The Nut Buster - The Strongest Clod Buster Chassis Ever

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weeb_beano
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The Nut Buster - The Strongest Clod Buster Chassis Ever

Post by weeb_beano » Mon Feb 13, 2017 2:53 pm

This was actually a project I started a few years back but now plan on seeing it through to completion.

There have been a variety of awesome chassis builds over the years by many talented people worldwide- but I am perplexed about one thing. How come nobody used one of the strongest materials in the world in their projects?

I mean, carbon fiber is like... 'okay'... Titanium is pretty decent for a peon's metal... and aluminum is nice but is more suitable for use in disposable sewage bottles. But anyhow... Behold. I present the material for my next chassis - the mighty coconut (Cocos nucifera). I'll let the pictures do the talking.

Behold. A pristine coconut specimen.
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How I imagine it will look like.
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The initial carving out...
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Advanced, space aged tools used during carving to remove the meat.
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A brilliant observation I made while recovering from an industrial accident.
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The hollowed out shell.
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More visualizing....
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Siting and mounting the suspension links.
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Compared to more conventional (BOOOOOOORING) monster truck chassis.
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Several coats of epoxy on the outside of the shell to water-seal it. The interior of the shell also received many ply layers of fiberglass mat.
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It's a roller...
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...after a break of a couple years with the birth of a child and renovating our basement...


Conversion to sensorless brushless...
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A body mounting system which was not totally stupid was made - out of a recycled PC power supply bracket of all things.
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Dual SkyRC Leopard 9T sensorless motors are being used for now. Not the hottest motors but this is mainly just a putzing around and bashing truck.
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Finally... with a body mounted.
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Another shot with a stock Clod reference body.
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I liked the Clod body so much after test fitting that I decided to get a few Lexan ones to tweak around.

Some stickers that I am working on, sort of a homage and parody of the original Clod...
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Well here I am for now. The truck runs but just needs some final touches.

Thanks for reading!

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matt1ptkn
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Re: The Nut Buster - The Strongest Clod Buster Chassis Ever

Post by matt1ptkn » Mon Feb 13, 2017 3:05 pm

:shock: What a cool project! I'm most curious as to how it runs with two brushless motors run off one ESC. I've always heard that this won't work. Was that just the electronics companies spreading rumors to sell more ESCs?
-Matt

My Trucks

"I wish there was a way to tell you're in the good old days, before you've actually left them."

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weeb_beano
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Re: The Nut Buster - The Strongest Clod Buster Chassis Ever

Post by weeb_beano » Mon Feb 13, 2017 3:43 pm

Actually I just ran into this problem last night... and the solution is not a simple answer.
For the long story short, just scroll to the end :)

When I installed the GoolRC Beast 80A I saw that the truck suffered from a LOT of cogging until some magic point around 1/3 throttle. I initially chalked this up to the configuration on the ESC and started tuning the punchiness but with no luck. Under LiPo the truck would flat out refuse to run, and the cogging went through the entire power band except at wide out throttle. I removed one of the motor connections- and the problems went away... despite the 9T motors... almost ZERO cogging at all. I began to wonder how that was even possible.

Why was this ESC so The North American beaver has a big tail smooth at low throttle? Could there really be a huge difference in first generation and current market algorithms on driving the motors? The improvement at low throttle was so big that it simply did not compute.

Instead of breaking out the oscilloscope I pondered that there might be some back EMF measurement coming out of the ESC so I started doing some reading. It turns out it is indeed very possible (and pretty easy) for a device like this to measure back EMF via analog to digital sampling across each of the motor connections, and comparing it to a reference 'neutral' resistance.I had tested this exact driveline configuration (but just ONE axle) on an older Jeti Master Car ESC which I had and that thing cogged a LOT at very low throttle. So until I to a teardown on this GoolRC ESC (which I won't) i believe that it is actually measuring backflow EMF coming out of the motors across each cycle of the three motor wires... this implies that even a sensorless ESC has SOME measure of knowing what the position of the rotor is. That means having motors in parallel seriously confused the hell out of my ESC until I punched it enough so that it was no longer measuring that back EMF. I ended up seriously impressed with this cheapo ESC having such a feature. Again- I am not 100% certain but basing this on some empirical testing on an admittedly small sample size.

So my plan B was to wire up one of my first generation Jeti ESCs in parallel and watched what happens. Spot testing showed zero cogging due to back EMF, and the truck behaved exactly on two parallel motors like it did with just one.

SO LONG STORY SHORT:
- Today's sensorless ESCs don't like parallel motors... because they are actually 'hybrid sensored' in that they measure a motor's back EMF to get a very accurate guess of the actual motor RPM and where the rotors are.

- You will be able to get away with parallel motors on an old generation sensorless BLDC controller which does not measure back EMF. Right now I can only confirm that the Jeti Master Car Sport (vintage 2003) can do this.

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andymac0035
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Re: The Nut Buster - The Strongest Clod Buster Chassis Ever

Post by andymac0035 » Mon Feb 13, 2017 7:42 pm

Interesting, first I've ever heard of that being possible. The old stand-by has always been that unless the motors could be kept in sync (matching rotor positions at all times), that the esc would be very confused. This "back EMF" stuff is new to me.

Back to the clod, I've seen a few pics of this truck somewhere, glad to see you finally are making a full build thread on it. :thumbsup:
The pic contest is going to be open till around midnight (eastern time) if this truck is a runner at this point, feel free to enter it. :wink:
(Or any of you 6x6's !!)

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weeb_beano
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Re: The Nut Buster - The Strongest Clod Buster Chassis Ever

Post by weeb_beano » Mon Feb 13, 2017 9:13 pm

Thanks Andy! Back EMF is totally new to me as well. I basically stumbled into this doc by accident http://cache.freescale.com/files/produc ... pdf?fasp=1from Freescale Semi where they talk about how to read back EMF from a sensorless control circuit to guess what the actual motor RPM was and that got me thinking. WARNING: It has lots of dry reading. The sort of hardware used for something like this is usually much more high end than typical R/C gear... so that's why I was impressed that this feature made its way into a budget ESC.

Of course I could be totally wrong, and back EMF is not being processed at all, but it sure looks like that's what is happening here. I suppose one way to test this is to put a really small BLDC into a circuit and see if the ESC is able to see it's back EMF. One of two things will happen... it will just continue to power the circuit despite having no feedback... or it will not energize any of the circuits because it can't detect any resistance changes.

But anyhow thanks for the heads up on the ToM contest. This truck is a roller but I definitely want to get the finished body in place first and then submit a photo. Regrettably the only recent photos of my rides are all indoors so I would love to at very least get some good pictures outside. I'll see what I can do :)

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weeb_beano
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Re: The Nut Buster - The Strongest Clod Buster Chassis Ever

Post by weeb_beano » Tue Feb 14, 2017 5:29 am

Well, I'm a bonehead. All I had to do was draw a circuit diagram of what happens when you add a second brushless motor in parallel and the simple answer is this- You are going to get back EMF in the circuit, messing up both motors. This has nothing to do with the speed control. As for why I got lucky with the Jeti the first time around- I simply didn't drive the truck enough- and of course I was indoors. All it needed was one minute outdoors on uneven terrain to debunk that whole thing. That explains that!

So long story short, I am now running the truck properly.
- I put two of my Jeti ESCs into use, joining positive to positive, and negative to negative on the battery leads to a Deans connector. I'm using these because I had them lying around. They came from my 6WD Clod, Tiamat.
- removed the red (positive) pin from one of the ESCs so I would not have dual BEC circuits fighting each other.
- Harnessed both ESCs together to a Y-cable and plugged everything in.
- MOST IMPORTANTLY I tested the truck OUTSIDE for a period of more than 60 seconds this time. Hah.

So in conclusion:
- I don't think that there is a back EMF sensor in newer ESCs. If there is, they would be advertised the hell out of.
- The smooth low end response on the GoolRC ESC I had was probably explained by a very gentle throttle curve, as opposed to the Jeti which was more linear and unforgiving on the low end.
- I'm an idiot and should have mathed a bit more before jumping to conclusions
- Two BLDC ESCs isn't such a bad thing. It's cumbersome, but not terrible.

Well at least on the bright side, I have put my idiot powers to use for all of you, so you won't have to encounter this sort of idiocy personally!

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matt1ptkn
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Re: The Nut Buster - The Strongest Clod Buster Chassis Ever

Post by matt1ptkn » Tue Feb 14, 2017 1:32 pm

Awesome info. Thanks! Next question: how did you attach the lower shock mounts? It looks like you may have just drilled the lower suspension links and screwed them on, but wouldn't that create a weak spot? Especially since aluminum is best for sewage tanks? :lol: I'm asking this because I have been trying to think of a simple way to mount shocks similarly to how you have done, albeit without the coconut. (Though I wish I lived somewhere where there was an endless supply of coconuts growing.)
-Matt

My Trucks

"I wish there was a way to tell you're in the good old days, before you've actually left them."

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weeb_beano
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Re: The Nut Buster - The Strongest Clod Buster Chassis Ever

Post by weeb_beano » Tue Feb 14, 2017 6:51 pm

matt1ptkn wrote:
Tue Feb 14, 2017 1:32 pm
Awesome info. Thanks! Next question: how did you attach the lower shock mounts? It looks like you may have just drilled the lower suspension links and screwed them on, but wouldn't that create a weak spot? Especially since aluminum is best for sewage tanks? :lol: I'm asking this because I have been trying to think of a simple way to mount shocks similarly to how you have done, albeit without the coconut. (Though I wish I lived somewhere where there was an endless supply of coconuts growing.)
You are right. Aluminum is really meant for just soda cans and sewage vessels and I feel embarrassed for even trying to work with it. That having been said I am even more embarrassed for not doing a great job of it either! There are coconuts taunting me even as I type this.

I used a 3/8" round as it was all I had available. What I did was just endmill a 1/8" groove into it. It's roughly V-shaped and is just enough material milled out so that the damper rod end fits. It really needs to be a bit wider so that more material is available for strength but I just sort of hacked this together quickly. The main drawback it has currently is that there is just enough clearance for the damper laterally. I would like to make a fancier set of lower links that does just that, and allows for more flexibility. This pic should show a bit closer but it's still a bit lacking in the details:

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ratpower396
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Re: The Nut Buster - The Strongest Clod Buster Chassis Ever

Post by ratpower396 » Wed Feb 15, 2017 12:12 am

any action videos??

rcupp
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Re: The Nut Buster - The Strongest Clod Buster Chassis Ever

Post by rcupp » Wed Feb 15, 2017 9:35 am

Thats flippin awesome!! =D>

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weeb_beano
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Re: The Nut Buster - The Strongest Clod Buster Chassis Ever

Post by weeb_beano » Thu Feb 16, 2017 4:51 pm

Thanks! I have been building a lot more than driving, and it's probably going to be that way for some time.
I'll try to get some video but it's pretty tough because most of my driving lately has been at night under very impromptu conditions.

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Re: The Nut Buster - The Strongest Clod Buster Chassis Ever

Post by Clodosaurus Rex » Mon Feb 20, 2017 8:07 pm

Out of all the questions i could possibly ask, the only one that can make it through the gales of laughter over... well, EVERYTHING... is...

How long did it take you to find the perfect nut?

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weeb_beano
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Re: The Nut Buster - The Strongest Clod Buster Chassis Ever

Post by weeb_beano » Wed Feb 22, 2017 2:43 pm

Hahahaha thanks :)
Glad you like this project :) It did not take long to find a good coconut because at the time there was literally a tub full of coconuts in the house at all times. Just casually browsing BJ's out near me which sells them... I would guess that 1 out of every 20 coconuts is a good size and symmetrical enough to be used as a chassis. I catch myself pondering getting a larger coconut and building a shaft driven chassis every once in a while. Bigger coconuts are structurally weaker though... but there is more room internally to reinforce with fiberglass.

I did manage to drive this truck outdoors for a little bit over the weekend. Sadly no video though... but it handles like a dream. Boatloads of power available even with the 6 cell stick pack I ran down. Handling is very crisp and predictable with the linear servo saver mod that I'm making for all of my Clods.

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An explanation of the linear servo saver mod:
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