What are the advantages and disadvantages of certain pitches and belt widths (eg. 5 mm htd 9 mm width vs 3 mm htd 15 mm width)? Why use htd at all? There are other pitch types, why are those not used (eg gt2, xl etc.)? Has anyone on the forum experimented with different pitch sizes and/or types or do people just blindly follow the norm. Sorry, my curiosity must be getting the better of me.
Yes, I have tested this fairly extensivley…
The size of the tooth & the width of the belt is proportional to the amount of torque it can transfer…
Basically, it boils down to the surface area of the belt meshing with the surface area of the pulley teeth. The greater the surface area the more torque it can transfer.
greater surface area = more traction between belt & pulley
If you want to use 3mm pitch the belt needs to be a minimum 15mm wide for a reasonable result. Any less and you will have the belt skipping along the teeth when accelerating & braking… Mostly the problems occur under braking as it requires much more force to stop the momentum. Accelerating is more of a gradual lowering of the load on the belt, braking is a rapid increase in load.
So basically if the belt is underrated for the desired load it will shred into pieces.
I wrote a little bit about this in my article about designing a drivetrain.
here is the snippet:
QUICK NOTE ABOUT PULLEY TEETH PITCH There is a way to have a smaller pulley & also maintain high reduction ratios. The most common tooth pitch for electric skateboards is 5mm Pitch. Tooth pitch is the measurement between two teeth. So if I had a pulley with just 10 teeth at 5mm pitch the circumference would be 50mm. If I had a pulley with 10 teeth at 3mm pitch the circumference would be just 30mm. So what this means is you can use a smaller pitch & increase the number of teeth and have a pulley that is actually smaller in circumference. So I could have a 15 teeth pulley at 3mm pitch with 45mm circumference. This is advantagous as you can have much larger reduction ratios and have the pulleys fit onto a smaller wheel. But there is a trade off! the smaller teeth can’t transfer the same amount of torque as the big teeth so you can get belt slipping issue. Running with 5mm pitch wheel pulley and keeping the wheel diameter at 83mm is enough to ensure you get good reduction ratio & good ground clearance, the maximum number of teeth I recommend for the wheel pulley on an 83mm wheel is 36 teeth. As the amount of teeth increases so does the diameter of the pulley making it closer to hitting the ground which is bad.
Hmm, interesting. You did mention that you’re coming out with 12mm belts soon. I’m guessing they’re 5 mm htd pitch. Would a 5 mm htd 12 mm belt have better torque transfer than a 3 mm htd 15 mm belt? What do the boosted boards use? It looks like a 3 mm pitch to me, not sure of the width.
I think boosted is 3mm pitch, their belt is 15mm or maybe 18mm wide.
yes, I have come to realise that 5mm pitch is the best option. It’s much more durable and can handle the torque we are driving with the big motors.
Are there disadvantages in going with a 12 or 15 mm belt vs 9mm?
- Increased cost of belt & pulleys
- Increase friction / rolling resistance
- Can’t mount DR motors easily / need very short motors as 6355 won’t have the space on a standard 184mm wide truck hanger
Yikes! Lots to think about. Thanks, Jason.
YEP… lots to think about when building an eboard!..
Here is a very good belt selection guide to give you some insight: belt selection guide
15mm belts are nice riding def add to the resistance and harder to fit things with as well.
Ooo thanks for that belt selection guide! Great for a n00b like me.
so an XL pulley can work or cant?
XL pulleys work mate. even a 9mm XL will do an alright job on flats, but will struggle with hills.
noted that a HTD belt is superior…
I was wondering about all this different belt specs but every resource seemed to be a super technical spec sheet endorsing a particular brand.
http://file.lasersaur.com/docs-thirdparty/The_World_of_Timing_Belts.pdf still pretty technical but explains stuff really well for example why are htd 5m different from 5.08mm XL belts is not only the pitch but the htd can carry more torque due to optimized tooth profile.
interesting read for people who are interested.
TL;DR if this post was too long to read prob not the right resource for you anyway
This made me look for htd pulleys instead of xl.
What is HTD?
Apparently it means “High Torque Drive”
I began with htd3m belts and went to XL belts but at the end I ended up using htd5m belts. I washed a lot of money and time buying htd3m and XL belts and pulleys