Re: Back for more..VEXpro 2014 Product Unveiling
 

I would wager they are actually making the claim that HTD is stronger than the traditional trapezoidal tooth, and not gt2. This is just conjecture though.

EDIT: I'm wrong, rewatched video. He was referring to gt2.

Re: Back for more..VEXpro 2014 Product Unveiling
 

We ran a 6wd WCD in the fall to test new ideas for the 2014 season, especially play around with belts. All pulleys had 24 teeth and were made of aluminum pulley stock. We had a tensioning system in place, but rarely had to tension after putting the belts on. It should be made to note that during these tests we added weight to our robot to reach 120 lbs so we could determine a factor of safety for each type of belt. During these weighted tests, we ran full forward, full backward, into walls, and rapid spin turns and reversing spin directions to test the belt reaction. While under lower weight and low risk driving both belts performed equally, however upon testing the heavier robot and heavier driving we found the GT2 belt start to ratchet, while the HTD belt stayed in place.

Re: Back for more..VEXpro 2014 Product Unveiling
 

Did you adjust tension between belt changes?

What width were the belts?

Did you use different pulleys or the same type? Which kind?

Re: Back for more..VEXpro 2014 Product Unveiling
 

The tension was the same on both HTD and GT2, and to compensate for any discrepancies we tried both belts multiple times, switching out between rounds.

The belts were 9mm wide, 5mm pitch.

All pulleys were the same aluminum 24 tooth cut from the same stock, all the same width.

Re: Back for more..VEXpro 2014 Product Unveiling
 

GT2 pulley stock is different than HTD pulley stock, which is different than regular timing belt stock. I don't think it's fair to compare belt performance when at least one of the belts is running on a pulley it wasn't designed to run on.

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These two links help compare that a little bit;
http://www.gates.com/brochure.cfm?br...cation_id=3881
http://www.gates.com/brochure.cfm?br...cation_id=3881

Re: Back for more..VEXpro 2014 Product Unveiling
 

I'm going to guess the pulley stock was HTD?

Re: Back for more..VEXpro 2014 Product Unveiling
 

I've done some searching on this claim and it seems difficult to directly find information to back it up, but using the information here, http://www.transdev.co.uk/catalogues...pretension.pdf

And making the assuming that a lower required belt preload for the same transmitted power would mean that the belt would be less likely to ratchet.
This is a pretty safe assumption because the preload is the belt tension needed to maintain contact given a transmitted power so lower preload better the teeth are at self maintaining contact.
Now assuiming that all factors are the same except k and f0, these are the properties derived from the belt tooth structure.

Looking on the website and at the offered belt profiles they do not offer exactly GT2 and HTD belts so i picked similar profiles, XL for GT2 and 5M for HTD.
Profiles can be seen here, http://www.transdev.co.uk/pages/belt...prene_main.htm
This would support the claim that a HTD profile would be much less likely to ratchet as it requires a lower preload to maintain tooth contact at a given transmitted load.

Re: Back for more..VEXpro 2014 Product Unveiling
 

A few of the cad models are messed up. The color of the models was a nice addition, but the wrong parts are used sometimes, especially in the shafts for the gearboxes. Often times they are too long and go through a motor. See the 3 CIM PTO box.

I'm also confused by the wcp 3 cim pto design. It's much thicker than it needs to be. To begin with, the distance the shifting dog travels is about twice what it needs to be. A quick reconfigure of the design let me slim the gearbox down by 1.25". There's a ton of wasted space. Also, the outer plate needs to hold 3 bearings, 4 standoff mounts, and 4 cylinder mounts, yet it has spots for mounting the CIMS. Again, this could be make significantly smaller.

I'll post a picture of what i'm talking about in an hour or so.

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If I'm not mistaken, the distance between the gear and the PTO is probably to allow versatility in adding Versahubs/Versapulleys; ie, you're not restricted to using pulleys of a certain thickness/can use multiple pulleys/sprockets.

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Are you talking about the space that holds sprockets for chain or belts, or something else? Plus, what Steven said.

Parallel symmetrical plates allow for quicker and more efficient fabrication, I would imagine.

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Here's what I'm talking about. I got the gearbox slimmer by 1" (3.5" to 2.5"), and switched the standoffs to screws in the CIM mounting holes. My design doesn't have bearings, but you get the idea.

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lol

I think you ought to read the product description again. That configuration is intended for a typical WCD setup. That is why there is a space for your sprockets.

:)


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Re: Back for more..VEXpro 2014 Product Unveiling
 

The PTO Kit reuses many existing parts, including the main output shaft, this would typically be cut off where it meets the opposite plate. Rather than creating slightly tweaked versions of a bunch of existing parts we chose to repurpose existing things.

Also space is required for the gear/sprocket/pulley attached to the Versadog, Hence why this kit is listed as an option to only work with the WCD version of the 3 CIM DS.

Re: Back for more..VEXpro 2014 Product Unveiling
 

Yup, my bad. I see what you mean about space for the plate sprockets. That being said, if you used a little sprocket that had the dog pattern in it, you could probably get away with this.