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.

  • Traction module 3

    lion mclionhead02/10/2021 at 06:57 0 comments

    Rock intrusion continued to plague the motors, so a new traction module was designed, to fully enclose the motors.

    This one flipped the isogrid panels so the sides could be printed in 1 piece.  It was sized for a .8mm line width, .32mm layer height.  The reduced part count made it fit much more accurately.

    The key was a novel motor shroud with a TPU o-ring that would theoretically keep rocks out.

    The encoders continued to plague the motors.

    The hall effect sensors were reoriented, which allowed them to finally sense the full range of motion.  They have to point along the circumference rather than radially.  The resolver in this configuration is thus the easiest way to detect motor position.

    The easiest way to cover the H bridges was duct tape.

    Torque limitations continued to plague the motors.  It turns out the cheapest source of large diameter motors for this task is inside hoverboards.  They're far cheaper than hobby motors of the same size.  They're sealed from rocks.  Hoverboards have long ago faded from popularity & their cheap motors might be going away.  The motors replacing them are much smaller skateboard motors, with much less torque, at a much higher price.

    The media was focused on the batteries in hoverboards, so the public became singularly focused on tearing down just the batteries while ignoring the motors.  There are very few teardowns of the motors.  

    These are sadly too big for the truck in mind.  They're too big even for a brushless gimbal.  It's remarkable how economies of scale during the height of the hoverboard craze made such large motors almost free, while tiny hobby motors are a fortune.

  • New controller charger

    lion mclionhead02/10/2021 at 06:19 0 comments

    The lion kingdom's 3 year old Qi charger was proving a disaster for charging remote controls. Putting a magnet in any controller would take up a lot of space, so there was no easy way to align them on the charger. Then, the unusually shaped controllers weren't held in position. The decision was made to finally make a new charging enclosure that would fix the controllers in the right position. It's a very loose position, but good enough. The status LED in the charger, once completely covered by the case, is now visible.

    Printed it out with the .4mm nozzle & .4mm line width. It has only .8mm thick panels. Called it quits after 2 prototypes.

  • Smaller tires

    lion mclionhead02/01/2021 at 07:42 0 comments

    The lion kingdom printed some smaller 90mm tires to get more climbing speed.  Tire designs are getting much softer & quieter, but not improving the traction.

    These introduced a shroud to keep rocks out of the motors.  These reduced the maximum speed from 10mph to 8mph & didn't materially improve the climbing speed.  The other options were higher voltage batteries, expensive.  There was more windings of lower wire gauge, not enough room.  There was using bigger motors, very expensive & reduces ground clearance.  

    The cheapest, most configurable option is a boost converter.  It's a way to use semiconductors to make a motor pass more current from a lower voltage.  The boost converter would allow the motors to be rewound again for higher torque & higher voltage or it could just be used to send more current through the existing windings.  The maximum torque is achieved with 70-80 turns of 32AWG, depending on room.  This requires over 40V to hit 10mph with a load, according to past notes.

    The current winding is 20 turns of 26 AWG.  It achieves 10mph with a load, on 12V.  The boost converter might require more turns of finer gauge to manage the heating.  It reduces range by up to 20% depending on the load.  

  • New controls, new tires

    lion mclionhead01/27/2021 at 06:50 0 comments

    The mane problems encountered during the 1st 74 miles were the paw controller's ergonomics, the tires being noisy & too hard, the battery cover coming off, motor encoders slipping out of alignment, lack of torque.  

    A pile of 3D printing yielded improved tires & a new paw controller.

    The new tires were about as compliant as TPU could get.  The mane variables are whether to have a tread, how curved they should be, how wide they should be.  They got down to $1.50 of material.  They were slightly quieter than the 1st tires.

    The paw controller was more of a manufacturability upgrade than an ergonomic upgrade.  The enclosure was made a single thickness.  The new controller is thinner & lighter than the old one.  There wasn't enough room to keep the isogrid or any of the markings.  The steering lever was shrunk to make it easier to steer while going in reverse.  The problem is lions stretch more in their right paws than their left paw so it's never going to be a perfect fit in both paws.

    The speed buttons were enabled, opening a new world.  Never before was it this easy to adjust the speed.  Lions immediately began stepping up the speed for every downhill, taking a lot of time off their runs.    Unfortunately, the clamshell tends to separate, creating a lot of variability in the analog readings.

    All manual steering or throttle ended up useless.  The confuser does a much better job than the lion, so binary steering & binary throttle were put back, using the analog readings to have 2 steps for steering.

  • The era of direct drive begins

    lion mclionhead01/16/2021 at 03:42 0 comments

    Prototype 2 died after .5 miles. The motor drivers overheated.  The motor encoders slipped out of alignment.  The manual steering proved difficult.

    A nearly complete redesign of prototype 2 yielded the 1st prototype to go 6.4 miles.  

    The chassis was widened 20mm.  The steering section was redesigned a 3rd time. 

    To cool the motor drivers, the L6234's were soldered upside down & bolted on the angle aluminum.  This entailed soldering 22 flying leads to breakout boards, but it worked.
    There was a long drawn attempt to hack an ESC to be a directly controlled H-bridge, but a stock ESC doesn't have enough serial port bandwidth to be updated at the required 16khz.  

    The traction module was redesigned for modularity.

    The motor encoder was redesigned to use 1 magnet & 2 hall effect sensors.

    The motor was made more modular, but it has a long way to go.

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

    The mane limitation was now the paw controller. The controls need to be spaced out 10mm in every direction & it needs to be bigger. 

  • Truck prototypes

    lion mclionhead12/30/2020 at 05:28 0 comments

    When lions started using RC cars as personal trainers, they had no functionality.  Range was unknown.  They ran on AA's.   They were controlled with the stock 2 pawed controller.  Seem to recall running at least 5 miles until the AA's went dead, holding the controller with 2 paws, then run/walking 5 miles back while carrying the RC car.  Another range test entailed running laps closer to the apartment.

    It took an eternity to develop  a power supply better than the stock AA's.  That entailed discarding the car's convenient battery holder, building a large battery tray, & mounting a lipo on top, making it top heavy.

    The custom truck was a step back from that to more primitive stages.  The previous vehicles were proven toy designs.  It wasn't known if the custom motors would make enough power, randomly lose alignment & die, how much power they used, if the H bridges would overheat, how long the PLA structure would last. 

    The 1st drive entailed much paralysis by analysis, unit testing, & redesigning.  The mane board got redesigned 3 times.  The no load tests showed 1/2A.  It burned 300mAh going nowhere.

    The direct drive motors were a big investment.  They needed sensors for slower speed, large diameter for torque, & to be outrunners to bolt wheels on.  They don't make large outrunners with sensors.  Ordinary 42mm diameter motors were rewound with 20 turns of 26 gauge to increase torque.

    Making sensored motors out of unsensored motors required very precise hall effect sensor placement.  The sensors had to be analog with sample rates above 50khz.  Digital sensors could only sample at 1khz which wasn't fast enough.  Then, the sensors needed to face a magnet holder on the motor shaft.  It was pure luck that modern motors have a shaft on 1 end for mounting magnets & a rotor on the other end for mounting a wheel.

    Motor encoding was a hard problem that required plotting the sensor voltages for all shaft angles, hoping the parts didn't shift.  It was a bit harder than a standard motor sensor, since slow starting required the position in the 360 rotation to be known rather than which phase to light up.  Sensing the 360 degree angle with a custom magnet holder required only 2 hall effect sensors instead of 3.  The motor controller still has many bugs & doesn't turn them smoothly.

    Then came custom hubs which could mount a tire on a motor.

    A cutoff of Chinese exports & runaway inflation dried up the entire supply of cheap tires of suitable dimensions.  Tires would have to be 3D printed out of TPU.  They had to be narrow to reduce power consumption.  The cost of TPU could actually be  competitive to what Chinese tires cost.  Several mathematically generated tire models were created, with curved spokes being the cheapest.

    These tires were like rock.  The hope was for the tires to be soft enough to not need shock absorbers.   TPU can be very hard, depending on the placement of arches & structural members.  The needed width of the tires remanes unknown, as it depends on how wide the suspension becomes.

    Battery placement, cargo placement, electronics placement, wire routing all came together over several months.  Chinese tires were slowly replaced with 3D printed tires as each tire took 12 hours to print.

    Motor control was based on the tried & true L6234 of brushless gimbal fame.  It has a thermal shutoff, but is harder to cool.  

    The prototype got a container from a past vehicle.  Radios & user interface were put in a separate enclosure.

    The steering section was a difficult problem.  The suspension has to be as low as possible & not flexible enough for the tires to rise up too far.  Modern vehicles are all based on ackerman steering which...

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  • The remote

    lion mclionhead12/10/2020 at 20:57 0 comments

    The journey began with designing a custom remote.  It needed proportional steering, proportional throttle, 2 momentary buttons for trimming speed, a power button, speaker, LED indicators, inductive charging, & to be ambidextrous.  It was a nosedive into designing lion machine interfaces.  It was achieved with just ordinary PLA.

    Inventing a hall effect joystick using just ball point pen springs & temporary screws for assembly was key.  It was not possible to make it waterproof.  An entirely new remote with binary controls would have to be built for waterproofing.

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