E.fric

precision friction drive mount

GTD have created a precision friction drive equatorial mount based on new concepts.

Here are the most important highlights and the technical sheet.

GTD E.fric tech sheet 1 10.2020

The mount can be separated in twoparts by 4pc easily accessible captivebolts (they cannot be lost). The tool forthis is included with the delivery and isuseful for locking the mount at thedesired elevation too.

Do not tighten any bolt until all havebeen driven in at least a few turns!

The counterweight shaft rotates with the declination axis. You can use it to mount a second small telescope or balance in declination with off-axis bored counterweights,when sliding the OTA is not convenient for some reason.

Use d30mm (30,2mm effective d) or 1,25” bore counterweights.

The azimuth pin of your tripod can be in awide range, not just exactly at the radius ofthe screws.

Tip: if instructed to adjust azimuth to the right,(or East) drive the screw on the right IN (youface North).

GTD E.fric tech sheet 2 10.2020

The central thread for locking the mount is a replaceable bushing, you can change between M10 and M12 for example.

The RA and DEC shafts are hollow so that you can route your cables to the OTA all internally. Even a DB15 connector will pass through the hole.

There is an adapter foryour Polemaster camera

on the DEC head.

GTD E.fric tech sheet 3 10.2020

The axes can be locked and disengaged by turningthe 2 triangles seen at right. Turn right to lock, left todisengage!

The screw is captive, cannot be withdrawn, do notforce it! The travel is about 3 turns in total.

They are small to prevent excessive locking force.

More info/instructions are engraved on the RA gearcover for your convenience.

You can use any (bipolar) stepper driver you wish.Just load the reduction parameters and go. Werecommend the On step controller. The driveparameters are engraved on the motor cover.(motorsteps, total mechanical reduction)

No encoder input is needed.Technical data sheet

GTD E.fric precision friction drive Equatorial Mount

Photographic payload 30 kg

Weight 18 kg

Latitude range 16 – 65 degrees

Azimuth pin radius, from center R 54 – 84 mm

Azimuth pin diameter, height D: 8 – 14 mm, H:10 – 40 mm

Telescope interface Losmandy rail

Tripod/pier interface Single central thread (size M10, M12, 1/2”-13)

Counterweight shaft diameter 30 mm (recommended bore size: 30,2mm to 1,25”)

Reduction R:480, D:360 (the exact value is indicated on the mount)

Motors (stepper) Nema 17 bipolar 200(Ra) or 400 (Dec) step, 1,5A max

Tracking precision Better than 2” ptv for unlimited time

Pointing precision 0,02%

Slewing speed Max 5 deg/sec, driver dependent

Electronics Any bipolar stepper driver with 8 bit microstepping and atleast 1A current output.(OnStep, TeenAstro, StarGo, Pulsar2)

Declination axis height above the pier base

GTD E.fric tech sheet 4 10.2020

The locking is sufficient if forcing the axis to rotate by hand makes the steppers rotate (remove the motor cables for this test).

Analytic formula (in mm) : 125 + sin(φ+19.3)x192.8 where φ is the geographic latitude

Geographic location Dec axis height (mm) Geographic location Dec axis height(mm)

15 233 40 291

20 247 45 299

25 260 50 305

30 271 55 311

35 282 60 314

Regularly dispersing silicone or paraffin oil on the anodized surfaces with a soft cloth orfoam will help maintaining the gloss.

In a permanent setup you can use 2pc M6x40 bolts instead of the Losmandy lock suppliedwith the mount. This eliminates the possibility of interference of the knobs if positioned on

the wrong side.

The image above shows the E.fric at 50 deg geographic location.

You can download the 3D model of the mount to find out the general dimensions

GTD E.fric tech sheet 5 10.2020

and to prepare your foam fitted transport case. The compressed file has a .step and two .stl extension files (the latter separately for the RA and DEC head). The model was createdfor approx. 40 deg geographical latitude.

Click here for the file!

The image above shows the main dimensions of the E.fric mount base and the range ofthe azimuth pin (for a 10mm diameter pin, larger pins reduce the range).

The mount is fixed exclusively by the central thread and the azimuth pin. The 3-3 holes at the side are for assembly purposes, not accessible for fixing on the pier.

The central thread is optional. The choices are (to be specified at ordering):

➢ M10➢ M12➢ 1/2”-13

The tapped bushing can be replaced/purchased aftermarket too.

Calculating counterweight

GTD E.fric tech sheet 6 10.2020

Pole

The schematic diagram below will help you calculate the counterweight need of your gear.The result will be conservative because the DEC gear is already acting as counterweight but it is not considered in the calculation.

200 mm 183 mm

B A

450 mm

Telescope

This is the maths:

A = the radius of your telescope tube measured to the face of the Losmandy rail.Use mm as unit!!!

B = the approximate distance where the counterweight will sit, from the center of rotation (RA axis). As you can see, this can be between about 200 and 450mm. The smaller the better, from an inertia point of view.

CW = the counterweight you will need at distance B on the CTW shaft

M = the weight of your OTA (the unit used here will be the unit of the CW)

CW = (A + 183) x M / B

Motor connection Coil A

To change motor rotation invertone of the coil wire pairs!

Orientation mark

Coil B

GTD

Innovation and Service since 1996

GTD E.fric tech sheet 7 10.2020