Losmandy G11 RA Axis for GM8 DEC — No Motor

Product Overview

This is the G-11 right ascension axis sold on its own, listed by Losmandy for use with a GM8 declination axis. That pairing is the GM811: the 5.625-inch, 360-tooth G-11 gear on RA, where tracking happens, against the lighter 2.8-inch, 180-tooth GM8 gear on DEC, where it does not. No motor is included — your existing RA servo motor transfers across. Pairing it with a GM8 DEC needs the cone convertor piece, which Losmandy lists as required for that configuration.

Who It's For

This is the upgrade a GM 8 owner reaches for when tracking, not capacity, is the limit. Periodic error is a right-ascension problem: the worm turns continuously in RA while DEC only holds position between guide corrections. Replacing the RA axis alone therefore buys most of what a G-11 offers, at a fraction of the weight a full G-11 head would add. It is also how a G11T owner builds a second, lighter head from the axes they already have.

Key Features & Design

• 5.625-inch, 360-tooth 7075 aluminium worm gear — the full G-11 RA gear.
• Dual-supported, ball-bearing-housed stainless steel worm, heat treated and ground.
• One 3.75-inch and one 2.00-inch thrust bearing plus two 1.50-inch needle bearings.
• 1.25-inch centreless-ground stainless steel shaft.
• Tangent-arm altitude adjustment and single-knob bi-directional azimuth of ±8.5°, as on the G-11.
• 5.0-inch laser-engraved setting circle with vernier, reading to 1 minute of right ascension.
• Adjustable friction clutch rather than a locking bolt.
• Motor not included. The existing RA servo motor fits.

Mechanical Design

Gear size is the whole argument. For a fixed rate of sky motion, a larger gear with more teeth turns more slowly, so the angular error contributed by any single tooth imperfection is smaller. Going from 2.8 inches and 180 teeth to 5.625 inches and 360 teeth roughly halves the gear's rotational speed and doubles the tooth count working against the error — which is why Losmandy puts the big gear on RA first and treats DEC as the place to save weight.

The worm driving it is the same ground, heat-treated stainless component used across the line, dual supported and housed in ball bearings at both ends rather than cantilevered off the motor. The polar axis is bored through for a polar finder, and the altitude and azimuth adjusters are part of this axis — so the upgrade brings the G-11's alignment controls with it, not just its gear.

Recommended Uses

Upgrading a GM 8 to GM811 configuration for better tracking under long exposures. Building a GM811 from parts, alongside the GM8 DEC axis. Replacing a damaged G-11 RA axis. Assembling a lighter second head for travel while a heavier mount stays on the pier.

Compatibility and Accessory Notes

• Pairing with a GM8 DEC: Losmandy lists the cone convertor piece as required for this attachment. If you are ordering the GM8 DEC axis at the same time, the cone is supplied with that axis.
• Pairing with a G-11 DEC: a male RA extension piece is the part Losmandy lists for existing G11T owners going this route.
• Quick release: the G11 RA extension dovetail and the RA extension kit let you swap heads without dismantling the axes.
• Motor: not included. Your existing RA motor fits; a second motor is worth adding only if you want both axes left motorised for quick swaps. The G11 motor-to-worm coupling is the part that joins the two.
• Tripod and pier: the MA tripod/pier adapter is the interface for this axis, on the LW tripod, the HD tripod with MA top, or a permanent pier.
• Polar alignment: the polar axis is bored for a through-the-axis finder — the optical polar scope with illuminator or the iPolar electronic polar scope.
• Clutch knobs: the clutch knob set fits if you want the handled knobs on the new axis.

Good to Know Before You Order

• No motor in the box. The axis is designed around reusing the motor from the axis it replaces.
• The adapter you need depends on which DEC axis it is going onto — a cone convertor for a GM8 DEC, an RA extension piece for a G-11 DEC. Tell us what the mount is now and we will confirm the piece before you order.
• This changes RA only. Declination keeps whatever gear is on it, which is the intent of the GM811 configuration rather than a compromise in it.
• Losmandy publishes 50 lb imaging capacity for a complete GM811 against 40 lb for a GM 8. Capacity is a property of the whole head, so the figure that applies depends on your final configuration.
• Specifications are Losmandy's published figures for the G-11 axis.

Frequently Asked Questions

Is it difficult to set up?

It is mechanical assembly: the old RA axis comes off, this one goes on with the correct convertor or extension piece, the motor and coupling move across, and the mount is rebalanced and polar aligned as usual. No gear timing is involved.

What does this get me over a GM 8 RA axis?

A gear twice the diameter with twice the teeth, on the axis that actually tracks. Losmandy's published imaging capacity for the resulting GM811 is 50 lb against the GM 8's 40 lb.

Do I need the cone convertor?

For a GM8 DEC, yes — Losmandy lists it as required. It is supplied with the GM8 DEC axis if you are buying both together.

Can I use my existing motor?

Yes. That is how the axis is sold. A second motor is only for keeping both axes ready to swap.

Will my tripod still work?

Yes — this axis takes the MA adapter, the same as a GM 8, GM811 or G11G.

Bottom Line

In short: the G-11 right ascension axis on its own, 5.625-inch 360-tooth gear, motor not included — the part that makes a GM 8 into a GM811 by putting the large gear where periodic error shows.