VEX part strengths

[efoote868]

For my senior design project, my group is looking to build a GoTo telescope. Since we're all electrical / computer engineers, mechanical design isn't really one of our strengths.

Mechanically, what we want to design is a two joint solution that allows us to spin and incline. We'd like our solution to be independent of both tripod and telescope - that is we can attach the solution to a standard tripod mount, and then also have a mechanism to attach to a telescope.


There are a few design considerations. One is that we need to have slow and precise movements, probably no more than 10 degrees / second. Also we might need relatively large amounts of torque, considering the size and length of some telescopes. The motion of action on the inclination needs to be close to 90 degrees.


There are lots of things appealing to me about using VEX. My primary concern right now is the part strengths. I'd rather not break a bunch of VEX parts to find out that I can't use it


Initially, my questions are:

How much weight can the turntable bearing kit support,
http://www.vexrobotics.com/vex/produ.../276-1810.html

How much torque can be applied to the square bar shafts,
http://www.vexrobotics.com/vex/produ...on/shafts.html

and gears,
http://www.vexrobotics.com/276-2250.html

And lastly, is this is type of information published anywhere?

[Nathan]

Originally Posted by efoote868

How much weight can the turntable bearing kit support,
http://www.vexrobotics.com/vex/produ.../276-1810.html

How much torque can be applied to the square bar shafts,
http://www.vexrobotics.com/vex/produ...on/shafts.html

and gears,
http://www.vexrobotics.com/276-2250.html

And lastly, is this is type of information published anywhere?

Unfortunately I don't think you're going to find that information published anywhere. I can't answer all of your questions, but you haven't gotten a reply in a few days, so I'll bite

I've never used the turntable, so I can't comment on that.

I can't give you an exact figure for how much torque the drive shafts can take, but I just tried twisting a shaft with two pairs of pliers and wasn't able to bend it permanently (it flexed a little bit, but not much at all). I think the shafts are made out of steel, so they're pretty strong (at least for a short length).

I haven't used the high strength gears, but I can tell you that the normal vex gears are pretty durable. I've really abused mine and have never had one break on me.

Originally Posted by efoote868

There are a few design considerations. One is that we need to have slow and precise movements, probably no more than 10 degrees / second. Also we might need relatively large amounts of torque, considering the size and length of some telescopes. The motion of action on the inclination needs to be close to 90 degrees.

You might have trouble with the Vex motors for this application. For a telescope you will need torque, precision, and repeatability/accuracy, and I don't the the Vex motors will meet any of those requirements. The Vex motors don't have a lot of torque (at least not in terms of moving a heavy telescope) and without some sort of feedback (making it a closed-loop drive system) you won't have any idea how far the telescope has been panned or tilted. I would suggest looking into using stepper motors. They will have far more torque then the Vex motors, will eliminate the need for feedback, and are extremely precise.

If I were you, I would head over to cnczone.com and ask for suggestions on the mechanical side of things there. This is a very cnc-ish project.

Good luck!

Nate

[ttldomination]

You might want to head over to vexforums. There might be people who are more in tune with these values.

- Sunny G.

[efoote868]

Thanks for testing with pliers.

After talking with my group, I think we're going to be using a combination of vex, erector/meccano, and a 3d printer.

The 2-Wire 393 motor has a free spin of 100 rpm, so if we gear it down 60:1 the output will be about 10 degrees per second (less, considering an added load).
This also gives it a stall torque of 885.6 in-lb, which should be enough .

Even better is the integrated encoder module at 627.2 per revolution, or 104 ticks per degree geared.


Once we have more things figured out, I'll make sure to share.

[efoote868]

Figure I owe CD an update on this project. We're done, and I'm about to graduate from Purdue.

http://www.youtube.com/watch?v=rroVH...ature=youtu.be

Not sure when the project's webpage will be archived, but until then it'll be here:
https://engineering.purdue.edu/477grp18/


The self-aiming telescope uses a compass and an accelerometer to form a coordinate system. It also uses a GPS to determine the time, as well as the position on Earth. The telescope communicates to an android device via bluetooth, the android device sends the star coordinates to the telescope mount, which calculates an offset and automatically moves the telescope.

VEX components used include the 269 motors and integrated encoders, along with gearing. Final gear ratios are 63:1 for elevation, and 16.5:1 for rotation.

The telescope's movement is accurate to within a tenth of a degree. Let me know if you have any questions.

[connor.worley]

This is really cool

[Taylor]

That. Is. Awesome.

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