@Henza64 Good pics.
Id say you need to find out how wide is the belt… and also what sort of pitch (teeth spacing) it is using…
Perhaps there are some letters / words on the belt which might give you more clues…
On a side note… im not sure how bigger 18 or 20 teeth pulley will be as it looks like there’s not much space left in the cover… Also, I have not had the chance to fit a different size pulley on my setup, so im not sure how that might influence belt tigthness… Im mentioning this because it looks like your motor cannot be adjusted, so you would need to get a really good fitting belt size in order to for it work…
Ok, so for now:
1) measure belt widht is it 9mm or 12mm… as that will determine what pulley you might need to find.
2) After size is known and some similar pulleys are found, some calculation / considering can be made to decide whenever everything (the new pulley) is gonna fit on the same axle, with the same belt…
if this does not work out (the mechanical part)
your options would be to increase the battery voltage (if you can guess what the max specs are for that specific esc - motor controller)… if there’s not much ways to increase the voltage (as that would also require to get - add a new battery), you might just wanna switch to a different esc, though not entirely possible to know would this increase the speed, if the voltage stays the same.
One more option - get bigger wheels, though im not sure how much bigger can you really go… and that would require for you to fit the same pulley to the new wheels…
I actually think a good way would be to write an email to them and ask what is the maximum voltage their esc’s can handle… perhaps there’s is a little bit of headroom and you can add 1-2cells more in parallel, if you get the chance to get a matching battery / cells, to the existing battery you got there…
Otherwise, if they dont tell you the esc’s maximum voltage there’s a risk of burning it / damaging it and having a need to get a new one instead… so yeah, for now there’'s like 3 options:
1) Try to change the gearing ratio
2) Consider fitting the pulley to bigger wheels (if you can get them)
3) Consider increasing the battery voltage, if the esc can handle that
4) Get new esc (also receiver for remote + remote, too, possibly) and tweak the settings or install higher voltage battery…
To sum it up, so far, the mechanical procedure looks like to be the least costly… but it might require some tweaking (your time) and searching on the net for the neccesary parts…
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Im not an expert though… these are the options I can come up with… perhaps someone can give you an even better advice… so yeah, see for yourself, how it looks on your side…