'Scooter' the lightweight GEM

[kinetic]

Hi all,

I'd been contemplating building a very lightweight GEM and Bartelising
it to make a good, light, portable GEM for some time.
Something I could setup in the yard to take wide field DSLR or throw
in the car for a trip to a dark sky, and run completely from a laptop
and batteries.

As the heart of any GEM needs a good, solid few T-pieces, the only starting
point seemed to be 2 inch pipe thread Tees with bearings installed.
This would certainly add some weight right from the start.
It would only ever have to take a DSLR or light APO or my 4" Bausch&Lomb.

Enter the scooters....

The kids have accumulated a total of 5 bloody scooters over the years and
if I had a dollar for every sunset, 'pick all the bloody scooters up and
put them away so I don't trip over them in the dark' moment.....well,
I could probably buy myself a G11.

I'd put a few into 'quarantine', a sort of twilight zone , where the kids
don't notice it missing for a few months, then it goes in the bin.

The twilight zone is, of course, the shed, where I can, unfortunately,
dream up some other use for such junk.

I've always been a sucker for aluminium extrusions and tubing and
couldn't help but think the scooters could be used for something useful
one day....then came the epiphany! :)

Here is the current work in progress....the lightweight GEM.
Everything so far has been too easy....the bearings can be preloaded
easily with the tubing and thrust race arrangements, I got the GEM
orthagonality pretty good by facing the Tee in the lathe, the counterweight
arm is the handlebars with the keyed, lockable tube being adjustable...

Pictures explain it all so far.....next step is to make a small worm
gear and drive to Bartelise the RA axis.

Steve

[leon]

Good on ya Steve, what agreat idea.

Leon

[mercedes_sl1970]

That's terrific. I've pondered over what could be done with a couple of those scooters we have lying around as well. Look forward to seeing the final product.

Andrew

[bmitchell82]

steve i love the pretty pink flowers!

But on topic i love this idea. even if you didn't have half a dozen of em laying around, the dump shop most definately does not only that they have push bikes... im sure something can be fiddled out of them!

Ill keep my eye stuck on this thread!

[kinetic]

Aw gawd, trust you Brendan to notice the flowers!
How can anyone take an ATM post seriously if there are
flowers on it....let alone the fact it's made from scooters :D

Both axes are very snug so far with a complete clean in kero,
regrease and preload. I'm gonna have to turn the 'wedge' clamp
180 degrees to fit a drive worm/wheel and worm carriage on the
back RA shaft. The idea of having the latitude adjustable with
the 'wedge' clamp might have to be scrapped.
(Only probably ever use this from latitudes 31-35 S anyway.
I could get that with tripod legs.

more flower pics for you Brendan :)

Steve

[bmitchell82]

oooh yeah thats what im talkin about! booyah!!!

your going to have to adjust the alt anyhow why not set it up with a push pull system because i can see fine adjustments being a right royal PITA with the quick release clamp and 2kgs of gear uptop.

Can your bartels system run autoguiding? if so you should look at the finderguider option and turn up a threaded puck. extremely light weight and will be perfect for the job!

I might even think of doing something silly like this because it would be great to have a camera tracking to some degree.

[kinetic]

A bit of progress on 'Scooter' today....
I bored out a beautiful little brass worm gear that I had until it was
a snug fit on the RA axis sleeve.
The sleeve is a threaded alum tube with a tangent clamp which grips
the section of RA thread with almost nil play.
This, for now, will do as the RA shaft.

I used an old VCR head as a mandrel to enable me to bore it out
to the right size.
I also made the first of two pressure plate clutches. This first one
will screw/bolt directly to the RA shaft and the other will clamp
the worm gear from the opposite side to provide slip/drive
pressure, just like on my big GEM.
The worm carriage is also shown, minus the thrust ball races.
I will probably run this through a 150:1 gearbox that I have and
use a 400 step/ rev stepper motor.

Steve

[bmitchell82]

great progress steve! Just the other day the lab i work recived its new metric lathe, new mill/pedastool drill and a few other bits and bobs. and there is a whole host of new tools.! :) might have to get in an do osmething this uni break

[hikerbob]

Steve thanks for the idea and posting details of your progress. That's a really simple fast and cheap way to get a fairly stiff lightweight mount.

Are you planning to drive on both axis?

Bob

[kinetic]

No Bob, only the RA axis.
I figure, for a DSLR wide field imaging platform I only need to
point to my FOV, engage the clutch and turn on the Bartel drive.
DEC gearing would add to the weight.

Steve

[bmitchell82]

ehehehe yes steve i have had some experience now. ive made a whole heap of stuff. the chuck on the old bertha is 12" and the same with the new metric one, i think the bed is 7foot or so? something like that but in any case its awsome bit of kit with linear digital gauges that get to 0.001mm accuracy... madness

[kinetic]

Some more progress:
2nd pressure clutch made (old VCR head) plus two cork clutch plates.
All assembled on the RA drive collar.
Worm with thrust races assembled and tested for mesh.
Feels good.

Steve

[peter_4059]

Steve,

This is a great thread (and story). My kids want to know what you are going to use the scooter wheels for?

Peter.

[kinetic]

Hehehe Peter, I was asked that by my kids the day this started :)

[hikerbob]

I've powered up the DEC axis drive tonight for a scooter based mount I started after reading Steve's opening post. Such a great idea.

There are still a couple of concerns - I'm struggling with getting the tension between the worm and gear just right and I'm not sure that the gear is as concentric as it should be. I've had the alt axis fitted previously but took it off for this testing and I still want to work out how I'll do the clutch on it.

I may revisit the motor and motor support as it's bulkier than I'd like but it's working to get me started. I'm also running an excess of grease at the moment.

The work is part of a turned down M12 2.5mm stainless bolt and the gear was made by pressing the blank against an M12 2.5mm tap in the lathe.

Anyway so far so good. Thanks again Steve for the idea.

Bob

761007610176102

[kinetic]

Good effort Bob! :)
Now I don't feel so crazy doing this:thumbsup:
That looks like the polar axis you're driving there, not the DEC
axis?
Take a close look at the clutch method I used. They work so
well, the slippage is beautiful, protects the worm gear and
just a little tighten on the pressure plate and it drives.
The clutch idea is courtesy Dave G.

Steve

[hikerbob]

Steve "That looks like the polar axis you're driving there, not the DEC
axis" - yep my mistake.

I'm using a pressure plate clutch setup on this. At the moment it's a thin sheet of rubber between the worm gear and a ridge on the shaft with a plate on the other side used to tension the whole thing. It seems to work very well but if I can source some suitable cork that looks like a better option. I can imagine the rubber binding to the aluminium over time then not slipping when required.

From the play I've done the whole set up seems to be very rigid, if I can get the tracking smooth enough it should make a great platform for wise field work.

I've not tried running the motor at tracking speeds yet, so far I've just plugged in an arbitrary figure to get it working. Using the basic stepper driver and the gearing I have I'd be doing 4.3 microsteps a second which seems lower than ideal. I'll revisit the stepper driver to up the number of microsteps.

Bob

[kinetic]

Almost there....
I jury rigged my Observatory stepper to drive it at a
theoretical tracking rate calculated on the reduction ratios.

Slews are also smooth, at least so far with a handheld stepper
coupled through some surgical tubing. My hand would be dampening
out the majority of any vibration that could affect a camera.

Steve

[kinetic]

A result.
8x frames 1min each ISO 800
Pentax DSLR , standard lens at approx 22mm.
(I need to check the EXIF) Edit: 26mm F8

Quick stack in DSS, sorry about the processing!

Dome GEM stepper used here, poked out the door of the
dome via an extension to the 6core cable :)
Bartel Drive Azimuth/arcsec/step set to new worm size
and a very rough polar align...
Man it's unpleasant polar aligning on a 5 degree night
on the middle of the lawn.
Gimme my permanent dome setup anytime!

Edit: 2nd process in Neb added

Steve

[bojan]

Fantastic work and excellent result Steve :-)
I too have one scooter, my daughter used to use it (and me... almost broken my leg once never climbed on t since..).
Maybe one day I will put it to better (and safer) use :-)

[kinetic]

Thanks Bojan,

I'm sorry, but this polar alignment thing is NO FUN AT ALL! :)
I had forgotten how unpleasant the "back to basics on the cold
lawn" business end of astro was !
I have given it away tonight after half an hour...:sadeyes::)

Steve

[bmitchell82]

Great to see that your getting somewhere with it all steve. :D but i have to say harden up :) 5 deg isn't that bad zero is bad :D

[kinetic]

Fresh out of the etch tank....Scooter gets herself a
circuit board of her own.

[bmitchell82]

tough as 6" gal nails steve :) even with pretty pink flowers and all :), i thought you might have even designed the PCB in a floral arrangement ;) now that would be cool :) CUSTOM... :)

how is scoots going? any more test runs/imgaes

[lacad01]

Only just stumbled onto this thread today. Pretty ingenious way to recycle old stuff :)

[Brundah1]

Steve,

Have you stated an IIS challenge here?

This is more fun than discussing DDM futuristic wiz bangers.

Could easily start a few projects a la drainpipe refractors etc.

Good on you, can't wait to see Scooter carrying a drainpipe refractor and a webcam :)

Keep the pics flowing.

David

[kinetic]

A few more pics.
Comet 103P Hartley2 and a shot of the LMC from this morning.
Bad gradients, polar alignment out, not saved in DNG RAW, but
nevertheless, a reasonable indicator of tracking.

Steve