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Unread 20-12-2014, 20:10
JorgeReyes JorgeReyes is offline
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pic: Low Profile Gearbox Front View

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Unread 20-12-2014, 20:14
Andrew Lawrence
 
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Re: pic: Low Profile Gearbox Front View

How is this mounted to tubing? It looks like it's only using the bearing block bolts to hold the gearbox on.

Also, slight tidbit - the ability to use multiple pinion sizes is a design and feature of WCP gearboxes, not the VEX ones. The DS and SS are made by WCP. VEX and WCP are resellers of each other's products. Just clearing that up so that credit is given where credit is due.
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Unread 20-12-2014, 20:40
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Re: pic: Low Profile Gearbox Front View

What is the weight?
How thick are the side plates?
Are you using a custom or COTS shifting shaft? If so, which one?
How is this mounted?
Are the cims acting as nuts for the standoffs? If so, consider changing that to just nuts or pemnuts.
How are the shafts constrained? Are they hex turned to round?

That's all for now. I can't tell much from this view, but it looks pretty good.
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Unread 21-12-2014, 01:15
JorgeReyes JorgeReyes is offline
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Re: pic: Low Profile Gearbox Front View

Quote:
Originally Posted by asid61 View Post
What is the weight?
How thick are the side plates?
Are you using a custom or COTS shifting shaft? If so, which one?
How is this mounted?
Are the cims acting as nuts for the standoffs? If so, consider changing that to just nuts or pemnuts.
How are the shafts constrained? Are they hex turned to round?

That's all for now. I can't tell much from this view, but it looks pretty good.
As is the gearbox weighs about 11.2 pounds according to Solidworks. I made the side plates 1/4" thick. The Shifting output shaft I am using is the one COTS shifting shaft and is the same one the is used on the DS.

It is this one:
http://www.vexrobotics.com/217-3635.html

The shafts are 3/8" hex shaft turned to 3/8" round but I might possibly use 1/2" hex and turn that to 3/8" because there isn't much material to constrain the shaft against the bearing with the 3/8" hex shaft.

I am in fact using the cims as nuts but I am curious to know why there is a problem with this. Would it be a structural issue?
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Unread 21-12-2014, 01:29
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Re: pic: Low Profile Gearbox Front View

Quote:
Originally Posted by JorgeReyes View Post
I am in fact using the cims as nuts but I am curious to know why there is a problem with this. Would it be a structural issue?
Not so much a structural issue as a maintenance one. It's a pain to have to remove the motors to disassemble the gearbox or to disassemble the gearbox to remove a motor.
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Unread 21-12-2014, 01:57
JorgeReyes JorgeReyes is offline
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Re: pic: Low Profile Gearbox Front View

What do you guys think of the gear ratios? Are they appropriate gear ratios for a 3 cim gearbox?

And also, Sanddrag, I hadn't noticed that the pulleys would hit the standoffs but I just raised the location of the standoffs to give enough clearance for the pulleys. Thanks for noticing that!
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Unread 21-12-2014, 02:17
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Re: pic: Low Profile Gearbox Front View

Quote:
Originally Posted by JorgeReyes View Post
And also, Sanddrag, I hadn't noticed that the pulleys would hit the standoffs but I just raised the location of the standoffs to give enough clearance for the pulleys. Thanks for noticing that!
Yeah, we totally missed it through multiple design reviews on one of our gearboxes one year. Didn't catch it until assembly. We vowed to never repeat that oversight.
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Unread 21-12-2014, 02:34
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Re: pic: Low Profile Gearbox Front View

Quote:
Originally Posted by JorgeReyes View Post
As is the gearbox weighs about 11.2 pounds according to Solidworks. I made the side plates 1/4" thick. The Shifting output shaft I am using is the one COTS shifting shaft and is the same one the is used on the DS.

It is this one:
http://www.vexrobotics.com/217-3635.html

The shafts are 3/8" hex shaft turned to 3/8" round but I might possibly use 1/2" hex and turn that to 3/8" because there isn't much material to constrain the shaft against the bearing with the 3/8" hex shaft.

I am in fact using the cims as nuts but I am curious to know why there is a problem with this. Would it be a structural issue?
That's a nice shaft.
3/8" hex turned to 3/8" will work fine. Look at the new Thunderhex usage examples to see how small a shoulder you can use. Bearings are very high precision, and you will have about a 1/32" shoulder on six points to constrain it.
As stated above, it's a maintenance issue. If you lose a CIM somehow, then having to take off the gearbox and reassemble it is a no-no.
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Unread 21-12-2014, 08:19
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Re: pic: Low Profile Gearbox Front View

Quote:
Originally Posted by asid61 View Post
If you lose a CIM somehow, then having to take off the gearbox and reassemble it is a no-no.
Under what conditions would one "lose a CIM"? In 10 seasons I have yet to experience a bad CIM or see one in person.
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Unread 21-12-2014, 09:33
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Re: pic: Low Profile Gearbox Front View

It's actually really difficult to just pull a CIM out of a gearbox without taking it apart. If you're using a 12 or 11 tooth pinion, the retaining ring on the CIM catches on the gear that the CIM pinion mates to. If you're using a 14 tooth gear, the pinion won't fit through the .755" hole for the CIM boss.

Also, if you did want to remove the CIM without disassembling the gearbox, I'd be willing to bet that the gearbox wouldn't just fall apart if one (or even all three) of the upper standoffs were removed.

If you wanted to disassemble a gearbox without removing a CIM, you'll have to remove one of the mounting bolts from each CIM. From experience, the CIMs don't fall out of the gearbox when this happens. They can't go anywhere because the one remaining bolt hold the CIM boss in a tightly fitting hole.

It looks like a solid design, and the gear ratios sound good too.
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Unread 21-12-2014, 10:36
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Re: pic: Low Profile Gearbox Front View

Quote:
Originally Posted by Jared View Post
It's actually really difficult to just pull a CIM out of a gearbox without taking it apart. If you're using a 12 or 11 tooth pinion, the retaining ring on the CIM catches on the gear that the CIM pinion mates to. If you're using a 14 tooth gear, the pinion won't fit through the .755" hole for the CIM boss.
Are you using an odd size of retaining ring? I've never had this problem before with the ring catching on other gears, but maybe I've just been lucky.

Quote:
Also, if you did want to remove the CIM without disassembling the gearbox, I'd be willing to bet that the gearbox wouldn't just fall apart if one (or even all three) of the upper standoffs were removed.
Take one motor off at a time and add nuts where the motors used to be. Not that hard to do really, it just requires a little thought beforehand.
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Unread 21-12-2014, 12:33
Lil' Lavery Lil' Lavery is offline
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Re: pic: Low Profile Gearbox Front View

Quote:
Originally Posted by Chris is me View Post
Are you using an odd size of retaining ring? I've never had this problem before with the ring catching on other gears, but maybe I've just been lucky.
It always happens to us. We can usually get it far enough out to wiggle it around the other gear, though.
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Unread 21-12-2014, 17:03
JorgeReyes JorgeReyes is offline
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Re: pic: Low Profile Gearbox Front View

Quote:
Originally Posted by Lil' Lavery View Post
It always happens to us. We can usually get it far enough out to wiggle it around the other gear, though.
Even though it is a lot harder to switch out cims, I'm still think I'm going to keep the cims where they are because chances are we won't burn a motor. As far as the cim pinions go, its doesn't require the gearbox take apart because I could just take it out and change it.

One thing that does concern me though is the ease of changing belts if they snap.
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Unread 21-12-2014, 19:03
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Re: pic: Low Profile Gearbox Front View

Quote:
Originally Posted by JorgeReyes View Post
Even though it is a lot harder to switch out cims, I'm still think I'm going to keep the cims where they are because chances are we won't burn a motor.
You have essentially guaranteed that you will now lose all of your cims during elims due to Murphy's Law.
But seriously, is it that hard to just add one more non-cim standoff? Two standoffs can hold your box together when swapping cims. In that situation, having through bolts to your cims is wise because it becomes easy to remove and add cims.

Last edited by asid61 : 22-12-2014 at 00:38.
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Unread 22-12-2014, 17:46
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Re: pic: Low Profile Gearbox Front View

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Originally Posted by Lil' Lavery View Post
It always happens to us. We can usually get it far enough out to wiggle it around the other gear, though.
Same here. It always catches, but I've never not been able to remove a CIM because of it.
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