I might have missed it but how thick is the box section used in the main chassis? 3mm?
The steel angle for the chassis is 40x40x3mm, the box section for the scoop arms, wheel cross spars etc is 40x20x2mm and the wheel guards were 50x30x3mm (or maybe 2mm) but have recently remade those with 50x25x2mm.

So in the previous installments, Shunt was born and built up to the point of being a (mostly) visually complete static display. The next steps were to get it moving then get the weaponry working!

January 2019

Work and life had kept me busy post-RoboNerd so didn't have time to do anything to Shunt for the rest of 2018. One of the first orders of 2019 was some rams for the bucket and axe. I guessed they were 40mm bore and 100mm stroke for the bucket rams but had no idea what stroke was needed for the axe. Thankfully I stumbled across a very grainy video of some house robot building/testing footage from prior to Series 3, where Malcolm James (Shunt's daddy) conveniently mentioned that the axe was driven by a 250mm stroke ram:



I opted for some hydraulic rams from a UK company called Flowfit. Reason for this was that they had the rams that seemed closest to original Shunt in terms of pivot point and mounting options, although they didn't look 100% right. Nevertheless, I forked out for these:

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I made up some brackets from some spare steel angle used on the chassis to fit the bucket rams, but the axe one would have to wait until I was ready to make the mechanism for it. Once the rams were on, I fitted the bucket and lifted it up - it didn't go far enough! Turns out 100mm stroke wasn't enough, even though the length of the ram was about right. I decided I'd worry about that another day though, and proceeded to fit some plywood to the base of the chassis and rig up a basic wiring circuit for drive. I'd also found time to modify the rear plough slightly so it looked less stumpy:

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The motors and wheels run on 3/8" sprocket and chain with a reduction of approx 6.5:1, and the system runs on a 6S lipo. There was an issue with the right-hand wheel where the chain would occasionally jump off due to being slack. Dropping down to a half-link solved the issue for half a revolution of the wheel but unfortunately despite my best efforts, the sprocket on the wheel was not concentric so the chain got too tight. However with some careful driving, the looser chain would stay on (but would need to be rectified with a tensioner later). This was a limited drive test due to space, but I have to admit to finding it quite surreal seeing Shunt driving in my back garden. The video also got a comment from Tom Gutteridge (classic era RW executive producer) on Facebook who liked it, so that was something



April 2019

Again another few months before I could progress with Shunt. Having got the drive working, it was now time to focus on the weapons. The more I looked at the rams, the more I realised that the 40mm bore was also too small. I needed 50mm bore rams with 150mm stroke for the bucket. Following extensive searching and cross referencing with pictures, I finally found what looked like the right rams (or 99% similar) on eBay. They were from China but only took 10 days to arrive and with minimal import duty. The rams themselves were pretty cheap too; I think about £120-£150 total for all three. They're only rated to 10 bar but as I wouldn't be running Shunt above this, that didn't matter. Once they arrived, I made new brackets for the bucket rams and test fitted them:

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These looked much better and I was certain I wouldn't find anything closer short of using the rams from the actual Shunt. While I had the robot in bits, I took a moment to take a picture of back-to-front Shunt, which suitably irked the fans on Facebook but I quite liked it

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Once that procrastination was done and dusted, I could no longer put it off - it was time to tackle the four-bar axe linkage mechanism. I knew this would be the toughest part of the build but thankfully some angles in the HR Ultimate Warrior DVD had good pictures of the various parts:

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I decided to go for the full 'prototype it in wood first' approach to make sure I wasn't making errors in steel.

Will continue this in another post shortly....