Designing
When designing robots, I try to have a pretty clear idea of what I want the final product to look like, so can focus on this and work backwards.
If not, I might just have an idea of some aspects I want to incorporate into the design (like what I want the weapon to be).
I didn’t really have a fully formed or clear idea of what the Robot was going to be, or look like, but I did have a deadline looming, and the deadline didn’t care about how inspired I felt, so it was time to get to work!
I like to have as much sketched out on paper as possible before starting on CAD, but since I didn’t really know what I was making, I thought about some things I knew I wanted in the design, and began laying out some of my components in Solidworks to get an idea of scale and where they would sit in the machine.
I had already been working on a modular drive assembly, so put in place the beginnings of the 4-wheel drive system, and the basics of the weapon system from Griffin I.
The hydraulic power pack contains, and pushes the oil driving the crushing power on the weapon.
I mounted the power pack, with the oil reservoir tank at the back of the machine so I could access it easier. I buried it in the centre of #1 and it was such a pain. If you have never worked with hydraulic oil, the stuff smells, gets all over everything and I hate it, so this was a must for me.
I drew out some rough dimensions for the clamp jaw assembly so I could begin to model some parts to see how it looks and how I am doing for weight.
I didn’t spend too long the figures, as they can all be changed easily later. At this point it was easier to get something on screen to modify, than to try and get it perfect on the first try.
I was happy with the overall size and shape of the placeholder weapon jaw assembly. I would have to run calculations and computer load tests on it once the design is a bit more complete to see it I needed to make it stronger to withstand the forces I would be putting through it, but it would do in the meantime so I could continue with the design.
I always have to be conscious of the weight. 110kg seems like an awful lot at the beginning, but quickly is reached once all the components are added. Here I am just over 87kg.
This is comparison between the MKI and MKII designs.
The drive motors still ran through the centre near the front wheels, and dictated the width of the robot. They and forced the awkwardly shaped hydraulic power pack to sit on top of them at an angle.
I made some attempts to work around the awkward geometry, but I was struggling to see how I was going to manage to put any meaningful armour around the reservoir tank, and I was even more concerned about figuring out a reliable way to self-right.
I thought I may be able to utilise the rear mount hole for the hydraulic actuator to mount a self-righting mechanism. The rear of the actuator moves through an arc as the crushing jaw moves up and down, but the hydraulic power pack was getting in the way and quite difficult to work around.
I made the (*hindsight* terrible) decision to switch out all the long 400 series Ampflow motors for the 150 short series.
My reasoning was that the short series are about half the ratings of the long series on paper. Since the long series were probably overkill, a short motor on each wheel should be plenty. It would offer more redundancy, and the wheels are mechanically linked anyway with two vee belts on each side of the drive.
The new small motors sat nicely shock mounted in the thick plastic chassis, which is starting to take shape above.
In theory this was a perfectly reasonable decision. In actuality, it caught fire.
The hydraulic system is now able to sit nice and low within the 40mm thick UHMWPE plastic frame. The plastic is much less dense than metal, so I am able to have much thicker sections.
I have used a lot of this material in my personal and professional engineering projects. It’s referred often as a wear plastic, and is used commonly on skid guides and chute lining because of its ability to resist abrasion.
I find its properties really useful for battle robots, and decided to use it extensively for Griffin II. It stands up to abuse really well, and because it’s plastic, it disperses shock though components more evenly so less fragile electronics and such inside will get broken.
You can see here how the hydraulic pack now sits between the drive motors and inside a pocket in the UHMW frame. I could have mounted everything lower, but I liked the ground clearance as it reduces the chance that I will get stuck on something during a battle.
I think a hydraulic crusher is a particularly difficult design because it requires its weight budget to be spread between a number of areas to be competitive.
Its primary function is a control bot, so I have to invest weight into a fast, powerful drive system to ‘control’ and outdrive the opponent.
However, because of the close quarter, drawn out fighting style of a control bot, the chance I will take damage is pretty high, so at least some weight is required for at least an area where the robot is able to take hits.
Hydraulic systems are heavy as far a weapon set ups go.
The weight of the actuator (that is also call the ram or cylinder interchangeably) determines how much crush force I can apply. As it increases in physical size, the force it can generate increases.
However, the actuator gets heavier as it gets physically larger and the weight of the jaw must also increase as it must withstand all the forces exerted by the actuator.
The weight limit means I wasn’t going to be able to make a well armoured robot, that had the drive I needed with a really heavy weapon system.
I decided to make the weapon more of a grabber, go for less crush force to reduce the weight of the weapon system.
This allows me to invest weight in strong, fast drive and resilient armour.
Another benefit of the smaller size bore actuator is that it moves considerable faster, as less oil is required to be pumped to fill it.
I couldn’t see the crushing beak set up lasting long against the bigger spinners, so started on more of a wedge shaped interchangeable weapon with less sharp edges for a spinner tooth to catch onto.
I added thick front armour so that even in the event that the front section is removed by something, robot will still function and be effective.
I then moved as much of the weapon mechanism behind this plastic plate to keep it out of the way of most things.
I always struggle working self-righting into a design, and this was no exception.
I thought about all kinds of articulations and mechanisms to self-right. I didn’t want to put in another motor or actuator since I had already invested a lot of weight in a powerful, reliable hydraulic set up, so I knew it was going to be some kind of linkage.
I looked at mounting wings that open up and tip it back sideways, or a rib cage type thing that opens upwards.
In the end, looking at the shape of the robot, it seemed like the most likely way it would successfully self-right was over the rear axle.
This is how I hope the self-righting would work. I tried to make the arms long enough so that I would not end up stranded on my side, and also made the overall profile or the robot curved, so It would tend to roll either on to the righting arms or onto its wheels.
The self-righting linkage arms also covered most of the top of the robot. I wasn’t able to design a top cover in CAD because the actuator moved through an arc, and the position of the hoses attaching it to the hydraulic power pack would be unpredictable.
This is the stage the design was at when I called it finished.
The design took longer that I would have liked, but the CAD is functional to the point where I was confident I wouldn’t have any problems with the manufacture, so I sent out files for laser and waterjet cutting and started getting machined parts made.