Mounting a Toughbox

[iyermihir]

I would like to use a Toughbox on a frame made out of 2x1 box tubing to direct drive one of the wheels, but I am not sure how to attach it to the frame. I have modified the plates on the Toughbox so that I can put the bottom two bolts that hold the Toughbox together through the tubing. Are two bolts enough or do I need more?

-Mihir

[Adam.garcia]

Two bolts should be plenty. I say this from both past experience with our robots as well as my limited engineering intuition.

Past Experience
--Every year, from 2009 to 2011, we direct drove wheels through a supershifter by mounting the plate with two 1/4-20 bolts. We had no problems at all with this.

Limited Engineering Intuition
--1/4-20 bolts, for the most part, are overkill when it comes to loads experienced in FRC. I know that other teams, such as 973, have standardized their bolts at a 10-32 (or -24, I forget) for that very reason. So, if you are having any worries, use a 1/4-20 and be secure in your decision for doing so, as it is a safe choice. If you want to see some further detailed engineering information, check out the link below:
Here

[iyermihir]

Thanks for the adivce.
Do you have any pictures of your setup?

-Mihir

[Tom Line]

Two bolts should be fine, but only if the outer end of the drive shaft is supported, especially since with direct drive you'll have a good chunk of the robot weight sitting on that wheel.

[daniel_dsouza]

Yes, two bolts is plenty to secure a toughbox to a frame.

If you have some unused Kitbot lying around, then some of the hex tube between the toughboxes would not be a bad idea. Our team mounted our toughboxes from last year with some aluminum angle, and the extra bracing provided by the hex tube really helped.

[AdamHeard]

Its not the strength of the bolts in question here, but rather the overall geometry of the joint.

2 Could be plenty strong, or a total failure. If you post a picture we could give you better help.

[DampRobot]

I would make the decision based on what was actually taking the load. If you were using thick wall tubing (1/8" or so) and supported the output shaft with bearings pressed in the tubing, go for it. On the other hand, if the two screws were going into thin walled (1/16th or less) tubing, and were the only thing supporting the gearbox (and the weight of the robot), I'd be a bit more cautious.

We did something similar in 2010, except we didn't direct drive the wheels. In addition to two bolts going through the Toughbox to tubing on either side, we used this to help support the gearbox.

Keep in mind, like AdamHeard said, if you give us more information, we can give you better advice.

[iyermihir]

I attached a side view and a front view.
The tube is 2"x1"x.125"
Thanks for all of the help.

-Mihir

[roystur44]

Better safe than sorry on thin wall tube. I would recommend welding on a .125" mounting plate and using 4 screws for mounting. If you used only 2 screws and one became loose you will run into problems. Sometimes a little overkill is a good thing.

[pfreivald]

I'm a big fan of overkill especially when it comes to drive train. If you can't drive, you can't play!

[waitwhat?]

Originally Posted by pfreivald

I'm a big fan of overkill especially when it comes to drive train. If you can't drive, you can't play!

I agree with this whole heartedly, the drive train keeps you in the game.

That being said, a good moto is "When in doubt, make it stout" meaning if a joint or mechanism looks questionable, beef it up until you feel comfortable with it.

You might want to capture the end of the drive shaft in a bearing, will help keep your transmission and drive shaft lined up as well as distribute some of the robot weight a bit.

[MichaelBick]

Originally Posted by waitwhat?

I agree with this whole heartedly, the drive train keeps you in the game.

That being said, a good moto is "When in doubt, make it stout" meaning if a joint or mechanism looks questionable, beef it up until you feel comfortable with it.

You might want to capture the end of the drive shaft in a bearing, will help keep your transmission and drive shaft lined up as well as distribute some of the robot weight a bit.

True, but I don't think it is needed. All the teams that do WCD have been cantilevering their drive shafts and have been fine for years(remember, their gearboxes are also sticking out more due to the space needed for the shifter and the sprockets). However, if you already are running the tubing on the other side you should but a bearing just because you can. I would consider though if you really need that outer tubing, as it can be a lot of weight that is not really needed. The joint can also be made stronger if you move the bolts higher in the tube.