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Posted by Jack Crossfire | Today @ 01:43 AM | 5,061 Views
Some ideas for mounting a motor on a metal angle were conceived. The problem is the metal angle has to be as wide as the screw holes, the seal has to be a wider diameter than the metal & the tire has to be a wider diameter than the seal. It takes a very wide tire to enclose the encoder & large diameter for most of its width to enclose the seal. The encoder would have to go inside the motor & the metal angle would have to be little wider than the motor shaft. It would have to fan out inside the seal to attach to the motor screws. This doesn't allow any motor cooling.

So the existing motor modules with large diameter tires remaned. The C rings still tend to pop out if it hits the ground real hard, causing the wheels to slide out of their bearings.
Posted by Jack Crossfire | May 15, 2021 @ 03:45 PM | 28,395 Views
Testing of Starship Autonomous Delivery Robots in Silicon Valley (2 min 52 sec)

It was 90% autonomous, at least 5 years ago. It's slow & noisy, being based on a traditional geared transmission. It has 6 wheels with the 4 corner wheels powered. It gets up curbs by lowering its center wheel & resting on its rear wheel. It uses skid steering. The tires are even more minimal than lion tires. There's no suspension. It's quite large.

Routes are mapped in fine detail. They have limited ability to avoid obstacles. They usually stop when confronted by a human instead of going around. It goes 4mph.

Top 6 Delivery Robots - Self Driving (Autonomous) Delivery Robots (7 min 56 sec)
...Continue Reading
Posted by Jack Crossfire | May 10, 2021 @ 01:44 AM | 2,246 Views
The cheapest way to try to reduce the overheating motors was by shrinking the wheel diameter to the smallest possible size. 74mm was disappointing. Maximum speed was reduced to 8.5min/mile. Hill climbing with a payload was slightly faster. It was noisier. It was really noisy with a payload, because the internal structure of the tire created hard points. The mane problem was the low ground clearance. The motor modules got really chewed up. The minimum ground clearance seems to require 108mm wheels.

74mm wheels work for skateboards because the only exposed part is a narrow shaft. They steer by rotating the entire shaft of the front & back wheels. Since only the traction wheels have to be small to provide enough force, the front wheels can still be 108mm & have all the steering hardware. The motors in the rear have to be fully enclosed in the tires with only narrow shafts joining them to the chassis.

So there's still a problem of overheating motors as the weather warms. The latest theory is to invest in 1/16" sheet aluminum. Manually cut out hubcaps to dissipate heat out of the hubs. Manually cut out strips to dissipate heat from the motor legs.

Making those 74mm wheels was a lot of work, but it was still infinitely easier than before 3D printing. 20 years ago, it would have entailed many days of cutting & grinding or wouldn't even have been possible. A younger lion did spend many years on robots where a big part of those years was spent manually creating parts that could have been spun out by a 3D printer in days.
Posted by Jack Crossfire | May 07, 2021 @ 12:55 AM | 2,202 Views
This 1st PETG wheel got some farsteners to keep the tire in place. PLA looked a lot better, even when it was melted. The wheel is still a disaster to glue together. The rings were finally printed as C's to make gluing easier, but they always deform.

Then, there was a PETG motor plate. It was rigid enough to do the job, but it became clear that it was better if the motor plate melted before the motor destroyed itself. The PLA motor plate was a fuse.

There is a vision of bolting an aluminum sheet between the motor plate & motor to try to cool it. There just have to be large holes for the shaft & wires. It might have to stick behind the motor.

Then, there's reducing the tire diameter all the way down to 70mm. RPM would have to increase by 108/70. Wheel diameter is constrained by the size of the motor shroud which is constrained by the size of the motor legs.
Posted by Jack Crossfire | May 05, 2021 @ 08:55 PM | 2,372 Views
The PLA parts got quite deformed. There was 1 crack. At least this gave some more direction on where to add reinforcement. There's definitely a place where sheet metal could be bolted in, to try to dissipate heat. The wheel hub is definitely holding back a lot of outward force. Not sure how best to farsten it to the wheel. It would need a lot of farsteners.
Posted by Jack Crossfire | May 04, 2021 @ 10:25 PM | 2,950 Views
It was big enough to fit the giant DSLR lens & a shirt, with flexing. 5.2 miles later though, the motors were lava despite not undergoing any stops & starts. Morbid thoughts & depression then ensued. It's pretty worthless if it can't sling the DSLR around.

Upgrading to 5060 motors is fading away. A 3:1 belt drive is gaining favor, but the starting torque suffers. A pancake motor is gaining favor. Another idea is bolting the existing motors to sheet metal & the sheet metal to heat sinks, to give them some minimal cooling. At least the DLSR is worth the heft.
Posted by Jack Crossfire | May 02, 2021 @ 09:56 PM | 2,445 Views
So the trick with having a power switch is the switch disconnects the mane battery but does not disconnect the aux battery. Once the aux battery is connected, there's no way to know if the mane battery is on without feeling the switch. It wasn't on & at mile 13, the aux battery died. Decided to switch on the mane battery without disconnecting the aux battery, thus a dead battery & fresh battery were connected in parallel. There was enough resistance in the cables, the aux battery had enough capacity, that nothing even got warm. The aux battery just recharged.

The ages old question was thus answered. A fresh battery & dead battery can be connected in parallel, as long as the cables have enough resistance & the dead battery has enough capacity.

With this inefficient arrangement, it still went 18.7 miles at only 262mAh/mile.
Posted by Jack Crossfire | Apr 28, 2021 @ 11:32 PM | 2,644 Views
So the up arrow had been glitching for a while. Lowering the radio power, not probing it when transmitting, making the debounce longer didn't fix it. The microscope revealed a spot of green, the sign of water damage. The clamshell wasn't keeping sweat out. The next step is what worked before, cleaning off the corrosion, a dab of hot glue acting like a conformal coat. This is all because the board doesn't have a solder mask like every toy. The speed buttons actually do have strong pullup resistors, the 3 10k's.
Posted by Jack Crossfire | Apr 28, 2021 @ 12:54 AM | 2,917 Views
What began in 2014 ended with all the plastic parts getting thrown away, after many thousands of miles. They were worn to bits. The 1st one ended up being the last one, with the 2nd one falling apart much sooner & getting torn down last year. Only the farsteners, electronicals, transmission, & metal parts remaned. Much was learned from it & it was all applied to the newest 3D printed trucks. The 3D printed trucks have the heart of the lunchbox, but they do the job much better.

The G-buggy, ECX Ruckus, & H-king Sandstorm were kind of forgotten. They only lasted a year while the lunchboxes could go forever.

There is still some belief the 2 transmissions from the lunchboxes may have a use. They're noisy. There's only 1 functioning motor. They provide a lot of torque at high RPM, but none at starting RPM. No mechanicals from any past vehicle were ever reused.
Posted by Jack Crossfire | Apr 27, 2021 @ 12:52 AM | 2,911 Views
Pole cam speed test (15 min 57 sec)

Came out to 9.8MPH going down hill with a tail wind. The days of 10mph footage are over until a bigger motor is installed. The thought has occurred of installing forced air cooling, since the motors are now sealed.

How a simple bearing became a monster. Some complexity came from not wanting it to require tools. Since it requires tools anyway, it might as well undergo a simplification. There's a growing list of improvements for it, yet all it does is pan. There's also a desire to bolt it onto the side panels.

The battery recharge went a lot faster with the radios just 5db lower, but the speed button continued glitching. The next theory was a mechanical defect, so it was replaced. Fortunately, the radios made it without requiring a power cycle.
Posted by Jack Crossfire | Apr 25, 2021 @ 06:29 PM | 4,159 Views
Ended up keeping frequency hopping on, adding more bytes to the preamble, reducing the power by 5db, taking the current channel out of the packet. There's no way the channels are ever going to crosstalk. A longer preamble might help with any framing errors. The RFX1010 datasheet has a saturated output power of 27dbm, a gain of 28db. The Si4421 says it outputs 7dbm. So it would need at least an 8db cut to avoid clipping the amplifier. The mane impact of clipping would be harmonics & power usage, rather than any data loss.

The speed buttons started glitching, which may have been from the battery dying & the voltage sagging from the amplifier. Reducing the power might help with this.

Even after 15 years of hacking custom radios, there's always more to do.
Posted by Jack Crossfire | Apr 24, 2021 @ 11:41 PM | 4,464 Views
So there was the problem of phone towers overlapping the 915Mhz ISM which was fixed by adding more power, but there were still occasional losses of signal away from phone towers. There was a software change to send the channel number inside the packet, in case there was crosstalk. This only made the signal losses worse.

It would work perfectly for several minutes, handling errors, then just recieve 1 packet every 2 seconds. It was always a constant rate of reception rather than a total loss of signal. It would scan, immediately get a packet, enter hopping mode & get no more packets. Then it would time out after 2 seconds & scan again, immediately getting a packet. Power cycling either the transmitter or receiver made the problem go away for a few more minutes. It didn't depend on how far away the radios were or the error rate.

It became a lot more reliable just by adding debug statements to the receiver. The debug statements caused the UART receiver to overrun, so the UART had to be reset, which might have been 1 problem. The UART registers showed frequent framing errors, which might have been another problem. This UART scheme had been used for years without getting into a permanent framing error or buffer overflow, though. The mane difference might be those applications didn't turn the radio off between every packet. It could require a software UART on the receiver if it's a permanent framing error.

This was impossible to debug without a spectrum...Continue Reading
Posted by Jack Crossfire | Apr 21, 2021 @ 11:02 PM | 7,418 Views
The answer is yes, lions have gotten fatter since the last container was printed. It's probably been going on ever since the 1st container in 2015. As the containers have gotten bigger, the amount of food has indeed increased. Once you realize 1 more noodle container fits, you always put it in. Overheating motors have not deterred lions from stuffing in as much as possible. There's always a need to find the maximum capacity.

At least the steering since the software I2C has been rock solid.
Posted by Jack Crossfire | Apr 21, 2021 @ 12:18 AM | 6,160 Views
So there was delamination in a tire, giving a vote for tapered edges. Only the left tire delaminated, showing it was a problem with the 1st layer in the printing process.

The mane problem was both motors got flaming hot again. This time, the left motor seized up. It's definitely from pulsing the throttle with a heavy payload. They burned 1.5Ah to go 2 miles. If the throttle is constant with a heavy payload, it gets by. The bolts started flying off, despite being impossible to turn by paw. M2.5 bolts are so expensive, it might be easier to replace the entire motor.

It's still nominally burning 350mAh/mile with a payload & softer tires in front. It may be time to upgrade the front tires. Motor seizing happened with the original hard tires.

The next revision of camera electronicals began. It's getting the full frequency hopping 500mW.
Posted by Jack Crossfire | Apr 19, 2021 @ 12:36 PM | 4,512 Views
The lion got dehydrated & was walking by the end. The robot burned 300mAh/mile with 9Ah of batteries & food. Went back to the original idea of a soft starting throttle which goes into auto when it's 100%.

Inductive charging for the paw controller is just as problematic as a JST connector. The mane problem is all 5V phone chargers have protections against a number of conditions. If there's no load for a certain amount of time or if there's a load for too much time, they shut down. You have to use an ATX power supply, a dedicated raspberry pi power supply, or a mean well, which are all too big & expensive.
Posted by Jack Crossfire | Apr 17, 2021 @ 04:12 PM | 3,536 Views
It was time to return to the original wheel design, with a much larger diameter. It turned out the PLA hub has no meaningful mass difference from PETG, so it might as well be PETG for the higher temperature. This design had retaining rings glued on the hub, which were a disaster to glue on. A better idea might be diagonal overhangs. Then, there was adhesive to keep the tire from freewheeling.

It held the hexogrid tire on in an 11 mile drive. Power consumption with 1 new tire & 1 old tire was 254mAh/mile with 14oz of food.

Getting such a large clamshell to keep the wheel in place is tricky. It might be easier with a traditional block of infill or spokes. Lions just hate having any material which isn't visibly appealing.
Posted by Jack Crossfire | Apr 16, 2021 @ 02:48 AM | 4,735 Views
5 miles went down like a brick. The webbing kept the tire from sliding 1 way, but the adhesive did nothing to keep it from sliding the other way. The result was part of it sliding away & part staying in place. That rules out farstening at any single point. Too bad TPU can't stretch like rubber.

Been putting off upgrading the camera controller because it's so rarely used, but it definitely needs an amplifier.
Posted by Jack Crossfire | Apr 15, 2021 @ 01:06 AM | 4,243 Views
As these things tend to do, the stakes have been raised to get a reasonable combination of traction & range. There was a partial hexogrid tire which proved too soft for the cost.

Because it takes so much more material to make a flat tread stiff enough, the decision was made to go back to a PETG hub with a thin TPU tire. This would limit the compression if the tire completely compressed. Helas, PETG is noticeably heavier than PLA, despite its heat resistance. It could probably get away with PLA since the motors rarely get flaming hot. The biggest weight savings may be abandoning the hexogrid. Like the SpaceX logo & the isogrid, sometimes you just want it to look good.

The lion kingdom has evolved its 3D printing game to the point of making the thinnest possible lines & planes with the thickest possible layers. The .4mm nozzle can print a .5mm wide line but takes forever. The .8mm nozzle can print a .9mm wide line but is much faster.

Since the tires slip around the hub, there's still a dream of bolting the tires to the motors, but they now have to transfer force a lot farther across a much bigger hub. A 7 hour tire with webbing had good compliance, transferred rotation to the motor, but easily slipped sideways. It would need some kind of adhesive, whether it bolted to the motor, if the hub clamped it as before, or if it clamped around the hub. It might as well be a plain cylinder.
Posted by Jack Crossfire | Apr 13, 2021 @ 02:14 AM | 4,693 Views
After the 13 mile fiasco, some documentation of tire compression with a typical payload. It clearly is a matter of traction vs stiffness. The flat treads need a lot more material to be as hard as the curved treads, but are necessary for any traction.

A tire with a slightly curved tread didn't get any stiffer. Changing the number & straightness of the spokes didn't make a significant difference. Putting the extra spoke material into more tread thickness might make it stiffer. Printing spoked tires with .4mm layers takes only 2.5 hours.

There is a new honeycomb design with a flat tread & integrated motor mount, but it takes 10 hours & the lion kingdom is low on filament again.
Posted by Jack Crossfire | Apr 11, 2021 @ 11:03 PM | 4,238 Views
A 13.75 mile drive with a decent payload went slowly & ended in battery death. The increased traction of these tires wasn't worth the reduction in range. It actually hit a wet patch & spun out, but these tires have never spun out as much as the stiff ones. It burned 335mAh/mile, still in line with the lunchbox but real slow.

The motors couldn't go very fast with the full payload on level ground & that was the deal breaker. There could be a new tire with a very slight arch to bring back just enough stiffness without requiring tons of material. Real car tires are flat, but it takes a lot of material to make them stiff.

What's needed is a tire which can be made stiff when it has a payload & flexible without a payload, without air pressure. Having a variable diameter based on desired speed would also be a win.