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Archive for January, 2021
Posted by Jack Crossfire | Jan 30, 2021 @ 09:13 PM | 8,563 Views
Having proven their effectiveness, the 110mm tires got new hubs with motor shrouds. There could be a sealed bushing completely enclosing the motor mount, using TPU. 1 part would fit around the screws & translate into a cylindrical shape. Another part would attach to the wheel. Between the 2 would be a captive ring of TPU.

Lions wouldn't go to a skateboard motor because they're heavy. Even the mighty ball bearing still relies on a bushing to keep dirt out. Eventually, dirt gets in, in car bearings & skateboard motor bearings.

The range appears to depend on the steering oscillation. The more the steering oscillates, the less range it has. Just a tweek to the steering PID constants made it drop to 200mAh/mile but it could be anything from 200-400, depending on how the confuser feels.
Posted by Jack Crossfire | Jan 29, 2021 @ 07:21 PM | 3,350 Views
So the 90mm tires reduced the maximum speed to 8.5mph & didn't materially improve the climbing speed. There was much scraping, but no visible damage to the undercarriage. Spinouts abounded despite the wider, flatter tires. In lieu of better tires, it could use some automated way of detecting a spinout & canceling the steering command. Otherwise, the user has to remember to pulse the steering.

No obvious rocks got into the motors, though rocks were stuck to all the adhesives. The underside definitely needs ramps instead of right angles & shrouds around the screws, so when it inevitably scrapes, it doesn't damage anything.

Having smooth tires on all 4 wheels made it incredibly quiet. It was inaudible on smooth ground. It would make a belt drive hard to do. Another drive with grooved 110mm tires on the rear wheels comes next. Then, 105mm tires might give a decent compromise between increased climbing speed, better stability, & lower maximum speed.

Another idea coming to mind is dropping in a variable boost converter. The inductor would only be switched in the circuit path when PWM was maxed out, thereby avoiding efficiency loss. It would have more flexible voltage than a bigger battery. It would just be heavy.

Checking the boost converter options, there's one that takes 8A input & outputs up to 20V in a 4g package. It requires an adjustable resistor to set the output voltage, so using a fixed voltage & having it always on would be the 1st step. It's just expensive. 2 would be required.

Posted by Jack Crossfire | Jan 28, 2021 @ 03:36 PM | 4,468 Views
The cheapest step was wider, flatter tires with no other changes. 90mm diameter at 1st, maybe 100mm if it can't clear obstacles. The moral of this story was never to use random z seams except for furry toys. They're actually very compliant, thanks to continued evolution in the strut design. A shroud was added to try to keep rocks out of the lower motors. Small rocks were already found inside a motor, causing it to bind.

Skateboard motors have all the wiring & attachment points on the inside of their bearings rather than the outside so there's no entrance for rocks. They have 3 hall effect sensors.


The next step for direct drive would be a skateboard motor kit, but lions are starting to lean towards an off the shelf belt drive.
Posted by Jack Crossfire | Jan 27, 2021 @ 05:04 PM | 5,090 Views
Slowing down to walking speed when going up hills or into the wind is so horrible, something must be done about the torque. The mane options are bigger motors, higher voltage, or smaller tires.

New batteries would require writing off the old batteries. Batteries are going up in price, on account of tariffs. Now that the election is over, Biden is not going to undo the tariffs. Based on bench tests, higher voltage wouldn't give a significant increase in torque.

New motors are also going up in price, but the most promising ones are PROPDRIVE 5060. Higher diameters go up in price exponentially.
There are no affordable motors that would give the equivalent of a linear motor right next to a 110mm tire diameter.

The cheapest option is using smaller tires & redesigning the chassis. As long as the stationary material joining the tires to the chassis is narrow, a ship with small tires can actually avoid tall obstacles. The rotating part just has to cover as much of the motor as possible, with the connection between the motor & the chassis being as narrow as possible. The chassis would have to get wider again. Maybe it could be partly a tube structure to save on material.

There's still the problem of the hall effect sensors requiring a lot of horizontal space. Structural redesign could shave a few mm off the sensor. The 5060 motor is just the equivalent of making the tire radius 8mm smaller, based on the torque equation.

The solution to the battery door flying open was revealed by a piece of plywood. It just needs a small handle.
Posted by Jack Crossfire | Jan 26, 2021 @ 06:31 PM | 4,816 Views
The dual innertube design was a beast of a CAD model, but worthless in every way except proving you can print tube tires. Despite using the same amount of material as a spoked tire, it was much harder because of its structure. It was also messier. The spoked design has proven to be the easiest to tune to a desired stiffness.

There were a few attempts to design a cellular structure, but these were made stiffer by the increased amount of material more than the structure. Treads make them slightly stiffer by adding material. The treads may or may not make any difference in traction. Because TPU doesn't have any friction, treads may actually decrease traction. Treads increase stiffness & make more noise, so the trend has been towards bald tires that rely on just more surface area. If the treads protrude enough, maybe they could grab leaves, but they don't improve friction. Another idea is using spikes.

The trick is printing subsections of tires, testing them for friction & stiffness, but the lion kingdom initially needed softer tires as soon as possible to reduce the motor problems.

Lions once had to spend $25 for a set of tires. The 3D printed tires burn $6 for a set. They're narrower & can't get over storm drains but handle every other obstacle. The lion kingdom is debating whether to decrease the diameter to improve payload. Many robots got by with smaller diameters & more scrape protection on the underside.
Posted by Jack Crossfire | Jan 25, 2021 @ 11:13 PM | 5,992 Views
The decision was made to stuff electronics in the latest design. The inductor ended up on the bottom to make more room for the battery. The wires need to be repositioned again to make still more room for the battery.

The eventful run featured fluctuating center values for the throttle. It didn't have enough power to go into the wind. A narrow tire got stuck in a storm drain. The battery cover fell off. Finally, the encoders got knocked out of alignment & a motor started spinning in reverse.

The mane problem is lions are using the speed buttons to go faster, which is bashing it a lot more. The next step would be softer tires.
Posted by Jack Crossfire | Jan 25, 2021 @ 03:40 AM | 5,422 Views
The next tire was designed to be perfectly smooth for maximum silence & used about a buck of material. The treaded tires already had trouble gripping plastic surfaces, but lions are desperate for anything to reduce the noise. It was still slightly stiffer than the stock lunchbox tires, but very compliant. The mane problem is the desire for a round surface to reduce wear & friction.

For the round surface to be compliant, it needs to expand axially & compress radially. If it was flat, it would only need to compress radially. Not connecting the spokes to the entire outer surface was an attempt at axial expansion, but it's still very stiff where the spokes do connect. Only a curved sidewall would truly allow axial expansion & radial compression, but a curved sidewall is hard to print.

More ideas are transitioning the spokes to a different axis near the tread. Unfortunately, TPU only becomes compliant if it's curved on 1 axis. If it's simultaneously curved on 2 axes into a dome, it becomes very stiff. The dual spoke idea gets pretty ugly & still has problems.

There's also connecting the spokes only in the center of the tread.
Posted by Jack Crossfire | Jan 23, 2021 @ 07:58 PM | 3,593 Views
Made this one as thin as possible, taking out all the artwork & using .8mm thick panels. Thickness is only limited by the switch size. Took out the temporary screws, which was a disaster. They need the temporary screws, even when the sticks appear to stay in place without them. An attempt at knurled areas was subjectively successful, if only because they created a widened part. A better solution might be hot glue or removable TPU caps. The button caps need more clearance. Lions tend to hit the power button when they go for the speed buttons, so that might have to be moved up or get some shrouds.

Got rid of the bulge, yet the extra length required is barely longer than a lion paw itself. It should be reprinted with the temporary screws before committing to soldering.
Posted by Jack Crossfire | Jan 22, 2021 @ 10:58 PM | 3,970 Views
Watching this video got lions thinking about pendulum robots again.

Can A Self Balancing Vehicle Drive on a High Wire? (6 min 30 sec)

The problem is gyro stabilized robots have to be perfectly balanced or their gyro quickly saturates. They either need automatic weight shift or a way to precess. Pendulum robots accelerate in the direction of their center of gravity to stay upright. If they stay unbalanced, they'll keep accelerating until they run out of power & fall over.

The problem is pendulum robots are slow because they have to accelerate a lot of mass. When they move, they're either slowing a lot of mass down or speeding a lot of mass up to keep their CG centered, but never moving at a constant speed. Lions once considered fastening a quad copter to a pendulum robot to stabilize it. It would burn a lot of power, make a lot of noise, & take a lot of space. What about attaching a moment gyro to a pendulum robot to absorb the short term inertia, allowing it to travel much faster?

Moment gyros have been fastened to stationary pendulums but never to make a pendulum go real fast. This is a good example of the kind of system which could make an inverted pendulum go fast. Maybe a moment gyro could be used to make a legged robot cheaper & faster.

Balance Control of an Inverted Pendulum with a Control Moment Gyroscope (0 min 24 sec)
...Continue Reading
Posted by Jack Crossfire | Jan 21, 2021 @ 07:53 PM | 6,271 Views
The speed paddles were finally enabled & debugged. Lions thought they would be rarely used, but in fact took to them like Americans take to socialism. They were quite easy to reach. Every downhill ended up getting a speed boost. Every uphill ended up with a speed cut. The run had a more consistent level of intensity & higher intensity than normal, but it wasn't the out of control variability that happens when a lion tries to pace himself. Having ground truth about the speed range would prevent the consequences of going too fast or going too slow to reap any benefit.

Lions previously figured running 6 miles at a constant speed set in the app was enough of an improvement over self pacing, but the ability to make minor adjustments with the flick of a paw could be a game changer. Lions still may end up lazy & go back to constant speed runs though.

Helas, the motors showed serious lack of torque without a payload while climbing the lion kingdom's steepest hill. The next step would be installing better connectors & wires.

Lions continue to ponder how to improve the paw controller. The desire for improvements didn't exist before 3D printing because improvements weren't possible. The steering lever could be smaller & closer to the rear. The steering lever needs knurls. The whole thing will probably stay dual thickness but get thinner. The way to make it thinner is to get rid of the isogrid & all the indented markings that are illegible anyway. It would just be a .8mm thick wall. It wouldn't look great, but it would be the most functional solution. Maybe it could get decals instead.

3D printed isogrids tend to look better than 3D printed flat surfaces. The dual thickness is a buster to model & manufacture, but greatly reduces the size. The mane trend making paw controllers easier to use over the years has been smaller size. It still makes it hard to seat on top of the charger.
Posted by Jack Crossfire | Jan 19, 2021 @ 10:46 PM | 5,608 Views
Another 8.7 mile drive with stuff came in with the same power consumption as an empty lunchbox: 237mAh/mile. The lunchboxes were pretty efficient, with their gearboxes & roll resistance.

The remote control revision ended up not compelling enough to use. The more compact design just became more natural over time.
Posted by Jack Crossfire | Jan 19, 2021 @ 01:44 AM | 6,530 Views
2 solid days of CAD modeling yielded another attempt to address the ergonomics. It may be that ambidextrous controllers can never be comfortable. Most of the work was making it thicker & a constant thickness. If anything, this made it easier to fit all the electronicals, model, & get rid of the shaft holes. It didn't make it any more obviously comfortable. A mane goal is to keep the thumb & fingers from interfering, which making it thicker may do.

Then, an attempt to widen it to 47mm failed. 42mm may be the widest that fits in a lion paw. It definitely got taller to 160mm. The new design has no holes for shafts. The speed paddles got closer together, which definitely made them easier. The mane change was moving the steering 10mm farther from the throttle. The original was definitely too much miniaturization at the expense of comfort.

Most of a lion's life is spent with the throttle fully depressed & the tiniest pressures being exerted on the steering. Only during the rare maneuvers do the ergonomics start to impact.
Posted by Jack Crossfire | Jan 17, 2021 @ 06:54 PM | 9,587 Views
With no payload, it managed the required 10mph on level ground, but slowed way down on a slight uphill. There are hillier routes for more testing. With a 2lb payload, it managed the required 6.66mph on the standard road grades. The 6.7 mile effort burned 280mAh/mile, more typical for the lunchbox. PID adjustment for throttle might be in need. Getting more performance numbers requires implementing the speed paddles, which requires dealing with android studio.

Some TPU bumpers were a desperately needed safety feature. Angle aluminum ends at 10mph are lethal. Even better would be some cubertruck front end, but lions only have black TPU. Maybe a PLA cybertruck front end could be adhered to TPU cushions. Lions bash it into curbs all the time, so TPU is a better option.

Lions are keeping an eye open for a cheap pancake motor. These motors were selected for the lunchbox tire diameter, but wider motors with thinner tires would be more ideal.
Posted by Jack Crossfire | Jan 16, 2021 @ 07:41 PM | 10,549 Views
10.3 miles burned 217mAh/mile. The last mile was with a heavy payload. This exposed a serious lack of torque, compared to the lunchbox. Integrals tend to wind up & send it flying on level ground. It can't get up any hills. The motors didn't obviously get hot. There's definitely a power band as evidenced by the integral windup.

The lion kingdom is undecided on what to do about the paw controller. Making just a mockup with those intricate controls takes forever. There's some debate about getting rid of proportional steering when it's stopped & even more, getting rid of proportional throttle. The hall effect throttle would just be for detecting reverse.
Posted by Jack Crossfire | Jan 15, 2021 @ 07:19 PM | 9,115 Views
Version 3 finally managed to go 6.4 miles with no payload, over hills & bumps, with minimal stops. Power consumption was a whopping 175mAh/mile. It could go over 20 miles without a payload, on a single battery. It could also go 10 miles on a much lighter battery. The motors might benefit from a hotter winding, pending speed tests & payload tests. The motors weren't obviously hot after the drive.

Despite the bumps, the encoders stayed in place. The PID controllers were soft. The hard tires made it squirly. The mane limitation was now the paw controller. The controls need to be spaced out 10mm in every direction & it needs to be bigger. The lion kingdom has been leaning towards getting rid of the isogrids & the dual thickness in favor of simplifying it.

The battery compartment needs foam. The bolts need lock nuts. The tires held up well. Despite the hall effect joysticks, binary steering proved much easier than analog steering.

The low power consumption was manely from the hard tires & very little contact patch. Less benefit was from being direct drive, lions believe.

The encoders still required printing spacers to tweek the alignment. They're not as stable as hoped, but at least they just need 1 magnet & 2 sensors. Having the sensors too close to the magnet causes bigger constant regions of voltage. Moving the sensors farther from the magnet axially creates more changing regions. There still might be a way to make the software use past encoder readings to deglitch the current reading.

The steering PID controller needs to reverse direction when driving in reverse. The lion kingdom only realized it after 7 years of failing to hold a straight line in reverse. The trick is transitioning between fwd & rev.
Posted by Jack Crossfire | Jan 14, 2021 @ 02:46 AM | 6,779 Views
A batch of heroic soldering, a reversed buck converter, & the motors came to life. Mounting those right angle hall effect sensors took some doing. Mounting the motors was another buster. Things aren't as modular as hoped.

A few dozen more farsteners would go a long way. Given how many farsteners were in the standard model copter, the lion kingdom might have over emphasized efficiency of farsteners. The wires aren't very vibration proof either. It could stand to use another plate with wire traps .

After voltage testing, a few strange sounds, the wheels lunged forward. It was still running firmware for calibrating the motors & it showed the drivers were installed correctly.
Posted by Jack Crossfire | Jan 13, 2021 @ 12:41 AM | 4,901 Views
After a moment of silence before sacrificing $30 of hardware, the decision was made to bend all the pins in reverse, grind holes in the enclosure, & bolt the L6234's on the angle aluminum with their heat sink sides out. It required 22 new jumper wires to put the L6234's on breakout boards. It now is quite packed, despite containing only 1/2 the total amount of wiring.
Posted by Jack Crossfire | Jan 10, 2021 @ 04:14 AM | 3,634 Views
It got all the way to the SPI connection being wired up when some more tests revealed the mane loop only ran at 15khz with the mosfets firing at either 8khz or 16khz. Lions believe it would need to get at least 100000 bytes/sec through SPI to drive the motors from the ARM. The hall effect sensors have 20khz bandwidth & each mosfet write would need 5 bytes. The 5 bytes would be a start code, power & phase for each ESC. There's not enough horsepower in the ESC to convert the hall effect sensors to a phase.

So it was back to improving the cooling for the L6234. It's actually rated for 4A but hard to cool. They recommend via stitching to a ground plane with heat sink on the back, but that adds thermal resistance. It could be the 1st time the lion kingdom paid for a manufactured board. The most efficient cooling is from mounting it upside down, covering the pins in captain tape. A heatsink could be bolted directly on it. That would take precise milling of the board or stacking 2 separate boards on each side of it. Quite a big assembly but maybe smaller than an ESC. Another way is just to lift all the pins so the chip can be soldered upside down. There's also doubling up the chips.
Posted by Jack Crossfire | Jan 08, 2021 @ 03:23 AM | 4,353 Views
The easiest way to drive sensored, direct drive motors is to drop in an e-bike motor driver. Those are much cheaper than hobby ESC's in price per watt, but they're gigantic & manely require over 24V. They also require 3 hall effect sensors instead of 2, sensing the actual rotor. They might be shrinkable by taking out the guts. This is quite an improvement over 10 years ago when there were no e-bikes & large motor controllers would have all been super expensive.

Given the limitations, the next option is hacking hobby ESC's. The supersimples from 15 years ago are rated for 35A but always burned out above 5A. Full power requires current & voltage to be in phase, but they're worth trying. They have no hardware UART exposed. Lions 4 years ago wrote ESC firmware with a software UART driver for debugging at 9600 baud. It's always depressing to reuse ancient code because it shows how clueless you currently are about something you found easy long ago.

The plan is to send commands through high speed SPI & have them both on the same bus. Programming them requires unplugging the STM32 & plugging in the arduino. The exact wiring for the least amount of unplugging is a problem. It almost makes sense to make a bootloader program them over 9600 baud UART, but lions expect them to quickly burn out & be replaced by a home made motor driver.

At least a mockup of the existing pieces revealed a lot of empty space. The glued corners are truly a mess.
Posted by Jack Crossfire | Jan 07, 2021 @ 03:14 AM | 24,896 Views
Another incremental improvement. It needs a piece spreading the struts on top, but is otherwise useful. It currently uses a bend in the wheel forks to adjust height. It would be stronger if the wheel forks were straight & it adjusted the strut height, with the struts having a spreader on top. This reduces ground clearance, though.

The rod ends split if they're tightened with a socket wrench. They have to be tightened with pliers.

The battery compartment could have more ground clearance if it had bends like the steering section. This would require gluing a lot more pieces.

After ordering another $40 of PLA, it became clear that perfection really requires a way to recycle PLA. Every model is otherwise going to end 90% of the way there.