belt drive VS chain drive

[VPpanther]

thank you for the quick responses

my first guess would have been that chain would be more durable because its metal, could you enlighten me on that?
and I'm not sure if we could do a drop center chassis because the rocking back and forth would severely impact what we're trying to do. The robot would probably only have to face level surfaces most of the time with the odd bump now and again (its actually for a sponsor to take to tradeshows and events to advertise). Would it be bad to just have all 6 colson wheels touching the floor at ounce? (i was leaning toward what 610 did last year but on a larger scale: http://prntscr.com/67dvyj )

We have a very tight budget so we sadly don't have the opportunity to test solutions before implementing them

[EricH]

Originally Posted by VPpanther

and I'm not sure if we could do a drop center chassis because the rocking back and forth would severely impact what we're trying to do. Would it be bad to just have all 6 colson wheels touching the floor at ounce?

What ARE you trying to do, in general terms?
What is the expected floor?
What sort of upper elements do you anticipate having--precision or "meh, whatever, it's close enough" in terms of motion?

Without knowing those, it's not going to be very easy at all to give anything like a "correct" answer, not that one exists. Knowing those, we can steer you around the pitfalls and away from any "incorrect" answers. This is especially important if you've only got one shot.


I would probably go with you don't want 6 colsons on the floor simultaneously, but that would also depend on wheelbase vs trackwidth--the higher the trackwidth/wheelbase ratio, the more "stick" you can get away with in your wheels.

[VPpanther]

Originally Posted by EricH

What ARE you trying to do, in general terms?
What is the expected floor?
What sort of upper elements do you anticipate having--precision or "meh, whatever, it's close enough" in terms of motion?

Well the robot is for a sponsor, they will take it to tradeshows and events to advertise their products. so the robot will most likely be facing clean level surfaces with the odd bump every now and again. upper elements wise it will have a humoniod type of structure with a head,shoulders, and arms so leaning toward precision. right now our dimensions are looking to be 34'' by 40'' and about 7-9 feet tall (the upper portion will be very light consisting of mostly sheet metal, so it will be very bottom heavy)

[EricH]

That's a bit better. 6WD colsons will probably work (and if it doesn't, you might be able to find some Lunacy wheels on AndyMark and use those--they're slick enough). That wide/long of a robot, you can probably get away with "flat" configuration, though I'd actually suggest using "mixed wheels", with at least one end being smoother/less "sticky" than the rest.

A couple of other items to bear in mind: I'd go single-speed transmissions, geared for a "reasonable" speed (say about 10 ft/second or less), but with two motors on each (in case of one failing). We're dealing with foot traffic here, so precision driving could be important. Also, some form of safety system should be on there, say a drivebase lockout (again because we're dealing with lots of people).

I'd agree on the superstucture being more "precision" than not; after all you don't want it rocking onto some potential customer's head while under the control of your sponsor.

[VPpanther]

oh okay, thanks for all the insight. I'll relay your suggestions to the team. much appreciated!

[GeeTwo]

Originally Posted by VPpanther

Well the robot is for a sponsor, they will take it to tradeshows and events to advertise their products. so the robot will most likely be facing clean level surfaces with the odd bump every now and again.

I know this may sound rather strange, but kiwi may actually be the best answer for this set of requirements, and will bring a bit of cool factor as well.

upper elements wise it will have a humoniod type of structure with a head,shoulders, and arms so leaning toward precision. right now our dimensions are looking to be 34'' by 40'' and about 7-9 feet tall (the upper portion will be very light consisting of mostly sheet metal, so it will be very bottom heavy)

Honestly, i'd shoot for plastic rather than sheet metal if you man manage it. Not only is it lighter, but it's friendlier/less intimidating. For all the negative things that Douglas Adams had to say about Sirius Cybernetics, I have to admit that "Your plastic pal who's fun to play with" sounds a whole lot better than "Your sheet metal pal who's fun to play with".

[Scott Kozutsky]

It's all about implementation. We had belts on our versachassis WCD last year and we switched to chain because the belts were breaking (they were waaay out of spec. load so that makes sense). The equivalent pitch diameter and width of 25 chain was much stronger and performed fine (24t 9mm belt vs 18t 25 chain).

My experience with chain and belt:

Belt is lighter, do not stretch, are quieter, and more efficient than chain.

Chains requires less precision, are much smaller for the same strength, are much easier to source (especially up here in Canada), can be easily modified to different lengths, have many more available sprocket sizes, you can easily make any sprocket you can't source if you have a CNC mill, and chains can be easily bolted to for a function.

We like the compactness and general ease of use of chain so we decided to use it over belt this year.

[roystur44]

Belt has a much better damping effect than chain. Try spinning a chain system and a belt system at a high rate of speed.

Belt is easier to keep aligned over a long distance between axles.

[Chris Fultz]

Check out this -

http://www.chiefdelphi.com/media/papers/2216

and this -

http://www.chiefdelphi.com/media/papers/2246

[asid61]

Originally Posted by Chris Fultz

Check out this -

http://www.chiefdelphi.com/media/papers/2216

and this -

http://www.chiefdelphi.com/media/papers/2246

I saw that before, but I never found a test for 9mm belt, at least not on the load ratings of it. I don't like belts because thay are so wide.

[brentyi]

Originally Posted by VPpanther

my first guess would have been that chain would be more durable because its metal, could you enlighten me on that?

Belts generally have steel or fiber glass tension members, which are pretty strong and keep them from stretching.

Quieter and lighter than chains, too.

[Sam_Mills]

Originally Posted by VPpanther

my first guess would have been that chain would be more durable because

Steel is more ductile than the fiberglass or kevlar that you will find in a lot of timing belts. Which is "more durable" or "stronger" depends on material properties which is an entire science in and of itself.

Just know that chain will stretch with use, and is harder to replace for someone who has no experience if you are just handing the drive off to a separate group. More information about the specific use of the bot would be helpful if you want the best possible answers.

As for wheels, Colsons all the way. They wear slower than Hi-Grips and have a higher friction coefficient with carpet. If the robot isn't competing you may want even higher durometer wheels than Colsons though, so that they wear even slower. Colsons can last 100+ matches on carpet, but if its on pavement at a demo, you will eat through an 0.125" drop before you know it.

[asid61]

As far as general drive trains go, I would recommend designing a WCD (cantaleivered wheels, drop center, 6 wheels, shifting gearboxes). We made a nice one in the offseason. For this year's bot, however, we simply applied the concepts learned from WCD (slots, tensioning, bearing blocks) and made a standard 4WD that has independently controllable wheels for switching to mecanum or "regular". The WCD gave us a lot of experience for the effort.

[String]

Originally Posted by VPpanther

and I'm not sure if we could do a drop center chassis because the rocking back and forth would severely impact what we're trying to do. The robot would probably only have to face level surfaces most of the time with the odd bump now and again (its actually for a sponsor to take to tradeshows and events to advertise). Would it be bad to just have all 6 colson wheels touching the floor at ounce?

Based on this, I'm not entirely sure you understand the complete purpose of drop center. Without drop center, using Colsons, and given the dimensions of the robot you specified earlier, your robot will have an awfully hard time turning. Drop center increases the ratio of width of wheelbase to length of wheelbase, decreasing wheel scrub while turning. A 1/8" drop is pretty much unnoticeable, but if you really can't have any rocking, consider using omni wheels.

[EricH]

Originally Posted by String

Without drop center, using Colsons, and given the dimensions of the robot you specified earlier, your robot will have an awfully hard time turning. Drop center increases the ratio of width of wheelbase to length of wheelbase, decreasing wheel scrub while turning.

Technically, you are correct in the reasons. However, you need to rethink the robot dimensions, specifically the length/width ratio (assuming 34" wide, 40" long).

They're 34" x 40". 1.17 length/width. A typical FRC robot that's difficult to turn has tended to be a 1.35 length/width ratio (28"x38"), and before that a 1.2 ratio. They'll have an easier time than most FRC robots, particularly given that the actual wheelbase will be shorter than 40", probably more like 36" which will give nearly a 1:1. If the ratio of length/width (actually, wheelbase/trackwidth) goes under 1, turning suddenly gets easier without a need for a dropped center. Ask Ether for the physics on how that works sometime, I'm a touch rusty.

There's a reason you rarely see wide-bots using drop-center--it doesn't really help their turning, and it adds to their overall "oops, I fell over again" factor.