more text on csm84 page

diff --git a/pcb/csm84/index.mdwn b/pcb/csm84/index.mdwn
index 9bf03384c5a71a85bdd1856bb42f2279479c0666..b4f1246393021057fb2277d942af44ca6be4dc62 100644 (file)
--- a/pcb/csm84/index.mdwn
+++ b/pcb/csm84/index.mdwn
@@ -18,6 +18,43 @@ over to using a modern control and vision system running OpenPnP, capable of
 loading [Altus Metrum](https://altusmetrum.org) and other products that make
 heavy use of 0402 passive components, and fine-pitch integrated circuits.
 
+## Challenges
+
+* The existing control computer will be replaced with a PC-compatible system
+  running [Debian GNU/Linux](https://debian.org) and 
+  [OpenPnP](https://openpnp.org).
+
+* It appears that the stock board for doing things like sensing axis limits,
+  operating pneumatic actuators, etc, is actually attached to the control
+  computer using SCSI-1, and is based on an Intel 8031 with external EPROM.
+  Bdale hopes to reverse-engineer the protocol in use over this bus and use
+  a simple SCSI-1 interface on the control computer to interface with this
+  working board, so that it doesn't need to be replaced.
+
+* The existing analog servo amplifiers are fairly tightly coupled to the 
+  control computer's electronics.  Since the CSM84 came with some DC servo
+  control modules that take step and direction inputs and thus look can make
+  the axis servos look like stepper motors to the rest of the system, we're
+  going to try using a Smoothieboard and these modules to run the axis servos
+  using the existing power supplies.
+
+* The axis limit sensors currently feed into the main system I/O board, but
+  we'd like the Smoothieboard to be able to read them.  This may require a
+  custom interface to extract those signals and feed them to the Smoothieboard
+  at appropriate interface voltages.
+
+* The existing vision system will be completely replaced by USB camera modules
+  attached to the new control computer.
+
+* The head-mounted vacuum sensor board will be replaced with something better
+  suited to OpenPnP's needs.
+
+* The reel feeders provided with the machine advance 8mm tapes by 4mm per
+  step, which is correct for parts that are of 0603 geometry and larger.  
+  To feed 0402 parts, we either need to modify these feeders for a 2mm 
+  advance, replace them with feeders that do 2mm advance per step, or just
+  throw away every other part on our 0402 reels.
+
 ## Sub-Projects
 
 * The stock machine has a nozzle vacuum sensing board that uses an analog