What did I do wrong? (SK3 & Pulleys)

It is looking a bit fail. I think it will work, but I also think motor shaft is too long? (But I used the things I got with the motor…


You don’t need to use all parts that come in the box. Remove that shaft extension. Also your wheel pulley looks a bit small. What kind of gear ratio are you aiming for?

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Gear ratio is: 14t/36t Jeah but then I have the problem how I can mount the pulley to the shaft…:thinking:

You need a pulley with 8mm bore and set screw and/or keyway. You have seen other builds?

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Jeah i saw that but I can’t mount a screw in mine. It’s flat. I think I need another pulley. But maybe it will work like that for the moment.

Do you think it’s bad to drive like that?

You will have massive forces on your motor bearing with that kind of lever arm. I would suggest to not ride it like this - how would you screw the motor to the mount anyway - you’d need like 3cm long screws just to reach the mounting plate. Also what does a flat pulley have to do with anything? I drilled a hole in mine in one of the grooves and put a set screw in.

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Thanks for this idea man! The solution to my problem :wink:

I thought it would not work with a hole there. But then I will try :slight_smile:


The SK3 comes with no keyway or nib for a grub screw. You’ll have to do that yourself :wink: better go the grub screw way. Its easier.

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Ok but I think then i have a little problem there is no more material inside the pulley for a grub screw… And the construction in the pictures is already finished… :frowning: idk what I should do now…

Maybe I will try to construct a mount for the motor like he is at the moment. Otherwise I should buy spare Pulleys. And they are so expensive…

Ok Option 2…

I go and buy new Pulleys :wink: What du you think about this setup:

Better would be that I don’t need the plate at the wheel because it will fit exactly above the hole. And the motor pulley would be a bit bigger that I can screw it on the motor shaft.

Ratio is a bit different.

you should check out some of the build threads. there’s a lot of pictures that you can look at. how are you planning to mount your motor? it doesn’t look like you have a lot of room on that truck. that truck doesn’t look like it’s gonna last for a long time either since there’s a lot of material missing. that wheel pulley seems really small for a 36t. what kind of pullley are you using? it might be a better idea if you just buy a kit from one of the sellers. it would save you time and money.

Are you using HTD 3M? If so, I think you will have big problems with teeth skipping on the 14T pulley on heavy and/or medium acceleration, be sure to carefully set the belt tension, when people say 14/36 it is with a 5M pitch, using 3M you should aim to a 50 or bigger wheel pulley and adjust the smaller for the gearing you want, I tried 50/18 but suffered a lot with teeth skipping and gave up

I think most people on here are using around a 14t:36t ratio.

those pulleys you have are too fine pitch. and the motor one should mount directly to the shaft…

Thanks for sharing your experience, I think I buy new trucks and new Pulleys. And i think i can not use a kit?.. because of the wheels? And I live in Germany…

But if someone can recommend me a kit I also would be very happy.

If not, I go and buy some new trucks. And then go for larger Pulleys. Maybe 20/48 like I said.


I’ve used 3mm pitch pulleys before, it’s definitely doable but they will skip at high torques unless you tighten the tension above normal.

You might try installing a pair of bearimgs on the motor mount, kind of like a tensioner on a car belt. Yoi will need a washer between the bearings and one on each side so they will turn freely. That would out more belt in contact with the pulleys.

I tried that too, no success, if you limit the torque (current) if should work, just do the reverse math to figure out the max torque it can handle and calculate the current based on your motor kV, but in my case that was too low to climb hills