https://www.youtube.com/watch?v=RV-4XTY2dXQ
Tommy
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The Mule lost half it's duct tape and went to a 54" cut path
Tommy
That is so awesome! Wish I had had that when growing up :-)
Very nice. I've still not gotten around to building myself a little outdoor rover with spinning sticks of terror made from 15mil full hard 301-SS and 50mil 6061-Al plates brazed together. Theory (based a bit on rodent teeth) goes that the thicker, softer aluminum provides mechanical support for the thinner, harder steel while also wearing down faster to keep a sharp, thin steel cutting edge on a thick stiff blade.
Any more broken drive shafts? What I was unable to describe so long ago was 'build a proper wheel hub', so that the bearings and support structure/suspension would be almost directly mated to the rim, as happens in most road vehicles, which would keep the length of the unsupported/cantilevered shaft very short.
jwatte, your never to old to have some fun, even while doing some of these repetitive tasks(mowing,plowing).Quote:
Wish I had had that when growing up :-)
tician , so far, so good.Quote:
Any more broken drive shafts?
I also see this as a problem with my original design, the problem becomes more pronounced whenQuote:
which would keep the length of the unsupported/cantilevered shaft very short.
plowing snow because of the 200lb of sand I add. when the next shaft fails I'l re-design it.
Tommy
True -- although these days, the chickens pick the back yard clean, and I live in a place where yards are small and it never snows...Quote:
jwatte, your never to old to have some fun, even while doing some of these repetitive tasks(mowing,plowing).
I have enough projects anyway! :-)
while the Original Design offered some advantages(more room for batteries)
, cost savings(used bearings and wheel hubs I had) and kept the center of gravity low.
but the shortcomings have forced me to redesign the drive system.
Attachment 6310
Going to have the new design implemented in time for heavy snow?
interesting!
Does the axle nub that sticks out about 1.5" beyond the sprocket go into the bearing? Is that enough to bear the load, or is there some other suspension?
Gertlex, NOAA is saying this is an El Niño year, so I'm hoping that will buy me some time. becauseQuote:
Going to have the new design implemented in time for heavy snow?
it's not only the drive system that is getting changed. I'm adding a front loading option.
Attachment 6315
jwatte , there is no other suspension, even with the Mule's weight of 320lb and the 280lb of sandbags addedQuote:
Does the axle nub that sticks out about 1.5" beyond the sprocket go into the bearing?
when plowing snow the bearing have held up for fours years.
all the failures happened at a turned down shoulder, the new design has no shoulders(1" keyed shaft the full length)
Attachment 6316
Mmmm, steel!
(Nice Bridgeport conversion, too!)
Are you using lead acid batteries for cost, or do they work better than lithium in cold weather?
(I imagine the batteries would warm themselves while running, though?)
jwatte, Using Lead acid Batteries for cost and weight, I have two commercial grade batteriesQuote:
Are you using lead acid batteries for cost
19"x 8"x 8" that give me about 100lb each, then five 60Ah deep cycle batteries that give me
about 60lb each. all but one of the batteries are configured for 24v for the drives, one deep cycle
battery is used for controls, cameras, and lights.
when this design is done(i'm very slow) it will have four commercial batteries and eight 60Ah batteries.
which should give it close to 1200lb of weigh on the four wheels. that should be enough to push my 50"
plow through 12" of snow.
Attachment 7140
going to have this type of setup(someday)
Attachment 7141
when I made the motor brackets, I made all four of them
Attachment 7142
Was there any particular reason for using the motor mounting plates as the central structural element of the new design? It would be much stronger and more reliable to replace the two short bars attaching the casters (and other two bars on the battery/plow side) to the motor mounts with longer, continuous bars extending the entire length of the bot and then mount everything to those bars. The battery holder and plow attachment section of the frame uses additional reinforcement to bolt to both ends of the motor mounting plates which helps a bit in distributing forces, but the casters just hang off the end of the motor mount plates with only one bolt per side. Making the casters cantilevered like that with the only bolt so close to the edge of the motor mounting plate will put a lot of stress on that area and risk the bolts being torn out of the motor mounting plate.
tician, the mule has multiple jobs to do, mowing grass,hauling stuff,plowing snow and collecting dead leaves. most of it's tasks can onlyQuote:
Was there any particular reason for using the motor mounting plates as the central structural element of the new design?
be done with two wheel drive(four wheel drive would tare up the lawn), the connecting bolts for the attachments are 1/2"-13 bolts.
Attachment 7143
the snow plow with the two front wheels is an attachment.
Attachment 7144
tician, the motor brackets are .625" hardened steel, and the bolts are 1/2"-13 grade 8.Quote:
risk the bolts being torn out of the motor mounting plate.
made blue chips when cutting the 1/2" holes at 300rpm in the brackets(very hard steel).
posted without refreshing:
What I was getting at is: three short bars bolted together at one or two points within a few thicknesses of their overlapping edges is much weaker than a single continuous bar. Even butt welding them together would be far superior to bolting like that. Extending the short bars under the entire length of the motor mounts so that bolts can be used at both ends will greatly reduce the stress experienced by the mounting plates, bars, and bolts. With just the one bolt connecting the caster bars at the end, the bolt is subjected to significant shear stress any time the bars are subjected to bending (batteries not properly balanced over pneumatic wheels, plow being forced upwards by ground/snow, extra weight added between casters and pneumatic wheels, etc.). With longer bars secured at both ends of the mounting plates, the bolts experience very little shear stress which makes them much less likely to fail or to tear out of the mounting plates or caster bars.
Imagine attaching two halves of a truck together with a short thick plate (<3" long) and just a couple bolts in the bottom flat of the frame rails located only an inch or so away from the joint - it will have essentially no resistance to bending and will very quickly tear the bolts out of the frame rail.
Using a much longer plate with regularly spaced bolts attaching up to a foot or so from the joint will greatly reduce the chance of the bolts shearing or tearing out, but does not help much in overall strength because of the small area moment of inertia of flat plate versus angle/channel/tube. Adding additional plate and bolts to the top flat of the frame rails significantly increases its strength and stiffness because the top and bottom are spaced by the height of the web to greatly increase the area moment of inertia.
tician, I wish I could apply the forces needed to cause the 1/2"-13 bolts to fail.Quote:
the bolts experience very little shear stress which makes them much less likely to fail or to tear out of the mounting plates or caster bars.
I like them wheelchair motors for projects.
https://m.youtube.com/watch?v=nsiwWWMe-ZQ
Attachment 7145
working on cameras
they are sweet motors, I have some with factory encoders in them.Quote:
I like them wheelchair motors for projects.
I like the light mount. Seems like it should get enough distance to give a more even spread than if it was just placed in front like headlights?
I think Tician's point is that forces, over time, may fatigue the metal when all the stress is concentrated. Building a "chassis" of two long bars, and bolting things onto that, would generally distribute the stresses better. If stresses aren't big enough, then it kind-of doesn't matter, which seems to be your assessment?
I have no idea whether your mule is actually close to a critical point or safely designed, I'm just interesting in running the numbers pointed out by Tician.
I looked up 1/2" steel bolts. Safe working load for a 1/2" bolt (grade 2/5/8) is 940 pounds shear, 760 pounds tensile. (Catastrophic failure, i e immedite breakage, load is about 10-20x higher, depending on grade.) Will your bot weigh 760 pounds or more? Will it rock left/right such that weight is unevenly balanced? Will it get stuck and apply more torque, or bump into uneven terrain so the load is increased by inertia? If so, 1/2" bolts may fail over time. The table I used: http://www.rdfasteners.com/pdf/boltstrength.pdf
If durability under bending stress is what you want, hardened will crack sooner than less hard steel. It of course depends on the specific loads, but too much carbon makes it brittle. There is also tempering where you harden, then "back off" by relaxing in medium heat for a bit, which gives a better trade-off between brittle and touch. Maybe that's what you're using?Quote:
"hardened steel"
I bet it will survive the few years before his next iteration! :D
Looking marvelous as always, Tommy!
jwatte, a work in progress, the parts I have done so far are the snow plowing attachment, but I want the lighting and cameras systemsQuote:
I like the light mount.
on the main unit(back section not made yet).
the best I can do is 300lb per tire.
If I had to question something, it would be the main axle brackets.
but the last frame used the same setup and held for four years.
Attachment 7146
Attachment 7337
Sucks to be me.
they are talking about snow in the forecast, yet the snow bucket is still not installed.
Attachment 7338
It seems I'm the reason for the slow down.
over thinking it.
Well, who's fault is that?Quote:
yet the snow bucket is still not installed
Oh, right then.Quote:
It seems I'm the reason for the slow down
What fun would it be without overthinking? :-)
Else you would just weld a 3/8" steel plate on front at a diagonal, that would plow just fine as long as you keep up when it's coming down. No fun in that. (Other than saving the work of doing the plowing manually.)
jwatte, I'm still scratching my head about what type drive to use to lift the bucket.Quote:
What fun would it be without overthinking? :-)
I have a ballscrew from a bridgeport mill, but with a pitch of .200" and a motor with 180rpm
it would take some time to lift the bucket(@20sec. with 4 to 1 gearing of the gearbox).
if I went to a chain drive, I could get it down to 5sec.
Also, could you bolt lifting arms to the side, to give you a longer lever? Put the pivot point at the back of the bot, lift somewhere in the middle, and put the bucket in front, for additional speed gain (and, of course, torque loss, so that counteracts your 4:1 gearbox ...)
Really, just add a harder/better/faster/stronger motor and call it good, I guess? :-D
I think this is why professional gear uses hydraulics... Build high pressure in a storage tank, use it when needed to actuate with high forces quickly, as long as you're OK with some mush in the system and some lag in the control loop.
Also, how far do you really need to lift the bucket? You don't really need to lift it much more than the regular ground clearance of the 'bot, right?
jwatte, with the way the bucket was made I have to lift it 18" just to dump it.Quote:
how far do you really need to lift the bucket?
I'm thinking of lifting a total of 34".
jwatte, this is where the overthinking come in...Quote:
I think this is why professional gear uses hydraulics.
hydraulics would be a easy to implement setup, I can get stuff at farm&fleet to do the job.
but, I need to start playing at 5 am so I can still get some work done that day, and with 30
neighbors that would be in range of the sounds the hydraulic pump, they may not let me play
in their space at that time. (that would suck!)
I have the same issue with electric winches.(too loud)
My neighbors don't worry about their lawn crews using weed trimmers at 6am, soo ....Quote:
30 neighbors that would be in range of the sounds the hydraulic pump
Buy a shotgun, ignore the neighbors? :-D
for the first try, I'm going with a #50 chain for the bucket lift and bucket dump drives systems.
Attachment 7341
I'm going to have the frame welded together this week.
baby steps.
Ooh, those look like linear guides! That is, indeed, overkill ;-)
jwatte, have to agree with you on that one, but it should be a very quiet lift.Quote:
Ooh, those look like linear guides! That is, indeed, overkill ;-)
the motors I planed to use for the lift&dump systems were motors I had
used a few years ago for an electric bike project(very fun project).
Attachment 7342
but, it seems I removed the electric brakes from them(crap!)
and for the lift& dump systems brakes are needed.
back to ebay.
when I started the mule project for convenience I had two battery groups,
12vdc and 24vdc with two different charging systems.
the 12vdc for PC , cameras and lighting, and 24vdc for the motor drives.
this year all batteries are going to be in one group, 24vdc.
(4) 12vdc 100ah batteries.
Attachment 7343
I'm also removing the PC(in the mule) and replacing with 2 Arduino Nano,
and replacing the wifi control communications with an Xbee.
while I should have some fixed 24vdc to 12vdc/5vdc regulators show up
this week, I'm still installing a 24vdc to 110vac inverter in case I need to
run an air compressor,110vac lighting or heater.
the only time I've had Arduino's lock up on me are when
I have serial port conflicts, so even with using 2 Arduinos(one is for safety checks)
I'm going to use I2c 16bit DAC(0-5vdc) for controlling all the drives, I2c 16bit ADC(0-5vdc)
for feedback.
Attachment 7344