3mm HTD vs 5mm HTD

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bugboy1641   100 µW

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3mm HTD vs 5mm HTD

Post by bugboy1641 » Mar 31 2015 4:47am

Hi folks,
As I'm new to this site my 'real world experience' is somewhat lacking. As I am at the start of my build/component acquirement phase I'd like to know whether what the general consensus is regarding using 5mm HTD belts/pulleys over 3mm?

5mm seems to be widely used. Is it that the pulley teeth sizes are more available or cheaper or it can just handle the torque better?
3mm HTD means you can run slightly smaller pulleys on the Driver and driven wheels which means more clearance from the ground for the driven pulley. I think a rough calculation shows that in pure surface area, 5mm beats 3mm, even with the 3mm meshing more teeth?

Its a just a curiosity thing,

Thanks
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spinningmagnets   100 GW

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Re: 3mm HTD vs 5mm HTD

Post by spinningmagnets » Mar 31 2015 5:40am

Yeah, the bigger the teeth, the more torque the belt can take before slipping. Of course more teeth engaged is better, but...

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onloop   10 kW

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Re: 3mm HTD vs 5mm HTD

Post by onloop » Mar 31 2015 6:18am

I have tested both extensively.

Both pitch profiles can work in eboard applications.

unless its absolutely necessary to reduce the diameter of your pulleys, say for ground clearance, stay with 5mm pitch.

If you go 3mm pitch you will need 15mm wide belts as a minimum.

The other advantage of using 3mm pitch is you can get much larger mechanical reduction.

This may be advantageous in some cases.

For example... The designer of the open source ESC called the VESC, who as you would imagine happens to be very experienced with BLDC outrunners, has stated for optimum outrunner efficiencies RPM should be around 8000-9000...

depending on your battery voltage, wheel diameter and motor KV you might not be able to install enough mechanical reduction using 5mm pitch. So 3mm pitch is useful here also.

Availability of pitch profiles is similar... suppose it depends if you are buying 1 or 100.

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bandaro   10 kW

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Re: 3mm HTD vs 5mm HTD

Post by bandaro » Jun 09 2015 8:32am

Onloop, I have a lot of, shall we say, musings, regarding your answers there. Lets begin :twisted:
If you go 3mm pitch you will need 15mm wide belts as a minimum
If you include a safety factor (but not shock loading, nor does 5mm) then on paper, the 3mm is better. From what I get from the gates design guidelines, the ratio/pulley sizes/speed and power fall inside the 3mm pitch belt range. This is further improved due to the shorter centre distances that we use. The 2mm even falls closer to recommended than the 5 in some cases.

Additionally, a lot of people running the 5mm belts are dangerously close to the minimum contact teeth, so if the same pulley radius is kept for the 3mm, the extra teeth engaged can leave the smaller pitch handling more power and less likely to break teeth.

In your testing did you experiment with this? keeping the same size pulleys etc? The larger pitch would however be better at absorbing a rock or stick in the driveline though, so that could be a factor in your findings. Am I doing something silly with my calculations and forgetting stuff again?
Both pitch profiles can work in eboard applications
As far as I know, boosted uses a 2mm pitch, correct? Granted I also think they have a large reduction, but they use 2mm pitch 9mm wide very reliably. I think it is more to do with how tight the install is than anything else. 5mm can withstand more 'inaccuracies' than the 2mm
Availability of pitch profiles is similar... suppose it depends if you are buying 1 or 100
I've waited 4 months for local suppliers to get things for me, so I go straight to sterling instruments these days, they carry everything you could ever need.


I would be interested to hear your tests/findings on the matter, I'm running a 3x9mm setup, and hoping it will work as well as it does on paper.

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buzztiaan   1 W

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Re: 3mm HTD vs 5mm HTD

Post by buzztiaan » Jun 09 2015 8:39am

bandaro wrote:5mm can withstand more 'inaccuracies' than the 2mm
this was my main reason to go to 5mm, using 2.5mm belts on my 3D printer has already taught me that configuring small pitched belts for optimal tension is a -pita-
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torqueboards   100 MW

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Re: 3mm HTD vs 5mm HTD

Post by torqueboards » Jun 09 2015 9:17am

I think boosted is actually 3mm pitch and 15mm width.

I like the 5mm pitch 15mm width and 9mm width. 3mm pitch and 9mm width should hold for dual motor. Wouldn't trust it with a single 3mm pitch 9mm width.
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2wayspeaker   10 mW

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Re: 3mm HTD vs 5mm HTD

Post by 2wayspeaker » Jun 09 2015 12:10pm

I come out to 5 pitch, 15mm width for a design power of 2,8Kw and 4kRpm

You should really get the design guide from the mannufacturer you want to order from and figure it out for yourself. You can also calculate for two points: Low rev High torque (starting) and High Rev low torque (cruising). (Instead of High Rev High Torque.)
bandaro wrote: I've waited 4 months for local suppliers to get things for me, so I go straight to sterling instruments these days, they carry everything you could ever need.
I can second this. Local suppliers are ridiculously slow (Belgium) no Idea why. If you know a trusted Eshop for pulley's they take customer care in much higher regard. Local shops are of the opinion that they are the only shop in town and service level wont matter cuzz you'll have to go back there anyway (or something)

I ordered a whole list of things for a cnc router, over 300Eur worth. I had to wait 3 months for all of it. This was with me harrassing them by calling them/visiting their shop twice a week. I also didn't get the quote until well after I received all my stuff (I only received the quote at the end of january when it was ordered in october) and I "had to pay quick" or they would be tardy to close their fiscal year. such a mess of a supplier.

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