4wd 1:5 onroad car based on stretched 1:8 truggy chassis

[othello]

I have almost completed my next project which i like to share with you. After having converted 1:8 buggys, truggys, sc-trucks and toying around with 1:10 and 1:8 onroad chassis i thought the next logical step is to step up to 1:5 onroad cars. Living in the city makes it difficult to find a spot for driving a nitro/gas chassis and the performance of a sports 1:5 onroad chassis without a tuning motor/pipe seemed not very appealing to me ... so it had to be brushless. Considering the necessary investment to convert a "true" 1:5 onroad chassis and having seen prices of spare parts led me to the only possible choice: Using proven and reliable 1:8 parts as basis of custom chassis.

I found a used 1:5 onroad body in good condition. I would have prefered a Porsche body but at this time there were no good offers. So i chose a Mercedes touring car body which is depicted here next to my 1:8 and 1:10 bodys.


1:8 buggy tires have almost the same diameter as 1:5 onroad tires but are not as wide. I had good success with GRP Endurance onroad tires on my 1:8 rally game chassis ... so they were my logical choice.

1:8 GRP Endurance tire compared to a GRP 1:5 onroad tire


1:8 Robitronic Mantis truggy axles were a good starting point as they almost instantly gave the right width when paired with my 1:8 tire choice.


With 1:5 GRP tires mounted i have to shorten the arms and cvds by 1.5-2cm to fit the tires under the body.

Next step led me to cut 2 Mantis truggy chassis and joining them to get the right wheelbase


After this step i chose the bruhless components and where to place them on the chassis. Which resulted in this first test layout.


ESC: Xerun 150A Pro
Motor: Castle 1520
Batteries: 2x Turnigy 6s 3600 used in parallel
Steering Servo: Hitec 5955TG

As i was never able to come up with a well balanced custom long CVD (on my previous projects) to join the center diff with the front axle i decided to join those with the aid of a second blocked center diff which required only a short custom CVD/bone. A rather unusual and not very efficient solution but as of yet it has proven to be reliable.

One of the last steps was to find a way to mount the body to the chassis. With some 1:8 parts in my spare bin i came up with this rather simple solution.



With mounted body


After a few test runs with the castle 1520 motor i stepped up to the Castle 1717 motor which was an easy fit when paired with a 22t pinion.


Depending on the batteries i choose the wheight ready to run lies between 6.2 and 6.4Kg (13.7 - 14.1lbs). I'am using lighter Zippy 6s 2800 paired in parallel (depicted on the image above ... the blue ones) or heavier Turnigy 6s 3600 also paired in parallel.

Gear ratio is 1:8.4 with a calculated top speed of 93km/h (58mph) without taking into account tire balloning. By changing the axle ratio from 42/10 (truggy ratio) to 42/12 (buggy ratio) i can augment speed to 110km/h (68mph).

If you wonder how does it perform, well here is a video while testing this setup on a rather small parking lot.

At this point there are still a few things to get done:
. In my opinion the chassis is too flexible and does need a top deck
. I have to come up with a typical 1:5 front bumper
. Damper setup has optimisation potential

[snellemin]

Pretty cool man. I'm liking the custom center shaft setup. The vid didn't open for me, but I bet it's a blast to drive.

[Arct1k]

The idler diff is a simple solution and should not add much drivetrain drag.

Seems to work v nicely. The truggy suspension should give you sone rally/auto cross options.

[othello]

Small update: i have finished a simple top deck



@snellemin
Vid should work with VLC Player . But i have rendered a WMV video version which should pretty much work on any Windows based pc with Windows Media Player.
Right now i'm only driving this big boy, so yeah you are spot on, it's a blast to drive ;-)

@Arct1k
I have limited suspension travel for onroad use but you are right it should also be a good basis for mild offroading/rallying when adding proper tires and another (rally) body of course. Hmm, have to do some research to find a suitable body. Good idea ...

[satttheman]

very nice build!

[Semi Pro]

nice

[Overdriven]

Very cool project. You're really getting your money's worth out of that Robitronic Truggy, this being it's second configuration!

[othello]

Video on a wide open space

After 6.5 minutes of top speed passes one of the rear tires was completely run down (and lost its insert). I charged around 4000mAh back which corresponds to an average current of 37A (With 22.2V average power: 820W). To get some decent runtime (10 minutes plus) with an even higher top speed i will need around 8000-10000mAh.

@all
Thanx guys. A truly versatile platform indeed.

[othello]

I have changed gearing to 1:7 and have mounted 1:5 GRP onroad tires which results in a calculated top speed of 110km/h (69mph).

short video from today

As the GRP 1:5 tires provide enough grip i will stay with them for now. I'm happy with the actual speed so gearing should also remain as such. Time to buy some new batteries to bump up run time to 10 minutes plus. 2x 6s 5000 wired in parallel should be the ticket for this target.

Track width is to wide but still works using the mercedes body

[_paralyzed_]

I love the looks of the car! I like the track width, I think the wheels look good sitting out a little.

Any chance of posting a video to youtube or something similar, I can't view the videos on a Mac.

[othello]

Thanx _paralized_ . You may install flip4mac on your mac in order to be able to watch WMV Video files. I have reencoded the last video as MP4 file. Quicktime should play it just fine.

Video as MP4 file.

[othello]

Update: i bought a new eagletree micrologger v4 and mounted it on this chassis. I'm now running 2 Turnigy 6s 5000 25C battery packs wired in parallel configuration.

Outside temperature has dropped and snow has already fallen. Nevertheless i have managed to make a few runs. But the data collected still has some flaws as setup of the logger is somewhat tricky.

I have put together a video of a speed run combined with the eagletree data.


From left to right:
- throttle input
- motor speed (rpm)
- motor current (amp)
- battery volatge (v)
- numerical values: Motor temperature (°Celsius) and consumed mAh

video link: WMV Video with eagletree data inserted
video link: MP4 Video with eagletree data inserted

The logger was set to measure 50 samples per seconds:
. Voltage: Add around 3V to the voltage and you should have the real battery voltage (one of the flaws i coped with on this run). Battery voltage should have been at 25.2V when i started this run but only 22V is displayed.
. current: When accelerating and pushing the throttle to the max, the logger measures between 170-180A (i bought the 150A version). I assume that amps are way higher. Current falls to around 80A when the car reaches top speed. The logger falsely shows a voltage of 19.5V at 80A. I assume voltage to be between 21.5-22.5V. Translasting to 1.7-1.8kw to maintain top speed. While braking you can see that amps are rising (the logger can't display negative amps = regenerative braking -> putting amps back to the battery). Average current depends on driving style and is somewhere between 35-60A (or 800-1400W).
. motor speed: You can see some erratic rpm spikes while accelerating and especialy while braking. i assume this comes from the way the ESC is handling the bruhless motor. When you ignore those peaks you will see that the motor tops out at 33000rpm when hitting top speed.
. motor temperature: Outside temperature was around 0°C (32°F). When making speed runs motor temperature only rises relatively slowly (in this case by 10°C within 2.5 minutes). I can safely discharge the batterys continouusly with this driving style (especialy at this outside temperature levels).
. Driving time: When driving as shown on this video a battery charge will last around 10 minutes plus (with 9000-9500mAh put back to the batterys while charged in parallel configuration).

At the end of the video i braked too late and did hit a snow mound (i have to do some small cosmetic work to the body ... aside from that nothing broke).

[brian015]

Othello - I saw this build before but did not get around to commenting - It looks really nice and seems to handle very well.

I like it!

[othello]

I have put together another video. This time i drove the car harder. A lot of sliding on the cold asphalt with harder throttle inputs and braking.

Video links:

WMV Video with eagletree data inserted

MP4 Video with eagletree data inserted

This obviously was harder on the components:
. Motor temperature rises by 26°C (78°F) within 3 minutes. Temperature rise can be as high as 10°C (50°F) per minute.
. On Average up to 60A are drawn out of the batteries per minute. Peak: 182A.
. Resulting in an average of 1,3kW und peak 3,6kW.
. Up to 1000mAh per minute are drawn out of the batteries.

At the end of the video one of the wings at the front of the body had almost detached itself. A result of the "crash" with the snow mound depicted in the previous video.

@Brian015
Thanx Brian. I'm really happy how it handles ... even during winter time when grip is at its lowest.

[Big House]

How did you fit the 1/5 wheels to your car? Thanks.