We are thinking of using plywood for our shooter sidewalls. We will be mounting 2 motors as well as bearings in the material. Has anyone had a problem doing this? We are thinking 1/4 to 1/2 inch plywood.
We do this all the time for prototypes and it will work. Our current shooter protoype is built from plywood. Be careful to reinforce the bearing holes by using a metal mounting plate. It doesn’t need to be very large, but will take the stress off the wood edges of the bearing hole and prevent them from wearing and loosening around the bearing over time (not usually a problem on prototypes, but very much one on a permanent mechanism.) Go with the heavier 1/2 ply too, since 1/4 ply is a bit too flexible for this kind of thing. I’d also suggest using metal motor mounts too, for much the same reasons as the bearings. Other than those cautions, it should work. Good luck!
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For the motor and bearing mounts would 1/8 aluminum plate be sufficient?
Yeah, that should be enough to do the job. They’re only there to reinforce the wood, so no need for anything too hefty.
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I recommend using the Vex face bearing mount. The come as two in one piece so they also work for a custom gear train. We’ve used them a couple of times with a Versa Planetary mounting on one side and the bearing for the driven shaft on the other side. The spacing is for an 84T count with 20DP gears. You can also cut them apart to use as singles where you don’t need the transmission function. Depending on the thickness of the wood and expected loading you can put them on one or both sides.
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You may run into issues if the location of the bearings do not match properly on the two sides. The bearings have a non-zero width so you can think of each bearing as a pair of contacts on the shaft; one on each side of the bearing. Thus, with two bearings, there are effectively four contact points. A shaft with more than two points of support/contact is over-constrained and may jam or have a lot more friction than expected. A friends team built an assembly like what you are building and when they slipped the shaft through one bearing, they could not get it to line up with the bearing on the other side. If there is only a small amount of misalignment between the two sides, allowing the bearings to not be fully seated on the bearing plate may allow enough movement to allow them to line up.
Self-aligning bearing blocks can tolerate a bit more misalignment. The following are only examples and might not accommodate the shaft size you are using.
https://www.skf.com/us/products/mrc/self-aligning-ball-bearings
Igus plastic pillow boxes maybe?
Anyways…we’ve mounted bearings in plastic and wood pretty often, and not really had problems with holes getting wallered out. I have 7/8 and 1-1/8" Forstner bits that have got a lot of use over the years for just this purpose.
If you think you need a metal plate, it doesn’t need to be very thick, 1/8" would be maximum thickness.
We did exactly this in 2020 for our shooter, nice thing with the face mount plate is if you aren’t driving the motor right on it you can cut it in half to get both sides of your shooter axle with one part.
It never saw an official field unfortunately but the shooter held up fine through practice and off-season demonstrations. We moved the shafts and have been using this as our test setup for launching cargo the past two weeks.
To minimize the over-constraint issue @philso highlighted you want to only put a bearing on one side of each plywood piece. I recommend clamping your two sidewalls together to drill holes through both pieces at once before assembly so the bearing holes line up closely. The standard hex bearings will tolerate a small amount of misalignment over a span - we have just under a foot between sidewalls and you could wiggle the bearing plate around a little before bolting it down without feeling the hex shaft bind as you spin it.
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That’s the general idea but I don’t think the plastic bushings are meant to be used at as high an rpm as one would find with a shooter.
With my friend’s robot, we had to attach the bearing plate to just one side, slide the shaft into the bearing on that side, slide on the bearing plate for the other side, align the shaft then fasten the second bearing plate. Otherwise, the shaft had so much friction it almost jammed.
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The issue can exist with one ball bearing on each side because the bearings have a non-zero width. In my friend’s robot, there were only two bearings in total but their manufacturing process had sufficient inaccuracies and misalignment of all the pieces in the structure that the bearings were significantly misaligned.
If we go with the plywood design (which we likely will due to cost) we will have it cut on the construction classes cnc router. Hopefully that eliminates misalignment
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Robot Droppings from 2016 “Stronghold” Sac Regional
Yes, it’s certainly feasible; remember it’s going to have to hold together for several days of matches.
Wood (especially baltic birch) is a fantastic strong material. There is no reason that there is any more misalignment than any other material, that comes from the manufacturing techniques. We have built entire drive trains out of it with no issues with bearings in it at all.
People are predigest against it because it’s not cool. It actually has some big advantages to it when it comes to easily attaching things with simple methods.
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What he said! If you use quality plywood you should not need any reinforcement plates. High ply count of a quality wood such as birch, maple, or other harder woods produce long lasting parts. You can even use a little wood glue on the bearings which will help keep it in place and will also strengthen the wood around the hole.
This is what we intend to use
Same, I really like the “cardboard → quick & dirty plywood → better plywood → final part” prototyping and design methodology. Works a treat. Especially with a few 3d printed parts in there for clean geometry where you need it.
Learn as much as you can from your quick mock up, prove the concept is either a go ahead or a no go, then move on. You can make a lot of mechanisms. Dissimilar redundancy is very important when you are trying to do things fast.
I haven’t had any experience with popler ply wood, but that is a “soft” wood, birch should be stronger.
Should be fine, poplar is a good wood and that stuff is 7 ply over 1/2". Use a bit of wood glue in your bearing holes and reglue them if you ever see them spinning or vibrating in their holes. As long as they can’t move they cannot enlarge the hole.
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Our local Home Depot has this. It says it is a hardwood…and is cheaper. Would it be better?
lol very carefully worded I see XD