Robot Cart Materials + Other Tips

Hi there!

So right now I am designing a robot cart for team 3467 - Windup Robotics - And I have an important question.

As far as materials go, we used wood for our last cart but want to switch over to metal, most notably aluminum because it is light and easy to transport. The issue is that there are multiple alloys available, and I feel that my team will debate whether to favor machinability, strength, etc.

Here are a few I noticed to have interesting qualities:
Alloy 5051 (medium to high strength)
Alloy 7075 (high strength)
Alloy 3003 (decent machinability)
Alloy 2011 (great machinability)
80/20 Aluminum (not sure what alloy, but heard this type is great for modification, shelving, etc.)

Any suggestions on the material or other tips? :smiley:

You forgot one: 6061 T6, which is the cheapest.

And to be honest, you won’t need the extra strength of some of the others.

If I was going to build a cart from scratch, I’d be looking at some combination of 6061 and 80-20.

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Thanks for the quick response! Gonna take a look into that…

80/20 is a product line, not an alloy, specifically it’s a type of aluminum extrusion. There are alternatives out there, but it’s the “name brand”.

As to what material specifically, the design dictates what ideal material is but for the most part aluminum is aluminum. You’re building a cart, not a rocket.

80/20 will be less machining (or none), but it does cost more than machining square tube or similar.

In our shop we mostly use 6061 (as Eric said, it’s cheap and easy to get with decent overall properties), or 5052 if a part needs to be bent.

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I forgot to mention: You probably have 6061 lying around the shop right now…

…if it hasn’t been made into robot parts yet! (Or even if it has been made into robot parts. Pesky lockdown.)

I am aware that 80/20 is not an alloy (forgot to specify lol).

Yeah it does seem that 6061 is a decent choice alongside the 80/20. I did hear from one thread that 80/20 was also great for holding shelves and other things, and for reconstruction of the robot cart over the years which we may or may not do so frequently annually.

Yeah, I do believe we have a supply of them not ready for machining yet, although we can’t worry about that 'til the covid crisis is over.

Speaking of which, would you say that 6061 is decent for machining? We may plan to drill holes or such to lower the weight considering the fact that we plan to put batteries in our cart alongside the driver station and such…

6061 is pretty decent for machining.

Quick-guide: https://www.mcmaster.com/standard-aluminum-sheets and open the “About Aluminum”. Looking at a “more detailed” description after selecting the alloy gets “The most widely used aluminum, 6061 is fabricated into everything from pipe fittings and containers to automotive and aerospace parts. It is strong and corrosion resistant, plus it’s easy to machine and weld.”

One suggestion, design adjustability into the cart. Make it so that the robot-carrying part of the cart can be adapted to fit any given robot. 330’s (aluminum tube) cart for YEARS had two slidable rails. Robot changes, rails slide over by loosening bolts. Plus if we needed to pack the cart and needed a little more space they could be removed. This allowed for us to put frame rails in different places.

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80/20 are basically industrial legos, you can take various pieces of stock and construct pretty much any truss structure with a hacksaw and fasteners, and if things are a half inch off then you just loosen bolts, move it, and re-tighten, no re-drilling holes. It’s nice. Surprisingly sturdy too.

I personally wouldn’t bother with drilling lightning holes unless you have large flat panels (and have time to kill). You’re not going to notice the missing couple pounds when pushing 150+ lbs of robot+gear. If you are concerned then switch to smaller bolts or to rivets (though rivets will loosen over time), steel weighs a surprising amount when multiplied, or reduce the thickness of the material.

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80/20 is made of 6105 T5 alloy. It’s a great choice if you want to be able to reconfigure your cart in each season, since you can move, add, or subtract elements much more easily than you can with a bolted or welded aluminum frame. Of course, it’s not quite as strong at the joints, but you’re unlikely to notice or have any problems with that, since the joining systems used in t-slot extrusion are still plenty strong.
6105 T5 is weldable, if for instance you want to weld the rolling base of your cart out of larger pieces of aluminum like 6061 T6 angle or channel and then attach uprights of t-slot to it. You can also end-bolt the pieces to other things (like angle or flat stock) by using churro bolts into the central space at the end of a t-slot section. We actually did this on our 2019 robot to attach the wheel carriers on our climbing mechanism to the t-slot that formed the extendable uprights. It’s remarkable solid.

Definetly isnt lighter weight, but our last robot cart was made out of 1.5 x 1.5, 16 gauge mild steel. It allowed for faster assembly and cheaper. The thing weighs a ton, but we also mounted a harbor freight cart on the top for lifting the robot, an electrical system to run an inverter and 2 car radiator fans (robot cooling), and also mounted a Gladiator tool cabinet on the back. The thing is a monster, so it probably has less to do with the frame being steel making it heavy. I think we put the cart together in just under a week before our first event in 2018. Our mentor that was doing photography for us during build/ comp season was across town with our programmer prepping autos for our first event, so I dont have many pictures of it being built, or without a robot sitting on it.

One tip is having 4 casters is really nice for moving sideways out of the way, or just maneuverability in general. If you do that, I would recommend adding someway to move the cart from the front. We always had somebody walking in front, holding onto a removable post, helping clear the way and guide the front end of the cart.

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