pic: Ira's Senior Project

[IraJason]

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[Jeremiah Johnson]

Looks pretty nice. Very neat and well designed. Is it just going to be a base or are you going to put some sort of attachment?

[Arefin Bari]

Ira, first I must say that you have done a great job with that chassis. There aren't a lot of kids who take there time and build a chassis during summer to get their hands dirty with simple things.

What size sprocket are you using on the wheel? (it's hard to see). Have you done any calculation on this and come up with how fast this little beast will be going? It seems like you are using pvc as spacers. If your team is in need of some sort of thing to use for spacing, I would suggest the shaft collars that can be bought from McMaster. It's not that expensive and it serves you well.

I also see only two speed controllers, does that mean you are using just one cims for each side? Another thing I wanted to talk about is CG. I can't stress this enough. Our team worked on cg very closely this year and we were able to build a robot that you can pick up <50 degrees and let it go and it will still not flip on it's back. We also had a robot that went under and tried to flip it. I know this is just a summer project, but there is a lot more to a chassis other than just wheels, chains, sprocket, transmission. If you are planning on putting more work into this, keep going, I am sure your team will be happy to use what you came up with. On top of that, it's very simple and we all like simple things. Kuddos to you. =)

[IraJason]

Arefin, you would be right in assuming there are only 1 CIM driving each gearbox. I decided that this thing was not really going to be doing much heavy lifting, so I put 1 CIM on each side and left access for a second motor open.

I'm still hoping to put something up front, which would be able to counter the weight that's in the back. This thing is definitely back heavy as it is right now. I'm also leaving it open for my team to use it as a base for testing out future ideas.

The sprockets on the wheels are the same as on the gearbox, which I believe are the 15 tooth sprockets from Andy Mark, so the output shaft to the wheels are at 1:1. I calculated the speed on this, and it came out to about 3.63 ft/s. No where near the speeds that some FRC robots get to, but for my purposes it will probably be plenty fast.

Code should be loaded up today to get it running, and I'll probably post another picture of that process later today.

And lastly, never underestimate the power of extruded aluminum. It may be a bit heavy, but it's so easy to work with. Pretty much all the metal on this robot is 1in. square 80/20. Our team has never had any problems with it, and both of our robots so far have been made out of extrused aluminum, and they have both taken quite a beating.

[Andy Baker]

Originally Posted by IraJason

The sprockets on the wheels are the same as on the gearbox, which I believe are the 15 tooth sprockets from Andy Mark, so the output shaft to the wheels are at 1:1. I calculated the speed on this, and it came out to about 3.63 ft/s. No where near the speeds that some FRC robots get to, but for my purposes it will probably be plenty fast.

....

And lastly, never underestimate the power of extruded aluminum. It may be a bit heavy, but it's so easy to work with.

Ira,

Way to go! This is a great project. Thanks for choosing AndyMark as a supplier for the gearboxes.

You may find that your resulting speed is a bit faster than what you calculated. Here is my speed calculation for your setup:

Working motor rpm: 4200
Gearbox reduction: 12.76:1
Gearbox output rpm: 329
Sprocket ratio: 1:1
Wheel rpm: 329
Wheel diameter: 4 inches
Robot speed: 5.75 ft/sec

Your use of t-slot extrusion is great. I love the way your have your wheel positions take up the slack for chain tension.

This is a cool drivebase to show off around school and other places. You may want to bow a piece of 3/32" or 1/16" thick polycarbonate over the top of the electronics to protect that expensive stuff.

So... what is next? What are you gonna use this thing for? Here are some ideas:

1. Chase Kressly around the school hallways.
2. Put a chair on it (and some simple bumpers) and make it a wheelchair
3. Put an air cannon on it
4. Contact a company and let them be creative with using your design, much like what Art Dutra did with this Mt. Dew "Dewbot".

Good job, Ira.

Andy

[Rich Kressly]

Originally Posted by Andy Baker

So... what is next? What are you gonna use this thing for? Here are some ideas:
1. Chase Kressly around the school hallways.

I see how it is. Maybe we'll train it to cut your hair ... without the bowl

Actually Ira and his senior project partner, Sam, are putting in a fair amount of work on this guy. The really cool thing is that Ira has graciously offered to donate the finished product to team 1712 when finished. Our current plans are to use it for a trainer for new team members and as a smaller demo machine that is easier to transport to places.

[IraJason]

Thank you Andy!

It seems I was using the wrong RPMs, which would gave me the lower speed. Thank you for calculating the correct RPMs and speeds for me! And the AndyMark single speeds used are great. I saw how well they worked on Deuce, our 2007 robot, and figured they were the way to go. I did have to drill a few holes in them though... The gearboxes are mounted to the frame by having the bottom of the gearbox bolted down through the extruded. To prevent the gearboxes from wiggling any, the crossbar across the top was added, which is another peice of extruded bolted to the tops of both gearboxes. The result is a pretty ridged setup, as those gearboxes don't seem to go anywhere.

We're also going to add another lexan sheet above the electronics to protect the expensive stuff, which is tomorrow's project. We were able to get the robot running with the radio today, which I'll probably put a picture of up soon.

Once again, Thanks Andy!

[Sylvia]

Ok, so I'm new to 1712 (as you know, Ira). Next year I'm going to be one of the team members using "Runt" to learn. I have to know next year's robot's drive's expected behaviors before testing (i.e. speed, torque, amp draw, etc.)
Kressly had me review Ira+Andy baker's calculations with me, changing variables and such to force me to learn (which is good, as I know NOTHING)

Here are my primitive calculations. Did I screw up?

The robot speed @ normal load = 4200 RPM
Gearbox Ration is 12.75:1
Gearbox to Wheel Ratio is 1:1
Wheel Diameter is 4 inches.

I was asked to change to a 24-tooth sproket on the output shaft of the gearbox, making the gearbox to wheel ration 2:1, then change the wheel diameter to 6 inches. My calculations were:

4200 RPM / 12.75 = 329.4117647 RPM output
329.4117647 x (2/1 gearbox to wheel ratio) = 658.8235294 = RPM wheels are driven at
658.8235294 RPM / 60 = 10.98039215 RPS (duh)
Circumference = d(pi) = 6(pi) = 19.44
10.98039215 RPS x 19.44” = 213.458823396 in/s
(213.458823396 in/s) / 12 = 17.77 ft/s

[Rich Kressly]

...and as you give feedback, please remember this is purely a theoretical setup. Our biggest interest as a team is in students (with Sylvia as a leader) learning how to calculate correctly so we get to know expected outcomes that can help us make better decisions in the future ...

[Andy Baker]

Originally Posted by Sylvia

My calculations were:

4200 RPM / 12.75 = 329.4117647 RPM output
329.4117647 x (2/1 gearbox to wheel ratio) = 658.8235294 = RPM wheels are driven at
658.8235294 RPM / 60 = 10.98039215 RPS (duh)
Circumference = d(pi) = 6(pi) = 19.44
10.98039215 RPS x 19.44” = 213.458823396 in/s
(213.458823396 in/s) / 12 = 17.77 ft/s

Sylvia,

All of this is correct. Good job on the calculations. Here is some advice:

1. Set yourself up a simple Excel file to do these calculations. Once you get your equations determined, then you can change a few variables (wheel dia., sprocket size, etc.) to get final speed results.

2. You don't need to track any decimal places past the tenths for this application.

3. Your 17.8 ft/sec makes sense, but it's too fast. Ira's setup was giving you about 5.8 ft/sec. If you increase the speed (by 2x) of the wheel by putting a larger sprocket on the gearbox, then you get 11.6 ft/sec. Also, if you increase the wheel size to 6", then that 11.6 is multiplied by 6/4, which results in 17.4 ft/sec.

What is the speed you want to go?

Keep it up,
Andy

[Sylvia]

Ok, I'll look into the advice
Thanks!