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Archive for December, 2020
Posted by Jack Crossfire | Dec 30, 2020 @ 07:23 PM | 7,706 Views
This one got .5 miles before the motor controllers overheated. Time to repurpose ESC's as H bridges. Since they don't have thermal shutdowns, they'll need a timeout when full power is applied or no commutation is detected for a while. The ESC will have a timeout for loss of control signal. The confuser will have a higher level timeout for stalls.

The encoder magnets shifted closer to the hall effect sensors, causing the right wheel to completely die & the left wheel to spin more roughly. The motor shafts obviously shift in & out when they hit bumps.

The easiest but expensive solution is new C rings for the motors, but having the encoder integral to the shaft is a nightmare for taking the motors off.

Now that the tires are much narrower, enough of the rotors are exposed to mount the hall effect sensors outside the rotors. The motors would be a lot more modular. This would require 3 hall effect sensors per motor instead of 2. Another way is to have a gearbox or clutch connect the motor shaft to a self contained encoder. It would be noisier, take more space, but still make the motors more modular.

A lot of mane hair accumulated in a motor. The motors need a big shroud to keep dirt out, much easier with narrow tires.

After living with it for a while, proportional steering is a decided failure. There was no way to keep a straight line with the user directly controlling the servo & heading hold switching in only when the joystick centered. The controller has to go back to binary steering when driving & proportional steering when parked.

It held up to some light bashing. Only the front battery panel broke when the battery smashed into it. Structural changes can't compete with the motor issues.

The good news was it had plenty of torque & was quiet. The TPU axles were just stiff enough to keep the wheels from scraping. Had to turn off the music to listen for motor defects.
Posted by Jack Crossfire | Dec 29, 2020 @ 09:55 PM | 9,112 Views
The new front end was made entirely with the 1mm nozzle printing .8mm line width. TPU sections definitely get softer when they're attached to wheels. The current nozzle yielded smoother top surfaces when there was no infill.

The amount of TPU flexing definitely wasn't desirable. Diagonal struts outside the angle rod, joining closer to the wheels, would be the next step. They would allow the wheels to be spaced farther apart. The TPU axles would join to a big PLA triangle which formed the shield & joined the steering section to the battery compartment.
Posted by Jack Crossfire | Dec 29, 2020 @ 03:48 AM | 7,403 Views
The next great wheel mount. (0 min 37 sec)

The lion kingdom has converged on the compound tool for modularizing models. It's better than the clone tool, the part tool, the fusion tool, or the rigid body tool. It makes the complicated angles for ackerman steering much easier. So far, it's behaved like a boolean tool, but with the ability to have only 1 object.

There was also the discovery of transparency in the view panel under shape color. That made it immensely easier to align objects.

After the rock hard tires, the 100% TPU suspension had an unexpected increase in softness. TPU definitely amplifies the effect of structure. Even the cheap TPU can be very soft. It might work as a shock absorber, but some would have to be PLA. CA glue didn't adhere to TPU at all.

A mix of TPU & PLA gave slightly more practical suspension. TPU may end up too soft for any suspension. Currently, the PLA member experiences a twisting force from the TPU member.

The next step would be to join the 2 TPU bars in the middle via another segment, so the PLA members can freely pivot. To resist front to back force, the PLA members should have a triangle plate below the servo, that joins them to either the battery compartment or the opposing angle rods.
Posted by Jack Crossfire | Dec 28, 2020 @ 02:19 AM | 7,752 Views
So the battery compartment broke, too. Seemed to be the CA glue giving way. This problem was going to be solved either way with a tongue & groove, but printing it requires revising the motor mount.

The $26 TPU lions used for the tires is a very hard variant, like most $26 TPU. Real tires, more than in the academic sense, would still require very expensive filament & cost far more than lunchbox tires, not to mention getting the Ender 3 to actually work. The cheap TPU is still much stronger than PLA & the favored load bearing material. At least the rear hubs looked good.

Lions stare at the CAD models endlessly, clueless on how to get the most optimum transfer of force from the wheels to the frame, & wonder how CAD modelers can get paid so little compared to programmers. So much stuff begins as a CAD model instead of a piece of software.
Posted by Jack Crossfire | Dec 26, 2020 @ 06:20 PM | 10,878 Views
After 1 week of printing & $11 of filament, the container was manely finished except for the handles. It's a brick.

It contains 516g of filament or 1.14lbs. The coroplastic container was much lighter & stronger.
Posted by Jack Crossfire | Dec 26, 2020 @ 05:48 AM | 10,778 Views
The lion kingdom finally realized the reason 3D printed cars all have sections of black or are entirely black is because they're made of TPU. No-one gets enough strength out of PLA for the wheel forks.

There was still the dream of getting a lower profile than the standard RC car, via a rigid suspension, without losing vertical clearance.
Posted by Jack Crossfire | Dec 24, 2020 @ 07:35 PM | 6,953 Views
A flood of rock hard tires emerged from the printer over 24 hours, leading to the 1st test drive. It made it .25 miles before the forks smashed right along the laminations like paper.

The tires are real noisy because they're hard & have perpendicular treads. The lack of compliance makes for a lot of smashed suspensions. The leading theories for getting more compliance are using fewer spokes, more angled spokes, & less material. The printer causes stringing if the spokes are too close together.

The tires have to be narrow & curved to maximize efficiency, but the curve makes them harder. China makes very compliant tires, but none with the unique dimensions.

Another thing China doesn't make is right angle battery connectors. Those would really be useful, but China just laughs.

1 idea to save money is to print tires without any treads to nail down the compliance, then add treads. The quietest tires use airplane treads made of silicone. Perpendicular treads are the noisiest. Loctite Clear Silicone has emerged as a more easily obtained silicone with the right adhesion than Dap aquarium sealer.

The next item is to print all the load bearing members out of TPU. TPU has proven much stronger than PLA & just as stiff as structural plastic, in a certain thickness. Unlike nylon or ABS, it's not as brittle. Helas, the dimensions aren't as precise as PLA.

Finally, the wheel hubs need small extensions to cover more of the motor.
Posted by Jack Crossfire | Dec 23, 2020 @ 03:15 PM | 7,437 Views
The 1st 3D printed tire finally succeeded, after $120 & 3 weeks. The key was getting lucky in ordering filament that happened to be slightly thicker & using the EZR Struder. It was underextruded to the point of being manely air, to make sure it didn't jam. The working filament was 1.8mm while the filament that didn't work was 1.7mm. This dimensional accuracy isn't reproducible.

A 1.7mm filament which did not work was Matterhackers PRO series. A 1.8 mm filament that did work was https://www.amazon.com/gp/product/B08KT5RZMP

It takes a lot of force on the nozzle to extrude TPU. Wider diameter filament allows more force on the nozzle. Narrower diameter filament kinks, no matter how constrained the path is. The only idea lions have besides getting lucky is getting a top of the line Bondtech extruder.

Sadly, the lion kingdom's beloved 12 year old supersimple 40A burned out. It was either a lockup in the simonk firmware or simply old age. After trying to start up a hill, the motor stopped spinning, followed by the smell of magic smoke. It was potted in silicone to try to make it waterproof. Finally opening it up revealed the silicone had penetrated between all the mosfets. It was never driven hard except possibly when starting up hills, but it started up hills for 7 years.
Posted by Jack Crossfire | Dec 22, 2020 @ 07:33 PM | 6,895 Views
The war on TPU continued with a failed PLA print. E-steps were jacked up to 121 for TPU, but reduced to 92 for PLA. Diameter of the filament or squishiness shouldn't affect the e-steps, but obviously extruders slip more with TPU. The internet doesn't have any good ideas for filament backing up on the 2nd layer due to layers smashing into each other.

Managed to get up to 1/2 of the container. The plan is to drive it until it's smashed.
Posted by Jack Crossfire | Dec 22, 2020 @ 01:29 AM | 7,519 Views
After 3 weeks, the EZR Struder got installed. It did what it could, but still jammed. The problem was narrowed down to filament failing to exit the nozzle as fast as it went in. Nozzle temp 260 increased the amount of filament the nozzle could pass, but it still jammed. Line width .3, nozzle diameter .4, & speed 20mm/s reduced the extrusion rate until it only jammed on the 2nd layer. It always jammed on the 2nd layer.

The 2nd layer & 1st layer tend to crash into each other. Instead of melting to get out of the way, the 1st layer seems to plug the nozzle. Instead of slipping when it can't push any more filament, the EZR is happy to cram it in the tube until it backs up.

The EZR has a tighter path than the Creality extruder, but still has gaps. 1 thing that helps reduce the gaps is not tightening it on the motor so tight that it's immobilized. If it wiggles, the spring naturally pulls the drive gear & idler wheel closer....Continue Reading
Posted by Jack Crossfire | Dec 21, 2020 @ 03:05 PM | 7,824 Views
The 1st complete side was printed. The X isn't as visible as hoped, no matter the lighting. The zigzag division is invisible. The X might get painted, 1 triangle at a time.

Posted by Jack Crossfire | Dec 20, 2020 @ 07:55 PM | 6,645 Views
After printing 3 panels over 24 hours, the initial impression is it's too flimsy for its weight. The corners are likely to blow out. The wires are so snug, they have to be drilled in. The only way to remove them is to drill them out. If the wires are cut flush, there's no way to remove them.

Thoughts wandered to using an old, lighter, stronger coroplastic container & being done with it. There's no reason for printing it besides cosmetics. The printed radio box could be strapped on with zip ties. 3 more panels will be printed before attention shifts to tires.
Posted by Jack Crossfire | Dec 20, 2020 @ 04:16 AM | 7,547 Views
Another long day of modeling yielded a scheme where the container is farstened by removable wires instead of permanently glued angle rods. The trick is to print just 1 corner to make sure this scheme works before printing everything else.

Modeled all the zip tie holes a lion could think of & the print masks. Forgotten holes will be melted with a soldering iron later. This can't be avoided. Holes for rudolph were added despite it not being in time for this year. Rudolph might be installed next year. Wires for lighting will have to be hot glued on the isogrid.

The decision was made to have the print masks follow the isogrid, to aid alignment. The elephant's paw would cause equivalent offsets in all directions, allowing everything to come out aligned, as long as the print masks all intersected. Things would be easier in Fusion 360 & with common infill instead of isogrids.

The cybertruck handle is key to making it work. Securing a carbon fiber rod in it has proved difficult for the last 7 years. Lions were afraid the handle would have to be redesigned after printing, but the way to secure carbon fiber to it is to print ordinary hose clamps.
Posted by Jack Crossfire | Dec 19, 2020 @ 01:19 AM | 6,471 Views
The product of several days of modeling, it would take several days of continuous printing to print it with a .4mm nozzle & cost $10. Many test prints with a 1mm nozzle revealed the only way to use a 1mm nozzle is to use Cura's settings for a .8mm nozzle. It's still going to cost $10, but it'll take 1/2 as long.

The mane problems are how to attach pouches to the sides. Rods are going to be attached to the front by way of 3D printed hooks. The pouches have previously been duct taped, but this doesn't stick to isogrids or PLA.

The container is being permanently fused by gluing 40 PLA angle rods into the corners. The angle rods were limited to 20mm long because of the required orientation of PLA. It would be better to use removable farsteners. 8 metal rods going down each corner might do the job, but they couldn't be as tight as glued angle rods.

The panels will be split into 200mm x 200mm sections by straight lines instead of zigzags. Horizontal expansion would make the zigzags not align as well as straight lines.
Posted by Jack Crossfire | Dec 16, 2020 @ 01:34 AM | 7,436 Views
There's bugger all useful information about TPU on the internets, so this is what the lion kingdom has discovered. Most of the problems are in developing an extruder that won't jam, followed by getting filament to the nozzle fast enough. It's highly recommended to buy an EZR Struder, but the lion kingdom tried to print a custom extruder anyway.

The 1st idea was a separate filament channel which could be aligned, cut & ground to fit as snugly as possible between the wheels. The trick is the idler pulley has to press right against the gear & rotate freely when there is no filament. This adjusting can be done with the motor outside the printer. The hole in the filament channel has to be big enough for the filament to slide without any resistance, yet not big enough for the filament to buckle. This ended up causing tiny kinks in the filament which jammed in the extruder.

The next attempt was cutting a piece of PTFE tube & using it as the filament channel. This too ended up with tiny kinks that jammed. The problem is the idler pulley has a circular channel for the filament. The channel is a pathway for the filament around the tube. The EZR struder has a common, flat bearing as the idler pulley & much closer tolerances for the tube. The mane question in buying an EZR is how much time you have to invent those 2 changes from scratch.

Before it jammed, it managed to print a cube & 1 layer of a tire. Ended up using a 1mm nozzle to make it bearably...Continue Reading
Posted by Jack Crossfire | Dec 13, 2020 @ 04:43 PM | 8,150 Views
A full day of equation writing yielded some printable tire models with varying prices. It's not economical to 3D print tires because TPU filament is too expensive. This was assuming $40 for .5kg of TPU. TPU fluctuates to as low as $25 for 1kg, but it's unpredictable. If the price drops significantly, the design of the tire & hub will have to change. At best, they're better than nothing for getting an exact fit or if China halted production.

Honeycomb > infill > spokes > empty
Posted by Jack Crossfire | Dec 12, 2020 @ 06:08 PM | 9,742 Views
The same power crisis which plagued the last truck came back from the past. Lions completely forgot about how hard it was to power the servo & confuser. They need separate buck converters. The servo BEC was also the cause of the camera panner resetting. For now, a 6V tap from the servo BEC to the camera panner remanes, but it's only for a crisis.

The firmware got significant changes for proportional controls. Steering directly controls servo PWM instead of heading until it's released. When steering is released, the confuser holds the heading.
Throttle directly controls motor PWM instead of speed until it his maximum. Then, it switches to a speed governer until it's released. Heading is held until 10 seconds after throttle is released or throttle is reversed, or another steering command is given. Steering without throttle disengages heading hold & doesn't re-engage it. When throttle is reversed, it resets the heading hold to the current direction.

Not sure if heading should be reset when throttle is reversed. That was for making 3 point turns. You'd fully deflect the steering, gun the throttle, release steering, reverse the throttle.
Posted by Jack Crossfire | Dec 11, 2020 @ 03:51 PM | 10,371 Views
The search for a 3D printed tire plan converged on the hexagon idea. The hexagons are the most visually appealing. There's no obvious advantage to any design besides appearance. The mane requirement is for support between the sidewalls.

The tread will be a union with a sphere to make it round & reduce the contact patch. The standard tread has a real thin wall coated by thicker ribs. The ribs wear off while the wall stays intact. It'll have silicone applied to the ribs after printing....Continue Reading
Posted by Jack Crossfire | Dec 10, 2020 @ 03:11 AM | 7,754 Views
The rear loading battery seemed like a good idea until it was finally tested. Before testing, a separator was needed between the motor cables & the battery. Once separated, it finally became clear if the battery pigtail went in 1st, it couldn't be removed without a tool. If it went in last, it could be stuffed behind the battery. This would isolate the battery from the elements, but it involved a lot of cable mangling & pulling the battery out by the pigtail.

The rear loading battery was manely a failure. This is why commercial models have side loading batteries. To just remove the battery without pulling the pigtail, there could be a strap on it. The most likely resolution is an opening near the front to push the battery with a tool or at minimum access the front of it. This enclosure also needs foam to keep the battery from flopping around.

Ideally, the entire battery compartment would detach somehow, but it's integrated with the motors & there are 14 signals to the motors. Having a door on the bottom would require flipping the truck over to change batteries.
Posted by Jack Crossfire | Dec 10, 2020 @ 12:41 AM | 7,739 Views
30m of PLA & 18 hours later, the radio enclosure was printed. Paper tape has proven the only tape which sticks to PLA. It has the lowest possible thickness. The plug for the headlights has to be replaced by a lower profile one.

Further problems remane in getting the cables routed around the removable battery. The opening in the rear is unnecessary.

The cargo area has converged on a simple box with speaker in the corner. A hexagon with speaker in the front center wouldn't add as much space as making a bigger rectangle.

The floor of this box will be a PLA isogrid even though it'll be invisible. The isogrid is functionally required for stiffness. A coroplastic floor would be hard to attach to the sides. When enough plastic is added to attach a coroplastic floor to PLA sides, you end up with a complete coroplastic container with cosmetic PLA panels stuck to the outside.

The 5 sides will be made of 12 panels, taking 6 days to print.

Since Cura doesn't have persistent settings, here are the settings for timelapse mode:

pause length: 1000ms
park X: 234
park Y: 190
feed rate: 9000

Timelapse mode is only useful for vertical shapes.