custom machined "GUN" knobs incorporating lightweight polymer cores encased in thick aluminum shells (see picture at left). These giant knobs are easy to grip and rotate using minimal tactile pressure and resemble the rotating cylinder on a revolver, thus the name "GUN KNOBS."

VSI's exclusive MICRO-DIAL (micrometer) ultra-fine focusing capability provides this focuser with the finest incremental focusing capability (by many factors) over any other focuser on the market (see picture below right). One full rotation of the micrometer's dial yields 0.00375" of travel with incremental indic interpolation that is repeatable to (better than) an unbelievable 75/millionths of an inch. VSI's Micro-Dial in not just another so-called fine focus control for visual observing like the ones offered on almost every other focuser on Planet Earth. To call a Micro-Dial fine would be like calling the space shuttle slow (17,500mph). Think thousands of times finer than anyone else's so-called fine focus control. A lot of experienced astroimagers, not familiar with VSI's relatively new Micro-Dial (with tactile sensitivity beyond any other) think that it is impossible to obtain critical focus without hands-off autofocus computer control. Not true! In fact, computer focus control is not as accurate or fine as VSI's manual Micro-Dial. Interpolation to better than 0.000075 inch. Do the math - indices vs steps.

Yes, you can [now] manually focus sharper, better, and finer than any computer controlled autofocus stepper motor. But only if you want to, as all TOADLOADERS can be equipped with temperature compensated autofocus so you can have the best of both worlds - ultra-fine manual and autofocus capabilities. And you disengage the TOADLOADER's motor and/or engage the Micro-Dial with the turn of a knob. No dysfunctional [autofocus only] motor locked shafts or, worse yet, knobless focusers! Oh, you wanted to do some [analog] eyepiece observing too. Sorry, no can do! Did I mention dysfunctional? What are they thinking? Not. Of course, DC servo (w/hand paddle) and/or autofocus stepper motor control are available (purchase stepper motor electronic hardware package from Technical Innovations, around $300, see Autofocus link for more info). Interchangeable docking and output rings (optional) are available for every telescope and application possible. Custom tube travel lengths are available by special order.

Over the years, VSI has continually taken the best features of all our previous focuser designs and incorporated them into new "super focuser" models. We do this not only to continually improve our products, but to [also] leave copy-cats in the dust. Of course, these VSI knock-offs are the greatest form of compliment! It tells you that VSI products are always the best by design, function and application. The only way to keep ahead of these imitators is to design new and creative focusers faster than they can copy our designs and incorporate them into their product lines. This unique design philosophy has pioneered our Crayford focuser development since John Wall first invented it back in the early 1970's (see "Brief History of the Crayford Focuser" below), and kept VSI on the "bleeding-edge" of focuser design for decades.

TOADLOADERS can couple directly to our Zerotators, Sidewinders, or Targetrons using the same 2.9" flanged format, so port rings are 100% interchangeable. You can create [what I call] the SUPER STACK (see picture at left), by simply stacking components in any configuration you want using coupling port rings (see OUTPUT ADAPTERS link above right, and SIDEWINDER Port Ring links) that only consume 1/8" of profile. Add a [1-inch profile] Zerotator (see Rotators link) and gain rock-solid, zero-flexure, super-fluid, radial ball-bearing Z-axis rotation of your entire imaging train. And our Zerotator can [also] handle any load you throw at it - guaranteed! All TOADLOADERS have been designed with the shortest profile possible (3"). The total SUPER STACK package (Toad, Zerotator and Sidewinder) at left consumes a mere 7" of profile!

Our QUAD-LOCK system is incorporated in our 2" reducer output port insert ring  (item #A312R pictured right) offering astroimagers a rock-solid coupling between a TOADLOADER's moving tube and your 2" barrel nose. Four tightening screws lock your 2" barrel nose into the focuser's moving tube - two 10-32 Nylon thumb screws and two [hidden] 8-32 set screws. The first two thumb screws, opposed by 90 degrees, lock your barrel in place from one end of the tube, and the other two set screws lock from the other end of the tube. This 4-screw application allows any 2" barrel nose to meld with the TOADLOADER's moving tube, creating a zero-flexure coupling. See VP Accessories link for more info on VSI's exclusive adapters.

To further reduce noise and vibration, and better isolate the focusing motor(s) from the focuser housing, the motor's drive shaft is [now] coupled to the Crayford focusing shaft using precision Delrin spur gears. VSI is switching from metal to Delrin spur gears because Delrin (an indestructable polymer resin) is more durable and lasts longer than metal. And, VSI uses only the best Delrin gears available, with double metal set screws that lock the spur gears securely to the motor and Crayford drive shafts.

What I consider to be the most important mechanical feature is the dual pressure points on the Crayford rod. Instead of one pressure point, VSI's Crayford design [now] uses a dual pressure point on the rotating drive shaft (supported with two pure virgin Teflon pads), which offers a fluid surface so near-infinite force can be applied with no possible warpage of the drive shaft (see picture at right). VSI's original single pressure point design has been copied by literally every other Crayford focuser manufacturer to date. This design upgrade doubles the pressure applied to the Crayford shaft, in effect doubling the holding power. By applying equal pressure along a full 1-inch length of the Crayford rod and the entire 1-inch width of the moving tube's machined flat, you create a more positive rack & pinion-like movement, while cutting your focusing/tactile sensitivity, necessary to move the focusing tube, in half. This creates an incredibly soft-touch, tactile manual focusing function that no other focuser can begin to offer. The TOADLOADER movement is not only as smooth as a 20 year-old, single-malt Scotch whiskey, but the silky action is extremely positive and reactive to the slightest touch, especially with those GIANT 2.5" diameter gun knobs.

Another exclusive VSI feature is the vibration dampening system. Note the stainless steel motor arm (see picture at right). Stainless steel, having a very high density, is the best material to dampen motor vibrations when a motor must be in close proximity to the eyepiece, like focusing motors. This undesirable vibration can easily transfer to what you see in your telescope's eyepiece.

WARNING: Be aware that all [so-called] Crayford focusers, are not really Crayford focusers. Deceptive advertising by many dealers, trying to take advantage of the Crayford's reputation, offer Crayford-type, Crayford-like or Crayford-style focusers that have very little to do with the true Crayford design. NO radial ball bearings, NO zero-flexure, NO fluid motion, NO ultra-tactile sensitive control, NONE of the above functions that made the Crayford the finest precision focuser on Planet Earth. These non-Crayford focusers typically use plastic pads to simulate Crayford bearings and other inferior construction techniques that diminish the Crayford name. Only a focuser that uses precision radial ball bearings (not slot-car bearings) can [rightfully] be called a Crayford focuser. - PBVS

VSI's Exclusive Zenith Lift System

VSI's Zenith Lift System (patented), installed on all TOADLOADERS, provides a unique lift feature that balances focus control at the zenith, or near zenith, observing/imaging positions. The Zenith Lift System (ZLS) was created so the astroimager, or visual observer, can easily take advantage of the more transparent overhead zenith arena. If balanced zenith lift is not needed, you can easily remove the springs by slipping the hooked ends over the Allen screws - instant gone!

FYI, this Zenith Lift System has nothing to do with backlash, as others have wrongly assumed in their display ads. They are trying to discredit the ZLS without even understanding its function. The more they try (desperately) to "poo-poo" VSI products, the more they humiliate and embarrass themselves. When will they learn that you can't destroy the reputation of a good product with words, especially words that only reveal their own jealousy and ignorance. A product can only destroy itself by its own actions. - PBVS

We all know that you are looking through about 100 miles of atmospheric distortions on your horizon, but you are only observing through about 10 miles of atmosphere at your zenith. Obviously, you will obtain the best astroimages and visual observations when your scope is pointing straight up.

The mechanical apparatus comprises two heavy-lift springs (pictured at right) that are attached between the focuser housing and the moving tube on both sides of the focuser. Also, the TOADLOADER's mechanical spring-loaded lift system will greatly assist your autofocus stepper motor and DC servo motor when working around the zenith.

HINT: By setting your focus point further in, or further out, you vary the amount of lift capability to better balance your focuser's load. In other words, rack your focuser in most of the way, and you have light lift for a lighter load. Rack your focuser out most of the way and you have heavy lift for extended imaging trains. Just set your SCT's primary focus at the inner, or outer, point of your secondary focuser travel for different loads. Of course, if your load is light, and you're observing near the horizon (say, in your neighbor's window) you don't need the mechanical lift springs. Simply slip the springs over the Allen head screws to remove them.

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Commercial 2" Focuser Size/Mass Comparisons

No words are really needed here, but do note the size of the Crayford bearings, where applicable.

Miniature Slot Car Bearings vs Large-Diameter Precision Bearings

A penny for your thoughts. These pictures illustrate the difference in size between the bearings used in all other Crayford focusers (that I know of) compared to the bearings in VSI focusers. What you can't see in the picture is the lack of quality, but we'll get to that later.

Anyone can purchase these miniature slot car bearings on the internet for about a dollar or two each in quantities of 10, as pictured above. Dealers can purchase them for under $1 each in bulk quantities, so why do Crayford focuser dealers [gladly] sell you a replacement bearing for $25? Ouch! I hear that people need to replace them frequently. A VSI radial bearing has never been replaced, ever! These slot car bearings are not even designed for loading. They are designed for hi-speed rotation, usually around 20,000 to 80,000 rpm. Whoa! That's fast! That means that their tolerance has to be very low to accommodate those extreme speeds. In other words, sloppy bearings designed for speed, not precision. Slot car bearing static load is [at best] around 13 lbs. and their dynamic load handling is around 44 lbs. That rating is for a precision bearing of the same comparable size because that is the only reference I could find. Slot car bearings don't even list their load bearing capacity, probably because they are way below the numbers that I referenced. What do you want for a dollar?

As you can see, almost two of these miniature slot car bearings can be dropped, side by side, through the center hole in a VSI bearing. VSI has always used precision, deep-groove, sealed chrome steel radial ball bearings in all focusers since day one over 20 years ago. For simple comparison, each VSI bearing has a static load capability of 310 lbs. (slot car = 13) with a dynamic load capability of 740 lbs. (slot car = 44). That load rating is times four [bearings] when it's on your focuser. And precision, deep-groove radial ball bearings have much tighter tolerances because they are not designed for crazy hi-speed operation - a few hundred to a few thousand rpm max.

What kind of rotational speeds are we talking about for a Crayford focuser? Fractional, less than one rpm. So why use hi-speed, low tolerance bearings in a Crayford focuser?  Maybe you would say cost. The large precision radial ball bearings I use are around $4 or $5 each. Not cheap, but not overly expensive either. Maybe it looks better to hide the bearings inside the focuser's housing? I would hide them too if they were that small. If the bearings were hidden inside the housing, they could even buy cheaper open-race bearings instead of shielded or sealed bearings. All VSI bearings are not just shielded, they are sealed so zero contamination can get inside the bearing's race, whether they are exposed to the elements, or not.

Another poor design on most Crayford focusers is their one-sided bearing mounting, using a shoulder screw. This causes the bearing to flex from the unsecured [screw-head] side of the bearing. VSI focusers use a 3/8" diameter stainless steel (SS) pin that is secured by SS screws from both sides of the bearing directly to the focuser's housing. This super secure bearing mounting provides ultra-secure, zero flexure movement of the travel tube. There are dozens of other reasons why VSI focusers are superior, expecially in load handling, to all other Crayford focusers on the market. This is just one more reason.

VSI's Coma Corrector Insert Capability

Our 3" ALPHATOADS can now accept all 3" outside diameter coma correctors on the market, including Astro Optik's Newton-Wynne 3" Coma Corrector (made in Germany), pictured at right. All ALPHATOAD moving tubes can be custom machined at no additional charge to 3.005" internal diameter to easily accept the insertion of these unique coma correctors.

Pictured at right (left black cylinder) is a standard 3" coma corrector with an optional T-thread adapter (available from Astro Optik's) bolted to the top that provides the exact 60mm distance between the corrector lens and your CCD chip. This one accepts any CCD camera that has a standard T-thread coupling, like the SBIG ST10 CCD camera (shown). Just screw the camera onto the coma corrector adapter (center image) and insert it in the ALPHATOAD (right image) and tighten the three thumb (or set) screws opposed by 120 degrees.

You can also use the 6" long coma corrector's barrel as a push/pull drawtube, if desired. When not using the coma corrector, just remove it and drop in our standard output adapters. VSI's output adapters include 2" barrel-nose, T-thread, 2"-24tpi thread, and SBIG's new 2.156"-24tpi thread for their STL11000 CCD camera (see OUTPUT ADAPTERS link above).

Of course, custom machined output adapters are always available. Although our ALPHATOAD's have a long 5" travel, shorter custom moving tube lengths/travels are also available by special order.

VSI's Dual Control Hand Paddle

Our Mega-Power Dual Control hand paddle incorporates individual IN/OUT speed-torque control for balanced load even at zenith positions. Just turn the knob below the push button (see picture at right) to change the speed of the IN travel of the DC Servo motor. Turn the other knob to control the OUT travel speed.

Other hand paddles have one knob to control both IN and OUT speed, so when you are observing near the zenith and push the IN button, your motor strains to lift the load at reduced speed and torque, and drops the load at a much faster speed when you push the OUT button. With VSI hand paddles, you can balance your load by simply adjusting the two individual speed control knobs. Your IN/OUT speed can be precisely controlled for any load and any observing elevation from horizon to zenith with a simple turn of a knob(s).

This new VSI circuit design instantly starts the rotation of the motor, even at it's lowest speed, as soon as a button is pressed. No more time lag between direction changes, like other hand paddles. This new paddle delivers super-smooth, "analog" speed control that is mechanically and electronically near-indestructible.

This paddle is used to control our DC servo motor only. It will not operate the Lunatico stepper motor. Uses 120vac wall-wart type power supply (included when ordering appropriate focuser package) or 12vdc car cigarette lighter (optional). Operating voltage: 12 to 24vdc.

The Importance of Dual-Motor Controlled Focusers

VSI motorized focuser models offer two types of motor control - DC servo and stepper.  In fact, VSI focusers offer the only dual-motor control on the planet (that I know of), allowing both motor types of remote focusing control with a fast and easy "slide-out/slide-in" motor switch-out (see picture at left). You can also disengage either motor from the drive train for hands-on manual focusing with the instantaneous turn of a knob.

Why does VSI offer these exclusive motor features? Because DC servo motors are analog and introduce no vibration or noise into the drive train like digital autofocus stepper motors, which are inherently noisy and cause step vibration (even when microstepping). DC servo motor control offers smooth, remote hands-off eyepiece focusing via the Dual Control hand paddle.

On the other hand, stepper motor control offers wonderful computer controlled autofocus for astroimaging, but is not capable of vibration-free driving of the moving tube, especially at resonant step frequencies, which cause your star images to jump all over the place when attempting to focus, making it impossible to remote eyepiece focus. This is why autofocus computer subroutines stop focusing, take a focus image, then do it all over again until perfect focus is achieved - a time consuming process, but acceptable. Although remote push-button control is offered on autofocus electronic hardware packages, via two push-buttons, you really can't use it for anything more than repositioning the focuser's moving tube to begin autofocus computer controlled focus procedures. It is simply a convenience feature. You can't do simultaneous visual eyepiece focusing with a stepper motor because it induces vibration when activated.

This little known motor control fact is very important when considering the purchase of a focuser that you want to use for both visual, remote eyepiece focusing and computer controlled astroimaging applications. You can't have hands-off remote eyepiece focusing and computer-controlled autofocus for astroimaging, unless you have a focuser with dual-motor control capability. This is something that the other single-motor focusers on the market don't want you to know, until it's too late. Unfortunately, this lesson is usually learned the hard way. Even though this info, that you are reading now, is buried [here] in this link, you may be one of the lucky ones, if you were seriously considering a dual-purpose focuser for both remote visual focus and computer-controlled astroimaging.

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Re-Engineering & Improving the Basic Crayford Design

Although most Crayford focusers on the market today utilize VSI's [original] central pressure point design, we continue to stay ahead of the game by continually improving our products, as noted by the myriad of improvements to our TOADLOADERS. VSI has always maintained only the basic Crayford concept. Everything else has been thrown out the astro-portal and redesigned from the ground up. We have modified the four-bearing support platform by supporting the bearings from both sides (a feature others have copied for many years now), using hardened steel drill rod shafts and a complete cylinder instead of a cylinder section, providing more than twice the stability compared to single-end supported, bearing mounting systems. We have also made the entire structure more massive, and increased the typical bearing size (approx. 1" diameter bearings). The drive shaft support mechanism has also been re-engineered to eliminate the weak, flimsy, distortion prone standard drive shaft mechanism (see above diagrams) provided by many other manufacturers. The above left diagram explains the internet reports of ball bearings literally exploding due to over tightening a poorly designed drive rod tensioning mechanism. If the two drive shaft bearings remain fixed perpendicular to the drive shaft, while the shaft itself is allowed to warp [away from perpendicularity] from over tightening, then the bearings will bind causing locking of the drive shaft and danger of an exploding bearing. Even replacing the ball bearings with bronze bushing-type bearings will not eliminate locking or pinching of the drive shaft from normal tightening of the tension mechanism. Increasing the diameter of the drive rod will relieve some of the warping, but it will also give you a much coarser [ratio] movement of the tube, which is not acceptable, at least at VSI.

To apply force at the center, instead of at the outer ends of the drive shaft, VSI uses two expedient and economical virgin Teflon pads backed by two adjustable, large Allen head set screws. Engineering studies have shown that, in this application, center mounted Teflon pads provide an inexpensive method to totally eliminate drive rod warpage and inherent concentric machining errors while allowing the user to adjust and apply a much higher force between the drive rod and the moving tube, without warpage concerns. The more force you apply to virgin Teflon, the more "slippery" it becomes, making it an ideal and economical substance for Crayford drive rod applications. With the available increased force applied to the drive shaft, you can eliminate the typical "sloppy" action notorious to previously ill-designed Crayfords providing a more positive "rack & pinion" action, and a much higher leveraged load handling capability for astroimaging, etc.

A Brief History of the Crayford Focuser

The Crayford Focuser was invented by English amateur John Wall of Dartford, Kent, England in the early 1970's. His inspirational focuser was demonstrated at the Crayford Manor House Astronomical Society and described in the Journal of the British Astronomical Association (Feb, 1971). Also, several examples were published in Model Engineer magazine (May, 1972). Curiously, the Crayford focuser is not named after it's inventor, Mr. Wall, but after the Crayford Manor House itself. Even more curious is that he never patented the design, which rendered it unpatentable over the years because of his existing published "prior art." Others have acquired patents for various minor modifications to the basic Crayford design, but such patents pale in the light of the revolutionary, original Crayford focuser implications. FYI, an interesting article on the Crayford focuser appears in Sky & Telescope magazine, Gleanings for ATM's (Sept, 1972, p182). Mr. Wall's original Crayford focuser appears at right (courtesy Sky & Telescope magazine).

I would personally like to thank Mr. Wall for magnanimously donating his invention, the Crayford focuser, to the astronomical community. The Crayford focuser, and Mr. Wall, will live forever in the hearts [and hands] of amateur astronomers throughout the world. It is the only focuser mechanism that offers true zero-flexure tube movement. In my humble opinion, it is the finest, most ingenious focusing control mechanism ever created! - PBVS

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