06-aug-2015SatNOGSHWCommunityCall

(03:51:16 PM) kd8qwt [18c004f2@gateway/web/freenode/ip.24.192.4.242] entered the room.
(03:54:10 PM) papamat: hello
(03:54:40 PM) kd8qwt: hello
(03:57:50 PM) pid: hello
(03:58:47 PM) papamat: kd8qwt: what cad do you use?
(03:58:55 PM) kd8qwt: Fusion 360
(03:59:22 PM) kd8qwt: It's still free for hobby use
(04:01:18 PM) kd8qwt: What DC motors are being looked at for V3?
(04:01:56 PM) papamat: oh is cloud based?
(04:02:06 PM) papamat: are you design inside a browser?
(04:02:19 PM) kd8qwt: Yes, but if the cloud is dead it will use local cache
(04:02:31 PM) kd8qwt: No, there is a client
(04:02:41 PM) papamat: let me find the link for the motors
(04:02:55 PM) kd8qwt: I use both Windows and OSX clients
(04:04:11 PM) jasiek: can you guys tell me more or less why there's a V3 of the rotator? eg. how the V2 was deficient?
(04:04:28 PM) papamat: https://www.ethercalc.org/V3motorSpec
(04:04:41 PM) papamat: this is the list with the motors we will try
(04:06:09 PM) papamat: https://community.satnogs.org/t/satnogs-rotator-version-3/226
(04:06:44 PM) papamat: the first post in this tread
(04:07:08 PM) papamat: have the bigger issues of the v2 design
(04:07:39 PM) jasiek: cheers
(04:08:03 PM) papamat: i think that those are the huge amount of friction and the lack of rigidity
(04:08:48 PM) kd8qwt: With a small windshield wiper motor and this controller I was able to get 8 rpm.  I didn't measure the torque but the shaft was very difficult to stop - https://www.pololu.com/product/2507
(04:10:08 PM) papamat: kd8qwt: https://www.robotshop.com/en/12v-501-170oz-inc-metal-gearmotor.html
(04:10:17 PM) papamat: we use this for now
(04:10:54 PM) papamat: omg
(04:11:00 PM) papamat: 30 amps?
(04:11:32 PM) papamat: you can turn the earth around you :P
(04:11:51 PM) kd8qwt: It doesn't get hot.  The moors don't use more than an amp or 2
(04:11:52 PM) papamat: what windshield wiper motor do you use?
(04:12:00 PM) papamat: yeap
(04:12:04 PM) kd8qwt: If I stall the motor it can get to 2 amps
(04:12:28 PM) kd8qwt: For an old Jeep.  I just looked for the cheapest wiper motor on ebay
(04:12:44 PM) papamat: in our motors we have 1.5 Amps too stalled
(04:12:59 PM) papamat: new or used?
(04:13:02 PM) kd8qwt: They were $28, but the same vendor has increased their price now to $48.  There are other cheaper vendors, but I haven't looked hard
(04:13:09 PM) kd8qwt: Says new
(04:13:09 PM) papamat: and how much did you pay?
(04:13:11 PM) papamat: ok
(04:13:20 PM) kd8qwt: It was $28 shipped
(04:13:56 PM) papamat: they are not much cheep
(04:14:00 PM) kd8qwt: Both the motor and controller barely gets above room temp, even after running for 30 min
(04:14:50 PM) kd8qwt: No, but they are more powerful, available pretty much anywhere, and can run 8 rpm
(04:15:07 PM) papamat: https://www.pololu.com/product/1213
(04:15:21 PM) papamat: we are using this driver
(04:15:32 PM) papamat: do you have any link for the motors?
(04:16:25 PM) papamat: with 8 rpm maybe you ll be a bit low speed-wise
(04:17:01 PM) kd8qwt: That's the lowest speed.  They can spin quite fast
(04:17:03 PM) kd8qwt: http://www.ebay.com/itm/130990255602?_trksid=p2057872.m2749.l2649&ssPageName=STRK%3AMEBIDX%3AIT
(04:17:56 PM) kd8qwt: The 8rpm goes into a belt and worm gear that takes it to 50:1
(04:18:41 PM) kd8qwt: My design is a bit larger and designed to carry more weight
(04:19:49 PM) kd8qwt: More aluminum pieces
(04:20:37 PM) papamat: the look heavy duty
(04:20:49 PM) papamat: my only concern is the speed
(04:21:03 PM) papamat: the belt drive is 1:1?
(04:21:15 PM) kd8qwt: 2.24:1
(04:21:26 PM) kd8qwt: Speed as in too slow?
(04:22:43 PM) papamat: the theoretical optimum speed is around 5degs/sec
(04:23:08 PM) papamat: so you have 8rpm
(04:23:27 PM) kd8qwt: Minimum
(04:23:44 PM) papamat: and the belt and worm ratio is 2.24*50
(04:24:27 PM) kd8qwt: Belt is 2.24:1 and worm is 25:1
(04:24:47 PM) papamat: oh
(04:24:49 PM) papamat: ok
(04:25:25 PM) papamat: so the ratio from the motor to output is around 50
(04:25:25 PM) papamat: ok
(04:25:29 PM) kd8qwt: I think that puts it in the right range
(04:25:50 PM) kd8qwt: I can easily reprint the belt ratio
(04:26:10 PM) papamat: 8rpm is 48degs/sec
(04:26:24 PM) kd8qwt: I have most of it printed.  I'm waiting for the stainless steel hardware to bolt it together
(04:26:35 PM) papamat: so you ll have about 1 deg/sec in output
(04:27:05 PM) papamat: your pulleys are printed?
(04:27:07 PM) kd8qwt: Excellent
(04:27:11 PM) kd8qwt: Yes
(04:27:14 PM) kd8qwt: GT2 3mm
(04:27:25 PM) kd8qwt: Everything printed in PETg
(04:27:37 PM) papamat: are they working good?
(04:28:02 PM) papamat: oh! I have never printed in PET
(04:28:15 PM) papamat: what temp do you need to print PET?
(04:28:18 PM) kd8qwt: I haven't bolted everything together yet, but from what I've tested so far I think it will work fine
(04:28:21 PM) papamat: is it expensive?
(04:28:21 PM) kd8qwt: 250c
(04:28:27 PM) kd8qwt: $29
(04:28:42 PM) papamat: 29$ per what??
(04:29:03 PM) kd8qwt: http://www.intservo.com/products/esun-petg-filament-1-75mm-1kg-spool?variant=963058195
(04:29:20 PM) kd8qwt: 1kg
(04:29:22 PM) papamat: is it have better mechanichal properties?
(04:29:39 PM) papamat: is not expensive
(04:29:53 PM) kd8qwt: It's very smooth, UV stable, and will not separate at the layers
(04:30:23 PM) kd8qwt: I've broken a few, and they all had random breaks.  Nothing along the layers
(04:30:24 PM) papamat: looks very nice
(04:30:32 PM) papamat: I ll test it asap
(04:30:44 PM) kd8qwt: Much better than ABS I think
(04:30:58 PM) kd8qwt: No need for an enclosure to print
(04:31:23 PM) kd8qwt: Bed temp at 90c and glue stick on the glass
(04:31:37 PM) kd8qwt: Low shrinkage
(04:31:46 PM) kd8qwt: Great for mechanical stuff
(04:32:42 PM) papamat: ok
(04:33:04 PM) papamat: I am searching a place to order now :P
(04:33:24 PM) kd8qwt: My BOM for 2 rotators is around $500.  That includes the pi and filament.
(04:33:51 PM) papamat: 2 rotators or 2 axis?
(04:33:51 PM) kd8qwt: It's a bit heavier than the V3
(04:34:02 PM) kd8qwt: y
(04:34:27 PM) dosman [~dosman__@140-182-31-84.ssl-vpn.indiana.edu] entered the room.
(04:34:32 PM) papamat:  have you designed your worm too?
(04:34:44 PM) papamat: hello dosman
(04:34:51 PM) kd8qwt: I used cheap skate bearings everywhere, so that kept the cost down there so I can spend more elsewhere
(04:34:55 PM) dosman: hello papamat
(04:35:10 PM) kd8qwt: I printed the larger gear and bought the smaller delrin gear
(04:35:18 PM) kd8qwt: From a Genie garage door opener
(04:35:24 PM) kd8qwt: $7 shipped from ebay
(04:35:36 PM) papamat: azisi have designed something to cut in your laser cutter
(04:36:04 PM) papamat:  kd8qwt: link? :P
(04:36:13 PM) dosman: :-)
(04:36:35 PM) kd8qwt: http://www.ebay.com/itm/Genie-Garage-Door-Opener-Worm-Gear-Part-33355A-S-Genuine-Genie-Part-/291051910468?hash=item43c40bb544
(04:36:39 PM) kd8qwt: $8 now
(04:37:10 PM) kd8qwt: I just couldn't print a gear I liked
(04:38:06 PM) papamat: nice
(04:38:18 PM) kd8qwt: It feels quite smooth on the PETg, especially with some sticky grease
(04:38:19 PM) papamat: how long time are you building it?
(04:38:40 PM) kd8qwt: I started shortly after I saw the V3 at Hamvention
(04:39:01 PM) kd8qwt: I started to build the V3, but I kept changing it
(04:39:18 PM) kd8qwt: Now it's completely different :)
(04:39:32 PM) papamat: :)
(04:39:50 PM) kd8qwt: The electronics should be the same, more or less.  My son in-law is doing the elecronics
(04:40:22 PM) papamat: are you gonna upload the design files under an open source license?
(04:40:38 PM) kd8qwt: The 2.5" aluminum tube running through the middle will take up to 1.5" pipe slid in
(04:41:00 PM) kd8qwt: Once I finish it and find that it work, I'll probably release everything.  I don't plan on selling it
(04:41:18 PM) kd8qwt: Don't want to support it actually :)  Hams are funny people :)
(04:41:37 PM) kd8qwt: It should be very rigid
(04:41:51 PM) papamat: we have some thoughts to host a wiki page to upload our designs and other open source designs too
(04:42:04 PM) papamat: hahahaha
(04:42:18 PM) papamat: ham are funny and a bit weird :P
(04:42:36 PM) kd8qwt: Especialy in large numbers like Hamvention :)
(04:43:05 PM) papamat: :)
(04:43:42 PM) kd8qwt: If you want to use any of my designed you are free to do so.  I can post what I have
(04:44:24 PM) papamat: I want to try it for sure
(04:45:32 PM) papamat: https://github.com/satnogs/satnogs-rotator/blob/master/t_slot20_connector.stl
(04:45:41 PM) papamat: dosman: look this part
(04:46:36 PM) papamat: we design it and built it as a replacement for those metal corners
(04:46:50 PM) papamat: let me upload some pics
(04:47:23 PM) kd8qwt: I have printed connectors like that before.  They work well, but there is still some flexing
(04:47:28 PM) dosman: excellent
(04:47:52 PM) kd8qwt: PETg should work well
(04:48:18 PM) kd8qwt: 4 layers and at least 50% infill
(04:50:10 PM) kd8qwt: It does add bulk to the outside, making it harder to add panels and such
(04:50:26 PM) papamat: yeap
(04:51:07 PM) papamat: and you need around 100 bolts to built the outer cell
(04:51:37 PM) papamat: https://papamat.m3design.gr/index.php/s/JMdwn8u0HFWkxqw
(04:52:17 PM) papamat: https://papamat.m3design.gr/index.php/s/iWHWlh6401VKCJA
(04:52:49 PM) papamat: https://papamat.m3design.gr/index.php/s/PbgEktgVeN0OWlJ
(04:54:45 PM) kd8qwt: Very nice
(04:55:31 PM) papamat: the 500$ are for 2 axis's?
(04:55:39 PM) papamat: or for 2 rotators?
(04:56:01 PM) kd8qwt: 2 axis, a complete tracker
(04:56:19 PM) papamat: ok
(04:57:07 PM) papamat: and what axis you ll gonna use?
(04:57:59 PM) kd8qwt: Not understanding the question
(04:58:14 PM) papamat: sorry for my english :P
(04:58:29 PM) kd8qwt: np.  It's quite good
(04:58:39 PM) papamat: we are using an 32mm pvc axis
(04:58:54 PM) papamat: what do you use?
(04:59:34 PM) kd8qwt: No.  63mm tube, 6.35mm thick
(04:59:53 PM) papamat: omg
(04:59:58 PM) kd8qwt: Then either pvc or metal pipe can be slid inside and bolted to the tube
(05:00:38 PM) kd8qwt: Like I said, larger and heavier
(05:00:49 PM) kd8qwt: PVC doesn't last long in the sun
(05:00:52 PM) papamat: nice
(05:00:56 PM) papamat: weap
(05:01:00 PM) papamat: yeap*
(05:01:10 PM) kd8qwt: I used skate bearings to keep the cost down
(05:01:34 PM) papamat: i saw this at the forum
(05:03:04 PM) kd8qwt: Then I use a trailer bearing seal to seal the large tube and keep as much water out of the inside as possible
(05:04:09 PM) papamat: nice
(05:04:13 PM) kd8qwt: I think this unit will be able to hold very large arrays
(05:04:54 PM) kd8qwt: Aluminum angle iron is used to brace and bolt the 2 units together.  That's not in the cad drawing
(05:05:01 PM) kd8qwt: Hence the $500
(05:05:31 PM) kd8qwt: The plan is to put it up and not take it down except to peek inside every once in a while
(05:07:41 PM) kd8qwt: If I seal the 10 turn pot, then noting inside can be damaged by weather
(05:08:00 PM) kd8qwt: Wiper motors don't need to be as protected
(05:08:20 PM) papamat: You can seal it with a good amount of grease
(05:09:07 PM) kd8qwt: Plus they are rated as continuos duty
(05:10:13 PM) kd8qwt: Continuous
(05:10:19 PM) kd8qwt: Can't spell today :)
(05:15:16 PM) papamat: you can use hall effect encoders too
(05:15:48 PM) papamat: you can made them completely waterproof
(05:16:33 PM) kd8qwt: True.  We may even eventually do that
(05:17:08 PM) azisi [~chatzilla@ppp079167009101.access.hol.gr] entered the room.
(05:17:45 PM) kd8qwt: The pot is geared down 4:1 from the main shaft.  We may make some changes there.  My son in-law is looking at sensors to determine elavation angle and az direction
(05:19:51 PM) kd8qwt: He's loking to add an LCD on the electronics housing that displays the current track
(05:19:55 PM) kd8qwt: Fun stuff
(05:20:54 PM) papamat: http://ams.com/eng/Products/Position-Sensors/Magnetic-Rotary-Position-Sensors/AS5040
(05:21:10 PM) papamat: check this for the positioning
(05:23:28 PM) azisi: hey, the magnetic encoder also used in http://reprap.org/wiki/Magnetic_Rotary_Encoder_v1.0
(05:24:30 PM) kd8qwt: That would make for a nice sealed unit
(05:25:03 PM) azisi: How to control the H bridge and potentiometer, with arduino?
(05:25:45 PM) kd8qwt: Yes, some version of arduino
(05:26:45 PM) azisi: yes, i think the two part epoxy is not affect the magnetic sensor
(05:27:18 PM) kd8qwt: Or just print a housing around the chip
(05:28:08 PM) papamat: you can try to order 2-3 pieces as sample
(05:30:12 PM) azisi: how do you mount the gear on the axis?
(05:32:01 PM) kd8qwt: The main printed gear has slots and the AL tube is drilled and tapped.  The slots are so I can slide the gear to align it with the small worm gear
(05:34:52 PM) kd8qwt: The mount for the work gear is bolted to the base plate, but the holes are large anough to make small adjustents to make sure the worm has the right contact point with the main gear
(05:35:27 PM) kd8qwt: I built a test plate and everything looks to bolt up well
(05:41:12 PM) papamat: dosman: are you here?
(05:41:32 PM) dosman: heya
(05:41:44 PM) kd8qwt: I think at this point we want to get it built.  Then we'll look at other enhancements and adjustments
(05:41:57 PM) papamat: do you want to make the pr in the v2 branch?
(05:42:02 PM) papamat: :)
(05:42:35 PM) papamat: when do you think it will be ready
(05:43:08 PM) papamat: ready as prototype I mean, not really for your rooftop
(05:43:18 PM) papamat: *ready
(05:43:58 PM) dosman: you mean the t_slot20_connector part?
(05:45:06 PM) papamat: no
(05:45:40 PM) dosman: sorry, else-window, missing some of the convo here
(05:45:42 PM) papamat: i mean this awesome bash script
(05:46:14 PM) papamat: the axis side generator
(05:46:46 PM) dosman: I'll see what I can do. I'm a git noob, and after the repo re-org I didn't want to screw anything up both on my side and your side
(05:47:04 PM) papamat: hahaha :)
(05:47:06 PM) dosman: I'd like to see that get in though :-)
(05:47:27 PM) azisi: i am also noob ...
(05:47:32 PM) papamat: all the hardware guys are git noobs
(05:47:37 PM) dosman: :-)
(05:48:00 PM) papamat: but we have the other to clean up our mess
(05:48:07 PM) papamat: *others
(05:49:54 PM) azisi: kb8qwt, the worm mount are 3d printed with PET?
(05:50:08 PM) kd8qwt: Yes.  Everything printed is with PETg
(05:50:35 PM) kd8qwt: All the bearings are skate bearings, so I use those in the worm gear mount as well
(05:52:42 PM) azisi: i think it is a weak point, because all the torque from the axis to worm goes there
(05:54:44 PM) kd8qwt: Yes, it is certainly a weak point.  The mounts are very stiff.  Are they stiff enough for a heavy antenna?  I don't know yet.  If not, I'll beef them up some more.  There are 2 8mm bolts holding one mount and 3 8mm bolts holding the other
(05:56:20 PM) kd8qwt: The axis won't be flexing under the weight, so any movement will be strictly from the gear on gear forces
(05:56:59 PM) kd8qwt: Which is much less than a regular gear
(05:57:58 PM) kd8qwt: Holding the gears together by hand, it takes a tremendous amount of force to push the gears apart
(06:00:01 PM) papamat: I think that the biggest amount of force is parallel to the small gear axis
(06:01:30 PM) kd8qwt: Yes, that is true.  The mounts are stronger in that direction.  I was thinking about printing a brace to bolt on top of both mounts, over the gear, just to attach the smaller end mount to the larger mount
(06:01:49 PM) kd8qwt: If it's needed
(06:02:08 PM) kd8qwt: I have CAD and a printer.  I can always print more :)
(06:02:14 PM) papamat: :)
(06:02:58 PM) kd8qwt: I do plan on adding weight to the elavation until something breaks.  Then I'll know where the weak part is
(06:03:28 PM) papamat: we use just a scale
(06:03:40 PM) papamat: and we pull with that
(06:04:49 PM) kd8qwt: That works too.  I don't have a scale, but I do have weights
(06:08:19 PM) kd8qwt: I think the worm gear mounts are the components that will fail first
(06:09:20 PM) kd8qwt: But I think that will be way past the maximum weight the rotators will be asked to handle
(06:09:31 PM) kd8qwt: Worse case I'll cut them out of aluminum on my CNC
(06:19:55 PM) azisi: your idea with skate ball bearings is great
(06:20:10 PM) kd8qwt: Those are so cheap they are almost free
(06:20:21 PM) kd8qwt: I paid like $14 for 64
(06:20:54 PM) azisi: haha
(06:21:15 PM) kd8qwt: The skate mounts are small and very regid.  There is a printed ring that bolts on the main shaft that rides between the bearings, preventing side motion
(06:21:38 PM) kd8qwt: For the elavation rotator only
(06:22:18 PM) kd8qwt: The az rotator has a surplus flange bearing rated at several hundred pounds at 5,000 rpm.  It was only $8 and it was new
(06:24:39 PM) kd8qwt: I think 3 skate mounts around the main shaft would be enough to hold it just fine, but there was room for 5
(06:27:16 PM) marshall_afk is now known as marshall_law
(06:27:47 PM) marshall_law is now known as marshall_afk
(06:30:52 PM) cshields: hi all
(06:31:02 PM) kd8qwt: Howdy
(06:31:58 PM) cshields: papamat: w/r/t git and hardware, I won't be around for the official meeting time today (sorry, in the office/SFO this week, stuck in meetings) - I do want to see how you would like to handle imperial-sized parts.  Once I finish testing them we should put them in the main repo somewhere I'm guessing
(06:32:21 PM) cshields: you can see them all ending in _imperial.stl here  https://github.com/cshields/satnogs-hardware/tree/imperial
(06:32:29 PM) cshields: the source files are named the same but this is a branch
(06:33:50 PM) cshields: it would be nice to come up with a workflow for how we want to handle this in the future.  I'd recommend we not try to maintain 2 branches of source parts but rather make the conversion to imperial after major milestones are hit  (in other words, one-time conversions to imperial should be easier than trying to keep imperial parts up to date with the other changes)
(06:38:04 PM) papamat: sounds nice
(06:38:17 PM) papamat: there is a feature in freecad
(06:38:24 PM) papamat: let us find the link
(06:38:44 PM) cshields: if freecad handled variables a bit easier like openscad did that is another option
(06:38:46 PM) papamat: i witch you can drive the value of a constrain
(06:38:51 PM) cshields: because really that is 90% of the conversion
(06:39:05 PM) cshields: right, I find that contraint and just change it  :)
(06:39:25 PM) papamat: from the in-program spreadsheet
(06:39:50 PM) papamat: we try to finde out haow exactly it works
(06:41:22 PM) papamat: http://www.freecadweb.org/wiki/index.php?title=Spreadsheet_PropertyController
(06:41:39 PM) papamat: is this feature witch is looking intresting
(06:41:48 PM) papamat: interesting*
(06:42:04 PM) cshields: I'm assuming that t_slot20_connector pasted earlier would be in place of the inside hidden connector?
(06:42:58 PM) papamat: yeap
(06:43:09 PM) papamat: we are doing some tests
(06:43:17 PM) papamat: can you read the history?
(06:43:32 PM) papamat: there are some photos too
(06:43:56 PM) papamat: we will made a post in forum too
(06:44:50 PM) cshields: did you see this one?  might be better for the corners as it holds all axis to 90 degree angles  https://www.thingiverse.com/thing:489216
(06:45:48 PM) azisi: yes, we print it and try it and failed
(06:45:53 PM) cshields: !!
(06:46:05 PM) cshields: well, shit.  heh
(06:46:22 PM) papamat: the problem is the way is printed
(06:46:47 PM) papamat: with a little amount of force the layers are separating
(06:47:00 PM) papamat: so we built the other
(06:47:07 PM) cshields: but is that an issue with the slicer or its settings?
(06:47:13 PM) cshields: or, ohhh
(06:47:19 PM) kd8qwt: Try PETg.  Layers don't separate
(06:47:22 PM) cshields: the vertical layers of the piece that sticks up
(06:47:35 PM) papamat: we will try PET
(06:47:36 PM) azisi: also we use M5 nuts without this http://www.thingiverse.com/thing:28788
(06:47:44 PM) papamat: definitely
(06:47:58 PM) kd8qwt: Also, the extrusions have a slight depression designed to pull the aluminum up to the plate being tightened
(06:48:09 PM) kd8qwt: So it does put stress on the plastic part
(06:48:25 PM) cshields: azisi: I plan on trying those next week  :)
(06:49:03 PM) cshields: but I can see how printing the sides vertically sliced would compromise some structural strength
(06:49:05 PM) kd8qwt: I've only tried the eSUN PETg.  I've heard that others do sep at the layers.  Not sure what the diff is
(06:50:40 PM) kd8qwt: Make sure you have at least 4 solid outside layers so the bolts have solid plastic to tighten aganst
(06:51:27 PM) cshields: azisi: was it 100% solid?
(06:51:46 PM) papamat: the thingiverse one?
(06:51:51 PM) cshields: yeah
(06:52:41 PM) azisi: with 20 -25% infill
(06:53:30 PM) kd8qwt: Should be at least 50% infill with ABS.  Even then it could crack.  PETg will hold up better
(06:55:21 PM) azisi: we will test PETg
(06:58:36 PM) azisi: with t slot 20 connector we use 12xM5 screws and nuts in each corner that means 16(all corners)x12, total 192 nuts and screws
(07:00:52 PM) kd8qwt: That's why I opted to not use AL extrusions.  Another option is to print a corner piece that wraps around the extrusion on 3 sides and only 1 bolt per beam
(07:01:41 PM) papamat: like some printers do
(07:01:51 PM) papamat: like mendelmax
(07:01:56 PM) kd8qwt: Haven't seen those
(07:02:11 PM) kd8qwt: My printer doesn't use extrusions
(07:03:44 PM) kd8qwt: Trading bolts for plastic
(07:06:10 PM) papamat: yeap
(07:07:37 PM) kd8qwt: Good trade if the plastic holds up
(07:09:23 PM) kd8qwt: On the other hand all the bolts look pretty cool
(07:13:37 PM) azisi: another idea is to use two screws per t slot 20 connector (196/2=98) and the part in the middle of it has a fin that inserts in to extrusion
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