NDD (New Deadbolt Day) SCX24 content...

[steve_rolfeca]

Bit the bullet on the weekend, and bought a red Deadbolt.

I like the form factor, and it seems well engineered. It took maybe 2 minutes to optimize the transmitter adjustments. Typical Axial RTR quality.

I haven't tried the USB charger yet, as I bought adapters for my full-size charger when I bought the truck. The battery in the box and the spare I purchased both charged quite quickly, without getting warm.

I like the idea of a crawler this light and low-powered. I don't think I'm going to be dealing with the constant breakages I suffered with my old mini rigs- a Losi Mini-LST truck and a couple of Kyosho buggies.

The suspension is absurdly soft and under-damped. The ride height is almost at full compressioin right out of the box. Still, it's ability to dig in to some mulch was impressive, and it was soon King of the Pile.

The little driver in the Deadbolt appears to be suicidal, though. Every time I offered him a little sidehill action or a steep climb, he promptly threw it on the roof!

It was pretty comical, watching it jounce around. Even a run through the grass was an opportunity for some upside-down action.

Despite being so top-heavy, I was impressed with the climbing ability on a clean, rough-cut plank. It was still climbining smoothly at 45 degrees. At 47 degrees, it was lifting the driver front, but it could still stop and re-start without sliding or toppling over. It didn't lose traction until 48 degrees, when it could still scrabble it's way up, but would start sliding back the moment I lifted.

I spent Sunday afternoon contemplating next steps.

I'd like to keep it as light initially, and focus on lowering the CG. I've been looking at the various options in terms of reversing the battery and receiver box, etc.

By the time that's all sorted, the first of the new farkles I've ordered should be starting to arrive: plastic and metal beadlocks, tires, a new servo and tray, etc.

 

[steve_rolfeca]

Tonight, I took a bunch of stuff apart, to see what I can change easily, and what I'll need to fabricate or order additional parts.

In the meantime, I slanted the back shocks.

After experimenting with a couple of options, I ended up simply moving the rear shock mounts forward one hole on the frame. Then I attached the shock, not to the normal hole in the shock mount above the frame, but through the frame rail, using the front mounting hole for the bracket.

This more or less maintained the stock ride height, but increased the articulation significantly.

Angling the shock softened the effective spring rate. Static ride height is nearly the same (the back end rides just a smidge higher than stock), but the shock is further down in it's travel, nearly at full droop.

To my surprise, this had a MAJOR effect on side-hill performance. I actually have to work at it a bit now to get the truck to roll over, and I was able to attack the mulch pile at much more aggressive angles.

However, it did nothing for the truck's straight-line climbing ability:

• I still have to place it on my incline plank, as it will simply flip over backwards if I try to drive up onto it.
• It still paws at the air, and eventually loses traction at exactly the same angle.

 

[vinceherman]

You said under-damped. I think there is virtually no effective dampening.
Many add the heaviest grease they can find and mount the shocks upside down to reduce leakage.

 

[Vmax]

Interesting, I had heard reports that moving the shocks to the frame was detrimental to side-hilling.

I've inverted the shocks and added grease, eliminated the bounce.

 

[steve_rolfeca]

Interesting, I had heard reports that moving the shocks to the frame was detrimental to side-hilling.

I've inverted the shocks and added grease, eliminated the bounce.

I've been taking some objective measurements, and comparing them to what I experience just banging around outside.

It makes for somei interesting comparisons.

For instance, I tested static sidehill rollover point three different ways:
- shocks at stock position.
- Rear shocks still on the mounts, but with the mounts moved forward one frame hole.
- The position from my previous photo, with the rear shock mounts still forward, but the top of the shocks attached to the frame by the front hole of the mount.

This gave me two progressively more slanted positions for the rear shocks, reducing the spring rate with each move because of the increased slant, and lowering the back of the truck slightly.

I used a smooth, unfinished piece of plywood as my "slant table" to measure when the truck would roll over.

Surprisingly, there was no measurable difference on these static tests. All three mounting positions gave me the same 36-degree rollover angle in a static test. So they have zero practical influence on the CG of the truck, as to when it's going to flop onto it's side while parked.

However, each time you slant the top of the rear shock forward, you noticeably increase the amount of flex.

Outside on the mulch pile, the Deadbolt is much more stable when actually driving sidehill on a rough surface.

Based on the static testing, I guess that the softer spring rate and extra flex explain why the truck has become more resistant to being flicked off the side of a hill as the wheels follow the bumps.

 

[steve_rolfeca]

The Kinectic shocks I ordered came in last night, so I experimented with them, starting at the rear.

The free length is much longer, at about 50mm. They offer a lot more droop as the brass inner shock body slides down inside the aluminum upper, and collapse down to be a lot shorter than the stock shocks when they're bottomed out.

The increase in flex is considerable.

Despite the soft springs, the static ride height ends up being quite a bit higher than stock, unless you move the mounting points to slant the shocks.

I tried a more drastic slant than I had with the stock rear shocks, by mounting the top of the Kinetic shock to the back screw hole on the battery tray.

This allowed a massive amount of flex and compression, to the point that the top of the diff cover acted as a bump stop when it hit the underside of the rear bumper bracket. Interestingly, with all that extra upward trael, the stock rear tires didn't scrub on the wheel openings. The Deadbolt body is clearly much better suited to extra travel, compared to the C10.

However, when I put it on the slant table, the static sidehill rollover point was still the same as the stock shocks, at 36 degrees!

Also, with the shocks slanted that far forward, the spring rate was so soft (and the internal friction in the shocks was high enough) that the back end of the truck would stick if I pushed it down into full compression. There was definitely a bit of binding going on inside the shock, even with some white lithium grease smeared inside to lubricate them.

I tried putting the stock shock springs inside the Kinetic springs, like so:

Because they are so much shorter than the Kinetic springs, they only started to compress at about half of the travel used up. This creates a mild dual spring rate with soft initial travel, and a little more resistance from there to full compression.

However, the extra spring also created more friction, so the shocks would still stick occasionally when fully compressed.

The kinetic shocks definitely work better when they are closer to vertical, to avoid binding.

Since I was liking the extra flex, I built the second pair of Kinetics. With the fronts installed using the stock mounting position, the whole truck sat a little higher than stock. Flex at the front is still impressive, but a little more limited because of interference between the servo and the ESC tray.

It's still pretty tippy when running sidehill, but the truck definitely climbed better, not only when hitting larger steps straight on, but also when approaching them at a slight angle.

 

[steve_rolfeca]

After thinking about this for a bit, and finding that the Kinetic shocks still hadn't improved the static measurement for sidehill rollover, it occured to me that the easiest way to lower CG, is simply to lower the whole truck.

That was when the new shocks finally started to really shine for me.

I had started with the stiffer of the two sets of Kinetic springs out back (because I had the rear shocks slanted), and the softer ones up front, with the front Kinetics mounted to the standard shock mount positions.

The setup I ended up with, was with just the soft kinetic springs at both ends, and the rear shock mounts still moved forward one screw hole on the frame...

...Except that I moved the top of both the front and rear shocks higher up on the truck, by using the screw holes in the body mount posts on the top of the front and rear shock mounts.

At the front, this slants the front shock forward slightly, and raises the mounting point about 3mm.

At the back, I did the same thing, bringing the top of the shock up and back, for a slightly more vertical shock angle than stock. However, since I still have the shock towers moved forward on the frame, the shocks are still angled forward.

This drops the static ride height of the front of the truck about 3mm, with lots of extra flex and travel still available in both compression and droop. This is a big improvement compared to the stock shocks. At static ride height, they sat about 2/3's of the way down into the shock travel. This didn't leave much upward travel to absorb bumps.

The truck now sits roughly level again, and only slightly higher than it did out of the box, I think. Here's the static ride height:

As these pictures illustrate, there's a lot more suspension travel between full droop...

...and full compression:

This is the first time that any of my mods have actually made a measurable improvement in the static rollover measurement on the slant table. It picked up another 3 degrees before it rolls off the plywood, and now it stays on the plywood right up to a 39 degree tilt. It can also drive forward and back across the slope without falling off, as long as I'm gentle with the throttle.

Here's some flex porn with the final setup:

Outside, it climbs much better than stock, and is noticeably less prone to flopping over on it's side.

This is all with the receiver and battery in the stock positions, no added weight, and the stock wheels and tires.

I already have extensions for the lighting and battery wires, and I can't wait for my Gens Tattu batteries to come in early next week.

Once they're here, I'm going to drop the CG a bunch by removing the battery tray, gluing or screwing the ESC between the frame rails out back, and chopping out enough of the ESC mount to let me strap the shorter 450ma Tattu battery sideways across the frame.

This will move the CG forward a bit, as well. I'm hoping for a noticeable improvement on the mulch pile, whether it's going up, down or running sidehill.

There should also be a small weight loss, from removing the trays. Hopefully, that will counter some of the extra load on the motor when I switch to heavier wheels and the RC4WD Patagonias that I ordered. I have both the Banggood monster truck beadlocks and a set of RC4WD white steelies coming in, so that will be fun to experiment with, as well.

 

[Gramps]

I found that the ESC mounting plate in the Deadbolt is about 3mm higher than the C10 or Jeep. Does change the body mounting position but I use magnets so the holes don't matter for me.

 

[steve_rolfeca]

While I was waiting for parts, I decided to take a bunch of measurements, and make a first stab at lowering the CG.

I took 4.3gr off the roll cage by shaving the lights off the front bar and removing most of the bracing. No longer CRB legal for King of the Hammers, but I don't think the driver figurine minds. I measured the weight distribution at that point. I came in at 57/43 front to rear, about 50.5/49.5 left to right, and 224.7 grams total.

While I was working on that, my Banggood HBX 2098B beadlocks came in, as well as a pair of short, fat Gens TATTU 75C/450mAh batteries.

This whole project is being done on the cheap, so I also bought four 500g scales off Amazon, instead of a fancy set of chassis scales. Takes a couple of minutes to do the weight distribution calculations, but no biggie. 0.01 gram resolution on those cheap scales, too!

Next, I trimmed the back of the receiver shelf, and removed the battery tray. That saved another 4.6 grams up high, and allowed me to glue the receiver between the frame rails and place the battery sideways across the frame up front.

I didn't fancy having the front shock towers only held up by one screw, so I left the back legs of the receiver tray mostly intact. As a result, the battery is carried pretty high, and tilted up toward the front:

When I reinstalled the stock wheels and tires, I discovered that this actually set the static sidehill balance back a bit, with the truck consistently rolling off my tilt board at about 37 degrees.

Geometry is hard...

 

[Mule]

Steve,
I'm pretty old school and never considered using a scale for CG. Makes sense... I still use the ole "crawls better or worse" trial and error methods. For me, I doubt I will ever do a comp unless it's with a bunch of chill guys. So, hacking and modding with the trial and error thing is where the fun is.
Seems the side hill action is a bit of width and some low slung wheel weights making the biggest difference. I know some guys like BBs, but, that seems to add some funky physics to the equation.

 

[steve_rolfeca]

A lot of water under the bridge since early December...

My Mod19 front low CG kit came in, along with an EMax servo (I splurged on the Digital version), a miscellaneous 3D printed servo tray from Shapeways, a set of RC4WD Patagonias followed a while later by the white steelies, and a stock link kit that I bought just to get some extra pivot balls.

As others have reported, RCWD tires do fit on the Banggood rims. But the rims stretch the Patagonias so wide, that they lose nearly a mm of rolling radius. Plus, the sidewalk profile rounds out so much that they lose some side bite.

Still the Banggod/RC4WD combo is a huge improvement over the plastic Banggood tires, and an increase in traction AND sidehill capability over the stock Deadbolt shoes, thanks to the wider track.

 

[steve_rolfeca]

I took the truck apart over the holidays, and did a bunch of stuff.

First off, was installing the Mod19 front receiver tray, and the links that come with it.

However, because I'd already glued the receiver out back, I cut the back off the Mod 19 receiver tray, to give me more options for front battery placement.

I don't like the stock battery sideways across the frame, even with the lower Mod19 receiver tray- it puts both ends of the battery right in the debris path when the wheels are cranked over and spinning, and also puts a lot of weight off to the side, outboard of the frame rails.

Instead, I used a strap to hold the stock battery longitudinally. Pushed to the front of what Mod19 intended to be the receiver tray, the back end of the battery rests comfortably on top of the transmission housing.

I also took advantage of the new mounting holes in the Mod19 body mount/shock towers to play with suspension geometry and body mounting.

With the posts in the lowest possible position, I was able to lower the front of the body enough that I had to trim the bottom of the grill area a bit, to get it to clear the top of the bumper.

Overall CG is now much lower as a result.

 

[steve_rolfeca]

Another thing that concerned me about the Banggood monster truck rims, was that the offset widened the track enough to put a fair amount of stress on the servo, and also meant that the truck was more likely to high-center side to side on tall, narrow rocks.

This was something I hadn't anticipated, so when the white steelies finally arrived from Amain, I moved the Patagonias over to them.

Now that I've seen the RC4WD tires on the intended rim, I'm less impressed with the Bangood rims.

Yes, the Banggood beadlocks work, but the diameter and shape of the bead area is a little off, enough that you have to kind of tease the tires into position for a good installation.

In contrast, the steelies suck the bead into position with almost no attention required.

Other advantages:

• The extra weight of the steel rims
• The fit. The track is still increased thanks to the wide rim and extra offset, but the sidewalls aren't pooched out as far as they were on the plastic Banggood rims.
• Traction. Now that the tires are on the right rim width, the corners of the tread are more square, and the edges bite a lot better on angled rocks and when running sidehill.
• Scale appearance. They look less toy-like, and fit the proportions of the Deadbolt better.
• Steering responsiveness. The stock servo doesn't bind up as much on the rocks, thanks to the more reasonable offset on the RC4WD rims.

I had feared the mounting process, after reading complaints about stripped screw holes in the RC4WD hex hub and problems getting the rims to seat properly.

However, they actually went together really well once I figured them out.

I did struggle a little with the first wheel, because I hadn't clocked the outer rim correctly in relation to the inner one. If you look closely at the Steelies, there is only one pair of bolt holes that are perfectly centered in the V between the spokes. If you don't start your screws there in order to keep the front and rear halves perfectly aligned, getting the screws started will be a nightmare.

The other issue, is that you really need a third hand while you're getting the rims aligned, keeping the beads pressed into the crack between the center barrel and the inner and outer rim faces, keeping the hex adapter perfectly lined up, etc.

Thankfully, I had already stolen someone else's third hand idea. I straightened a paper clip, reshaped it like a staple with long arms and an 8mm wide center strap.

Armed with that, it was a breeze to align the rims and hex, poke the arms of the staple through from the outside of the assembled wheel, using the two bolt holes that line up with the wheel spokes to hold everything together, and then pull hard on the arms of the staple from the back and bend the arms out to apply pressure.

This keeps the wheel halves aligned and sucked together, while you're starting the screws.

With that taken care of, the last three wheels went together faster and easier than the Banggood beadlocks.

 

[steve_rolfeca]

Aaaaarggghhh!!!

Tons of good detail photos of my mods, but can't get anything to display lately.

Using Google Photos, and I've tried various methods. I can get two or three different lengths of link depending on how I do it, but nothing seems to work.