Can we replace a heavy steel chassis with a lighter aluminum spaceframe (or better, a monocoque), and how?

My team and I realized that we would need a stronger chassis than a normal aluminum chassis because a friend’s robot kept getting its c-channels bent. However, our team does not have steel cutting tools and our coach does not think very highly of steel as a chassis material. Could we use a spaceframe or monocoque design to sidestep this issue, and how could we do it? Thank you!

Hi! I would use cad but why would you build an aluminum chassis? Tbh I would build a steel base to be more stable. Try and stick to steel if you can. If not sorry I can’t help you. Any other questions?


Unsure of what spaceframe or monocoque refer to in this context, but I would recommend building a normal aluminum chassis. Your coach is right that steel is not an ideal chassis material, and the channel bending issue is definitely not a common one.


That is pretty odd unless you are my team mate…

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just build your chassis better. A properly build aluminum chassis shouldn’t bend. if you show up photos of your chassis we can help you improve it.


Definitely. I have been building steel all my vex career (not including IQ) so is that the best way? What d you guys thing for the lift or systems and for the base?

Aluminum for everything is what I use. It’s lighter, and with proper bracing, it’s sturdy.


Steel is bad, and extra weight.

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With good build quality, aluminum is fine for pretty much everything.

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Not sure how long has been your vex career.

but to be competitive, you will need the chassis to be light weight to allow you to move faster.

As for stability, you can mostly resolve this issue by taking note of your CG during design phase and also adding an anti-tipping wheels if necessary.

And to answer your question regarding lift - use aluminium too. so that you can have a faster lift as well.


Your coach is right actually.
Again, thats if you want to be competitive, else steel is ok for any parts of the robot.

There are many ways to reduce the chances of your c-channels getting bend.
I wouldn’t say eliminate, because at high level games especially, defensive plays are normally a lot more aggressive, there will be certain amount of bending at the end of the tournament.

You can try using a c-channel box/block or stand-off for your chassis.

This video has both methods…

Stand-off at the side of the chassis - around 16sec mark.

C-channel box/block method - 2:20min mark

Combination of both - around 1:25min mark

And as what @Doctortictac mentioned - use brace especially for your lifting mechanism.


Having a heavy robot is also advantageous though. A heavy robot is less likely to slip when pushing another robot. And weight isn’t nearly as bad for a V5 robot as it was for V4.

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Generally speaking - yes. The heavier the robot, definitely will give you more friction and harder to be pushed off.

Again, this can be mitigated with small little… gadgets :slight_smile:

eg. those that played against 8059A during TP worlds will agree that it was built like a tank, almost impossible to push, and yet light enough to sprint around.

Edit to add: while it is true that v5 motors are strong enough to carry a steel robot, at high level, you want to squeeze out every ounce of advantage that you can get. Even if it means my robot will reach the game element half a second faster than yours.
Again - as i mentioned earlier - steel is ok for anything, unless you want to be competitive.


I mean, heavier bots would definitely be able to muscle lighter bots out of the way through sheer momentum. It’s a tradeoff really, do you want more power at low rpms or more power at high rpms.
Heavy bots could be particularly useful when all robots are contesting a single point on the field

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the highest tier robots are always all aluminum. But I do think steel on your chassis can be competitive, especially if the rest of the robot you build is light. I think this year, robots won’t need to weight as much, so a steel base could be competitive for the purpose of shoving.


Not always true that a heavier robot will definitely be able to push a lighter robot around.
As I mentioned, you can add certain design features to prevent your robot from being pushed around.


I’m curious (and an empiricist); there seems to be a lot of assumed wisdom that lighter robots are faster than heavier robots. Perhaps this was true with Cortex and the older motors, but has anyone demonstrated this with V5? Within the realm of reason, how much faster would a chassis-only 4 motor tank drive be, compared to the same chassis with an additional 15 pounds?

I’ve seen similar postings regarding X-Drives being faster than tank drives and Mecanum drives being slow/not able to turn as fast. Just curious if anyone has actually demonstrated any of this in a practical environment, rather than just performing the maths.

X drive are faster just because of the way the wheels are angled, makes them 1.41 times faster than a standard tank. You can clearly see the difference with X drives. Mecanum drives are about the same speed going forward as tank, but are slower at turning because the rollers don’t really help you turn like they do on an all-omni drive.

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Additional 15 pound is actually a big deal.

It is already past midnights over at my side. But I will do a simple and simplified calculation with the data from specs tomorrow.

But off-hand, assuming same amount of torque from the motor, a lighter robot will definitely have a greater acceleration.
And at high level competition, you want to gain every bit of advantage that you can get.


I understand that. However, when I see posts where teams seem to indicate that they prefer the new bearing to the old because the new one only needs 1 screw/nut while the old bearing needs 2 screws/nuts and that makes the robot “lighter” and therefore faster, my intuition is telling me: “Either they have A LOT of bearings or their ‘optimizations’ for weight are misguided”.

I chose 15 pounds as a guess at what a reasonably fully functional robot would weigh on top of a base chasis. I may ask my team to do the same - build a base chassis, and load it with weights in some graduated form (5, 10, 15 pounds, maybe 1,2,3…15 pounds) and see what the results are.

I get the calculations. I get the concept. Not many dump trucks win NASCAR races. That said, is there a measurable speed difference between a 15 pound robot and a 14 pound robot? Probably between a 40 pound and a 10.

The maths say (at least according to the internet) there is a 1.41 speed advantage for X-Drive over skid-steer. Has anyone verified this experimentally?

Part of where I’m going with this is to shift the focus from “optimize everything” (or, “optimize the thing I heard on the Internet”) to a more cost-benefit analysis given that time is the most precious resource. Perhaps, rather than spending the time to shave .25 pounds by halving the screw count a team might be better off gearing up their drive train from 200RPM to 257RPM.