OK, so three weeks ago I said I had a chopped / hacked / optimised Sawppy power unit under development in OnShape. Well, I'm finally done.
For those not following closely (most?), I figured I could afford to optimise the power unit a bit, safe in the knowledge it was unlikely to require significant future modification, regardless of whatever else I end up doing with the rover. Thus I've spent a bit of time pondering the power supply set-up in order to satisfy my overly-finicky sensibilities.
Quick list of mods to the OS (Original Sawppy) power panel & battery tray.
spacers either side of the tray to keep the battery centred and aligned
integrated battery connector socket in the floor of the tray
recessed, panel-mount fuse holder on the power panel face
next size down voltmeter unit
voltmeter wires exchanged for pins so as to accept the battery balance plug
mostly hidden cable conduit in battery tray base
terminal block mounted on back side of battery tray
End result is a power unit that can be easily disconnected and quickly dismounted from the rover body. Pretty stoked with it. A nice example of what I'd suggest was fruitful pondering. Maybe it took too long, but that's fine.
Next sub-project is mounting the RCU components (pi, buslinker, tx) within the body of the rover. I already have some ideas there, but I'm sure more will come as I periodically stare at it intently whilst mumbling to myself at appropriate intervals.
Still waiting for my extra link cables from China...
Yeah, so the Xmas deadline came and went and the machine ain't near done yet. Doh!
Mostly, I ran out of time with the festive season crashing my spare moments. Although the root cause was actually a lack of progress MONTHS AGO. And so the project's critical path to completion (if it had a Gantt chart) became simply unachievable in the planned time-frame. No amount of additional resource allocation would have overcome the situation.
And, tbh, I'm quite enjoying the pondering aspect of this late-stage build phase so "time taken" is less of a concern than it was. Up to recently, I've pretty much just followed the solid, public-domain Sawppy recipe as laid down by @Roger. So the foundations of the machine are good. Now I'm wandering through the final electrical / mechanical build.
Generally, I'm not one to go with my first thought on anything - my first thought is rarely my best thought and quite often it's just someone else's thought anyways. Thus I'm happy to drop in and out of things, thinking hard and then dropping it, waiting for inspiration to strike. Dangerously close to procrastination, admittedly, but it works for me. My professional life abounds in hard deliverables, deadlines & budgets, so the stretchable slack in personal projects is a precious commodity.
OK, so quit rambling...
Progress has been on the wiring harness and tweaking the design of the official power unit.
Harness: In a nutshell, I deconstructed, chopped, spliced, soldered, heat-shrunk & rebuilt the three metres of triple-stranded wiring that came with the LX-16 servos to create the compact, neat, tidy shape I wanted. I've already used up all of the supplied wire, so I've had to order some more to finish, but that's OK. Our good friends at AliExpress will deliver the four additional link wires shortly.
The harness I've cobbled together mostly hides neatly in the offside channel of the 1515 extrusion with the help of some printed clips that I knocked up in OnShape.
So I'm stoked with the loom / harness.
On the power unit, I've decided that regardless of anything else that I might decide to do with the rover, the power unit will likely remain as it is so I'm doing my own optimised version. Thus, I have hacked, almost-complete versions of the standard battery tray and power panel sitting in OnShape. Design tweaks are around neatness / tidiness of wiring again. Some more pondering still to do ;)
So, yeah progress is slower than originally planned, but that's because I've decided (belatedly) to row my boat gently down the stream rather than be in too much of a hurry :)
Minor dramas in the process - I had to get the Dremel out to do some ...err ... free-hand adjustments to the wheel bearing mounts. In a nutshell, I had to shave some plastic out of the bearing recesses so that the back-to-back bearings would sit close enough together to allow the retaining E-clip / circlip to sit in its slot on the axle / shaft.
Next job is fitting the servos and then to work out the dimensions of the wiring loom.
So I finally have the software sorted and I can "drive" the servos on the kitchen table by logging onto the Pi's network with my smartphone. A eureka moment of sorts!
I pause here to thank @Roger for responding with generosity and verbosity to my requests for help in the last few days. Thanks, dude. I dig your style.
. Anyways, I did some dumb things on the way to this interim destination. I'll briefly lay out my errors below for the possible benefit of someone else having a crack at this project with the same limited exposure / ability as myself.
Misdeed #1: Save your edits. I evidently managed to skip this bit a couple of times even with the confirmation messages reminding me to do so.
Misdeed #2: If you are going to copy/paste rather than type text into files / command lines then make sure you select the whole text string / body - don't skip the last few characters.
Misdeed #3: When I edited the config_lewansoul.json file I got the format of the 4th line wrong - I missed the quotes on the path string. This is correct:
Misdeed #4: Well not so much a misdeed as a tip. If you run in test/develop mode on a laptop / PC then you may get an error message telling you that you do not have permission to access TTYUSB0. The answer is here if you run some variety of Linux: https://sudomod.com/forum/viewtopic.php?t=6075
Misdeed #5: if you don't have the Lewansoul Buslinker board powered up and plugged into the laptop / Pi when you point your browser at the appropriate address then you'll get Internal Server Error 500.
So, having achieved wireless control of benched servos, now I get to complete the mechanical build and get stuck into the electrical build. Noice!
Yeah, been away from here for some time. Other priorities have crashed the rover project to a large extent, although there has been progress.
Got the threaded inserts finally and put them all in place
Finished off the core chassis mechanical build with the differential & tie rods
Assigned the servo IDs - I just matched the standard scheme here for simplicity
Got the Pi sorted - Sawppy-tuned SGVHAK software loaded, wireless access point enabled
Having achieved all that I figured I'd go for a servo bench test before I go screwing it all together. This is the kitchen table right now.
And this still picture is a perfectly accurate representation of the action on the bench right at the moment, 'cos it aint working :)
The software seems to be doing it's thing, but the servos aren't responding.
Witness the Chassis Configuration screen after an Angle / Velocity command from the interface.
I'm thinking that the last line on the screenshot above is the issue. I have no idea what that means though, just at the moment. Gotta work that out when I get a chance.
For me and this kind of stuff, it's a case of trying something and then troubleshooting my way out of failures, learning as I go. I'm not sure it's a terribly efficient way of working - the google rabbit holes you jump down in search of (cascading) answers takes up time & energy. She'll be right though.
Anyways, having come to a frustrating halt here I have other things to do this arvo so I have to pack it up and try again at a later date.
I've always said this is a WWII job ("over by Christmas") and that's still the goal. Less that 50 days to go though now.
...yeah, well, as predicted, progress has been slower than I would have liked. BUT, we do have the various shafts for the machine sorted now!
Picture below is my own version of the "lathe" required to cut the shafts to length and to lay down the grooves for the retaining clips. Drill in a vice. Angle grinder with 1mm cutting disc. I tried the Dremel but the geometry was not quite conducive to accurate grooves.
Tip for anyone following - the grooves really don't need to be very deep at all. Shaft OD is 8mm. Retaining clip ID is 7.5mm. So the groove only needs to be 0.25mm deep.
I came close to going too deep on the fist shaft. We bought chromed shafts (not just straight mild steel) and leaned a bit too hard to break through the chrome the first time. Lesson learned - not probs after that.
Very useful thing was the old kitchen chair I used as a tool rest of sorts. Hard to be very accurate when going free hand.
Another problem with chrome shafts is that you can't mark the measurements on the steel very easily - had to wrap a piece of masking tape around the blanks so that I could set out the marks.
And - big news - we got washers in the mail (!!!) so we can finish most of the mechanical build. Still waiting for the threaded inserts though :(
We have all the electrical / power bits now too, so overall we're pretty much sorted for having all the pieces of the jigsaw sitting ready to go.
Raspberry Pi capability is rising. Been reading, taking notes, watching & mucking about.
So I figured I should publish an update on progress, but progress has been slow over the last couple of weeks:
Life has intruded and time has been a bit hard to come by
Still waiting for some critical bits from China - washers and threaded inserts specifically
Finished all the 3D printing - full set of parts done including a few spares
Most of the electrical / power items have been delivered already
Ran out of some screws, so had to order more ( I messed up the original order quantity)
And that's about it, right at the moment. The time thing has mostly impacted the Raspberry Pi control system part of the exercise. I have to read, understand and work through the documentation in a solid chunk of time, not piecemeal.
I need to extract the digit over the next little while or winter will be gone and the sun will tend to draw me outside the house. I need to finish the mods and put the dashboard on my car back together before the weather improves, too. More intent required.
I said "...by Christmas" when I started this project.
We're still still working through the prints (see pic below)...
Aluminium extrusions cut to length...
Most of the first round of orders from AliExpress have arrived...
Ordered a bunch more things related to powering the beast...
At some stage, I'll publish a detailed list of everything we purchase...
Revived an old laptop to run things through with a fresh Lubuntu install (replacing Win XP that replaced full Ubuntu that replaced Win Vista)...
The more I read, the more I'm getting a bit intimidated with the whole control system thing. I have zero problem with the mechanical & electrical build - I'll happy work away at that kind of thing all day, any day. Car-related tinkering is my forte. But the whole software part is well outside my comfort zone.
Early in my life I was into coding / software, but my interests subsequently drifted to mechanical engineering - with "computers" being essential tools but definitely something that specialists dealt with in detail, not me.
So with regards to all things "Pi", I'm rising from a low base. Going in I certainly expected a struggle, but jeez my brain hurts a bit at the moment.
I'm sure I'll work it out one way or another. Plenty of time. No hurry. She'll be right!