Re: Help - Can't figure out way to connect spool to webbing
 

Aloha,

What we ended up doing was 3d print the spool and guide.
On the spool where the two bolts goes through to assemble the two halves we put in a large enough cut out to accommodate the strapping as well.

You just sew the end of the belt to make a small loop for the bolt to go through when you assemble the spool the belt is on.

It keeps the belt quite flat when spooling since the loop is below the barrel where the strap winds up.

It can feed either direction. The second part is a guide to keep the belt centered while spooling. Though the sides were high enough that it wasn't really necessary.

Here is a picture of the spool on the robot, you can zoom and hopefully see.

http://www.chiefdelphi.com/media/photos/42355

I will post a picture of just the disassembled spool and update this with the link when it is available.

We ran this through two regionals and the champs and never had an issue..

Still working today.

Any questions?

Re: Help - Can't figure out way to connect spool to webbing
 

I would recommend using a full belt or chain so that you are powering both the up and down direction.
Gravity does work... just not that well in some situations. You can get belt that you basically cut to length. Then I recommend having the ends be on the carrier portion of your elevator.

This loop style is also beneficial as you can put the motor down in the belly thus lowering your center of gravity (which is generally a good thing).

Re: Help - Can't figure out way to connect spool to webbing
 

Howzit!!

The picture has gone through and is now posted..

Here is the link

http://www.chiefdelphi.com/media/photos/42415?

You can see the recess for the bolt and looped end of the strap.

The spool is printed to use the 1/2" hex directly out of the transmission.
We basically mated two Vex Pro 2 CIM, 2 speed transmissions together. one used the motors and two speed selection really helped when the load got heavy.
The second transmission was setup to shift between a free wheel spin and a one way ratcheting system. We just used a ratcheting wrench and cut a small hole for the reset of the wrench it to stick out of housing.

If you are interested I can post pictures of the assembled winch system.
Or CAD files if you like.

Also as mentioned it would be a good idea to get that motor and spool down into the chassis. Yes the strap will be longer but it will not affect the amount of strapping you need to winch..

Our system was gravity return and with the weight of the tool we never had an issue with the lift lowering when empty.

Good luck,

Aloha.

Re: Help - Can't figure out way to connect spool to webbing
 

Decided to just wait to comment on this thread until we finished. We chose the first option of tapping the holes and using a soldering iron to burn holes through.

It was a great experience learning how to tap holes and it allowed us to end with a much more robust product.

Here is a video of the lift working.

https://youtu.be/0oAcXcJqIbg

Here are some pictures of the finished spool






We are going to do some finishing touches like adding the ramp (which is why the motor is not lower in the Chassis and possibly adding intake rollers.

Thanks everyone for your suggestions. This is the first bit of success our team has had in years. A lifting robot may not mean much to a lot of you but to us its awesome.

There is going to be a reveal video sometime late this week!

Re: Help - Can't figure out way to connect spool to webbing
 

That's awesome! I am glad you got it working. Do you know what you're using for a tote grabber yet? With that belt design, you might be only limited to one that opens and closes as opposed to "Indiana clips" since it's only powered up.

We have hinged lexan plates. Indiana clips were our first choice but hinged plates allowed us to use just gravity.

Re: Help - Can't figure out way to connect spool to webbing
 

It's great that you're lifting now!

BTW, what is the ratio on that gearbox, and how many game pieces are you looking at lifting at a time? We geared ours down 8.45:1 (KoP equivalent gearbox), then another 32:15 (2.13:1) with chain, and drove that on a 15 tooth #35 sprocket. As I figured at the time, we had a theoretical 40A lift force of about 250 lb and a free lift speed of 2.3 ft/s. That speed seemed like plenty, as we would rarely be lifting more than a foot at a time, and we wanted to have plenty of surplus force so we could get a load of six totes with RC moving with authority. As you appear to have about a 2" sprocket, you'd need a gearbox somewhere around 30:1 to get the same force and speed.

As it turned out, we rarely lifted more than four game pieces at a time, but it was due to our inability to form interlocked stacks, not our lift that limited us.

The longer I'm involved with FRC, the less likely I am to count gravity as an ally beyond providing normal force for wheel traction. Don't just carry game pieces; hold them.

Re: Help - Can't figure out way to connect spool to webbing
 

I would recommend spring-loading it downwards with a constant-force spring, or using pneumatics to actuate your hinges, instead of relying on just gravity. Gravity is sketch when you least want it to be.

It's a 27:1 Banebots p80.

Re: Help - Can't figure out way to connect spool to webbing
 

Congratulations, and thank you for sharing your success. It is a really powerful thing to get a system working.

Did your team use any calculations to get to the gear ratio? If so, what calculations did you use?
If not, are you interested in calculating what expected performance should be?

Re: Help - Can't figure out way to connect spool to webbing
 

We did not do any calculations we just found the motor/gearbox combo on our supply shelf and used it. We knew we needed a high gear ratio but thats about it.

I would be interested in doing calculations though. Less for us and more for the people we are demoing for... But... I don't know where to start.

Re: Help - Can't figure out way to connect spool to webbing
 

It's just a matter of following the torque and speed through the gear ratio and wheel (or in this case spool) circumfrence. From the last page of the motor performance curves, you can see that at a 50A draw, a CIM generates about 130 oz-in of torque. You're gearing down by 27:1, so you get, in the frictionless case, 130 * 27 oz-in of torque. Your spool radius is pretty close to 1" (measure where the webbing contacts the layer inside), so you can get as much as 3510 oz, or 219 lb. In practice, you'll probably get about 80% of that, or 180#, which is enough to pick up a tall stack of totes briskly.

For top speed, use the "free speed" of the CIM, (page 1 of the curves document) which is 5310 rpm. Divide this speed by 27, and multiply by the circumference of the spool (because the speed was given in revolutions, we need a whole wrap). This gives a total (for a 1" radius spool) of 1236 inches per minute. Divide by 12 to get 103 feet per minute, and by 60 to get 1.7 fps. Again, using an 80% frictional factor gives 1.4 fps. Note that this is for an empty load! Your speed will be reduced somewhat when carrying a load. For a given load, you track the lift force back to a torque, and find the speed associated with that torque, and follow back through forward.

Re: Help - Can't figure out way to connect spool to webbing
 

Here is a great resource for calculating the required gear ratio and motor combination.

http://www.chiefdelphi.com/media/papers/2815

Re: Help - Can't figure out way to connect spool to webbing
 

Congratulations on the progress.

This would be an ideal opportunity to learn about adding something to stop the carriage before it hits the top or bottom, and possibly damaging itself. The most obvious would be to use a limit switch at the top and one at the bottom. Other options include distance measuring devices such as an ultrasonic sensor or a Lidar (that is what we used). Each has it's advantages and disadvantages and this is a good time for your team to learn about them.

Once you add the manipulators (arms, claws, hooks, etc.) for picking up the totes, you may find that you will want to relocate your motor so that the spool and strap are centered on the carriage. Otherwise, the carriage may twist as it is lifted, spread the two vertical tubes and become de-railed.

Keep up the good work.