chimera project : bodyless Cr01

[farfab]

I finally received the lipos i was waiting for, so i took some time to work on this project.

I decided tu put the transmission back to its original position ie with the motor in the front, and to cut the chassis plate a bit more to fix the new "rollcage" made of 3mm delrin lower.

These roll bars are much lighter (8 gr each) and should help with the cog.

As the new skid i made moved the mount points for the lower links, i had to shorten them in order to keep the same wheelbase.

I also cut the previous skid down to "delrin french fries" :

i then drilled and filed them to make a set of chassis brace.

I made a lexan tray for the esc, and used it to hide some wiring as well.

I sticked the bec to the front side plate of the transmission case using some 3M Dual lock

I also received another cheap towerpro servo to replace the previous one that broke down, got it installed but still need to make a steering rod to get it working.

I opened the Futaba Rx case and tucked the antenna wire inside, i will see how it behaves that way.

Here are some pics of the rig at the moment :

With the small lipos it now weighs 2420 Gr / 5.3 lbs with 57% of the weight to the front.

I still have to tear apart the shocks to smoothen the rear suspension travel and to make some lexan body panels.

I have just one tiny problem with this setup, the tranny case with the motor at the front requires a longer front shaft to work properly, while checking the suspension travel i had the unpleasant surprise to see the male side of the front shaft pop out :x

So i'm currently waiting on some longer junfac universal to fix this problem and to start fine tuning this build once again.

To be continued ...

 

[farfab]

As i still haven't received the 120-155mm junfac shaft i need to test this setup, and having read an interesting tutorial on Antisquat Vs Torquetwist, I decided to mess with the upper links.

I had to torture this poor rig until it finally told me where i could aproximately find its COG :

I used Ms Paint to quickly determine where was the instant center from each axle

and what i should aim for

Then i decided to tear the chassis appart to drill some new "mounting holes" for the upper links.

With the upper links attached like this, i get massive antisquat from both axles .

I also shortened the front upper links to declock the front axle, getting way more caster than before.

An unexpected result was the front junfac shaft not "poping out" anymore (male part engages by 2-3mm but it will do for the moment ;-))

So i tested it on a hastily made course

Having coped well with the wood logs, i then decided to run some packs on my favorites rocks.

After 10mn it had crashed on every course i used to climb, obviously the rear axle had so much grip that on steep climbs it would capsize the rig.

I changed the rear mounting point of the upper rear links like this

And it then performed like a charm, rear axle with massive squat allowing the rear tyres to slip/skid (i don't know the precise term in english) when facing a steep climb and front axle with loads of antisquat getting much more grip than before.

On a side note the steering setup with heavy caster is really a good improvement, combined with the stronger servos (Bec @ 6,5v) it is very efficient.

I'll wait for the replacement junfac shaft to continue the tests, don't want to destroy the one i currently use.

To be continued ...

 

[carlos46]

Can I ask you how long you can bear to ride on the 1300 lipo?

 

[farfab]

I've been out of town for a week and meanwhile i still haven't received the longer junfac shaft i ordered :x , so i haven't made any progress on this project.

From the 3 packs i ran with the last setup, i'd say the 1300 lipos give around 35/ 40 Mn running time depending on the driving and the playground...

I'll check more precisely as soon as i can.

 

[farfab]

At last i received my longer Junfac shaft, i got it installed and took my rig for a spin.

After 20 Mn, my left front wheel decided to live a life on its own :evil: rolling away from the car :evil:

The wheel axle had just broke at the base of the cup, i was so furious i just threw it away on an impulse.

Back home i made a picture of the right one :

As they seemed pretty weak, i decided to go back to a pair of Tamiya reinforced wheel axles i had in stock.

I managed to attach the wheels despite the wider Hex by using a thin M5 locknut and some Locktite 243.

As i found the rear suspension too stiff, i decided to tear appart the rear shocks and install the 3 holes pistons instead of the 2 holes ones i was previously using.

i also decided to remove the inner springs i had previously installed :

to replace them by some delrin 6mm washer i drilled and cut from some chassis braces i had left :

Then i filled the shocks with some 10w40 motor oil i had for my 1:1 car.

I also changed the mounting point of the shocks on the chassis to allow them to work more "vertically", i moved the rear upper links on the axle side above the servo plate and i put a longer horn to the rear servo to gain some steering throw.

I quickly ran 2 packs in it this morning and encountered zero issues.

here are some pics from this session :

I'm pretty pleased with the way the rear suspension worked with those modifications.

It is much smoother than before and it gives a bit more travel than with the inner springs.

The rear steering is more efficient too with the longer servo horn.

I still have to play with the weight distribution as i find the front a bit too light in the steepest climbs, and i still have to make some body panels and a lexan protection for the lipos...

To be continued...

 

[farfab]

Happy with the results from the previous session, i decided to go back to the meanest playground in the neighborhood.

Inspired by mirandayopo, i chose to do so using my mtb and my old trekking backpack :

I was really bluffed by the way my rig performed on these rocks, as a consequence i didn't take any picture nor made any video (even if i had carried all the necessary equipment to do so).

I had not enjoyed driving my rig that much in a while, partly because i had not been able to do so during the last month, but mostly because it allowed me to climb some rocks i wouldn't have believed it could.

The only issue i encountered came from a sharp rock that almost cut one of the Bec wire.

So, back home i decided to quickly do some body panels to protect the exposed components :

I also decided to modify once again the rear upper links atachment to the rear axle :

they go back under the servo plate again and are much closer together than before(will see if this prooves to be more efficient).

As a result the Rx sits lower and has moved a little towards the center of the chassis.

To be continued...

 

[asw27x]

thats a nice bike who makes it?

 

[SteveVanB]

That's an Ellsworth. Uber nice bikes!

 

[farfab]

Thanks for the comment !

As SteveVanB said, this bike is an Ellsworth Truth.

I bought this frame at a great price 4 years ago, and took almost a year putting the bike together; as mtb components / parts tend to be more expensive than rc ones ...

I'm pretty happy with the final result, it has a distinctive look and still performs well compared to “modern” frames.

On a side note, one should always carry another pair of shoes when going rockcrawling using a mtb with spd pedals, Shimano spd shoes are definitely not adapted to rock climbing ...

 

[farfab]

Just a quick picture to show the last modifications i made on the chimera, while waiting for a more complete post :

To be continued...

 

[farfab]

A week ago i decided to make some real body panels, once cut, i painted them with a spray can i had bought months ago at the lhs but had never used.

The cap on the spray can was looking like silver/chrome, here's the result after 5 layers on clear Lexan :

Not too happy with the results and being short on Lexan, i used some brake fluid to remove the paint and clean the body panels :

Once done, i washed them with soap and water to remove the remaining brake fluid and went back to the Lhs to find a more appropriate colour.

While waiting for the paint to dry once more, i decided to remove the antenna wire i had tucked in the rx (it caused too much glitches and gave a ridiculous range).

I soldered a new antenna wire to the Rx and managed to have it wrapped around one of the braces at the top of the chassis.

As i changed the colour of the body panels i used the set of plated wheels i had in stock and painted the beadlock rings accordingly.

I recycled the first body panels i had made into some lipo protections that i painted the same colour as the body panels :

Here's the result :

I had to make another version of the hood though, as this one would pop off to easily while crawling.

I came up with a basic solution that allows it to open in order to attach the lipo plug to the esc :

These last pictures were made during a test session a few days ago, i'll post a video soon.

To be continued...

 

[farfab]

I found some pictures of a "misshapen clone" of my rig :

Not sure what to think about it :|

 

[farfab]

So here's a new video available in HD i made a week ago :

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It was filmed on the same playground as the former video.

It highlights 2 facts :

- the clearance is a little better without compromising the Cog too much (for exemple it now can clim the big rock at 3' without having to do it Foff style)

- the supension is smoother than before but still a long way from being perfect (too much squat on the rear axle makes it difficult to use full travel, but it's the best compromise i've achieved at the moment)

As a result, i resumed the hunt for some 3mm Delrin sheets, as i intend to build enhanced chassis plates for this rig.

I might as well try a more efficient transmission case depending on the bargains i'll be able to find.

To be continued ...

 

[carlos46]

It is not yours?
I thought at first glance that you have changed the design.
Where did you find?
I therefore also inspire you.
With just minor changes.
I have a black material and instead use an axle reversed by RCTRAX dig.

 

[farfab]

Hello Carlos46, i found the pictures of the other rig on a french rc forum.

It seems that someone took inspiration from my work, i honestly had a good laugh at the sight of this "thing" :lmao:

How's yours looking ?

Are you happy with the RcTrax Dig Unit ?

 

[carlos46]

I have not used it.
The work employs me so that the models have little time.
So far I only přimontoval Dig for transmission.
I had a little wedge, since it did not fit exactly, but perhaps it will work well.

 

[farfab]

Thanks for the picture "thumbsup"

It looks like a pretty bulky dig unit, can you tell me the lenght between your output shafts using it ?

Do you know how much it weighs ?

From what i've read until now, these units tend to wear out pretty quick and they can be difficult to find.

I think a Rc4wd R2 might be lighter, tougher and besides, there's plenty of spare parts available...

 

[carlos46]

Actually I do not know how much it weighs.
The model I'm just riding a hobby, so I hope it lasts a while.
This wear is certainly possible. But I do not know.
I have no experience with it yet.

 

[OSRC]

Pretty nice evolution of the CR, nice job!

(like the bike too, I just retired mt 15 year old GT and went 29'er myself)

 

[farfab]

Thanks for your comments !

just retired mt 15 year old GT and went 29'er myself

What was the most disturbing, modern frame capabilities or new wheels size ?

Concerning the rig, I'm currently waiting for some 3mm delrin sheets i found and a R2 transmission with Dig.

I hope to have some time to work on this project soon.

To be continued...