[WIP] RC (not IR) Racecar

[z3_2drive]

Ok, recently I wanted to try and make a truly RC lego car but I did not want to try and find the lego one since it's rare, huge, and might not offer as good performance, so (these parts are pretty pricey, but you get what you pay for) we got a motor controller, ESC and remote. The motor controller is pretty heavy-duty so I might use it in the future if I buy a hobby kit crawler. I got my 4th buggy motor, and we made a new battery pack from better batteries with twice the capacity and more power, and it's only a 3-cell pack for 4 motors so it saves on weight and space. I made a direct drive (no differential) but I think it will handle fine considering my last large PF car was the same way and it had no problems, and lego differentials won't be strong enough and will result in lower efficiency. I'm making the frame and front axle but have little time since school started again. I'm also waiting for the clear project box to keep the ESC and motor controller in, safe from damage. Here are the photos of it so far:

^ground clearance is low and there is some negative camber upon compression. I did this because it's simple, strong, and it will reduce the chances of it flipping at the speeds it will reach

^I love the way the motors and servo react to the new remote, all smooth and proportional as it should be, all is adjustable, my days of running after my large projects are finally over! I'll keep you guys updated when I make reasonable progress.

[piterx]

:D im a 99% purist....and you're in that 1% of cases that i totally approve :P

looking forward for a demo video :)

[z3_2drive]

:D im a 99% purist....and you're in that 1% of cases that i totally approve :P

looking forward for a demo video :)

Haha, I try to push limits to get fun and interesting results, while trying to use as many lego-only parts as possible to keep the fun in building and customizing-and I never cut parts-I did before a couple times and I regret it now But here I get the best of both worlds, performance and no loss of signal and the ability to build whatever I like A demo video will definitely come when I finish the prototype of the chassis

[piterx]

can't wait for it :)

im at work on a ultralight...once i'll finish my current 4x4 ill focus on that...i think you'll love it :D

[EyesOnly]

4 RC-motors on 3 cells. I can't wait to see it in action. I sure hope you have a big area to test it in. Hopefully outdoors.

[skriblez]

This looks awesome!

[Svad]

This is gonna rock

[camaudio]

Do you have links to the motor controller/remote?

[z3_2drive]

Do you have links to the motor controller/remote?

Thanks for all the comments :) I will post a link when I get my prototype finished. Today the project box arrived, so I tested the car with just an axle and two wheels as a placeholder in the front, and I Iove it! Acceleration is smooth and I can drive it slowly indoors and spin the tires and watch it rocket forward with enough space And having the car against a wall, the torque spins the tires at speed, no stalling I will have to be careful driving this Edited August 28, 2013 by z3_2drive

[clarkdef]

Really nice man, really nice. I'll tell you right now that uni joints don't like high rpm aswell as a lot of force to move a lot of weight, try to keep it at no more than 800g, also this is a good rule to reduce the seriousness of crashing. I use lipos because they are very light and two buggy motors, but going with other rc unit may bring costs down.

The bumper is very important, I use a bounce type but a skid type would be better.

[piterx]

cmon z3 i wanna see how it goes :D

so curious!

[tibivi]

I love fast moc's, so i've tried this setup too, very similar construction of yours. I took the silver champion wheels, in the end it did almost 25 km/h it overtook the 8675 outdoor challenger at full speed.

These things are really fun if you have a lot of space (and a good condition for running )

Enjoy your car :thumbup:

Greets,

Tibivi

Edited August 29, 2013 by tibivi

[Rishab N]

This is gonna be epic

[750ACE]

What brand components are you integrating? I have HPI components that I experimented with my parts.

[Kwon]

The ultimate one, can't wait for its speed :)

[z3_2drive]

It is a Futaba remote and receiver, but i forgot who the motor controller is made by. Anyway, today I rushed and built the prototype in an hour and a half, pressured on time because I had to leave home. I tested it at the new location where i'll be for the weekend, and my conclusion: U-Joints are OUT! They don't even come close to handling the torque. But before they came apart I was able to reach some pretty high speeds and I wasn't even at full throttle so my next step is to do a complete re-build so the rear axle will be a simple live axle or maybe no suspension??...and i will have another go at the front axle to make something more robust. The point is...IT WILL BE DONE!

[750ACE]

Direct drive with live axle. Lego at one time produced metal axles I believe.

[clarkdef]

Yes I mentioned those u joints above haha, ends up you witle down to a very simple system. Awesome bumper and accurate steering becomes the main concern, and low weight for handling and crash control.

[AndyCW]

Live axles will be fairly easy to implement with the 8110/9398 axle parts. Looking forward to the video of this. I was worried about the U-joints and we now know what is too much for them. Could you fit the jumbo HD U-joints in there? v/r Andy

[z3_2drive]

anything larger than the 3l's would be hard to implement and would make the car too wide. The unimog hub idea sounds interesting, so I'll be experimenting with it in my free time

[Junpei]

How about a swing axle with one of the red u-joints? Is that too unrealistic? At least it's suspension.

[z3_2drive]

How about a swing axle with one of the red u-joints? Is that too unrealistic? At least it's suspension.

Too much difference in camber during travel, don't worry I will brainstorm many ideas BTW in my haste to build the prototype I stumbled upon a neat way to secure irregular objects (like the battery) to the frame...simply use pneumatic tubing! A tight wrap 2 or 3 times and a way of securing the ends will ensure that nothing will come loose :thumbup:

[z3_2drive]

UPDATE: Since I'm away from my collection I fixed the joints and went back out for some proper testing to collect some observations about what needs to be improved on in the re-build. I was careful not to mash the throttle in order to spare the joints, but still had to pop them back into place about 10 times I did various tests:

Top speed: crazy fast, so glad for the proportional steering and super long range I wouldn't be able to chase this down at full sprint

Handling: Turning circle is much smaller than I thought it would be, and overall handling was pretty good except for wheel wobble at high speed* The camber helped for sure but it is actually not too necessary.

Strength: This is the car's weakest area, mostly due to the rushed build. Also due to the low ride height (I hit a bump/raised piece of the road and the front shattered but was easily fixed) which reminds me I need to make a bumper for the re-build.

My conclusion: The next prototype will be more of a rally-style with higher ride height and long travel, more robust suspension for the front and a new live axle for the rear, so I can use the power without the fear of smashing it somewhere but all in all I'm pretty f*cking impressed :thumbup: I may take a video, but don't count on it

[AndyCW]

The 8880 hubs might be stronger and eliminate the need for one of the u-joints. This may free up enough room for the HD u-joint. These hubs might also eliminate the wheel wobble that you mention. You can also use them to get ackerman geometry, caster, camber curve, and other geometries. Reducing the diameter of the wheels will also relieve some of the stress on the u-joints. v/r Andy

[Junpei]

If you're using the 8880 hubs, make sure it has a camber curve, caster, etc. as AndyCW said, because even the smallest bump will hit the suspension hard. I'm not really sure about them though, I have read somewhere that they create a lot of friction.

Do you have to use 8880 wheels?

Also, how do the u-joints not pop out? They don't seem to be aligned with anything.