3D printed truck

3D printed running aid

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The ultimate running aid was big enough & the 3D printed truck became so big that it was decided to separate the 2.

The high cost of good RC truck kits, diminishing need for such kits & the noise of gearboxes made lions look elsewhere for a robot platform.  3D printing a truck from scratch, with only a few metal parts still being off the shelf, was the next step.  The only parts which have to be outsourced are the motors, steering servo, & steering knuckles.  Everything else is 3D printed, made of coroplastic, or home made electronicals.  The size was based on the original Tamiya lunchbox.


Motor numbers are comprised by their diameter & length, so a 4248 has a 42mm diameter & 48mm length.

The current ship has a Propdrive 4248 of any KV rewound with 20 turns of 26AWG according to the diagram.   It doesn't produce enough torque to go up hills.

A Propdrive 5060 with lower AWG & more turns would be a better match.

Steering knuckles:

These have to match the wheel base, to achieve ackerman steering.  Lions use

Jazrider Aluminum Front Steering Knuckle Upright For Tamiya RC CW01/Lunch Box

from fleebay & size the wheel base to within 1" of a lunchbox.  

Steering servo:

The lion kingdom uses discontinued trackstar brushless servos with servo savers.  Brushless is required to get any life out of them.

The 3 mane components are the steering module, traction module, & the coroplastic container.  They're held together by  aluminum angle rods.

The tires are 3D printed out of TPU for a lot less money than Chinese ones.

The final mechanical piece is the paw controller.  It uses springs from ball point pens.

Electronicals provide semi autonomous throttle & steering.

  • Translucent controller

    lion mclionhead07/03/2023 at 22:13 0 comments

    The current waterproofing & having all the LEDs on the inside worked, but growing pains with the orange beast finally reached a point where it was time. The mane problem was the power button constantly getting accidentally bumped when it was in leash mode. There were cosmetic desires for a glossy enclosure, better LED visibility.

    There was once a theory that an easily accessed power button would allow emergency killing of the motors. In reality, there was never a case where accessing the power button would have killed a runaway vehicle. The throttle stick always worked. If it got stuck, it was faster to unstick it than reach for the power button. The power button would not interrupt the leash & the leash now does half the driving. It was finally time to add some minimal guarding to the power button.

    Assembly still takes 2 days, manely involving fiddly bits, removing the old circuit intact, reaming holes. PLA rivets are much harder to undo than hot snot. Undoing them melts plastic parts & removes a layer from the inductor. It pays to make the PLA rivets smaller.

    The 1st sock rapidly turned yellow either from biological matter or sunlight. It definitely smelled like biological matter. There's a warping from the clamshell not fitting perfectly. Stick controllers still need lubrication. The hall effect sensors got moved to where the datasheet showed their hotspots + a .2mm margin & they reported nearly the exact center.

    Time will tell if a glossy exterior was a good idea. The sock might grip better with a buildtak finish.

    The next big feature is going to be OTA firmware updates. It's not possible to get the oral cues perfect as is. There should be a way to put the radio in a serial port passthrough by holding power & a direction button. Then it can run a bootloader. It's a big job.

    There's a growing desire to make the panels 1mm thick. They were made .8mm thick before lions were fully educated on PLA tolerances. There's a growing desire to make the power button exposed on 1 side & riveted in. The current hot snot system is a mess. Maybe it could be scotched over for waterproofing. Maybe it could be passively clamshelled in. The 3 button caps could actually be smaller. Still no better system than hot snotting the hall effect sensors.

    The mane problem with the translucent controller is it gets hot in sunlight & alignments change. 

  • Nose cone development

    lion mclionhead04/14/2023 at 23:39 0 comments

    As previously seen,

     the cheapest way to get more speed was seen as creating a modular nose cone rather than expanding the motors, using hotter windings, or expanding the battery.  The nose cone had to be field removable without tools, stowable so the leash could be accessed, & not cover the headlights.

    The 1st step was converting the headlights to a narrow strip.

    Various nose concepts followed, with cardboard, coroplastic, & PLA.  After many miles, the best performing one was 3 sided with permanent string holding the bottom & a removable string farstening the top to the truck.

    Ideal speeds with a nose cone:

    #    dist    sec    min/mile
    1    213    43    5:42
    2    201    44    5:45
    3    203    44    5:44
    4    208    46    5:49
    5    201    46    6:3
    6    211    44    5:51
    7    205    46    5:52
    8    208    44    5:53
    9    206    47    6:0
    10    204    45    5:43
    11    211    43    5:42
    12    200    44    5:47
    13    203    46    5:58
    14    306    70    6:6

    Typical speeds without a nose cone:

    #    dist    sec    min/mile
    1    208    48    6:9
    2    305    73    6:24
    3    405    98    6:28
    4    408    103    6:43
    5    404    100    6:35
    6    404    100    6:34
    8    400    101    6:45
    9    407    110    7:14

    Speeds with a nose cone were highly variable, depending on weather, payload, wheel alignment.  Without a nose cone, it was guaranteed to have a hard time getting above 6:30/mile.  With a nose cone, there was a possibility of it getting above 6:00/mile.

    There's no correlation with the number of sides of the nose cone.  A 2nd nose cone on the back might buy it more speed.

    The latest nose cone is glossy & collapsible.  It rests on the bumpers while clearing the leash.

  • Charging stand upgrades

    lion mclionhead01/21/2023 at 23:06 0 comments

    To make the controller waterproof, the TPU sock eventually had to be permanent which meant updating the charging stand.

    In this process, the charging inductor cracked.  Those are really fragile.  If the enclosure is too small or you try pulling it out when any PLA rivets are holding it in, it's going to crack.

    The temptation is to press it when grabbing the charger. The problem is the new design fully exposes the inductor & nothing supports it in the middle. Below it is an air gap followed by the circuit board. At least Walmart has qi chargers locally at a reasonable price. The easiest solution is to not PLA rivet it & have some kind of foam press it out from the circuit board. It has a packing tape cover which could also prevent it from rotating.

    The lion kingdom's PLA riveting skills have improved to melting it with a brushing motion of the soldering iron rather than keeping the soldering iron stationary. This keeps it from sticking to the soldering iron. Then use the mark 1 lion paw to press it in position before it cools.

    With the sock now permanent, it would have to be translucent to see the charging LED.

    Translucent TPU & PLA entered the printer.  The decision was made to retire orange PLA & hard black TPU.   TPU is manely used for tires.  The hard variant had very little use.

    Panels which dominate lion prints come out a lot clearer than walls.  It not obvious whether the filament came wet from China.

    The charging LED is now visible.  

  • New remote

    lion mclionhead01/10/2023 at 07:30 0 comments

    The mane desires in a new remote were improved water resistance & replacing all the hot snot with PLA welding.

    PLA welding was a successful failure.  1 switch still ended up needing hot snot.  The best way to install the hall effect sensors was still to put a dab of hot snot down 1st, then press the hall effect sensor on, then flatten the dab. A dab of grease on the hall effect sensors still made a big improvement. Grease should not go anywhere else as it causes sticking.  The only reason the joysticks get stuck is friction with the hot snot & grease.

    A new trick with PLA welding was to melt the PLA with the iron but use the mark 1 lion paw to press it down. It adheres to the iron but not to the lion paw.

    In the interest of water resistance, a sock covers the entire handle.  The sock is removed for charging.  If there's any evidence of how bad lions are at 3D concepts, it took a long time to realize the finger grip could be part of the sock. It actually holds water but doesn't have enough friction to stay on. 

    The mane problem is the welds don't go as deep as hoped. No point in using orange PLA if the sock is covering it. Low cost TPU is quite good for covers like this. Trying to stretch it over the steering stick was hopeless, so it got a cutout.

    The leading idea to get it to stay on is taping the PLA to make it thicker.  Other ideas are to print ridges inside the sock or make the sock narrower at a point.  The problem with making the sock expand around the enclosure is welding the sock requires fitting it around the enclosure 1st.  It would need a blank smaller than the enclosure just for welding.

    Power consumption was 50mA, so a 260mAh battery is only going to last 4 hours on a good day. It needs the 400mAh battery which somehow fit in the last one. The 260mAh required a lot of coaxing to fit in there. If the radio constantly transmits, it burns 120mA. The transmit duty cycle is 5ms on & 35ms off. The PIC has to run at full speed for the sounds.

    There's 1 heroic bodge wire to connect MISO to the radio. Despite every effort, the radio failed to initialize without several power cycles. The datasheet says Vdd needs 1ms ramp time. The LP2989 has a 5ms ramp when probed.

    Merely cleaning the flux got it to start despite the LP2989 issue. Getting rid of 100uF of capacitance didn't do anything.

    After fighting to get the sock over the LEDs, it was decided to put the LEDs inside the case & hot snot the LED holes shut. With orange PLA, the red charging LED shows nicely but the green transmitting LED is barely visible. Transparent PLA would be ideal, but there's a real need for white PLA for an LED diffuser. Nylon paper might work as an LED diffuser, which would make transparent PLA the better deal for fabrication.  LEDs that diffuse through the enclosure should be a bigger part of all designs.

    The hall effect sensors are 1.3mV/G so they never saturate.  There is a desire to make the handle narrower to compensate for the sock size.  The steering lever should be either square or longer to compensate for the sock.

  • Secrets of the Si4463

    lion mclionhead01/09/2023 at 19:38 0 comments

    It was finally time to build a new remote control for better water resistance.  Sadly, the original Si4421 radios were discontinued & problems with the RFX1010 burned the last 2 of those chips.  It was never figured out why those failed after working in 2 boards.  The Si4463 promised to make enough power to not need a front end & has a higher bandwidth.

    The Si4463 is 10 years old but already a beast.  It requires all 4 SPI pins.  It uses the MISO pin for flow control. While the datasheets show the pinout & an example schematic, they don't have any inductor values. 

    The new dance is separate RX & TX antenna pins.  For transmitting, a simple 100nH seemed to do the job.  There's no plan to use it for receiving.

     The register descriptions in the datasheets seem to be obsolete.  All the register values are documented by the Wireless Development Suite (WDS3).  Bringing it up is not possible from the datasheets.  The WDS3 has a radio configuration application which generates all the required code.  

    You have to export a custom project after setting all the configuration bits.  The header file option doesn't work.  The 2 key files it generates are



    The key object is the RADIO_CONFIGURATION_DATA_ARRAY.  It's just an array of packets to send to MOSI with flow control codes.  The 1st byte is a packet size.  Then you send the packet.  Then you poll the CTS register before reading the next packet. 

    SPI is MSB 1st.  The datasheet didn't say that.  The flow control procedure is in the radio_comm_SendCmdGetResp function.  Part of the auto generated array is a firmware patch which requires 512 bytes.

    The only requirement for using a UART to modulate the signal is declaring 1 of the GPIOs as an input & selecting Direct TX as the project.  Set the other GPIOS to TRISTATE & they can be connected to ground.  Then send a START_TX with 0 for all the arguments.  That is auto generated in the si446x_start_tx function.

    The other trick is setting the deviation to match the Si4421.  That's how far the carrier shifts above & below the center frequency for modulation.

    For frequency hopping, the channel is sent in the START_TX command, but this is only accurate to 30Hz.  The base frequency is accurate to 1Hz.  The base frequency is set by the RF_FREQ_CONTROL_INTE_8 & RF_MODEM_AFC_LIMITER_1_3 registers.  The channel spacing on the Si4463 is only accurate to 30Hz  while on the Si4421 it was within 10hz.  To save power, use the channel number in the START_TX command.

    The PA power level is 0x7f for full power & 0 for lowest power.

    There is a desire to resend the packet multiple times per hop, but this requires a receiver change.  Without a unique ID in each resend, it seems to screw up the hop timing.

    The ramp up time for transmitting is under 1ms on the Si4463, which greatly reduces the amount of current required from the 5ms required by the Si4421.  

    Going into standby mode

    The mane thing is all the GPIOs have to be configured as TRISTATE or INPUT.  If it's driving the GPIOs, it sucks 10mA in standby mode.  Then you're going to put it into standby mode when not transmitting.  Poll CTS 1st, then issue the CHANGE_STATE command for standby/sleep mode.  Polling CTS after the command might wake it back up.  This drops the current to 0 when not transmitting.

    Of course, the typical usage involves long delays between state changes, so you shouldn't need to poll CTS at all.

    Startup difficulties

    The mane reason it won't start up is the ramp time for Vdd being too high.  The easiest solution is to connect SDN & drive it high until Vdd is done.  Thus, it takes 5 digital signals to start up.

  • Dead motor #2

    lion mclionhead11/23/2022 at 00:07 0 comments

    3 months after the left motor winding died, the right motor winding died.  This one died in the dead of winter no less & smelled like burned enamel.  It was last rewound on April 29 so it only lasted 7 months.

    Left Motor windings:
    Nov 27, 2021: 20 turns 26AWG
    Sep 24, 2022: 20 turns 26AWG

     Right Motor windings:
    Apr 26, 2022: 20 turns 26AWG
    Nov 22, 2022: 20 turns 26AWG

    The left windings lasted a solid 10 months.  The right windings were staggered.   They're rated for 150C & they're confirmed to melt at 300C.  Lower temperatures allow longer duty cycles, but all temperatures eventually melt.

    Suspect running faster more often is burning them out.  At this point in the history of motor rewinding, nothing new could be added.  The question is when is rewinding motors going to take more time than designing a temperature sensor.  

    The leading ideas are thermisters & thermopiles.  Temperature sensors are not standard in electric bike motors, despite Louis Rossmann's vlogs.  

    Guys just epoxy them to the motor windings.

    This one is siliconed to a motor case.

    The leading idea is cutting down the heat sinks since they're not doing anything, permanently farstening thermisters to the heat sinks next to the motors.  The heat sinks did a good job tracking motor temperature, but didn't remove any heat.

  • Unitree robot

    lion mclionhead11/11/2022 at 02:20 0 comments

    China made a bit more progress towards the ultimate goal with another robot dog.

    This one is specifically marketed as a running coach & food transporter.   At the $2700 price point, payload is 7 lbs freedom units.  Maximum speed is 5.5mph freedom units.  Prices beyond $3500 enable speeds over 8mph.  Range is 1 hour.  It tips the scales at 26lbs freedom units.  Of course, the reviewer didn't test any of the parameters.

    It uses direct drive brushless motors.  There's no mention of walking on unimproved terrain, navigating obstacles, navigating crowds of animals.  It has a bulky 2 paw controller & relies on a brain to navigate.  It has some ability to stay in a fixed position relative to the user, through machine vision, but also shown is a GPS tag as a backup.  They emphasize the SLAM functionality.  

    There's a 3-6 month warranty, depending on the component.  The lion robots need major servicing by 6 months or 1000 miles.

    Lions aren't sure they'd want to haul 26lbs of robot around if it died, but there's definitely a lot to be gained by making it heavier.  The lion robot is sized for its typical role.  The typical need is a maximum speed of 10mph, payload of 5lbs, range of 4 hours, light enough to carry 6 miles if it dies, manual driving.  

    We're not sure why everyone in the video is sitting in an office to stare at confuser screens.  It seems everyone in the transportation business is required to go to an office.

    Bosstown dynamics always claimed the high mass & pinch points were the reason for its dogs not being intended for consumer roles.  In typical chinese style, the users are expected to take risks.

  • Rudolf update

    lion mclionhead10/23/2022 at 03:16 0 comments

    Installing roborudolf is the 21st century equivalent of decorating the tree.

    There is a desire to repaint the antlers with metallic brown, but this would entail rebuilding all the LED strings.   Reprinting the antlers would fix some fitment problems.  Another desire was flattening the tips of the antlers.

    The headlight becomes another difficulty when the nose is installed.  The red LEDs might be enough to replace it, if driven at their maximum voltage.  The plastic dome could be taken off.  The headlight could be installed above or below the nose.  Maxing out the nose would entail yet another voltage converter.

    Metallic brown is definitely more fitting for a robot.  It went on more even than flat brown.  Printing .8mm nozzle .32mm layers took up more ink.  The ideal antler is metallic brown TPU, but that would be much harder to bond.  These were printed as solid halves with 20% infill.  The easiest way to bond was gluing a right angle out of 1 half & the base, then gluing the remaneing half.

    New antlers fitted with lights.  The metallic brown is less obvious in the dark.  

    Locked & loaded

  • Propdrive dreams

    lion mclionhead10/22/2022 at 20:12 0 comments

    #    dist    sec    min/mile
    1    205    45    5:49
    2    209    46    5:47
    3    200    46    5:59
    4    203    46    5:58
    5    201    48    6:22
    6    200    47    6:12
    7    311    71    6:19
    8    312    70    6:11
    9    304    75    6:34
    10    303    76    6:42
    11    401    98    6:29
    12    403    97    6:24

    The lion kingdom evolved a routine of increasing interval distances as the headwind slowed it down.  In this case, the headwind was weaker than expected & the 400's ended up faster than the 300's.  There's not enough power to hit 6 minutes in the headwind as previous robots did.  

    The propdrive 5050 is believed to have the key to 6 minute pace intervals.  The weight increase could be manageable.  It would fit in the latest wheel design.  It only wouldn't fit in previous wheel designs which directly copied the dimensions of the lunchbox.

    A pair was once $90 & after bideflation, was $120.  The lion kingdom worked out a way to pay so much money when larger motors in the form of a hoverboard would be cheaper.  It's all about saying the premium is for miniaturization.

    There's still the idea of having large diameter motors on the outside, extending the container all the way to the bottom, & making the container narrower.  The electronicals & batteries could go inside the motors.  This idea could also involve extensions of the container inside the motors.

    The most radical idea is having a single traction motor which wraps around the entire container.  It would require a tank tread to achieve the various bends.  The motor is shaped like an oval.  The problem is carrying the vehicle by the tire, mounting the camera on it, storing things which are taller than the motor.  It's not believed having a single motor passing down the middle of the container would be practical.

    The trend is large, hollow motors with the container integrated in the empty parts of the motors.  It's believed these motors can be constructed out of electromagnets bolted onto a linear PETG framework & permanent magnets embedded into TPU.  Smooth sliding of the TPU over the PETG would take some creative bearings & seals.  Chinese do sell bare ball bearings without the races.

    A gearbox or belt is just a way to increase the diameter of a motor, but compress it into a smaller area & make a lot of noise.

    The leading candidate for increasing the speed is an aerodynamic nose cone.  The problem with a nose cone is it's going to cover the headlights.  It could be translucent PLA.  The headlight could attach to the front of the nose cone & the front could be on top.  The nose cone has to fold up & fit in the container.  It might work if it hangs from the top.  

  • Camera pole problems

    lion mclionhead10/11/2022 at 00:49 0 comments

    Something so simple can be complicated if you're poor enough.  The camera pole developed a hair more friction.   Then it started jamming, revealing the servo didn't make any torque at its highest speed.  The trick with servos is they don't make any torque at their rated speed.  Their rated torque only happens at low speed.  They automatically slow down as the load increases.  A stepper just stalls.

    Running it on 6V buys more torque, but the raspberry pi can't run on 6V & it's still not jam proof.  There's actually a sharp cutoff between high torque & low torque.  The cutoff rises with increasing voltage.

    More importantly, the L6234 falls over below 6V.  The camera pole originally ran on 6V before the raspberry pi.  There would have to be a different regulator for the raspberry pi or a lower speed would have to be found for the camera pole.

    There can be 5 more wires to the motor sensors.  It can go back to stock servo firmware, with PWM being used to control speed.  Its Silabs F330 microcontroller could be reprogrammed as a stepper driver to run on 5V.  Stock servo firmware with PWM is unlikely to be precise enough.  The rest are a lot of work with little payoff.  

    No-one has ever hacked a servo's firmware.  Using the sensors would entail making a speed governor instead of stepping on a schedule.  The most effective solution is using the F330 as a lower voltage stepper motor driver.

    The camera pole has always used a stepper motor out of a belief it offered the most speed control.  If speed governors are the future, it would be a lot easier & smaller to use an N-20 gearmotor with some encoder.  It could be a use case for back EMF but it would take some testing to see if the range of motion was enough for back EMF to be stable.  The easiest solution is just an open loop H bridge driving an N-20 gearmotor, but the N-20's in the apartment are too fast.  It would need some ramping for the PWM & it wouldn't be predictable enough to use machine vision.

    There are other gearboxes in the apartment which could attach to stepper motors, but they're big.  Stepper motors are big because they need a big old motor driver with heat sink.

    The original pancake motor with gearbox never failed.  It was just big.

    The decision was finally made to hack the servo to use its own 5V stepper motor driver.  That 7 day investment solved the torque problem, reduced the voltage to 5V, & freed up another L6234.

    The camera pole came back with a vengeance.  The total power consumption with lion tracking was still 350mAh/mile.  All this stepper motor work is quite worthless compared to a 360 cam.  Maybe it's worth it if you have spare parts to make up for the $200 of mecha it would require from scratch.

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James Rowlands wrote 09/14/2022 at 09:14 point

Hey! This looks like a neat project, as well as your running aid. Does that auto-follow? If so, how did you implement that?

I plan to one day produce a 'cycling aid', along the same lines, with enough of a payload (>20kg) to be useful on grocery runs. Do you think your printed truck would be a suitable RC vehicle for this? Or perhaps a starting point? I'd be after a vehicle that can keep up with, brake faster than, and handle the kind of terrain a bicycle can.

  Are you sure? yes | no

lion mclionhead wrote 10/23/2022 at 03:12 point

Definitely need hover board motors for 20kg.

  Are you sure? yes | no

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