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! ;)