Before I start, let me preface this by saying that yes, I know there is a previous post on the subject. However, the answers to this post did not lead to a productive answer to the question.
Here’s my question: where can our team find more sprockets for the KoP wheels (the normal wheels contained in the kit)? We’ve looked on and off for the last week. We finally found something we thought would work, but the screw-holes didn’t line up.
We know this part number is the one that didn’t work out: 35377159. I don’t think our team has the capability to machine the steel, so we need something with pre-drilled holes.
One last request: if you know where to find these, just say so; please save the “search before you post” rhetoric for later.
Do you really need the steel sprockes, or could you use the aluminum ones from IFI instead? they include spacers, so you can mount them out from the wheel a ways. You may need to tap threads into the holes in the wheels. I haven’t tried to put the aluminum sprockets on the new AM plastic wheels, but the bolt pattern seems to be the same (6 each 10-32 on a 1.875" circle), so they should work.
Our mentors have told us that normal operation of the wheels places significant wear and tear on the wheels such that you really should use the steel sprockets. However, if you know this isn’t the case, could you elaborate further?
If the robot were running for months straight, then yes, steel would probably be in order.
However, you’re running your robot for two minutes at a time, perhaps 50 times tops over the course of a competition season (unless you go to a metric ton of off-seasons). In that sort of situation, I have empirical evidence that suggests that aluminum sprockets, such as those sold by IFI, AndyMark, and perhaps others, wear acceptably. If you’re really worried about it, bring a couple of spares (though you should do that as it is)…but you should be fine in most situations with the aluminum sprockets properly installed.
WE used the IFI AL 28 tooth sprockets last year with Custom made spacers on the Skyway wheels. IFI is selling 24 tooth AL sprockets. If used with the Andy Mark KOP wheels, I would recommend some type of reinforcing Spacer.
Is there a reason that you cannot drill a new bolt hole pattern in these parts? There are many, many sources for 24-tooth #35 roller chain sprockets. But for almost any application, you may need to do small amounts of post-purchase machining on a part to make it exactly fit the particular requirements of your design. You should be prepared to drill new bolt holes, broach keyways, enlarge the bore, remove the hub, or other minor tasks. You should not be trying to avoid modifying off-the-shelf parts to make them fit your need - you should be enjoying it. It is part of the creative, fun part of creating a new design.
Some have already commented that they are upset they cannot just purchase the exact part they need and bolt it on their robot. What ever happened to the idea that part of the challenge (and part of the fun) of FIRST was creating your own design out of raw materials? If we do nothing but rely on bolt-on solutions, then we are largely relying on the engineering efforts of others, and doing little true engineering of our own. And that, I submit, lessens the experience for all involved.
The real world does not go together like an Erector set. FIRST robots should not either.
To follow-up on what Dave said, we had to purchase extra gears as well. We couldn’t find the EXACT duplicate items either, so had to buy non-broached gears.
We don’t have a broach kit, as the full kits cost upwards of $300 dollars. We also do not have an arbor press, another $100 or so. Therefore, we had to call upon some local teams to see who would be willing to help us with the broaching.
After a couple quick emails, I was able to find several teams in the area that were willing to help me with our broaching needs. Turn-around time was 1 day! Try to find that with any other supplier!
So, even though YOU do not have the resources, there are over 1,000 other teams out there that just may. Don’t be afraid to ask another team for help. The broaching took an hour of their time, and they were more than willing to actually do the work for me. (I had to fight them off…)
I’ll second everything else here. With the short operational time of FIRST robots, we can get away with aluminum and shockingly narrow safety margins all over the place simply because we can always swap a spare and there’s not a lot of time for things to go wrong.
Off-topic:
Guys, he just said he doesn’t think they have the capability to machine steel. 57 enjoys playing with chop saws, lathes, mills, and rotary dividers as much as the next team, but come on. Telling people “shame, shame” because they don’t have machine tools? Is this where we’re headed?
Perhaps they merely want to focus their efforts on the hard stuff, and buy the easy stuff off the shelf. Time is short, and perhaps they have financial but not human (or machine) resources. He was just asking.
The wheels use rather large sprockets, with many teeth, and usually the chain wraps more than half way around the sprocket, so the load on each tooth is relatively small. The aluminum sprockets are strong enough for use on wheels, and the smallest size you can commonly get is 24 teeth, I believe.
However, the transmission sprockets are a different story. Some use as few as 9 teeth, so the load per tooth is significantly higher.
The general way of doing things is to use steel sprockets at the drive end of the chain, and aluminum sprockets at the wheel end of the chain. It works.
Ben, that is exactly on-point. One of the things that every new team learns is that there is always more than one way to skin a cat. Need to add more sprockets to the robot? Get additional parts similar to those in the Kit Of Parts. Can’t find exact duplicates? Get one that is close enough, and work with it to allow it to be used. The sprocket doesn’t have the right bolt-hole pattern? Borrow a hand drill and drill out a new one. Don’t have the right skills to drill the new holes yourself? Talk to your mentors and see if they can help. They don’t have the right skills? Talk to nearby teams and see if they can send someone over. They can’t make it? Take it over to them and see if they can do it on site… etc etc etc
There are lots of ways to get things done. It takes some perseverance, creativity, and innovation, but one of the great things about FIRST is that there is a tremendous community out there to help you make it happen if you can’t do it all yourself. My fundamental point is that before you have to resort to buying your a way out of a problem, make sure that you really tap all the resources that you have at your disposal. Some of them may not be obvious at first, but they are there and can add to your experience.
One untapped resource could be a “KOP sprockets wanted” post on CD…my guess is many teams are not using them, and there are literally several hundred of those sprockets sitting on shelves and in boxes going unused, right now, as we speak. I personally know of a pair of sprockets, but I don’t have authority to give them away.
You migth check the rules first though, as the parts might not be available for sale anywhere, so using “free” ones might not be allowed.
The first point I would make about this is that you should be able to find more of the types of things that are in the Kit of Parts. There should be a FIRST-related site where you can go and order more of any part that comes with the kit. I know, for example, that IFI Robotics has part of this list (but only with the things they make, obviously). Why are you not able to just go online and order another part? If the answer is that FIRST wants us to practice our drilling skills, then why do the sprockets in the KoP come pre-drilled?
Furthermore, I understand that there’s more than one way to get things done. We’ve already ordered two omni wheels from Andy Mark to see if we can come up with some other solution than 4WD. However, we also wanted to look into the possibility of getting more sprockets. I’m also not sure why you think we should be looking for the most complex solution to a problem (buying pre-drilled or at least easily-drillable parts seems much simpler than drilling new holes in a steel part, which our mentors tell us is much more difficult to machine). We also did ask local teams if they had extras of these parts, and we have not yet gotten any replies.
When we’re trying to solve a problem as simple as our drive train, we’re going to be looking for a simple solution; getting two more KoP sprockets should be doable. We are examining the alternatives, and one of them should be to get these sprockets. You seem to be critiquing me for not doing exactly what I’m trying to do with my post.
We know this part number is the one that didn’t work out: 35377159. I don’t think our team has the capability to machine the steel, so we need something with pre-drilled holes.
A regular ol’ hand drill will get through steel, but you’ll need to be very precise with your measurements.
As far as aluminum sprockets go, let me share a little story. Our rookie year (2004) we purchased these humongous steel sprockets thinking we would need them. We used 1/4 aluminum in our base, and made our goal grabber out of steel. We had a very elegant robot until around 3 days til shipdate when we weighed the thing. 143lbs?!!??!? Oh Noes!!! We lost a lot of our ball holding ability to cut the weight down, as well as drill quite a few not-exactly-in-a-line speed holes. We ended up making weight (which was 130 lbs with the battery).
Fast forward 4 years…
A few nights ago we got a package from AM containing our aluminum 25 sprockets for this years drivetrain. While sitting in our room someone pulled out these giant steel #35 sprockets and we couldn’t stop laughing thinking about how we thought that we needed that much strength.
If I may, I’d like to add a couple of thoughts.
This thread is a healthy thread and I hope a lot of FIRSTers read it.
It is about a specific quest for a specific item, 2 sprockets. Hopefully, at some point, someone will post and say they know how to obtain them.
In the meantime, suggestions, alternatives, ideas, and opinions have been shared. The FIRST community is one that cares deeply about the success of every team and its members. And it cares deeply about the new/newer teams. Sometimes the threads in CD offer unique opportunities to the FIRSTers that post here, interactions with each other that opens the window into the world of FIRST philosophy and applications a little wider. That can be frustrating when one is looking for a specific answer to a specific question and met with alternatives and suggestions encouraging one to be innovative and creative. For now, resolving the sprocket dilemma is important yet, at the same time thinking about and perhaps applying some of the suggestions offered would not be a waste of time or effort. I read this thread and saw it to be a thread of enrichment and helpful support because that is what it is.
Many wonderful ideals have been expressed here. I, for one, agree with them fully. I also know from first (not FIRST) hand experience that those ideals are not reachable for all teams in all locations. Although I much prefer to teach the “Give a man a fish and feed him for a day. Teach a man to fish and feed him for a lifetime” principle, I think for the sake of the teams that exist outside the “ideal” world I will give an answer to the original question.
Drive sprocket:
McMaster part # 6280K371 $8.23 ea.
Wheel sprocket:
Get it from IFI.
IFI-SPROCKET-35A24 $9.99 ea.
I realize that part of my inspiration was getting my hands dirty on the mills or lathe, drilling holes etc. Personally, I hope we never see the day that you can just bolt together an arm from XYZ company, a drivetrain from ABC company, and a ball collector from DEF company. However, I am a systems engineer, and a lot of our stuff is short turn around, just like FIRST. When you work in those conditions and you work in a HS shop that in total has a band saw, a table saw and a drill press, you look for the way to spend more time on certain parts of the design while taking shortcuts on others. To me, milling out a sprocket is not that exciting, and I would bet that in 80% of the teams, the kids dont do that (its probably sent to the sponsor, to other teams or anything of the like). So whats the difference if you find a resource to buy it from (wisely using your time like a systems engineer would) or you send it off to your sponsor to do for you? Its the same to the kids… but maybe they learn or get inspired by designing in inventor, or putting the transmissions together or putting on the chain.
The entire reason FIRST gave us the “kitbot” in my understanding is so that the disadvantaged teams would be able to make more than just a box that sat on the floor. They could focus more on arm design than just making something that could move around the field. I dont see how buying a sprocket with holes takes away from the design process. If Dean really wants a FIRST team in every school, and everyone has to do their own broaching or steel drilling, he had better buy a full machine shop for every school, or FIRST needs to allow more “system” style designs.
But anyways, sorry Im a bit off topic, although I think the question has already been answered. The IFI sprockets are probably closest. We use McMaster Carr to buy ours and then add broaches or keyholes (at our sponsors place). I think Ben’s idea is the best… if you can find a team near you willing to help, or even one that would be willing to overnight parts they did for you, that would probably be the easiest if you dont have the machining resources.
In the past Team 104 has had no money and only hand tools. That didn’t stop us from making adapters for IFI AL sprockets last year for the KOP wheels. We found a LDPE 5/8" cutting board at BED BATH and BEYOND, using 2 hole saws made some donuts. Drew some lines for the spoke slots and cut with a hack saw with 3 blades on it. Problem solved for about 8$. 2 sets from IFI would have cost 44$. The IFI AL sprockets were 1/2 the cost of the custom steel sprockets and less than half the weight. Some times your have to practice the fine art of kluging. In past years I submit that Team 104 has been the King of Kludge. There should be an award for the cheapest kludged bot that places highest in the rankings.
I don’t know, Team 306 might give you a run for your money
Team 306 was staying at a mission building in downtown Pittsburgh for the regional because our mentor’s friend was looking forward to meeting us, and it proved to be a cheap alternative to a hotel :rolleyes:. Anyway… the 'bot broke, and I had to make a hacksaw out of what the mission house had in its shed, It was interesting. I’d say that is pretty kludge
