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Complex belt system

Justin 5553

By: Justin 5553
New: 12-02-2017 11:37 AM
Updated: 12-02-2017 11:37 AM
Views: 1093 times


Complex belt system

Can this work ?

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12-02-2017 12:13 PM

AriMB


Unread Re: pic: Complex belt system

You probably want to support the ends of those cantilevered shafts. You might be able to get away with cantilevering the shaft in the top left corner, but the other ones you should definitely support.

Other than that, do you have any specific questions?



12-02-2017 01:02 PM

Justin 5553


Unread Re: pic: Complex belt system

The shafts on which pulleys are attached are constrainted enough, they fit in other bearings behind the big plate. The problem is more about the tensioners that have no other support that what we see on the picture. I will put another plate to support them.

This being my first belt system, i'm a bit afraid of the tension on the belt, my team has no experience with it and i don't know how sensitive to bad tension such a system would be. Can poor tension (like tensioner 1 mm away from its ideal position) ruin a system like this one ?

Thank you for helping



12-02-2017 01:14 PM

AriMB


Unread Re: pic: Complex belt system

In my experience with belt paths with bearing tensioners, you should make your belt paths about 1mm undersized. Then you can wrap some electrical tape around the bearings to shim them out to proper tension. That should also ensure that you can assemble the belt system even if manufacturing tolerances make it a bit larger than preferable.

Belts need a good bit of tension to carry a substantial torque without skipping (a lot more than chain). Make sure if you're cantilevering those belts centimeters off the plate that your axles aren't flexing (even if the axles are properly supported on the other side of the plate).



12-02-2017 01:39 PM

jasonpatel555


Unread Re: pic: Complex belt system

If this is meant for an FRC application, you could probably not use the tensioner on the top belt or the vertical belt. And the note someone else already made about supporting the ends of the shafts is spot on.



12-02-2017 03:54 PM

BetaHelix


Unread Re: pic: Complex belt system

I would agree that the tensioner on the top and vertical belts are unnecessary. When working with belts it's best to use exact center to center distances (plus a bit) instead, except in ones like the motor pinions, where that one is needed for adequate wrap.



12-02-2017 06:40 PM

Justin 5553


Unread Re: pic: Complex belt system

Quote:
you can wrap some electrical tape around the bearings to shim them out to proper tension
Thank you for the advice !

About the tensioners on the top and vertical belts, i don't choose the center to center distance, this is determined by the diameter of Steamworks balls (this system is a feeder for a turret). At least this is true for the vertical belt, i can maybe modify the horizontal one so as to delete the tensioner.

I didn't thought about shaft bending, but i think a 1/2 in hex shaft made of 7075 aluminum can withstand the force due to belt tension whith this configuration.



12-02-2017 09:04 PM

GeeTwo


Unread Re: pic: Complex belt system

Quote:
Originally Posted by Justin 5553 View Post
I didn't thought about shaft bending, but i think a 1/2 in hex shaft made of 7075 aluminum can withstand the force due to belt tension whith this configuration.
I agree with the advice about a second plate, but if you're going to cantilever a shaft, use steel rather than aluminum. Even though soft steels are no stronger than aluminum, they flex a lot less under load. Also make sure that the shaft is supported in a second bearing somewhere - don't make a bearing apply torque.



12-03-2017 03:12 AM

BetaHelix


Unread Re: pic: Complex belt system

Quote:
Originally Posted by Justin 5553 View Post
i don't choose the center to center distance, this is determined by the diameter of Steamworks balls
Where are you ordering your belts from? My team has ordered mainly ordered from SPI/SI, and they have a lot more sizes available than Vexpro or Andymark. In addition this C-C calculator might be useful, https://www.bbman.com/belt-length-calculator/.



12-03-2017 05:13 AM

Justin 5553


Unread Re: pic: Complex belt system

Quote:
Where are you ordering your belts from?
I'm french so i order my belts from a fench supplier (called Michaud Chailly to lower the delivering and border customs costs. They also offer a lot more sizes than VEXPro and WCP.

Quote:
make sure that the shaft is supported in a second bearing somewhere
It is



12-03-2017 05:23 AM

R.C.


Unread Re: pic: Complex belt system

Quote:
Originally Posted by BetaHelix View Post
Where are you ordering your belts from? My team has ordered mainly ordered from SPI/SI, and they have a lot more sizes available than Vexpro or Andymark. In addition this C-C calculator might be useful, https://www.bbman.com/belt-length-calculator/.
Personally I would skip the tensioners on everything except the wrap on the motors with the 12T pinions. Also remove the bearing on the inside of the plate and add a supporting plate with a bearing to support the shaft. DO NOT go to steel, its a pure waste of weight and steel hex is severely undersized.

While SDP does have more sizes than what WCP/VEXpro carry I only use VEX/WCP belts. The reason I recommend using the above is getting spares at events or from other teams is much easier. We've had people ask us at events and throughout the season if we have some random oddball size belt. The answer is normally no, teams normally have some form of a VEX/WCP belt laying around or spares for their robot. If you a have to use a belt from another supplier match the tooth size so If your at an event you can find someone with spares. It sucks to need a 70T belt but you used a 73T on your robot.

We also have a useful calc for 3mm/5mm HTD/GT2 belts.

http://www.wcproducts.net/how-to-belts/



12-03-2017 06:45 AM

AriMB


Unread Re: pic: Complex belt system

Quote:
Originally Posted by R.C. View Post
Personally I would skip the tensioners on everything except the wrap on the motors with the 12T pinions.
Quote:
Originally Posted by Justin 5553 View Post
About the tensioners on the top and vertical belts, i don't choose the center to center distance, this is determined by the diameter of Steamworks balls (this system is a feeder for a turret).
If the C-C distance is fixed for the required ball diameter and compression, do you have a suggestion for how to remove the tensioners and still get the right spacing? AFAIK you need the tensioners to ensure the correct path length while keeping the C-C distance that you want (i.e. not the nearest C-C distance that fits available belt lengths).



12-03-2017 04:58 PM

R.C.


Unread Re: pic: Complex belt system

Quote:
Originally Posted by AriMB View Post
If the C-C distance is fixed for the required ball diameter and compression, do you have a suggestion for how to remove the tensioners and still get the right spacing? AFAIK you need the tensioners to ensure the correct path length while keeping the C-C distance that you want (i.e. not the nearest C-C distance that fits available belt lengths).
Ari

Im not following here. Why would a belt path be related to a ball diameter or compression? Or why would you create that setup? We used a ton of belts this year on a pretty cool robot and didn't have to do any of that, same goes with any of our past robots.

For the OP and others. In the case of the model just shift the motor mounting around or vary the length of travel for the ball or game object. Since there is a wide selection of belts you're looking at .25"-1" of shift.

I see merit in the tensioner for the two motor setup not cause of the belt length required but the wrap created around the smaller 12t pinions.



12-03-2017 05:18 PM

AriMB


Unread Re: pic: Complex belt system

Quote:
Originally Posted by R.C. View Post
Ari

Im not following here. Why would a belt path be related to a ball diameter or compression? Or why would you create that setup? We used a ton of belts this year on a pretty cool robot and didn't have to do any of that, same goes with any of our past robots.

For the OP and others. In the case of the model just shift the motor mounting around or vary the length of travel for the ball or game object. Since there is a wide selection of belts you're looking at .25"-1" of shift.

I see merit in the tensioner for the two motor setup not cause of the belt length required but the wrap created around the smaller 12t pinions.
I can't speak to the model requirements or why the OP can't move the shafts, but the OP said that the shafts for the top and vertical belt runs are fixed. Maybe the OP can comment on why they said that and perhaps we can figure out a way to move them around. Meanwhile, since I can't see the whole model, I'll take their word that those can't be moved even a few tenths of an inch. If this is the case, the easiest way I can think to get the proper tension would be with bearing tensioners. I'm not saying that they're necessary with proper design (and you've clearly shown that they aren't), but that this is the only way I can think to make it work with those strict requirements.



12-04-2017 06:45 AM

Justin 5553


Unread Re: pic: Complex belt system

Quote:
Why would a belt path be related to a ball diameter or compression?
This belt system aims to power the entire feeder with only two motors. It also ensure that all the wheels run at the same speed. The C-C distances are the distances between two sets of wheels that take the balls on their way to the turret. This feeder work with wheels and ramps so the balls get from one ramp and wheel to another ramp and wheel. So I can adjust a bit the distance between two wheels but not that much given the max space my feeder can occupy.
That is at least true for the vertical belt, the horizontal one is more flexible. This belt power a gear that power the wheels that throw the balls into the turret (confusing? ). So i can maybe adjust the position on this gear so as to remove the tensioner.
Quote:
I see merit in the tensioner for the two motor setup not cause of the belt length required but the wrap created around the smaller 12t pinions.
That is indeed what this tensioner is here for. I could have moved the motors so as to avoid using tensioners but there would not be enough teeth that mesh to be able to transfer enough torque.



12-04-2017 07:28 AM

Cothron Theiss


Unread Re: pic: Complex belt system

Quote:
Originally Posted by Justin 5553 View Post
...It also ensure that all the wheels run at the same speed...
Are you sure that's something you want?



12-04-2017 11:44 AM

Justin 5553


Unread Re: pic: Complex belt system

Quote:
Originally Posted by Cothron Theiss View Post
Are you sure that's something you want?
Your mean that it would be better to accelerate the balls ?



12-04-2017 12:11 PM

Cothron Theiss


Unread Re: pic: Complex belt system

Quote:
Originally Posted by Justin 5553 View Post
Your mean that it would be better to accelerate the balls ?
Well, as we saw in many of the best shooters this year, the more you can accelerate the ball before the final flywheel, the more consistent your shooter will be. Also, the more gradual you can make the acceleration, the less energy it will rob from your system overall. If we assume the ball has zero velocity when it enters the system, you'll probably want the first rollers to be slower with more reduction and the latter rollers to be geared higher to get the ball to higher speeds.

So not only is there some reason to gear the rollers at different speeds, but there might also be something to be gained from gearing them separately. Right now, the belting is so complex because you're trying to mechanically link two motor sources to four outputs. I think you could split up the two motors between the first and last pairs of rollers. This would simplify the belting and would prevent the changes in motor speed from intermittent loads affecting the other pair of rollers.

This change would have the disadvantage of reducing the torque available when you first start intaking a ball since you only have 1 motor available to the initial acceleration, but I think that splitting up the inputs would make the system quicker, more consistent, and cheaper to make. Though I'd love to hear if there any other differing opinions.



12-04-2017 03:55 PM

Justin 5553


Unread Re: pic: Complex belt system

Quote:
Originally Posted by Cothron Theiss View Post
the more you can accelerate the ball before the final flywheel, the more consistent your shooter will be

There might be something to be gained from gearing them separately. I think you could split up the two motors between the first and last pairs of rollers. This would simplify the belting and would prevent the changes in motor speed from intermittent loads affecting the other pair of rollers.
About diffferent gearings, I agree, the less energy your shooter has to transfer to the balls, the better it is. If the shooter could only give the balls the good direction, that would be great. But I'm worried about a system that makes the balls enter the turret with too much velocity. It could maybe cause "jams".

I think gearing the rollers differently is a good idea. It helps avoiding jams in the feeder (if not too fast and if the balls are greatly guided) and afford a better repartition of the global torque on each roller.

About gearing the rollers separately, don't you think it can cause jams in the feeder ? If a ball behave weirdly and slow a roller, the other rollers won't adjust their speed and less torque will be available to take this ball out so the other ones will acccumulate behind it.
However, I agree it would make the mechanism much simpler and cheaper.



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