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speedy_w_beans

Speedy's GF01 Heavy Dump Truck Build Thread

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I have a squire speed gear set somewhere. I can count the teeth when I get back to the UK if you want

Please do! Then we'll know all the possible ratios with certainty.

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In addition to tucking the motor close to the chassis, I've been thinking about how to do the same with the steering servo. I have a few of these micro servos in my parts box, and they take substantially less volume than a standard servo. The torque output is about one third of the standard servo (1.4 kg-cm vs. 4.3 kg-cm), but that may not be a problem with a slow, light vehicle.

IMG_2404.JPG

Here's a side view of the micro servo versus the standard servo. I found a recess in the chassis near the front where the micro servo can hide. The standard servo is shown in its normal mounting location.

IMG_2406.JPG

Top view... You can see how the micro servo is much closer to the center of the chassis. Between the motor and the servo, the goal is to keep the yellow chassis posts as unobstructed as possible for the hydraulic cylinders lifting the dump bed.

IMG_2407.JPG

That is not a lot of Torque, is the micro servo Metal geared? It does look better sitting closer to the front but how is the steering linkage gonna work?

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That is not a lot of Torque, is the micro servo Metal geared? It does look better sitting closer to the front but how is the steering linkage gonna work?

Agreed, that's not a lot of torque. I've used them in drift cars before because the response speed was more important than torque. The one in the picture is just a plain cheap nylon gear unit; I do have a metal geared, high-voltage, 3.6 kg-cm micro servo in case this one doesn't work out. It doesn't hurt to try it and see what happens.

For the linkage I'm thinking about designing a replacement arm for the center of the chassis and using a shorter turnbuckle. I still need to check a some clearances while cycling the suspension before committing.

I follow your build with great interest. Keep the good work on! I am excited about the next steps...

Thanks!

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On the previous page I was still trying to sort out the LED lighting system. It was driving me crazy! I swapped between three radios and receivers, tried a few different ESCs and servos, and spent a few hours going through the programming over and over to make sure I wasn't missing something in the flow chart. It seemed like the turn signals were responding to steering just fine, and it seemed like the fourth channel was toggling the headlights and aux lighting, but the throttle channel and the third channel weren't working as expected. On one radio/receiver the throttle worked but the third channel did nothing; on another radio/receiver neither the throttle or third channel worked. In another case I could make the third channel lighting work with the throttle, and the reverse lights would work with the third channel! I was able to confirm all radios and receiver channels by attaching servos and seeing them move, so I had pretty good confidence in the radios and receivers. Eventually I noticed the LED on the TBLE-02 ESC was flickering erratically, so I disconnected the third and fourth channels from the receiver to see if "just the basics" would work. Lo and behold, I had good throttle, steering, braking, and reversing on the LEDs.

I started to suspect a short circuit somewhere and took a guess it might be in the interface box that sits between the receiver channel wiring and the cable running to the main control box. The main reason for starting there is all the receiver wiring is permanently installed/soldered in place; everything else has a connector. It's likely a person soldered the wiring to the circuit board in a factory somewhere.

IMG_2411.JPG

Sure enough, I found the signal wire for channel 2 throttle and the signal wire for channel 3 were shorted together. You can see in the magnifying glass how the two are touching each other; they connect to side-by-side pads on the circuit board.

IMG_2412.JPG

After cleaning up the solder joints everything started working as expected! Toggling channel 4 causes the front headlights, front aux lights (blue), and dimmed brake lights to turn on. Toggling channel 3 causes the turn signals / hazard signals to flash. Steering on channel 1 causes either the right turn signals or the left turn signals to flash. Reversing the throttle on channel 2 causes the brake lights to show brightly the first time; the second time the back-up lights turn on and a piezo buzzer chirps a familiar "beep--beep--beep" tone for safety. After all that time, it was just a single solder joint shorting two channels together!

IMG_2417.JPG

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I felt a lot better with the lighting working as expected, so I've started to work on the steering more.

Micro servo and horn... There were a few horns included with the servo; this one has the widest arm -- useful when drilling out a hole for the ball connector.

IMG_2418.JPG

Ball connector attached. I trimmed the unused arms as the servo is very close to the chassis.

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Ball connector flipped. After checking some clearances with the front suspension this will work better.

IMG_2421.JPG

Here are a few measurements and a crude sketch of the center steering arm. The idea here is to make the arm more L-shaped so it sticks out the side of the chassis a little bit.

IMG_2422.JPG

Next up is a little CAD work and printing a replacement arm.

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Modeled in CAD...

Steering_Bellcrank_FreeCAD.jpg

Prepped in Slic3r for printing... The outermost green skirt is just to get the material flowing. The green near the part is support material printed in PLA, the same material used for the part itself. The part needs support because one of the arms is not at bed level (Z=0); without support the part would droop and sag during printing, making it useless.

Steering_Bellcrank_Slic3r.jpg

New arm side-by-side with the original arm...

IMG_2423.JPG

The support material broke away pretty easily with needle nose pliers and flush cutters. There was only one spot near the two ball connectors that needed more work with a hobby knife.

IMG_2424.JPG

I need to clean up the large hole a little more before pressing in the ball bearings.

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Here's a little progress to report as of this afternoon/evening.

Servo clip design...

Servo_Clip_FreeCAD.jpg

Sliced...

Servo_Clip_Slic3r.jpg

There's a piece of servo tape holding the servo against the chassis; the clip keeps it from rotating when pushing or pulling the steering rod. I'm thinking of a version 2 that will also tie into the upper camber link screw, but this is good enough to test the concept in general.

IMG_2425.JPG

Here's the servo and center steering arm installed. The new center arm works fine. There's enough throw to steer completely right or left; the front uprights limit movement before the arm contacts the chassis. The elevation of the servo lets the turnbuckle clear the left tie rod even with the suspension fully compressed at any steering angle.

IMG_2426.JPG

The original steering arm only had to move to the point where the ball connector threads aligned with the chassis edge. The same movement is possible here.

IMG_2427.JPG

IMG_2428.JPG

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Great job on the servo install Paul - very neat and hopefully gives you room to work out solutions for the other modifications ;)

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I'm heading out of town for the next week and a half, so there won't be much activity in this thread. For now I'm just measuring parts in case I have some free time to do CAD work while on the road...

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All right, back from travel...  Between the work itself and being 12 time zones out of sync, I didn't get anything done on this build.  But, this weekend I had a little time to start modeling wheels to replace the HPI Mk.8 short course wheels.

The concept is a two-piece wheel with either a rear hubcap or a front hubcap installed on the end of the axle.  Initially the two halves of the wheel are aligned on the axle and 20 M2x8 screws (leftover from a CR01 build) secure the two halves together.  Then the tire is installed to the wheel; the front bead stretches over the front channel, and the rear bead is held in place with very thin double-sided tape similar to what is used for F1 and RM01 foam tires.  The wheel is installed to the axle and held in place with a M4 serrated flange nut.  Because I swapped the wheel hexes from the normal 9 mm width to a 5 mm width, there is actually 4-5 mm of leftover axle sticking out from the nut.  Either a front hubcap or a rear hubcap is then installed to cover the axle nut and complete the wheel.

Rear wheel half...

Wheel_Rear_Half.jpg

Front wheel half...  (Smaller than the rear because the HPI Geolander tires are sized for short course truck wheels.)

Wheel_Front_Half.jpg

Rear hubcap...

Wheel_Rear_Hubcap.jpg

Front hubcap...  (The spacing between the pockets is the same for both rear and front hubcaps.)

Wheel_Front_Hubcap.jpg

I ran the models through Slic3r and can see some adjustments are needed for some of the smaller features, so that will have to happen before doing a test print.

As time permits I'll work on version 2 of the steering arm and servo clip, test print some wheel parts, and work on the gearbox design.  I'm still waiting on those miniature ESCs from HobbyKing.  I do have a thinner/smaller servo (with just as much torque) and some cheap landing gear retracts coming to see if I can leverage those as well.  All these mechanical parts will converge, I promise.  Then we can get to the cosmetics of the body and the lighting.

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Well, at the beginning of this week it seemed like all I could make was scrap plastic.  I started with the wheel design shown above and tried to print it, but it seemed like something was just a touch off with the printer.  The vertical walls were printing jagged, and the accumulation of errors for each layer was causing the nozzle to rub against previous layers, making the situation worse.  The two wheel parts to the bottom and left just didn't have the print quality I was after, and some of the layers were not bonding together as well as they should.

I tried raising the extruder temperature 5 degrees, slowing the maximum print speed down, remeasuring the filament diameter, and adjusting the feed multiplier on the printer downwards to 99% or 98%.  On the next print with a second design I saw much better quality and better layer bonding.  Unfortunately I decided to try adding support material to the second print, and that proved much harder to remove than expected.  The wheel to the top of the picture shows the support material still in place around the outer diameter of the rim; all that scrap in the middle of the picture was dug out from the back side of the wheel.  It turned out to be a lot of work with too much potential to damage the wheel, so I started working on a third design.

IMG_2429.JPG

The third design came out pretty well.  There's a front half with the bolt pattern around the inside diameter, and there's a back half with the 12 mm hex pattern.  The center cap actually replaces the stock wheel nut.  Unfortunately the nut pattern on the center cap is too small to see, so it looks like I'll be changing that to make it as visible as the nuts on the wheel itself.

IMG_2433.JPG

On the real truck the center caps tend to be different sizes on the front and rear wheels.  Like the front cap, the rear one will need the nut pattern enlarged to make it more visible.

IMG_2434.JPG

If you didn't notice already, I'm switching from the Yokohama Geolander short course truck tires to RC4WD Dune tires; the tread pattern is much more realistic when compared to the actual mining truck tires.

IMG_2435.JPG

Caterpillar-Mining-Truck.jpg

I can see I'll need to do a fourth version of the wheels to correct some issues:

  • Fix a small size issue with the rear wheel hex
  • Add more lip and some detail near the tire beads
  • Tweak the depths and diameters of the center caps; adjust the nut size to be more visible
  • I may have to replace the axle stubs with shorter units to allow for more shallow center caps

As they say, "I'm gaining on it!"

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9 hours ago, speedy_w_beans said:

Well, at the beginning of this week it seemed like all I could make was scrap plastic.  I started with the wheel design shown above and tried to print it, but it seemed like something was just a touch off with the printer.  The vertical walls were printing jagged, and the accumulation of errors for each layer was causing the nozzle to rub against previous layers, making the situation worse.  The two wheel parts to the bottom and left just didn't have the print quality I was after, and some of the layers were not bonding together as well as they should.

I tried raising the extruder temperature 5 degrees, slowing the maximum print speed down, remeasuring the filament diameter, and adjusting the feed multiplier on the printer downwards to 99% or 98%.  On the next print with a second design I saw much better quality and better layer bonding.  Unfortunately I decided to try adding support material to the second print, and that proved much harder to remove than expected.  The wheel to the top of the picture shows the support material still in place around the outer diameter of the rim; all that scrap in the middle of the picture was dug out from the back side of the wheel.  It turned out to be a lot of work with too much potential to damage the wheel, so I started working on a third design.

IMG_2429.JPG

The third design came out pretty well.  There's a front half with the bolt pattern around the inside diameter, and there's a back half with the 12 mm hex pattern.  The center cap actually replaces the stock wheel nut.  Unfortunately the nut pattern on the center cap is too small to see, so it looks like I'll be changing that to make it as visible as the nuts on the wheel itself.

IMG_2433.JPG

On the real truck the center caps tend to be different sizes on the front and rear wheels.  Like the front cap, the rear one will need the nut pattern enlarged to make it more visible.

IMG_2434.JPG

If you didn't notice already, I'm switching from the Yokohama Geolander short course truck tires to RC4WD Dune tires; the tread pattern is much more realistic when compared to the actual mining truck tires.

IMG_2435.JPG

Caterpillar-Mining-Truck.jpg

I can see I'll need to do a fourth version of the wheels to correct some issues:

  • Fix a small size issue with the rear wheel hex
  • Add more lip and some detail near the tire beads
  • Tweak the depths and diameters of the center caps; adjust the nut size to be more visible
  • I may have to replace the axle stubs with shorter units to allow for more shallow center caps

As they say, "I'm gaining on it!"

 

The wheels do look awesome though!!!

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I went out to buy some primer and paint this morning, and I think I have a good design now...  Time to fire up the printer and see how this looks in the flesh...

Wheel_V4.jpg

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A little more sanding, a little more priming, some Camel Yellow, and I think four of these will do just fine...


IMG_2436.JPG

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Reading this thread again, I am really appreciating all the work you are putting into what many of us would write off as a cartoonish basher. Not that there is anything wrong with cartoonish bashers, but seeing an approach that prioritizes scale on such a chassis has yielded some astonishing results here. Excellent work!

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Thanks guys!

I've been in mass production mode for the past few days printing four sets of wheels, a revised steering bellcrank, and a revised servo clip.  The bellcrank and the servo clip were redesigned to eliminate support material; this yields cleaner parts.  The servo clip was also adjusted to grip the servo better and position it better.  Time to work on the motor gear reduction unit next...

IMG_2438.JPG

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That truck is going somewhere.

How about double tire rear wheels?

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7 hours ago, waterbok said:

That truck is going somewhere.

How about double tire rear wheels?

Thanks!  Yes, double rear tires was something I really wanted early on.  I tried several combinations of wheels, offsets, and tires.  It would be a whole lot easier if the rear of the truck was a solid axle, but with independent suspension arms and the location of the shocks, it's not going to happen.  Even Tamiya compromised a little in their original Mammoth Dump Truck kit and had single tires/wheels on solid axles.  Cutting the back half off the GF01 chassis and replacing it with a solid axle is a little more than I want to do this time around.  As Dirty Harry says, "A man's got to know his limitations."

 

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I'm working on the main gear reduction unit design, but got distracted today when the postman brought me some "servoless retracts" from HobbyKing.  I've been looking at these as a potential solution for making simulated hydraulic rams lifting the bed of the truck.  Not knowing much about RC aircraft, I only gambled $7 during a recent flash sale to see what is inside one of these things and to consider if the guts could be reused for my purposes.

Here's the link to the item itself:  http://www.hobbyking.com/hobbyking/store/__12883__Digital_Servoless_Retractable_system_1pc_.html

Looks simple enough...  A few things caught my attention initially in the HobbyKing listing.  First, the unit only has a servo lead coming out of it.  That means it is entirely powered by a BEC routed through a receiver, and it accepts standard radio signals to control movement.  I guessed there had to be a control board inside which would make radio programming easier.  The long cylinder in the picture suggested a motor and maybe even a worm drive inside it, but I couldn't tell with certainty.  My hope was a three-position switch could be used to command full extension and full retract on a worm drive to move a ram inside a cylinder.  Anyhow there were enough clues to make it worth purchasing.

IMG_2441.JPG

Here's the bottom of the unit.  There's a mounting plate for attaching it to a plane's frame.  The center section rotates 90 degrees to extend or retract landing gear threaded into it.  Note the exposed motor casing.  I did create a temporary setup with a radio, receiver, battery, and BEC.  Using the steering channel to test the unit out, momentarily steering one way or the other caused the center piece to rotate completely one way or the other.  Center steering position did nothing; it neither initiated movement nor did it stop movement already in process.  The unit could not be stopped or positioned anywhere except at the two endpoints, so it doesn't behave like a servo.  Once you trigger it, it goes completely to one end or the other.

IMG_2442.JPG

I started taking the unit apart.  First the mounting plate came off.  If you look closely, you can see part of a threaded rod and a nut in the center of the unit.

IMG_2443.JPG

Four screws later and the side of the unit came off.  Now I was pretty excited!  Inside is a control board (as expected), a motor and gear reduction drivetrain, a small ball bearing, a threaded shaft, a cross bar threaded onto the shaft, and a rotating landing gear mount.  The cross bar rides in channels in both halves of the enclosure.

IMG_2445.JPG

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Here's a bottom view with the rotating landing gear mount removed.  You can see the complete threaded shaft, cross bar, and limit switches mounted to the bottom of the circuit board.

IMG_2447.JPG

Here's the top side of the circuit board.  It looks like any other servo board, except the motor and position feedback potentiometer are not mounted to it directly.

IMG_2448.JPG

I started thinking about how to replace the threaded shaft with a longer one, and also how to relocate one of the limit switches to provide longer travel.  The final output gear is pressed onto the 2 mm threaded shaft.  This would require a new enclosure (expected), and it would require transplanting the gear and ball bearing onto a new custom 2 mm shaft.

IMG_2450.JPG

Remember those brushed motors / gearboxes I abandoned for moving the whole truck around?  The motor is the same size as the one in these retract units!  On top of that, the output shaft is 3 mm, which is easier to mate to a new threaded rod with a coupler.  I'm starting to think I can steal the servo lead, control board, and limit switches from these retracts and combine them with the separate motor/gearbox combo units, then source some threaded rod, couplers, and some nuts.  Then design a new enclosure to make it all look like a proper hydraulic ram.

IMG_2453.JPG

The idea still needs to percolate in my head some more, but I'm pleased with how the control board functions.  It was worth $7 to tear one of these apart and understand what is inside.  There definitely seems like a path forward using some of these parts and designing some new parts.

 

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Here's version 1 of a gearbox design to print tomorrow.  The small cap is meant to cover the flanged bearing that is pressed into the cover; this is just to hide the rest of the bearing from view on the outside of the gearbox.  The cover captures the base of the motor and is secured to the gearbox body with five screws.  The gearbox body has another flanged bearing pressed into it.  There are some internal posts capturing the face of the motor, and some internal bosses the screws thread into.  There's about 0.5 mm of slack so the gears can be shimmed into alignment.  It'll be easier to see how it goes together once I print these out tomorrow and test fit the parts.

Gearbox_Bearing_Cap.jpg

Gearbox_Cover.jpg

Gearbox_Body.jpg

The motor actually sticks out of the case a little bit, but it should *just* clear the chassis with 0.25 mm or 0.5 mm to spare.  The output shaft gear should clear the lower motor support posts with 1 mm to 1.5 mm of clearance.

I guess we'll see how it turns out...

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