Need advice on motors, gearboxes, and ESCs
 

I'm a FIRST alum and am now part of the robotics club I started at my university. We just started a multi-year project that will hopefully result (many years from now) in making a full-sized vehicle operate autonomously (think DARPA grand challenge).

This semester, we're building a very basic small vehicle to use as our first-phase development platform. The chassis is going to be about 24" x 16" and the total weight of the vehicle/robot should be around 30lbs. We're wanting the vehicle to be able to drive up to about 6 mi/hr. Here's a very (very, very) rough concept design.

We've been looking for motors and gearboxes for our vehicle and it occurred to me that the ones FIRST gives out in the yearly KOP might work really well. What do you think?

If you think that's a good idea (or if you have other suggestions), any advice on where to purchase from?

Appreciate your advice!

Re: Need advice on motors, gearboxes, and ESCs
 

That's a good start. However, you may like looking at either swerve or holonomic drive because that will give a much greater maneuverability. I'll post an image of my VEX Holonomic robot tomorrow.
Also, what is the gear ratio and what motors are you planning on using? Have you planned that out?

What control system are you planning? A cRIO system may take up all the thirty pounds if not designed correctly. There are many parts, a lot of which are quite heavy!

Re: Need advice on motors, gearboxes, and ESCs
 

I don't think they'll want a swerve or holonomic. They're scaling up to a car--read up on Ackermann steering (it's been used in FRC before, BTW).

And the OP specifically said they don't have a specific gear ratio and motors yet--they're still in investigation.

On that topic--BaneBots motors should probably have enough power.

Re: Need advice on motors, gearboxes, and ESCs
 

I agree it would get a little complicated, but if they like the idea, it isn't even close to impossible!

Nathan,
If you can give me a tad more information, like:

Motors you are interested in
Wheels you are interested in
Battery voltage
and a few more details, we can help you design your drivetrain, and calculate gear ratios and find the correct gearbox

Re: Need advice on motors, gearboxes, and ESCs
 

Let me put it this way:

They are scaling up to a CAR--like the DARPA Grand Challenge or a Google whatever-they-call-it. No car on the market today has a holonomic or swerve. None. (Besides maybe a self-park feature, but most of that is done with the car steering itself.)

Therefore, a driving requirement of the design is that it has to scale to a CAR. Leaves Ackermann steering--and the basic design shows their steering mechanism.

Re: Need advice on motors, gearboxes, and ESCs
 

Yep. Holonomic may not be the best idea, nor would be swerve. However, we can help Nathan calculate the gear ratios!

Re: Need advice on motors, gearboxes, and ESCs
 

Hi,

I was thinking a Banebot with a 4:1 or a 16:1 ratio- Though considering my suggestion is based off mere speculation, it would be a convenience to then drive an output shaft by way of chain or direct gear contact to allow for a change in ratio (either up or down) if you find you need more power to move the load, or want a higher velocity.

Hope this helps,

Re: Need advice on motors, gearboxes, and ESCs
 

I have been working on a spreadsheet to help with motor and gearbox selection. It may be useful for you. The final speed calculations are optimistic, but relative results should be reasonable.

Re: Need advice on motors, gearboxes, and ESCs
 

Suggestions for motors are great and all, but may not be the best for the application. An FRC setup will most likely work for you, but I urge you to define the requirements.

What are the major areas of functionality and concern? These could be things such as maintainability, maneuverability, reliability, durability, etc. For each of the requirements, outline an objective (what you really desire) and a threshold (the minimum that you will accept). The space between the objective and the threshold is the trade space - you will use this to determine if your solution is workable.

Here are some of my first thoughts on requirements:

So far, I have two "requirements": 30lb weight and 6 mph. Do you have a maximum weight allowed? A minimum speed?

What acceleration is required? This will help define your motor HP and gearing/transmission requirement. It will also help define your electrical power requirement.

How will you get electrical power? Internal combustion engine with a generator-inverter setup? Battery? Fuel cell? Solar? This will help define motor power limits or operating time.

What is the vehicle operating time? How long will it be using full power? What other electrical loads are required?

What ground clearance is required? This will help define wheel diameter and relates to the HP and transmission requirement.

Re: Need advice on motors, gearboxes, and ESCs
 

Since 6Mi/Hr is a medium jogging speed, I believe BAG motors with the versaPlanetary gearbox of 10:1 may work. However, this is solely based off the wheels you use! BAG motors run at about 14,000 RPM, so that means that you will get 1400 RPM, which seems great for that sort of speed. You probably won't drive too fast. The motors should easily achieve more than 6mph!

Re: Need advice on motors, gearboxes, and ESCs
 

How about a miniCIM in a versa-planetary? It is surprisingly trivial to modify a CIM to work, all you need is a hacksaw and a tabletop vice. On a 6" wheel you would need a 15:1 gearbox, which would yield you 7MPH and plenty of torque for a 30lb machine

Re: Need advice on motors, gearboxes, and ESCs
 

What size wheels you want to use plays a big role in the gearing you want. Any idea how big you want your wheels to be(even a range would be good)?

Re: Need advice on motors, gearboxes, and ESCs
 

I am a fan of the MiniCIMs. A full sized CIM can draw over 100A and the FIRST ESCs are all rated ~60A. The spreadsheet I posted has a pulldown option for MiniCIM plus you could always add other motor curves. MiniCIMs with 6" wheels and 12.7:1 ToughBox Nano is probably much more than is needed. Bag Motors could also work, but I have not done the math.

Re: Need advice on motors, gearboxes, and ESCs
 

Any motor can pull a ton of current if you stall it. If you are actually pulling 100A consistently you are doing something wrong.

I agree that Bags or Mini CIMs are your best option here. Everything else does not handle heat well(which for drive would be awful). However gear ratio again depends on your wheel size.

Re: Need advice on motors, gearboxes, and ESCs
 

I'd go with either CIMs or MiniCIMs. BAG motors have such a high RPM that they self-destruct their internal bearings. That is the reason why our shooter needed to have it's motors replaced so often. Also, if you aren't stalling the RF-775s, they are fan-cooled so they shouldn't get very toasty under normal working loads. CIMs are able to cool off all right because of the surface area and size of the motor. BAG motors just overheat all the time!

I agree that pulling 100 amps continuously from a motor means that you are doing something wrong. That is nearly the max threshold of CIM windings! ;)

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?

Re: Need advice on motors, gearboxes, and ESCs
 

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.

Re: Need advice on motors, gearboxes, and ESCs
 

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".

Re: Need advice on motors, gearboxes, and ESCs
 

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.

Re: Need advice on motors, gearboxes, and ESCs
 

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).

Re: Need advice on motors, gearboxes, and ESCs
 

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.

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 :P

Re: Need advice on motors, gearboxes, and ESCs
 

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!

Re: Need advice on motors, gearboxes, and ESCs
 

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!

Re: Need advice on motors, gearboxes, and ESCs
 

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.

Re: Need advice on motors, gearboxes, and ESCs
 

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

Re: Need advice on motors, gearboxes, and ESCs
 

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.

Re: Need advice on motors, gearboxes, and ESCs
 

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.

Re: Need advice on motors, gearboxes, and ESCs
 

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 :D


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!