Post your home made scope
Posted 03 February 2013 - 09:30 PM
Posted 04 February 2013 - 12:16 AM
- Chassetter likes this
Posted 04 February 2013 - 06:07 AM
Here's my 10inch F4 Serrurier truss I recently completed.
Mirrors are from Orion Optics in the UK, trusses are carbon fibre, secondary spider is from guitar strings to minimize diffraction spikes, I've used guitar machine heads to adjust tension. Mirror Cell is a 6 point cell made from Aluminium square pipes rocking on a horizontal bolt held with clamps.
Posted 04 February 2013 - 06:09 AM
So how did it turn out? was the mirror as good as you had hoped.???
Absolutely gorgeous, the most beautiful restore Ive ever seen.
Posted 04 February 2013 - 06:14 AM
It has a picaxe microcontroller based stepper controller with timing belt gear reduction to minimize PE.
RA Bearings are 50mm Bearings. Current RA shaft is Delrin with a steel Rod insert, but I'll be changing this to a steel tube.
I've added ST4 autoguiding by using a picaxe to monitor the 4 pins of the guidecam's ST4 output and adjusting the step gap duration in the stepper controller to either speed up RA or slow down RA.
Posted 04 February 2013 - 08:59 AM
Unfortunately this counterweight device won't work well because as the tube rotates from vertical to horizontal, the amount of torque around the altitude axis increases greatly. The counterweight device in your picture produces a constant torque so it will balance at only one position. Possibly you could make it work by offsetting the center of the counterweight support disk so that the torque increases as the tube rotates to horizontal. But ideally the counterweight should hang from an arm that is parallel to the tube, in which case why not mount it directly on the arm or tube?
The idea isn't that brilliant; it is a derivative of Porter's Springfield Mount.
I have something similar in my head but my counter weight hangs and uses the rocker box as a rail to glide on.
It is possible to build spring devices with torque that varies so that the tube is balanced at all positions. I've built one myself and have seen some others posted in this forum. But I think the simplest way to build a Newtonian that is balanced around the eyepiece is to just use a counterweight at the opposite end from the mirror.
Posted 04 February 2013 - 09:43 AM
Unfortunately this counterweight device won't work well because as the tube rotates from vertical to horizontal, the amount of torque around the altitude axis increases greatly.
i don't make changes in torque for my dobs, when I balance my dobs the torque is constant.
the only thing I see is an twist caused by weight on one side and not the other but that is easily remedied.
But I think the simplest way to build a Newtonian that is balanced around the eyepiece is to just use a counterweight at the opposite end from the mirror.
thats not consistent with your first statement.
Posted 04 February 2013 - 10:46 AM
Posted 04 February 2013 - 11:20 AM
But a true Springfield is more better!
Posted 04 February 2013 - 11:35 AM
@all: Very nice scopes are shown here!!!
Posted 04 February 2013 - 11:55 AM
show me your math...
Posted 04 February 2013 - 12:27 PM
My (technical) English is much to bad for explaining such things, I´m sorry, but you can read it in every book about primary physics or technical engineering...
Maybe there would be some other guys, who speak English much better than I, and who can explain it. I also don´t know, whether, and when how, I can write math formulas here on cn...
Posted 04 February 2013 - 01:35 PM
the lever arm on the scope I drew is about 6in away from the center of rotation, and the 6in mirror is approx. 32in away from the center of rotation.
so if I rough in the torque balance eq.
6in*(x)lbs = 32in*(y)lbs
so in this equation where do you implement the angle of momentum.
Posted 04 February 2013 - 02:18 PM
Here is a link to calculate springs (compression-, extension- and torsion-springs):
Maybe it would help.
In case of your Dobson, you get a torque moment depending on the length of the leverarm, the angel of the lever arm to the gravity force vector and the wight force at an arbitrary point on the lever arm.
Please excuse my bad English...
Posted 04 February 2013 - 04:51 PM
I hope we haven't totally derailed this topic. There are some wonderful ideas here. Markus, your travel scope at the top of page 6 is magnificent!
Posted 04 February 2013 - 05:49 PM
Mathematically, the torque due to the mirror is proportional to the sine of the angle of the tube away from vertical.
just one more thing.
on the mirror side,from angles 0-45, torque=Length*lbs*cos angle, from angles 45-90, torque= length*lbs*sine angle.
so at 45* the torque is the least.
Still working on my travel dob
Posted 05 February 2013 - 07:48 AM
Posted 05 February 2013 - 09:33 AM
Could that be done with bolts with knobs??or would they get in the way of when packaging up for travel?
Posted 05 February 2013 - 09:45 AM
The box near the focuser holds five of the most used eyepieces. The finder is a 5" f/9 to allow for wide-field views.
- Chassetter likes this
Posted 05 February 2013 - 09:49 AM
Posted 05 February 2013 - 10:07 AM
nough said, totally true
- tim53 likes this
Posted 05 February 2013 - 10:17 AM
since it's made out of 3/4 ply, I need to raise it about a 1/4 in, so I made plates to raise it up. I have press fit knobs for the allen head screws. i'm using them here on the alt bearings
also its better to come in from the aperature hole side with the screw, the alt bearings kind of get in the way, on the backside it fine. compare the previous pic with this.
so goes my life make it twice before I get it right.
Posted 05 February 2013 - 10:21 AM
Hows this for ugly? It is a 42" f/4.
I would have to agree, that is very ugly indeed.
now if you had a dragon [for heavan] or a tiger [for earth] burnt into the wood somewhere it would add the coolness back.