Re: Need advice on motors, gearboxes, and ESCs
 

I doubt speed was the root cause of the BAG motor failure. Improper side-loading on the bearing due to a shaft-mounted shooter wheel or an overtensioned belt was likely a root cause if the bearing itself failed.

Re: Need advice on motors, gearboxes, and ESCs
 

I believe bag motors had an electrical problem, not a bearing problem. 550s for one run much faster than them so I would think that the Bag bearings would be fine.

We have found that fan cooled motors tend to heat up regardless of what you do. Both our shooter 550s(100% at 10 seconds at a time) and our drive 550s(constant starting and stopping) all got really hot. I personally wouldn't reccomend fan cooled motors for a drive application unless you are thinking of using another fan to cool them.

I think that a bigger problem is your Bag motors is your application. You have many CIMs working together to speed up your robot. On the other hand your shooter ratios may not be ideal so you may be working your Bags extra hard.

Re: Need advice on motors, gearboxes, and ESCs
 

Thanks for your replies, everyone, we really appreciate your help!

Here's a little more information to clarify a few things:

• We're wanting to use normal wheels (not a holonomic drive) and steering like on a car
• We had a mechanical engineer give a presentation to our club and he also recommended Ackermann steering, so we'll be trying to implement it somehow with a servo
• We'll be using a cRIO for the control system
• We estimated that the weight should be around 30lbs, but to be safe we should probably plan for twice that, or 60lbs
• If we end up using FIRST motors, then we'll probably get one of the standard batteries that FIRST robots use (12V motorcycle battery?), as long as that doesn't put us way over our weight limit

Wow, that looks like it might be really helpful. Thank you!

Thanks for your help! Here's some more information:

• The weight we're shooting for is 30lbs (not sure how realistic this is..), so let's plan for up to 60lbs
• The maximum speed needs to be at least 4 mph, but we'd like it to go up to 6 mph
• I'm not sure on acceleration, but it's not a huge issue since speed isn't our primary concern
• We need it to be battery operated. What type of battery we use mainly depends on how much power the motors draw, so we don't know what battery we'll be using yet
• We'd like an operating time of at least 20 minutes of running non-stop, which would hopefully translate to at least 40 minutes of on and off use. Obviously a longer running time is preferred, though!
• We'll be using a cRIO as the control system and will have a couple of low power sensors and some kind of camera (possibly an Xbox Kinect)
• We need at least 2" of ground clearance, so we were planning on using 6" wheels

So far we've had these motors recommended:

• Banebot (possibly with a 4:1 or a 16:1 ratio)
• BAG motors with the versaPlanetary gearbox of 10:1 (but they might be bad, according to a few)
• miniCIM in a versa-planetary

Where do you all buy your parts from? Is there any particular place you recommend?

Re: Need advice on motors, gearboxes, and ESCs
 

You can get all these parts from vexpro.

Based on the 60lb max requirement, this puts you well into MiniCim territory. MiniCims on a 10:1 versaplanetary is perfect for your application.

Re: Need advice on motors, gearboxes, and ESCs
 

*Standard disclaimer* The following is meant to be a guide, and by no means is an exhaustive list of what needs to be done.

I understand your objective weight is 30 lbs, but that's really hard to achieve; 60 lbs is more reasonable. I would suggest using this number, assuming no mechanisms or devices are mounted to your vehicle. 30lbs will likely be your drive chassis, wheels, and transmissions.

Those are good numbers on speed. You can take these (6 and 4 mph) to determine the velocity against the ground required at each wheel. This speed will be used to get a gear ratio with the motor.

The reason for acceleration is to find horsepower (think in terms of Work). For now, you may want to make an assumption - maybe 6 mph can be reached in 6 seconds (just make something up). The horsepower rating is required to size the motor needed to accelerate your vehicle in a given time. In conjunction with the scrub force on the wheels and your wheel size (width and diameter), calculate the torque required for each mode of operation (forward, reverse, turning). This will allow you to size the motor get torque.

From here, build a "mission profile", where you lay out how the vehicle is intended to be used: turn on with a systems check, 10 seconds idle, 15 seconds full power acceleration, 85% cruise for 10 minutes, deceleration to 0 mph in 10 seconds, accelerate to 3 mph for 4 seconds at 100% power, drive an 8% grade hill while maintaining 4.5 mph, accelerate to 6 mph at 85% power, etc. This is a simple bookkeeping method that will allow you to size your battery. Using the required current draw from this profile, you can verify or select a battery that will provide the proper current for the time you need. For this vehicle, you may be able to use the standard 18 Amp-Hour 12V battery used by FRC, but it has to be proven first.

Some prototyping of the drivetrain and measurement of each motor's current draw in a loaded system will help validate your initial assumptions or prove them to be incorrect. From here, you can size your battery appropriately.

Is there a reason for the cRIO? Speed of development (LabVIEW), sponsorship? Ruggedness? If weight is a concern, I would suggest driving this system using an Arduino and coding through LabVIEW or the Arduino IDE to save at least a pound and a half. Additionally, the MyRIO should be entering the market soon (if not already). It is the platform that the 2015 FRC RoboRIO was leveraged off of (as well as the NI cRIO 9068). Either of these should handle the Kinect output in real-time, assuming there is a LabVIEW driver built.

Re: Need advice on motors, gearboxes, and ESCs
 

Thanks, we will check those out!

Thanks for all of your advice, we will get working on that!

My mistake, we actually are planning on using the MyRIO.. The reason is due to sponsorship and also because we thought it would be a good opportunity for students to learn how to use LabVIEW.

Re: Need advice on motors, gearboxes, and ESCs
 

We took a dead motor apart and found that the bearing was shattered :(

Re: Need advice on motors, gearboxes, and ESCs
 

For the batteries, here is a good alternative to the standard ones!
http://www.andymark.com/product-p/am-0844.htm

Also, Yes, I agree with stinglikeabee that 30 pounds is unreasonable. MiniCIMs weigh 2.16 pounds, themselves, meaning that using two of these is 4.32 pounds! Then, you have the weight of your transmission and wheels. After that, you have your chassey. Then comes your Control system, which typically isn't too light! Then, you have you battery, which is more-or-less a block of lead :(. You will find it hard to fit it into 30 pounds. Also, if you go for 60 pounds, fill up the rest of the weight with more batteries to give you the runtime! If you are aiming for that high of a runtime, you will probably need to use Lithium Ion, or LiS/Li-Air/LiHOH, if they release that technology anytime soon:(
Here's a link to PolyPlus, developing some Lithium technologies ;) http://www.polyplus.com/

For the Gearbox/motor:
6 Inch wheels means .5 ft. = 2turns/foot
1 Mile is equal to 5280 ft.
6 miles = 31680 ft. * 2 = 63360 rph (rotations/hour)
63360 rhp / 60 = 1056 rpm

You need to get your motors to 1056 rpm! That means that a MiniCIM will be able to give the RPM at a max of 1:6 reduction gearbox!

A versa planetary with 1:5 reduction shall do the work and actually get the car to possibly 7mph!

However, at 60 pounds, you would be stressing the motor/gearbox a lot, so you may need two MiniCIMs working simultaneously!

If you use four MiniCIMs, you should get a punchy throttle!

With a Kinect, you will probably need a coprocessor, requiring a UPS for safe shutdown, and other complexities. Unless you are really good at OpenKinect of OpenNI or another vision suite, this is very advanced! The cRIO can process the images from the AXIS Camera!

I hope that you found this useful! :D Please let me know if I did any math wrong


Sorry about the double-post. I didn't know how to multi-quote! :]

Re: Need advice on motors, gearboxes, and ESCs
 

You are not accounting for friction. Furthermore, free speed assumes that there is 0 load on your motors. My calculations (MiniCIM on a 10:1) is based on JVN's design calculator which accounts for both of these. Also your calcs are way off because a 6" wheel is actually 18.84 in/rev(1.57ft/rev).

Re: Need advice on motors, gearboxes, and ESCs
 

What number did you use for "Speed Loss Constant" ?

Re: Need advice on motors, gearboxes, and ESCs
 

Good catch Ether. I was looking at a 15:1 or 16:1 VP(not a 10:1) with a 81% speed loss constant

Re: Need advice on motors, gearboxes, and ESCs
 

Yeah. Good catch. I do suck at match. The car would be going at 18 miles an hour :yikes: :D . You would have to be Usain Bolt to chase that car :D. Also, my calculations are based off an ideal model, no friction, no heat, 100% efficiency!

Re: Need advice on motors, gearboxes, and ESCs
 

That's a good start.

Re: Need advice on motors, gearboxes, and ESCs
 

Sorry about the late reply. I doubt that the motor was sideloaded, though that is a possibility. We had a gearbox attached, and that was direct-driving the shooter wheels. At the RPM that our shooter wheels were turning, I'm pretty sure that the forces would try to correct the side-loading slowly!

Re: Need advice on motors, gearboxes, and ESCs
 

Well, it's a new semester and we're ready to buy this stuff for our robot!

Here's our shopping list so far:

Motor:
2 x Mini CIM Motor
2 x 12t CIM Motor Gear with Mounting Hardware (these are needed, right?)

Gearbox:
2 x VersaPlanetary Gearbox

• Base VersaPlanetary 1:1 with 1/2" Hex Output
• VersaPlanetary 10:1 Gear Kit with Ring Gear

2 x VersaHubs

• VersaHub (1/2" Hex)

Wheel:
4 x 2008 FIRST Wheel w/ 1/2" Bearings (am-0148)

ESC:
2 x Victor 888 Motor Controller
1 x 3-Wire Extension Cable 36" (4-pack)

How does that look?

Does anyone know if we need any additional hardware to get everything (such as the gearboxes and wheels) connected together?