Thanks all for your feedback and dustpan enthusiasm!

On the ground clearance front, I've probably got 3-5mm from the base, although the screw heads probably need to be countersunk, so that probably takes away a mil or two. I've thankfully only got a few screws holding it together at the moment, so shouldn't be too bad to do that.

I considered asking for the mounts to be adjusted when I ordered them from Nat, but trusted my measurements as I wanted minimal ground clearance. With the information from Sam about the Robodojo floor, I would have probably planned differently. I'll probably only cut the mounts down if I really have to, even if it is just a matter of pride at this point haha. (Thanks for the advice though, Nat. I'll definitely bear it in mind).

I suppose the ‘simple’ option is bigger wheels, but then you need to know if they will fit in the room you have, is there any adjustments in the motor mounts?
I've found some 120mm trolley wheels on Ebay, which should give me 10mm clearance. They are hopefully arriving this week. There isn't much room above, so I will have to either cut out a wheel arch in to the top HDPE panels on the bandsaw, or just make new top panels out of the 10mm Polycarb I have. Either one shouldn't be too much effort.

Is this a temporary thing or not?
I would say yes, because it was just a quick fix to get a rough drive test in before it went dark. At the same time though, I didn't have any better options, so also no .

I would drill a hole through the bolt that your wheel is on and the hub of the wheel (I see you are using the same type of wheel as Azriel is) and then put a bolt through that to make it all secure.
That makes a lot of sense! The bolt holding it in at the moment is the reverse thread bolt from the drill chuck, would that be secure enough to drill in to, or would you drill through the drill shaft it is screwed in to as well? I imagine the holding pin/bolt would have to be quite thin, so would it stand up to impact well?

Alternatively, for the wheel issue, where you have that washer on the outside of the wheel, get a bigger diameter washer, drill two holes in that and the wheel and bolt them together like that?
Definitely a possibility. I'll likely look at a combination of both, make sure it is extra secure. Cheers!

The bolts on the dustpan, countersunk bolts perhaps? Once those two are done, give it a retest and see what that does for you.
I think I know what the plan is for the dustpan already. The metal is relatively quite thin, so countersinking isn't an option. When I started, I was torn between either using nuts, bolts and washers to secure it or to put a small block of HDPE in the back wall of the pan before screwing through that with wood screws to spread the surface area. Wood screws would sit flatter than bolts, so I think that is the option I'm going to try next.