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Mechanical Differences Between MHX-2400 & MHX-2420

Discussions pertaining to the mechanical issues (e.g. enclosure, fasteners, etc.) of Pumpkin's CubeSat kit.

Mechanical Differences Between MHX-2400 & MHX-2420

Postby aek » Fri May 16, 2008 7:33 am

From a CubeSat Kit user:
quote:
We recently decided to switch to the MHX 2420 S-Band radio and ran into a small interference problem that I thought you would like to be aware of. The new radio is a little bit smaller in the Z direction and weighs about 20 grams less. Both of these are benefits but it creates one small problem. The previous S-Band radio was two PCBs stacked on top of each other and the new one is only one. This creates an interference with the MCX RF connector and the frame, see attached pictures. We will either "raise" the radio up with longer stand-offs or cut a small notch in the frame right above the USB port.

Not a big deal but I thought you like to know for future revisions and customers since you can no longer purchase the MHX 2400. As well if you know anyone looking for some 2400's we have a couple extra. Not looking to sell but if someone is in desperate need we could possible help them out.

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aek
aek
 
Posts: 1888
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Re: Mechanical Differences Between MHX-2400 & MHX-2420

Postby aek » Fri May 16, 2008 7:46 am

We now have an MHX-2420 in-house (as well as some MHX-2400s) and can confirm this issue.

To summarize, the changes in the construction of the MHX-x20 series OEM wireless modules (e.g. MHX-2420, MHX-920A, MHX-420, etc.) have made the new MHX units "considerably less tall" when the bottom of the (now single) PCB of the MHX module is used as the origin. This lowers the position of the MCX RF connector relative to the FM430 and the cutouts in the CubeSat Kit Chassis Walls. It also lowers the maximum height of the MHX module (i.e. it increases the gap between the top of the MHX module's shield / can and whatever is in Slot 1 at 25mm above Slot 0 where the FM430 is located).

Ideally, one needs to end up increasing the 13mm standoffs that the MHX mounts to by around 2mm to restore the location of the MCX RF connector to where it was when the MHX-2400 series units were used (ca. 17.25mm from the top surface of the FM430 PCB to the center of the MCX RF connector). Unfortunately, that compromises the engagement of the MHX module's pins into the H5 connectors (not enough engagement). So for now, we recommend adding 1.0mm-1.5mm of M2.5 washers between the FM430 and the 13mm standoffs in order to raise the MHX-2420 enough to re-locate the RF MCX connector close to where it would have been with an MHX-2420. Alternately, one could make ones own 14.25mm M2.5 F/F threaded standoffs. Even with the raising of the MHX-2420 module, it may be necessary for users to cut away a small portion of the cutout in the CubeSat Kit's Chassis Walls and/or Base Plate in order to get full clearance for the MCX RF connector.

Another possible solution for customers with skilled service technicians is to replace the H5 connectors with one that gives better engagement when the MHX-2420 is raised up to be 15mm above the FM430 PCB. We have not yet identified such single-inline female headers.

This problem affects all RevA|B|C FM430s, and all RevA|B|C|D Chassis.

It is likely that we will change the H5 connector and increase the length of the MHX standoffs in future revisions.

We should have an MHX-x20 3D CAD model online soon so that one can distinguish between the MHX-2400 and the MHX-2420 ...

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aek
aek
 
Posts: 1888
Joined: Sat Aug 26, 2000 11:00 pm

Re: Mechanical Differences Between MHX-2400 & MHX-2420

Postby aek » Fri May 16, 2008 9:19 am

Please also note that the MHX-2400 is now obsolete and I believe Microhard has no more available ... everyone is using (and getting) the MHX-2420.

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[This message has been edited by aek (edited May 16, 2008).]

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aek
aek
 
Posts: 1888
Joined: Sat Aug 26, 2000 11:00 pm

Re: Mechanical Differences Between MHX-2400 & MHX-2420

Postby aek » Wed May 21, 2008 10:04 am

OK, Here's the latest:

1) By using Samtec ESQ-113-37-G-S and ESQ-117-37-G-S, we achieve the ability to mount the MHX-2420 higher above the FM430 with still-adequate engagement of the connectors themselves.

2) Placing the top of the MHX-2420 at 23mm above the FM430 seems to be the right overall location for the MCX RF connector. Note that in current MHX-2420 production, the MCX RF connector is tilted slightly upward ... dunno if this is intentional or not (it's not pretty).

3) This results in a standoff height from the FM430 of around 16.25mm.

4) This locating of the MHX-2420 (16.25mm above the FM430) results in an under-MHX clearance of greater than 14mm.

So, using the Samtec connectors above and using four roughly 16.25m standoffs, this locates the MHX-2420 in the correct position with sufficient engagement in the connectors.

Also note that compared to the MHX-2400, this setup i) has an additional 1mm of clearance between the top of the MHX-2420 and the bottom of whatever is in Slot 1, ii) is 30g lighter (but there is an additional mass associated with the 3.25mm longer standoffs), and iii) leaves a larger space underneath the MHX module -- this will be important for the next generation of FM430 electronics.

Please note that these changes will be applied from Rev D units forward. Users with Rev C and earlier units should procure the Samtec connectors as samples and have a qualified assembler replace the existing H5 connectors, and fabricate their own 16.25mm F/F M2.5mm standoffs.

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[This message has been edited by aek (edited May 21, 2008).]

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aek
aek
 
Posts: 1888
Joined: Sat Aug 26, 2000 11:00 pm

Re: Mechanical Differences Between MHX-2400 & MHX-2420

Postby aek » Wed May 21, 2008 10:10 am

One more thing ... for those developers interested in doing their own MHX-compatible modules, please note the following:

1) You should use one 0.062" PCB.

2) Maximum component height on the top side of the PCB is 6mm.

2) Maximum component height on the underside of the PCB is 2-3mm.

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[This message has been edited by aek (edited May 21, 2008).]

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aek
aek
 
Posts: 1888
Joined: Sat Aug 26, 2000 11:00 pm

Re: Mechanical Differences Between MHX-2400 & MHX-2420

Postby aek » Thu May 29, 2008 7:29 am

We have revised the height of the (future) MHX-x20 standoffs to be 15.6mm ...

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aek
aek
 
Posts: 1888
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