Speedy's GF01 Heavy Dump Truck Build Thread

[speedy_w_beans 4272]

Time for some inspiration:

Liebherr

Caterpillar

[speedy_w_beans 4272]

Komatsu

Belaz

[speedy_w_beans 4272]

Tonight I worked on the hinge pins. The kit screw pins work for many people, but after having a few them loosen on their own some years ago, I appreciate the solution Tamiya uses on many of their touring car chassis -- the front and rear uprights use grub screws to lock the hinge pins in place.

I've simply replicated this design approach with a drill press and a Dremel rotary tool. The suspension arms have been drilled to accommodate grub screws, and the pins have flats ground into them to mate with the screws. The pins will not rotate on their own, and they will not slide out of the holes in the arms and uprights.

Here are the arms installed in the chassis again, and the grub screws are installed locking the pins in place.

IBIFTKH had suggested some softer springs to also slow down the suspension response, so I found some of the touring car springs he suggested and also some DF03 setting springs to test. Here's my measurement setup:

A small hobby vise clamps one of the jaws of a pair of digital calipers. A small digital scale rests on top of the vise. The calipers are spread initially, a spring is placed on the scale, and the one jaw is lowered until it just starts to contact the spring. The calipers are zeroed, and then the spring is compressed by a known amount and a scale reading is recorded. The difference between the final scale reading and the initial scale reading, divided by the distance measured by the calipers, provides a spring rate which can then be used to compare springs directly.

Here are the springs I tested:

And here are the results:

In the table above I use the term "mass" and the units "grams" because that is what the scale reports on its display. In reality, the scale is always reporting gram-force. When the spring is uncompressed the gram-force reading is the mass of the spring as sensed due to gravity acting on the spring. When the spring is compressed the gram-force reading is the force of the spring due to the compression of the spring across a known distance as well as the mass of the spring with gravity acting on it. By subtracting the uncompressed reading from the compressed reading we get gram-force due to displacement only. Dividing gram-force by displacement provides the spring constant, and finally the spring constant is converted to more standard units (Newtons/mm). Note: The on-road blue and white springs overloaded the scale with 5 mm of displacement, so I had to measure them with only 3 mm of displacement.

The GF01 kit springs have a spring constant of 1.15 N/mm. All of the onroad springs are stiffer, so that implies the suspension will not move as much for the same forces acting on it. The DF03 front buggy springs, though, are softer. In particular the black front springs measure only 0.70 N/mm, which is a substantial drop in spring constant. Even though these springs are longer than the GF01 kit springs by about 5 mm, the ride height collars on the dampers are 3 mm (rear) and 6 mm (front), so it should be possible to remove these collars, use the DF03 black front springs, and enjoy the softer ride/larger suspension movement/slower chassis response. With a little bit of load thrown in the truck bed the whole vehicle should squat a little more, too.

In the short term I plan to try the GF01 kit springs just to see what happens. Remember I filled the CVAs with 3000 cst oil already, and the suspension is already overdamped quite a bit. If I need to slow the vehicle response down more I'll definitely come back to this topic and give the DF03 springs a try. If I can find some 2WD front buggy springs, like those from the DT02 or DN01, I'll measure those too as I suspect 2WD front springs are even softer than 4WD front springs.

[Percymon 2184]

Nice work Paul

[speedy_w_beans 4272]

This week the miniature motors with gear reduction units arrived.

It's difficult to appreciate how small these are until you put one next to a regular 540 silver can motor...

The output shaft is 3 mm in diameter (measured and checked at 2.98 mm). Since the normal bore for a pinion is 3.18 mm (1/8 inch), I had to add two layers of Scotch tape to the shaft to fill the difference. The shaft has a flat on it for the pinion grub screw, and there was no problem spacing the pinion out 14 mm from the face of the motor per kit instructions.

It is a bit of a challenge to mount the motor when it is smaller than the pinion gear.

[speedy_w_beans 4272]

I opted to design a simple adapter to capture the motor and provide some mounting holes like a standard 540 motor.

The exported STL file then went into a slicer for generating the printer G-code file.

Part being printed...

Here's the final part with the motor and gearbox pressed into it. The friction fit was almost perfect!

The motor, gearbox, and adapter mounted to the chassis using the standard holes and machine screws.

At this point I attached a few clip leads between the motor and a 2S LiPo battery. With wheels/tires attached and letting the chassis roll across the floor under motor power, I've concluded the model is a little too slow. It would be better if this model was about 3X faster. Back to the drawing board on motors!

[Dougritt 31]

You have a super engineering mind! This is fun to watch...thanks!

Doug

[IBIFTKH 1369]

Loving your approach to this. Your spring-testing rig is genius!

It would appear that the 53163 and 53440 spring sets contain different springs, even though some have the same colours. My testing methods are much less precise (squeezing spring between thumb and forefinger!) but the 53163 springs all feel softer than the stock springs. There's also a visible difference when the truck is running, it's less bouncy and you can see the suspension moving more.

Interesting that the DF03 springs are a possible option, would never have thought of that.

It's a shame your motor choice didn't work out, it was a neat solution.

[kontemax 1725]

I believe you are searching for the most complicated solution to slow down your truck.

I suggest an 85T motor and a smaller battery, 6V for example, or less.

Max

Both of you are 100% correct; I forgot to mention looking at a few 85T motors. From the specs I could find they were rated at about 8000 rpm at 7.2 V; this is about half the speed of a silver can. Another factor to consider is I want to add (fake) hydraulic cylinders to lift the bed of the truck later in the build. Ideally there would be a very flat pancake motor with low running speed and super-smooth startup to take the place of the kit motor; unfortunately I haven't found anything like that just yet.

[Nitomor 2122]

Great job on the technical approach. I really enjoy seeing this sort of measured R&D.

[Nitomor 2122]

Would a heli type motor be any good for your packaging requirements?

http://www.helipal.com/product_info.php?currency=GBP&products_id=4714&gclid=CIvE6viW8MsCFRITGwoduI0O1Q

[speedy_w_beans 4272]

Loving your approach to this. Your spring-testing rig is genius!

It would appear that the 53163 and 53440 spring sets contain different springs, even though some have the same colours. My testing methods are much less precise (squeezing spring between thumb and forefinger!) but the 53163 springs all feel softer than the stock springs. There's also a visible difference when the truck is running, it's less bouncy and you can see the suspension moving more.

Interesting that the DF03 springs are a possible option, would never have thought of that.

It's a shame your motor choice didn't work out, it was a neat solution.

Thanks! FWIW, I ordered a set of 53163 to measure; they should arrive some time this week. When they get here I'll measure the full set of 53163, a set of 53702 DF02 springs, and a set of 54221 TRF201 front springs. I went looking for the 54666 CC01 barrel springs, but they're out of stock at Tower at the moment. Maybe I'll get a set of those to measure at some point.

I believe you are searching for the most complicated solution to slow down your truck.

I suggest an 85T motor and a smaller battery, 6V for example, or less.

Max

Good thought as others have suggested too. My main issue with a 540 motor right now is size; it sticks out so much from the chassis that it will get in the way of the dump bed lift mechanism I plan to do. I'm on a mission right now to miniaturize as much as possible and package it all very tightly against the chassis; that includes the motor, servo, ESC, receiver, lighting, etc.

Would a heli type motor be any good for your packaging requirements?

http://www.helipal.com/product_info.php?currency=GBP&products_id=4714&gclid=CIvE6viW8MsCFRITGwoduI0O1Q

I have one of these on my desk at the moment; at 950kV it's about half the speed of a silver can. There's a 750kV version available too.

I'm also looking carefully at these PS3 Dualshock and XBOX 360 vibration motors.

More to come...

[MadInventor 3884]

Speedy,

With regard to the motors, have a look at these guys:

http://www.mfacomodrills.com/

They do a massive selection of motors with reduction gearboxes of massively varying ratios. I used 3 540 based units in my skidder build, 1 to lift the blade, 1 for the steering, and 1 for the winch. They are good quality items and there must be something there that will suit. Looking quickly at their catalogue, they do re-280, 380, 540, and up sized motors with reduction gearboxes of differing mounting options.

I went for an epicylic gearbox (942D series) for the winch for strength and ease of mounting.

[speedy_w_beans 4272]

We have a bunch of PS3 controllers lying around, and since we never use the rumble/vibration function with games, it's easy enough to see if one of these motors will work.

The organ donor...

Five screws later and the back is gone. The motors are in plain sight.

Removing the motors was easy. Unplug the battery, remove a screw holding the circuit board in place, and the whole assembly unclips from the front shell. The motors were just taped in place, and a soldering iron broke the wires free of the board.

Removing the eccentric weight just took a little twisting with some needle nose pliers...

Comparison between the rumble motor and the kit motor...

[speedy_w_beans 4272]

The motor's shaft diameter is 2 mm, but the pinion gear's bore is 3.18 mm. I didn't have any adapter sleeves, so I printed one, pressed it on the shaft, and then used the motor to spin it while grinding it to final size with a file.

Pinion fitted...

The motor fits nicely against the chassis.

I took some measurements to see how much current the motor consumes. No-load current is about 40 mA; stall current is about 400 mA. I wanted to know this to size the ESC. The current is so low, though, that just about any ESC will do.

Testing with the kit TBLE-02 ESC... Startup is nice and smooth. I held the motor in place against the chassis just to gauge speed and torque at the wheels. The torque is ok, but the speed is a little fast. Overall it's not a bad motor. It could benefit from some 2:1 or 3:1 gear reduction to get more torque and less speed.

[speedy_w_beans 4272]

I also took a closer look at an outrunner motor like Nitomor recommended. Here's a 950kV compared to the kit motor. The size is smaller and the rated speed is about half of the kit motor, but the shaft is exiting the motor on the wrong side.

The motor comes apart after removing a single e-clip. Compared to the usual car motor, these aircraft/helicopter motors are "inside out" with the windings on the inside and the magnets on the outside.

With a vise, some blocks of wood, a dead blow hammer, and some punches I was able to relocate the motor shaft so it exits the base of the motor now. This is the side that makes sense if mounting it directly to the chassis. I lost the groove for the e-clip, but the motor naturally wants to stay together. Also, with a sleeve between the bearing and a pinion gear the motor won't come apart anyhow.

I did a quick test of the motor with an ESC to see how it started up and managed low speeds. I couldn't use the same TBLE-02 ESC because it only works with a sensored motor; intead, here's rebadged Hobbywing EZRUN. Startup was abrupt in both directions, and the slowest speed was still quite fast.

Comparing all these motors...

Kit motor:

+ smooth startup

+ top speed

+ available torque

- low speed control

- physical size

Miniature brushed motor with 30:1 gearbox:

+ physical size

+ smooth startup

+ low speed control

+ available torque

- top speed

Outrunner:

+ physical size

+ available torque

+ top speed

- smooth startup

- low speed control

PS3 vibe motor:

+ physical size

+ smooth startup

+ low speed control

+/- top speed

+/- available torque

Next steps...

[Nobbi1977 1793]

Just a thought. Are the gears in this the same as the WR-01 if so they do a high speed gears set so you first mini motor would work.

[speedy_w_beans 4272]

Just a thought. Are the gears in this the same as the WR-01 if so they do a high speed gears set so you first mini motor would work.

Hi Nobbi, I did some checking and it looks like the same gear bag (0555092) is used across most of the wheelie models including WR01, WR02, WT01, and GF01. Are you talking about the Square SGW-30 gear set for the GF01 and/or the Square SWR-30 gear set for the WR02?

It looks like these gear sets allow for either 23T or 25T pinion gears vs. the standard 18T or 20T pinion gears. This alters the gearing by 5 teeth on the pinion.

Here's a bunch of information; some of it might be useful, some of it not:

- Tamiya reports two different gear ratios for the GF01 (18.03:1) and WR02 (18.3:1). This doesn't make sense since both models use the same gear bag.

- I counted the teeth on all the gears and have the following to share:

Diff gear - 50T

Large counter gear - 50T / 26T

Medium counter gear - 45T / 20T

Small counter gear - 39T / 26T

- Calculated gearing for stock gears and an 18T pinion is 18.03:1; calculated gearing for stock gears and a 20T pinion is 16.23:1.

- I can't find any information for how many teeth are on Square's small and large counter gears.

- If Square just subtracted five teeth from the small counter gears to make room for five more teeth on the pinion, then the calculated gearing is 12.30:1 (for 23T pinion) and 11.32:1 (for 25T pinion).

- If Square also adjusted the teeth between the small and large counter gears, then possibly the gearing is even lower. It stands to reason they did something here; otherwise there is no reason to supply a new large counter gear. If anyone has an actual tooth count from these gear sets I can re-calc the ratios.

The high speed gear set is a pretty big change at around 50% more speed! That's not quite enough for what I'm looking for, but these gears definitely add value (especially if you own a Honda City Turbo). Thanks for bringing this up.

[speedy_w_beans 4272]

Ordered a few of these this week...

http://www.hobbyking.com/hobbyking/store/__68472__20A_Brushed_ESC_Turnigy_TZ4_AWD_Drift_Spec.html

This is a small brushed ESC for the Turnigy TZ4 1/28 micro touring car. ESC dimensions are 22 mm x 21 mm x 11 mm - about the same size as a micro servo. The 20A capability is more than enough for the PS3 vibe motor. I looked at airplane ESCs, but they didn't have a great size advantage and there is no reverse function. I also looked at boat ESCs, but again they didn't have a major size advantage compared to normal car ESCs. I tried a leftover servo board, but getting a consistent neutral throttle was challenging and the top speed of the motor was reduced. For car ESCs I considered the kit TBLE-02, a Tamtech TEU-102BK, and a Hobbywing QUICRUN 1060 before settling on this.

[Nobbi1977 1793]

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

[kontemax 1725]

What about a 380 motor?

Max

[speedy_w_beans 4272]

What about a 380 motor?

Max

This might be a little fast as well.

I found a nice page on Mabuchi's site that lets you explore their common motor configurations:

http://www.mabuchi-motor.co.jp/en_US/product/p_0306.html

As you know the kit silver cans are typically RS-540SH and maybe RS-380SH. I found it really interesting you can get slower running motors in their standard catalog as well. Take a look at:

- RS-540PH

- RS-545SH

- RS-380PH

- RS-385PH

- RS-385SV

The nominal voltages in some cases are higher, so the speed will go down with the normal NiMH or LiPo pack.

[speedy_w_beans 4272]

Some 53163 springs showed up today, so I measured them in addition to the DF02 and TRF201 springs as mentioned earlier.

The springs...

One of each to measure...

I used the same technique as used earlier to measure the springs; here's the updated table.

Based on these measurements it looks like the TRF201 front springs, DF03 front springs, red DF02 front springs, and two of the three 53163 springs are softer than the kit GF01 springs. The buggy springs look like great options for a softer suspension while staying close to the original spring length.

[speedy_w_beans 4272]

The postman also brought a 2 mm to 1/8 inch collar for the motor, a 15T pinion gear, and some 1/8 inch steel rod. I have all the parts now to get started on a motor/gearbox for the side of the chassis. Hopefully the TZ4 brushed ESCs arrive soon; I'd like to integrate one with the motor and gears in the same housing.

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.

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.

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.

[speedy_w_beans 4272]

Speaking of hydraulics, I bought a few more of the miniature motors with gear reduction units. The 30:1 units I had tried earlier were too slow to move the chassis at a reasonable speed, and they will definitely be too slow to run a screw drive and raise/lower the bed realistically. The new motors have 10:1 gear reduction. Assuming the screw drive has M3-0.50 threads on it, the 10:1 motor should be able to make the hydraulics extend 75 mm in about 5 seconds. In the picture below the 10:1 motor has fewer gears.

I'm expecting to use at least 5 channels for throttle, steering, LED control, and dump bed lift control. A few years ago I burned some open9x firmware into this transmitter to turn it into a surface vehicle transmitter instead of an airplane/helicopter transmitter. The key features I really like about the open9x firmware include up to 16 custom mixes, free assignment of all inputs and mixes to receiver channels, and custom curves/math/logic operations. I use this with my CR01 Unimog currently.

For LED lighting I'm trying a GT Power Bluetooth 4-Channel Truck Light System. I'm not so interested in pairing the main board with a sub board, but the main board has quite a few LED output drivers in addition to some programming options and some manual LED control via extra transmitter channels. I'm still sorting this out, but it looks like there are enough LEDs to implement headlights, brake lights, reverse lights, turn signal/hazard lights, and a few channels of auxiliary lights.