neep help

Technical Technical Discussion
1

Greeting,

We are a new team this year and are in need of some help. The team has decided to focus on building a “goal post” apperatis that will hinge down off the front of the robot to help guide the ball while pushing and passing. We do not know how to motorize the “goal post” so we can raise and lower it. We have several motors left over but do not know what to do. One thought was to attach a spring to the front of the upright post attached to the frame and the other end of the spring to the hinged part of the goal post putting the spring in tension therefore pulling it down over the edge of the frame and then having a winch attached to the other side of the goal post to pull it back up. However, after reading the rules this morning that would be illegal as the non-electrical device, the spring, would be storing energy while at rest. We could always switch the spring and have it pull the “goal post” back up and the winch pull the “goal post” down but then we do not know how to make a winch out of a motor. We can not find a pulley kit at andymark to turn one of our motors into a winch. Your help in any way is much appreciated. Feeling stressed! :ahh:

2

Your explanation is a bit unclear, and pictures would help a lot but from what I gather you could use pneumatic pistons to achieve a similar effect. Here is a random video that shows pistons pushing our and retracting an arm thing. Winches/springs are much more complex than pneumatics, thus should only be used in situations where pistons would be inefficient or wouldn’t work well.

3

I suggest reading R34 again. Particularly R34-C. Pay careful attention to the part in parenthesis. (I could swear I saw a Q&A on this, [strike]but now I can’t find it. If someone does, it’d be great if they could link it.[/strike] Actually, I found it. Q74, which directs everybody asking to R34-C.)

We could always switch the spring and have it pull the “goal post” back up and the winch pull the “goal post” down but then we do not know how to make a winch out of a motor.
I can think of at least one other configuration, with the motor’s winch pulling in both directions, eliminating the spring entirely (but, as I noted above, R34 doesn’t ban storage of energy at the start of the match). I’ll get to the winch part next.

We can not find a pulley kit at andymark to turn one of our motors into a winch.
We do apologize that you guys have to do some engineering. I’m pretty sure VexPro doesn’t carry pulley kits either.

That said, AndyMark does carry hubs, lots of hubs. I suspect attaching a round piece of material to one of those, with a hole drilled for whatever cable you’re using to pull with, will do quite nicely. Out of curiosity, what motor are you thinking of using? I might have a couple of suggestions on that too.

One note on the pneumatic suggestion: If you aren’t already using pneumatics, I’d hold off on that until you’re sure you’ve got enough weight to spare for a full system/you know somewhat how to use them.

4

Thanks for the responses. Unfortunately, I am at home right now so I can not take pictures of the robot. I will try and do so tomorrow and post what we come up with. I thought of using either the 2.5 CIM motor and we also have a mini CIM motor.

I reread rule 34 and can see a little gray area there where we could use the spring. I’m curious how we could make the winch lift and lower the goal post.

I’m thinking of making a pulley myself out of wood, say a 2-1/2 circle made out of oak and then two 3" circles out of thin plywood and gluing them together. I could bevel a hole on the outside edge of the inner circle before gluing everything together. I would then file a slot on the inside bore for the 2mm key and make the inside bore a press fit onto the output shaft of the motor.

The reason why fabrication is difficult is that this is our first year with no experience and very, very limited tools and materials.

The pneumatic system sounds interesting but I have no experience with it. A winch makes sense to me even if its more work. However, I am going to look into the pneumatics, thanks.

5

You don’t want to do that. Typical recommendation is that 4 of the 2.5 CIMs go to drivetrain; the MiniCIM could work but will almost certainly be too fast without gearing. I’d suggest a window motor instead, or maybe better, AM2235 (snow blower motor), which can be paired with AM2279 (a hub) to attach with your custom drum.

I reread rule 34 and can see a little gray area there where we could use the spring.
That’s not a gray area. It’s black and white: You can store energy at the start of the match by “deformation of robot parts”, AKA springs.
I’m curious how we could make the winch lift and lower the goal post.
You’ll need a couple of extra pulleys for the cable routing, but it’s actually not that hard. Tie the ends of the cable to opposite sides of the goal post apparatus so that one pulls down and one pulls up. The winch goes somewhere in the middle, with a few wraps around the drum.

I’m thinking of making a pulley myself out of wood, say a 2-1/2 circle made out of oak and then two 3" circles out of thin plywood and gluing them together. I could bevel a hole on the outside edge of the inner circle before gluing everything together. I would then file a slot on the inside bore for the 2mm key and make the inside bore a press fit onto the output shaft of the motor.

The reason why fabrication is difficult is that this is our first year with no experience and very, very limited tools and materials.

That sounds like it could work. Again, though, I’d suggest taking a look at the AndyMark hubs, as noted above. Make sure you’ve got enough thickness for your cable, whatever it happens to be, to lay down nicely.

As a suggestion… It might be to your advantage to glue a couple of pieces together first, and use a holesaw to do the circles.

6

Thanks for the tips. I wrote the motor number and the hub number down.

As far as making the pulleys, I would use 3/4 stock for the inner hub but doubling that up makes sense too.

I’m not following you on the extra pulley system. I googled pulley systems and still am not sure. Could you try and describe it again. Thanks and thanks for ALL the help. Can’t wait to get back to working on the robot tomorrow.

7

Essentially, you’d go to the local hardware store and get a couple of pulleys from the hardware section. They don’t have to be very big, just big enough for your cable/rope/string–all you’re using them for is redirecting the cable. Sometimes the line coming off of the winch drum can’t go straight to where it needs to be, so something like this is used to redirect the cable so it goes to where it needs to be, at the angle it needs to be at. I’d get two and place one higher up on the upright section and one down near the bumper zone (below it, if there’s a gap in the bumpers).

One thing to note if you go this route: You’ll want 3-4 wraps of cable/string/rope on the winch, or some other method to keep the winch from slipping too much.

8

Still trying to wrap my head around the pulley system. Would I need to mount the motor/winch above the “goal post” when standing up or could it be mounted down low, say within the chasis?

What gearbox do you recommend I go with if I use the mini CIM motor since we have it?

9

Either one. The reason for the pulleys is a simple redirection.

In the attached picture, the black circles are pulleys. The green one is the winch pulley, which can be moved anywhere. The red is the cable, running over the pulleys (and around the winch several times) and tying to the goalie post at both ends.

What gearbox do you recommend I go with if I use the mini CIM motor since we have it?

First of all, what OTHER motors do you have on hand?

For a MiniCIM, stock, you’ll be running at pretty close to free speed, which is rated at 6200 RPM, let’s call it 6000 RPM to account for the loading of the cable and to make some math easier–this translates to 100 revs/second. For reference, the proposed winch will feed out 7.8 inches of cable/revolution. 780 inches of cable being fed out/second is quite a lot, to say the least.

Let’s assume that you only need to feed 20 inches out to deploy the goalie post, and that you want to deploy/retract in 1 second. For this, I’ll also assume a 2.5" winch diameter, resulting in 7.8 inches of cable fed in or out in 1 revolution. That’s roughly 3 revolutions of the drum, in 1 second. 3 revs/second = 180 rpm. For a MiniCIM, that’s 6000 rpm/180 rpm or a roughly 33:1 reduction. Not too bad (I expected worse) but we gotta use a CIM-based solution due to mounting constraints, and it’s gonna be a multi-stage reduction due to gearbox design rules of thumb (no more than a 10:1 on any given stage).

VEXpro doesn’t really have anything that’ll work, unless a VersaPlanetary could be adapted to a CIM input. AndyMark has their GEM planetaries (3-stage is the only one that will work for this), AndyMark Planetaries (again, the 3-stage is the only one that will work), OR 3 Stackerboxes (1 double, 1 single) with appropriate modifications to take the CIM and stack them all. One more supplier: BaneBots. They have a P80 that you can use a PDV on that should work.

With respect to which of the above gearboxes I’d recommend, I’d probably go with the Stackerbox (which will take more work to put together), but for space reasons I’d go with a GEM 3-stage. BaneBots has gotten better, but some folks still remember past failures (and while they’re cheaper, you still need to get a mount kit).

Now here’s the thing. There are a lot of other motors allowed and/or in the kit. Some of them are lighter, some of them are slower (hint: less reduction needed), some have anti-backdrive capability. Some may be just about free (if you’ve got 15 FIRST Choice credits, the Van Door motor is a good one). Or, if your BAG motor is still available, you could throw a VersaPlanetary on there. You could also change the

Crude winch.png
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Crude winch.png
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10

Thank You very, very much. You have been a wealth of knowledge. I will study your drawing and figure out the pulley system.

The other motors we have from the kit are: (2) CCL 9015 motor, and is a “RS-500 series” DC motor, (1) bag motor and (1) gearmotor consisting of a 3-stage planetary gearbox and a RS775 series motor. Will one of these work better?

11

I’ll go through a few options. Note that all of those motors should have more than enough power; it’s a matter of getting them down to the right-ish speed.

RS775: 19500 RPM, so it’s REALLY, REALLY fast. A 3-stage BaneBots gearbox indicates a 64:1, most likely, so you’d need to slow it down some more.

BAG motor: 14K RPM rated, so it’s WAY too fast. 77:1 reduction would be called for; VersaPlanetary can do a 70:1 or 81:1, so that would probably work, maybe tweak the drum size to get a better speed.

AndyMark 9015: 16K free speed. Needs about an 88:1 reduction; using the PG71 gearbox would make for 71:1, so getting close.

If you happened to have some FIRST Choice credits left, there are some window motors and a couple other motors available that are lower speed with sufficient power.

12

The Banebots RS775-18 has a free speed of 13000 rpm when run at 12v. Also, I believe Patriot Force is referring to the PG71 motor in this instance.

13

If the PG71 is being referred to, then that’s already covered by the AM 9015 motor–I used the non-gearbox specs, then added the gearbox.

13K RPM isn’t too bad (I forgot about the reduced 12V speed). That would be another one for either a BaneBots 64:1 or a VersaPlanetary.

14

We have successfully used the AndyMark PG series gearmotors to run winches. PG 71 is in the KOP, but is probably too slow for your application.
The other two turn fast enough to possibly be of use to you.