pic: 4587-Sheet Metal Chassis V.2

[Adrian Clark]

Originally Posted by Cash4587

How about this?
This isn't too bad for complication and it saves so much room. Although it does cost quite a bit for the bearing bore gears and for the bearings, It will leave plenty of room for electronics, at least I would say so.

http://prntscr.com/40ilna
http://prntscr.com/40ile3

I like it, I think you've got the right idea. You could totally get away with this but here's some thoughts.

What made you choose a dead axle over live axle? And in this setup do you plan to cantilever the gears? I think you could save weight if you ran live axle gears as you could fit a much smaller gear in between the cims.

I think you could simplify it a bit by removing one of the gears between the gear on the module shaft and the closest cim.

I could be totally wrong here, but in those renders is the robot not as long?

-Adrian

[Cash4587]

Originally Posted by Adrian Clark

I like it, I think you've got the right idea. You could totally get away with this but here's some thoughts.

What made you choose a dead axle over live axle? And in this setup do you plan to cantilever the gears? I think you could save weight if you ran live axle gears as you could fit a much smaller gear in between the cims.

I think you could simplify it a bit by removing one of the gears between the gear on the module shaft and the closest cim.

I could be totally wrong here, but in those renders is the robot not as long?

-Adrian

I had planned to run these as dead axle cantilevered gears on shoulder bolts I chose dead so it could be ran on the shoulder bolts. If I did run it live axle, wouldn't it be more weight or close to the same, as I would have to run the axle all the way through and use more bearings?

I don't quite follow you on removing one of the gears. I put that many on there so I could remove the belt that attaches the two butterfly modules together.

In this configuration the robot would be the same length and width, but it could be easily modified and changed.

Sorry for any mistakes I typed this on mobile.

[Adrian Clark]

Originally Posted by Cash4587

I had planned to run these as dead axle cantilevered gears on shoulder bolts I chose dead so it could be ran on the shoulder bolts. If I did run it live axle, wouldn't it be more weight or close to the same, as I would have to run the axle all the way through and use more bearings?

I don't quite follow you on removing one of the gears. I put that many on there so I could remove the belt that attaches the two butterfly modules together.

In this configuration the robot would be the same length and width, but it could be easily modified and changed.

Sorry for any mistakes I typed this on mobile.

I assumed you'd be supporting the gears on either end, so disregard what I said about weight. Also disregard what I said about removing one of the gears, I kinda forgot the modules were in the way.

I'm very cautious about cantilevering gears because it's hard to tell when a gear is properly supported for an application. More often than not this kind of setup causes high wear and inefficiency. I'm not sure how your setup would handle load, it could be fine but it's definitely something to be wary of. I might run a simulation later to see what happens when a setup like this is under load.

If I do run a simulation i'll also check the loading on the pinion gears. I'm not sure they'll like having power from four motors running through them. The pinion load is definitely something to worry about with a setup like this, and it could make things a lot more complicated if they can't handle the load.

Aside from proper gear support and weight, something to keep in mind when placing your gears is how you're going to fit in braces for the outside frame. Another thing to consider is the process for changing a motor. You'll want to ensure the cutouts are big enough to get some fingers around the motor.

As for the robot length, when I looked at the render it looked shorter because the cims were closer together. Looking back I see that it's the same.

-Adrian

[ekapalka]

Originally Posted by tim-tim

Three thou is way too much interference for a press fit.
Around half a thou (.0005") is pretty standard in FRC. I suggest getting a 1.1245 (or 1.124) and .8745 (or .874) reamers to do the final finish.

Here is an old thread to reference: http://www.chiefdelphi.com/forums/ar...p/t-98825.html

I don't mean to change the subject, but this information has highlighted a problem for me. I've been designing a gearbox for quite some time, and I've clearly been making a huge mistake with the hole sizes for the bearings I'm using. If an AndyMark flange bearing has an outer diameter is 1 inch, in accordance with this, the hole diameter for the bearing should be 1.0005 in? That seems really close. Could you just verify before I go back and change everything? Thanks

[AdamHeard]

Originally Posted by Adrian Clark

If I do run a simulation i'll also check the loading on the pinion gears. I'm not sure they'll like having power from four motors running through them. The pinion load is definitely something to worry about with a setup like this, and it could make things a lot more complicated if they can't handle the load.

I agree. The pinions on the end could potentially see 8x stall torque under direction change, which is huge. I don't think they will hold up.

[Adrian Clark]

Originally Posted by ekapalka

I don't mean to change the subject, but this information has highlighted a problem for me. I've been designing a gearbox for quite some time, and I've clearly been making a huge mistake with the hole sizes for the bearings I'm using. If an AndyMark flange bearing has an outer diameter is 1 inch, in accordance with this, the hole diameter for the bearing should be 1.0005 in? That seems really close. Could you just verify before I go back and change everything? Thanks

Most teams use interference fits for their bearings. Doing so is an easy way to retain the bearing and accurately locate it. For a good fit, as tim-tim suggested, you want about .5 thou interference. This means you should make your bearing bore .5 thou smaller than the diameter of the bearing.

However, there is no universal rule for bearing fits. What size you make the hole relative to the bearing OD depends on how tightly do want to retain the bearing if you want to retain it all, the size of the bearing, and what method you're using to make the bearing bore. There's a lot of info on this subject here on CD, the thread tim-tim linked to is a good place to start.

-Adrian

[AdamHeard]

Originally Posted by Adrian Clark

However, there is no universal rule for bearing fits. What size you make the hole relative to the bearing OD depends on how tightly do want to retain the bearing if you want to retain it all, the size of the bearing, and what method you're using to make the bearing bore. There's a lot of info on this subject here on CD, the thread tim-tim linked to is a good place to start.

-Adrian

There actually are fit tables that can be used to calculate based on what type of fit you want.

For FRC though the standard is generally .0005-.001 under as you stated.

[ekapalka]

Originally Posted by Adrian Clark

Most teams use interference fits for their bearings. Doing so is an easy way to retain the bearing and accurately locate it. For a good fit, as tim-tim suggested, you want about .5 thou interference. This means you should make your bearing bore .5 thou smaller than the diameter of the bearing.

Oh... smaller diameter. I thought I had misread that. Thank you very much

[AllenGregoryIV]

Originally Posted by AdamHeard

I agree. The pinions on the end could potentially see 8x stall torque under direction change, which is huge. I don't think they will hold up.

Cooper, what if you took the pinions out of the gear train and just had the gears interact with each other. The pinions could mesh under each of the gears. Also you might be able to mount the gears with tube axle and a plate that is supported off the outer frame member (hex side) that would also act as your stand off for that frame member.

That setup would provide support to the outer rail, allow you to remove motors to save weight (if needed) but maintain the power from the remaining motors going to all wheels on the side.

Something like this
https://docs.google.com/file/d/0Bwvy...VCLVdvdlU/edit

That was extremely quick CAD just to show the idea. The MiniCims are 12:54 and the CIMs are 12:48 that should have the 48 and 54 tooth gears all spinning at around 1300rpm unless I did my math wrong, which is very possible.

[Cash4587]

Originally Posted by AllenGregoryIV

Cooper, what if you took the pinions out of the gear train and just had the gears interact with each other. The pinions could mesh under each of the gears. Also you might be able to mount the gears with tube axle and a plate that is supported off the outer frame member (hex side) that would also act as your stand off for that frame member.

That setup would provide support to the outer rail, allow you to remove motors to save weight (if needed) but maintain the power from the remaining motors going to all wheels on the side.

Something like this
https://docs.google.com/file/d/0Bwvy...VCLVdvdlU/edit

That was extremely quick CAD just to show the idea. The MiniCims are 12:54 and the CIMs are 12:48 that should have the 48 and 54 tooth gears all spinning at around 1300rpm unless I did my math wrong, which is very possible.

Wouldn't that mean I would have to spin every other motor in opposite direction? Seems like a good idea but after all this, I don't know if I would be that comfortable spending a lot of money on gears just to leave a little extra room for electronics. Although this type of drive would be better if the motors were within the drive rail, I don't know if it will end up being that way in my final design.

[Cash4587]

I did some more playing around and came up with this. It could be a whole lot simpler to do and if I get the geometry right, It could be run in either this configuration OR in the 4 cim 4 mini cim configuration. It would only be different in where the motors are mounted. It is just a bit more tricky to figure out how to still have easy access to mounting holes with the six cims in this location.

http://prntscr.com/40u5lx

[AllenGregoryIV]

Originally Posted by Cash4587

I did some more playing around and came up with this. It could be a whole lot simpler to do and if I get the geometry right, It could be run in either this configuration OR in the 4 cim 4 mini cim configuration. It would only be different in where the motors are mounted. It is just a bit more tricky to figure out how to still have easy access to mounting holes with the six cims in this location.

http://prntscr.com/40u5lx

How's power transferred to the wheels in that one?

Another version of the wheel well idea using belts in the power transmission. 2 90mm belts to the wheels and a 100mm belt connecting the two 60t gears.

https://docs.google.com/file/d/0Bwvy...RBZzYxZFE/edit

[Cash4587]

Originally Posted by AllenGregoryIV

How's power transferred to the wheels in that one?

Another version of the wheel well idea using belts in the power transmission. 2 90mm belts to the wheels and a 100mm belt connecting the two 60t gears.

https://docs.google.com/file/d/0Bwvy...RBZzYxZFE/edit

There would be belts going to each module. Belts might be do-able. Seems like a lighter design than all the gears.

[asid61]

If you are doing a press fit, the best way is to give the part to the machinist and let them decide. For example, the vex bearings we recieved this year were actually about 1.124" in diameter, which would have ruined the press fit.
Unless you have a really good sheet metal guy, you might get holes that are +- ~0.002", which will ruin a press fit. Plan on reaming or locktiting any bearing holes in sheet metal.

[Cash4587]

Originally Posted by AustinSchuh

Nice! Looks like a solid design, and like you got all the tricky bits right.

I'd put some material back in the front and back of the frame. Those parts take a beating... You can drop some of the material on the top of the frame, and on the rails holding the wheels. The frame itself will be strong enough, and the holes make it easy to inspect your robot for wear. Point impact loads from other robots and field elements should be your biggest loads. You can take the inner frame rails down to 060 as well. Reinforce the bearing holes when you do that.

Consider lightening the belly pan, and adding PEM nuts in for your electronics. Those small touches take a design to the next level.

I'm interested in using PEM nuts now for a specific feature on the chassis. Could you provide more information or an old thread that gives more info on these?