Need advice on motors, gearboxes, and ESCs

[nathannfm]

Hi other Nathan (lol)

You won't need the 12 tooth pinion gear if you are using the VersaPlanetary. You should know that these gearboxes are not actually designed to work with CIMs and MiniCims, some modification is necessary (I am not sure what you have to do but I bet you could find it by searching CD) I am suprised no one mentioned the P80 gearbox. http://banebots.com/c/P80K-S4 (the grease and CIM mounting kit are wirth it for $12 more) I would recomend this over the VersaPlanetary for a CIM to wheel drive robot as these gearboxes are designed for CIM style motors and are much beefier. You are also going to need a battery, here is the standard FRC battery. http://www.andymark.com/product-p/am-0844.htm You are going to need a battery charger, and it would probably be a good idea to put breakers in your circut so you don't fry things.

I you are scaling up to a car I would recommend these wheels http://www.andymark.com/Pneumatic-Wheel-s/309.htm and if you take my sugestion and use the banebots gearbox you will need this hub for that wheel http://www.andymark.com/product-p/am-0077a.htm
If you use the versaplanetary you will need a wheel with a hex hub. The wheel you selected has a bearing in it, this would be used if you were driving the wheel with a sprocket and chain (or belt) and the wheel was spinning on a dead axle and from your simple CAD it doesn't look like you are doing that.

[Paul Copioli]

Originally Posted by nathannfm

Hi other Nathan (lol)

You won't need the 12 tooth pinion gear if you are using the VersaPlanetary. You should know that these gearboxes are not actually designed to work with CIMs and MiniCims, some modification is necessary (I am not sure what you have to do but I bet you could find it by searching CD) I am suprised no one mentioned the P80 gearbox. http://banebots.com/c/P80K-S4 (the grease and CIM mounting kit are wirth it for $12 more) I would recomend this over the VersaPlanetary for a CIM to wheel drive robot as these gearboxes are designed for CIM style motors and are much beefier.

Emphasis mine.

I will not editorialize, but the stated manufacturer's maximum torque spec for the P-80 is 85 Ft-lbs. The stated manufacturer's maximum torque spec for the VP using a 10:1 is 74 Ft-lbs. If you use qty 2 3:1 stages on the VersaPlanetary (like the P-80 9:1), then the torque rating jumps to 116 Ft-lbs so I don't know where you can claim the P-80 is "much beefier".

[magnets]

I too agree that the versa planetary is a better gearbox. I doubt you'll see an issue with your situation with either gearbox, but the P80 isn't great for high torque applications. I've broken those stupid things more times than I can count on our 07 arm.

[Nathan]

Originally Posted by nathannfm

You should know that these gearboxes are not actually designed to work with CIMs and MiniCims, some modification is necessary (I am not sure what you have to do but I bet you could find it by searching CD)

Thanks for pointing this out (as well as for your other advice)! I didn't realize that.. Looking at the VersaPlanetary product page, it looks like the BAG motors work with it without modification, but the downside is that it appears that the BAG motors are only about 1/4 as powerful as the MiniCims..

I found this blog post:

http://blog.spectrum3847.org/2013/01...-mounting.html

The good news is, it looks pretty easy to do the modification (just cutting the shaft).

[nathannfm]

Originally Posted by Paul Copioli

Emphasis mine.

I will not editorialize, but the stated manufacturer's maximum torque spec for the P-80 is 85 Ft-lbs. The stated manufacturer's maximum torque spec for the VP using a 10:1 is 74 Ft-lbs. If you use qty 2 3:1 stages on the VersaPlanetary (like the P-80 9:1), then the torque rating jumps to 116 Ft-lbs so I don't know where you can claim the P-80 is "much beefier".

Wow, I didn't realize this, I didn't see the torque spec stated on the product page for the VP, I was just basing that on size. Sorry.
I mainly recommended them because they are specifically designed for CIM use, are there any plans to officially support the VP on CIMs in the future, it sure seems like people would want that.

Originally Posted by magnets

I've broken those stupid things more times than I can count on our 07 arm.

We broke one on our 2011 arm and it nearly cost us a regional win (but we are pretty sure that was user error) I guess I should start recommending the VPs

[cfair]

I want to put in my 2 cents for the versaplanetary. See the attached spiral shaft (where the anodizing has flaked off). It wasn't meant to be a spiral, but a 100:1 versaplanetary followed by a 7:1 vexpro single stage managed to twist a 1/2" aluminum hex shaft into a twizzler shape. The planetary was undamaged. The motor is an RS-885, and that bronze bushing on the end on the versaplanetary output shaft is very important! We have used many banebots planetaries in the past, and I am pretty sure they wouldn't have all their teeth after this experience. Kudos to Vexpro and IFI!

[Nathan]

Thank you all again so much for your advice. We've decided to go with the CIM motors (full size) and VersaPlanetary gearboxes.

With a 5:1 gearbox and 6" wheels, that gives us 1717 oz-in (107.3125 in-lbs) of torque with a speed of 6MPH.

Do you think that's enough torque to move a ~60lb robot?

I attached a spreadsheet with our list of parts and speed/torque calculations. Any final advice you could give us would be great!

Thanks!

[protoserge]

Originally Posted by Nathan

Thank you all again so much for your advice. We've decided to go with the CIM motors (full size) and VersaPlanetary gearboxes.

With a 5:1 gearbox and 6" wheels, that gives us 1717 oz-in (107.3125 in-lbs) of torque with a speed of 6MPH.

Do you think that's enough torque to move a ~60lb robot?

I attached a spreadsheet with our list of parts and speed/torque calculations. Any final advice you could give us would be great!

Thanks!

If I'm correct, your calculations are based on the motor free speed (CIM is ~5100 rpm). Once loaded, this speed will be reduced. You should expect about 4100-4300 rpm at peak efficiency loaded. The JVN calculator uses an 81% "speed loss constant". You may want to reference this for your calculations.

Overall, not a bad start

By the way, I'd encourage you to check out the Mars Society's University Rover Challenge next year.

[JamesCH95]

I'm sure that I'm a little late to this party... but having a bit of experience with this sort of project I figured I'd throw my $0.02 in.

Have you considered retro-fitting a large-scale RC to suit your needs? It will give you experience with retro-fitting and reverse-engineering (very important if you're going to try this on a real vehicle) and has automotive style suspension and drivetrain, ackerman steering, and boat-loads of part and aftermarket support. You'll be focused on a quick retro-fit and modification and then your autonomous/control code, rather than building something from whole cloth.

After much design and deliberation that's the path I chose for my project.

You might consider something like this, ideally one that's sold without an engine.

http://www.hobbytron.com/RedcatRacin...andrail.htm l

[Answer42]

Originally Posted by cfair

I want to put in my 2 cents for the versaplanetary. See the attached spiral shaft (where the anodizing has flaked off). It wasn't meant to be a spiral, but a 100:1 versaplanetary followed by a 7:1 vexpro single stage managed to twist a 1/2" aluminum hex shaft into a twizzler shape. The planetary was undamaged. The motor is an RS-885, and that bronze bushing on the end on the versaplanetary output shaft is very important! We have used many banebots planetaries in the past, and I am pretty sure they wouldn't have all their teeth after this experience. Kudos to Vexpro and IFI!

Rs-885? I've never heard of this motor. Where was it from and what were you using it for? If you don't mind me asking.

[protoserge]

Originally Posted by Answer42

Rs-885? I've never heard of this motor. Where was it from and what were you using it for? If you don't mind me asking.

It is quite possibly a typo referring to RS-775 (it certainly looks like an RS-775). That would be my guess. Here's the full list of Mabuchi motors.

[Nathan]

Originally Posted by stinglikeabee

If I'm correct, your calculations are based on the motor free speed (CIM is ~5100 rpm). Once loaded, this speed will be reduced. You should expect about 4100-4300 rpm at peak efficiency loaded. The JVN calculator uses an 81% "speed loss constant". You may want to reference this for your calculations.

Overall, not a bad start

That's a very good point, I hadn't considered that the motor speed spec was without any load.

Using 4100RPM instead of 5100RPM as the motor speed gives us a speed of 4.6MPH, which is probably the slowest we'd want it to go. So we'll definitely be going with the 5:1 gearbox ratio (any higher than that would make it too slow..).

I'm not really sure how to calculate how much torque the robot will need to move, so I guess we'll just assume 107 in-lbs is enough and hope for the best

Originally Posted by JamesCH95

Have you considered retro-fitting a large-scale RC to suit your needs?

We already started making the chassis, but that wouldn't have been a bad idea :-)

Thanks again for your help, everyone. We'll probably order the parts this weekend or early next week. I'll post a few pics once we get the robot built!