Questions about building a West Coast Drive with VersaChassis

[Joel Glidden]

The blue part is just a bent aluminum sheet metal bracket (1/8 in thick). It bolts to the TB mini through the top two holes that secure the mounting plate to the plastic housing. Then it is secured to the top of the robot frame via four 10-32 screws and rivet nuts (McMaster 93483A661). The green cylindrical parts are just some stand-offs we made from half inch round stock that we drilled through with a .196" clearance hole. We secure the gearbox to the side of the frame by just running a long 10-32 screw through the TB, the standoffs, and the frame.

Refer to drawings 4293_2014-005 and 4293-2014-018 for the standoff and the bracket.

Edit:
Also, we cut the bottom off of the TB mounting plate for ground clearance. You can just trace the profile of the housing on the plate and then use a band saw to cut it down. Drawing 4293_2014-019 shows all the mods we made to the mounting plate.

[Monochron]

Thanks for all the replies everyone, the project is really coming along. A couple new questions that I came up with:

1. I have never tapped anything harder than aluminum before, but we have a fairly decent set of taps that isn't showing too much wear. How possible is it to tap the ends of this shaft in order to secure pulleys/wheels?
2. I can save some money by going with round shafts in stead of hex. Will this long shaft (meant for the ToughBox Nano) work in the ToughBox Mini?
3. Here is my total list of items to purchase, is this a reasonable price to pay? I was expecting a little lower as it would end up being a good deal greater than the voucher amount you get if you go without the KOP drivetrain.

[Joel Glidden]

1. The taps you've been using for aluminum should work fine for that shaft.
2. See below for a screenshot of the TBNano round shaft installed in a TBMini. It fits, but you will need a hex bearing. Also, there are two things to note. First, the hexagonal portion of the shaft protrudes about .150" beyond the bearing. Make sure it's not going to interfere with anything in your design. Second, the TBNano shaft is .335" shorter than the TBMini long hex shaft that is used in the 4293 design.
3. Will take a look at your shopping list as soon as you share the gDoc with me =)

[Monochron]

Originally Posted by Joel Glidden

[*]Will take a look at your shopping list as soon as you share the gDoc with me =)

Ha, duh. Fixed, should be open to everyone now.

[Joel Glidden]

Seems like chain and sprocket would be cheaper than belts and pulleys. Also, I'm not sure why you need the WCP side bearing blocks. Do you have CAD you can share?

[Monochron]

Chain and sprockets may be a good idea as our team has no experience with them. I would have to factor in the costs of chain accessories like a breaker and holder(?), though, as I never want to do chains by hand/pliers again like my old team used to.
If I go with the round shaft I should be able to save ~$20 by switching to sprocket/chain, but the cost of accessories would mitigate that. Still though, trying something new has its benefits.

As for the side bearing block, I was going to use it to hold the bearings for the gearbox shaft. I was kind of assuming that you had something similar in your model as you aren't using the VersaBlock at the gearbox.

As for CAD, unfortunately no. I started learning CAD recently but don't actually have a spare computer to put it on. We are trying to find mentors to teach CAD, but as of now I am the only one learning it.

[Nemo]

If you use #25 chain, get Dark Soul Chain tool, which costs about $40 with shipping. It eliminates the connecting links (weak links).

Chain for one WCD costs $10 vs ~$50 for four belts, so it pays for itself. With the sale on the AndyMark pulleys, the cost isn't much different either way, so I would focus more on whether you'd rather end up with belts or chains. I think it would be cool to run belts, but I also like having a bunch of sprockets and chain around so we can make up a manipulator chain connection pretty easily without ordering a specific belt or stocking a dozen different belt sizes. Chain is annoying in some ways, though.

[Monochron]

Originally Posted by Nemo

If you use #25 chain, get Dark Soul Chain tool, which costs about $40 with shipping. It eliminates the connecting links (weak links).

Chain for one WCD costs $10 vs ~$50 for four belts, so it pays for itself. With the sale on the AndyMark pulleys, the cost isn't much different either way, so I would focus more on whether you'd rather end up with belts or chains. I think it would be cool to run belts, but I also like having a bunch of sprockets and chain around so we can make up a manipulator chain connection pretty easily without ordering a specific belt or stocking a dozen different belt sizes. Chain is annoying in some ways, though.

Man, I would like to use that but if I go with #25 chain then I can't use the Vex Double Sprockets (They only sell #35 doubles) meaning that I would have to get 8 Single Sprockets which pushes the price even higher than with belts.
I do really like the idea of training the students with chains but adding in the cost of accessories pushes this up around $60 more than with belts. It's a tough choice.

[Nemo]

Originally Posted by Monochron

Man, I would like to use that but if I go with #25 chain then I can't use the Vex Double Sprockets (They only sell #35 doubles) meaning that I would have to get 8 Single Sprockets which pushes the price even higher than with belts.
I do really like the idea of training the students with chains but adding in the cost of accessories pushes this up around $60 more than with belts. It's a tough choice.

You can always go with the lower cost choice for now and then revisit it in the future.

[Monochron]

Yeah that's a possibility. Any suggestions for other #35 chain breakers? most of what I have found so far has been for chain sizes in the hundreds.

[Lil' Lavery]

Originally Posted by Monochron

Yeah that's a possibility. Any suggestions for other #35 chain breakers? most of what I have found so far has been for chain sizes in the hundreds.

This looks like the tool we use.
http://www.amazon.com/Koch-7725010-R.../dp/B004HKIU4C

[Joel Glidden]

Originally Posted by Monochron

As for the side bearing block, I was going to use it to hold the bearings for the gearbox shaft. I was kind of assuming that you had something similar in your model as you aren't using the VersaBlock at the gearbox.

I use a flanged hex bearing pressed directly into the frame opposite the gearbox. Really this is bad practice. You shouldn't have more than two bearings on a shaft, and I have three (two in the gearbox and one in the robot chassis). I get away with it because two of the three bearings are hex bearings and they have a pretty sloppy fit with the hex shaft.

If you're going to do the same thing with round shaft, make sure you spin the output shaft by hand or wrench once you have the gearbox mounted to the chassis. If the torque required to spin the wheel is inconsistent or excessive, the bearings are probably over-constraining the shaft. This will kill your efficiency and lead to fatigue problems later if left uncorrected.

[Monochron]

Originally Posted by Joel Glidden

I use a flanged hex bearing pressed directly into the frame opposite the gearbox. Really this is bad practice. You shouldn't have more than two bearings on a shaft, and I have three (two in the gearbox and one in the robot chassis). I get away with it because two of the three bearings are hex bearings and they have a pretty sloppy fit with the hex shaft.

Huh, I didn't know that, thanks for mentioning it. I can't really tell from pictures of other WCDs around but how is this usually handled? For instance the WCP gearboxes all come with two bearings; should you mount them with no bearings in the tubing?

[Phalanx]

Originally Posted by Monochron

Yeah that's a possibility. Any suggestions for other #35 chain breakers? most of what I have found so far has been for chain sizes in the hundreds.

For #35 chain I'm kind of partial to this one:
http://www.ombwarehouse.com/-35-Chain-Breaker.html

BTW, for #25 I recommend:
http://www.davesmotors.com/s.nl/it.A/id.2258/.f

If you notice, they are both similar in design and operation.
I highly recommend both of them.

[Monochron]

Originally Posted by Phalanx

For #35 chain I'm kind of partial to this one:
http://www.ombwarehouse.com/-35-Chain-Breaker.html

Awesome I was looking for a #35 version of that DS one. One question though, the thing I remember hating most about chains is trying to put pins back in to assemble the chain once it is under tension. Using a chain holder seems like it would make this significantly easier, but it looks like the chain breaker you linked may not be able to be used with a holder. Can you use them together? Or do you have to manually pull the chain in that breaker to line it up?