Building An E-Crosskart Buggy: The tube chassis

In this video I begin building the 55 kw off road electric crosskart buggy. Crosskarts are basically large, powerful off road go-karts built for racing on dirt and snow/ice tracks. I won't be racing this machine, so it's being built with more aggressive tires and a higher than normal ground clearance for ripping around in the trails. 

​The chassis is made with 1.25" and 1" diameter x 0.12" thick wall DOM steel tubing. It can also be made with the same size HREW tubing, which is similar to DOM in dimension but has a welded seam and is more affordable. DOM is basically welded tubing like HREW that's been worked over a mandrel and ground and polished to precision inside and out so there's no welded seam to deal with when it's finished. DOM is slightly stronger than HREW, but not necessarily required for chassis building unless race regulations call for it.

dom tubing: metalsdepot.com

hrew tubing: metalsdepot.com

I first begin the build by laying out the bottom and side profiles of the chassis on a level workbench and a sheet of MDF that was attached at a right angle to the bench with 2x4 wood braces and screws. The reference lines drawn represent the center of the tubing, and make it easier to measure, mark, and fit each piece. The chassis was built in two halves that were later joined with crossmembers.

​I used my TB-3 rotary draw bender from Kaka Industrial to bend the tubing. It's a bit pricy for a manual tool and might be a bit too much for the avg DIY'er to invest in, but if you're into this kind of stuff and plan on building more than one tube chassis in the future, then forget about miters - this is the tool for you. It works great, and I'm really happy to have it in the shop. This bender saved me a lot of work. 

image credit: kakaindustrial.ca

​To avoid making mistakes, I bent each piece for both sides of the chassis and placed them next to each other on the layout lines to ensure they match in length, bend angle, etc.

When necessary, I used my DIY tube notcher to notch the ends of the tubing where it needs to marry with another piece. The tube notcher saves a lot of work compared to using an angle grinder and it makes clean cuts that fit tightly with no gaps to save more time and $ when welding later. When I was satisfied with the fitment of each piece, they were tack welded in place.​

When the two halves of the chassis were finished, I removed the upright plywood from the bench and set up the halves so they were lined up with each other and spaced the right distance apart, then cut and welded the crossmembers between them. When the crossmembers were in place, I moved on to the diagonal bracing. The bracing went in the bottom, sides and back of the chassis. Its purpose is to form a truss assembly in these areas so they can support a load at any point and transfer it to the suspension, similar to how the roof trusses in a home are designed to carry and transfer a snow load from the middle of the roof toward the exterior load bearing walls. 

Once the halves were joined and the bracing was installed, I built a couple of wooden stands to set the chassis on at the desired (unloaded) ride height to prep for the suspension build. You can read more about that in the next post.