Non-FIRST Motor Suggestions?

I am looking for motors to drive a radio controlled robot I plan to build. This is not FIRST related, and therefore doesn’t need to be FIRST legal. The drivetrain setup would be like that of a zero-turn lawn mower, with the two rear wheels independently driven and casters in front. Just to be safe, they would need to be capable of moving 200-250 lbs.(with both of them combined). As for the electrical system, I’m not really stuck to one voltage. I thought 24 volts would be best, but I can’t seem to find suitable motors for this, at least not reasonably priced. I could probably get by with 12 volts. I’ll probably use AndyMark’s Cheap and Dirty Radio Control System(I am aware that the radio receiver needs a different power supply; this isn’t an issue). I read that Fisher Price Power Wheels motors are capable of moving 200+ lbs, would those work? If so, would Victors/Talons work for controlling them? I know they were in the FRC KOP for a while. Any other suggestions that have controllers easily available, and preferably aren’t too expensive?

Thanks in advance!

What kind of surface will this robot drive on; e.g., carpet, grass, mud, etc.?

How fast does it need to go?

Will it need to climb hills, push/drag loads, or accelerate quickly?

Give us more detail and the CD community can help more.

AmpFlow is commonly used in Battlebots and the like. I’m sure you could find something to your liking.
http://www.robotmarketplace.com stocks a lot of different motors, both for and not for FRC. That being said, it’s hard to beat the value of a CIM.

Also, how long will it be running at a time? (CIMs are a very good value for short runs, but their design makes them unwise for a 60-minute enduro.)

If your looking for a low-cost solution to those requirements I would recommend getting the base of an old electric wheelchair. Lots have two rear wheels independently driven and casters in front, they normally have a 300watt motor on each side, have decent sized pneumatic wheels and have electromagnetic brakes( if this is needed for you).

http://www.neonsquirt.com/_Media/img_1044_med.jpeg

The electronics system is pretty simple, and you might be able to use the original control system but with just two servos controlling the joystick of the wheelchair. Colin Furze did something like that and it a quite good cheap solution. https://www.youtube.com/watch?v=nUpzC1QP8z4

Wheelchair motors are generally 24volts, and if you wanted to use other motor controllers, REV Sparks are probably the best low-cost version and they can operate on up to 30volts. The Talon SR, SRX and Jaguar are also capable for operating on 24volts.

This doesn’t need to go fast; probably not faster than 5 MPH(7.33 FPS). It would need the ability to drive on most surfaces, but it would mostly be driving on concrete, asphalt, and maybe dirt, grass, or gravel. Hill climbing ability is important, and so is weight pushing and pulling. The low speed should allow for high torque gearing. I checked wheelchair motors, and they seem to be on the expensive side. I considered CIMs, but I’m not sure if they could handle this much weight. Could they run at 24 volts? The runtime would vary, but the battery would limit it. It would mostly be fairly short though.

Almost any power of motor can be geared such that you can go up a really steep grade with a heavy load. The lower the power, the slower you will go though.

For instance, the 5 mph you spec’d out, if you want to go 5mph up a steep grade, is a vastly different answer than 5 mph top speed and maybe 2 mph up a steep grade.

5 mph is 2.24 m/s. 250 lbs is 1112 Newtons.

If you assume a rolling resistance of 0.03 (which is pretty easy on hard ground with a decent wheel/tire) your rollinr resistance would be:
1112*.03=33N With a speed of 2.24 m/s, the power at the wheel would need to be 74 Watts. Not that much power.
Now if you want to climb a 60% grade (again hard surface), this would be a very very steep hill that would be difficult for a person to walk up.
The tractive effort portion is about 0.51, and the rolling resistance of 0.03 would combine to a needed 0.54 TE/GVW to do the climb or:
1112*0.54=600N which at 2.24 m/s would be 1344 Watts again at the wheels.

If you want to walk along with this robot, it will likely outpace you on such a hill as a fast walking pace up a hill that steep is about 2.5 mph or just over 1 m/s. This would reduce power demand to 600 Watts which aligns well with that wheelchair sized set-up.

If you geared for peak power at 1/ms, the robot would likely have a top speed close to 2 m/s which would mean you could get by with a single speed gearbox.
If you don’t expect to climb that steep of a hill, you could gear it a little faster to hit your top speed, and just know that with steep hills or high rolling resistance (sand/mud), you may run at a high power demand which could risk overheating motors.

you may want to look into electric scooter stuff:
Here is a new kit for relatively cheap:

Though you would need two kits and it would be a bit overkill for the power you need.
Here are some other possibilities more in line with what you might be looking for.

I wasn’t necessarily suggesting just getting the motor/gearbox assembly.
The entire wheelchair base, seems to fit your requirements well. You should be able to get the base of an old wheelchair much cheaper than the cost of the motors, gearboxes, wheels and frame. I have a base of an old wheelchair around the side of my house, that had been thrown out simply because the SLA batteries had died.
Old ones are pretty common going for free( in Australia anyway), otherwise an operational wheelchair( but with dead batteries) can be got for less than $100 online.

One CIM( at 12volts) on each side should easily be able to drive the robot at 7.33fps.
I would not recommend running CIM’s at 24volts. First of all doubling the voltage, means double the motor RPM. This will mean you need a massive gear reduction if you want to go 7.33fps( especially if you use big wheels say 8 or 10inch). Secondly increasing the voltage from 12volts to 24volts is going to give to increase your power by 4 times. So your 24volt CIM’s will be outputting almost 1350watts.

Running one CIM at 24volts, is going to cause a current draw higher than normal FRC motor controllers can handle, forcing you to move to expensive high current motor controllers more typically used in Battlebots, such as Victor 883/885’s and the new VEX Victor BB controller. Running the CIM at 24volts, will also massively decrease the operational life as they are case sealed it will be unable to dissipate the heat. The brushes will also wear out quickly( although these are pretty simple to replace in CIM’s).

I have decided to go with two CIM motors, as I’m familiar with them and they have gearboxes, controllers, etc. easily available. The duty cycle isn’t much of an issue, as they won’t be running long or working as hard as they do sometimes in FRC. I think I’m going to go with BaneBots 220 gearboxes, or maybe Toughbox Micros. The BaneBots seem more durable, but the Toughbox has higher torque(I think? 12.75:1 vs. 4:1). I know I would probably need bearings and mounting brackets, but would I need any additional hardware to mount the AndyMark 8" Pneumatic Wheels to either of those gearboxes? The link for the hubs doesn’t work. The wheels’ load capacity is listed at 120 lbs., but that’s for one, I’m assuming. So two would have a capacity of 240 lbs. I know robots weigh more than that with a battery and bumpers…

The AM pneumatic wheels have a 1" through-hole and a 1.875" 6-bolt circle; hubs will be required to mate these to any gearbox with an output shaft. For the TB micro, this will be a 1/2" hex shaft, for TB mini it will be 1/2" hex or 1/2" round keyed shaft depending on what you order, for BaneBots 220 it will be a 1/2" round keyed shaft. The hub from AM is http://www.andymark.com/Hub-p/am-0096a.htm or 0.5 in. Hex Hub - AndyMark, Inc for hex; http://www.andymark.com/Hub-p/am-0077a.htm for round keyed. I added the TB mini into the mix because it is only a couple of dollars more than the TB micro, and can be upgraded to a second CIM very easily; unless you are really sure that you’re going to have enough capability with one CIM per gearbox, it makes sense to hedge the bet and get the 2-motor capable boxes. Also note that the Banebots gearboxes can be stacked, so you can have gear ratios of 4:1, 16:1, or 64:1, though each reduction comes at an increase in weight and cost.

OK

1st overall gear ratio - from CIMs to 8 inch wheels - recommend you find a link (search CD) for the JVN calculator - nice spreadsheet helps you get reasonable on what ratio will drive you and not overload. I think you will find you want 1.5x or so more ratio than the toughbox gives. This can be done by chain and sprockets between gearbox and wheel, mount wheel with 2 bearings on a dead axle (3/8" bolt) mount a sprocket with a spacer to the hub (sprocket and spacers from AM or VEX), and other sprocket to transmission output shaft. Remaining consideration is spacing of wheel axle to transmission output shaft - use a chain distance calculator (search). If you have a way to adjust chain tension, all the better.

In regards to the gearboxes, you need to carefully consider your gearing. A Toughbox Micro( geared for 12.75:1) is going to mean that your robot is geared for about 14.6fps with 8inch wheels(without losses), that is double the speed that you said you required, with only one CIM on each side and 240lb’s of robot weight, that seems like it is going to be difficult for your motors and you will have very little capacity to go uphills without huge current draws. You definitely cannot use a 4:1 BB gearbox , that is simply not enough gear reduction( you would need to use a massive sprocket in order to get your 2rd stage reduction which probably wouldn’t be practical) you would need to use the 16:1 at a minimum.

In regards to durability of the gearboxes it pretty much depends on how you are going to be mounting your gearboxes. If you are planning to have two axles with 120lb load on each, you certainly need to support your gearbox shaft well. You will need to make sure that you have a support on both sides of the gearbox shafts. With the micro, you should be able to use the gearbox shaft( made from 4140 steel) as your drive axle, but you will need to support each side with bearings. I would recommend that because of the 12.75:1 reduction of the Micro, that you should have a separate axle for your wheel and have a 2:1 or 1.5:1 belt (15mm as a minimum or use #35 if you don’t want to risk any failures) or chain (#35 as 25 won’t be strong enough). If you opt to use a Banebots planetary gearbox, you will definitely need to have a separate axle as the output shaft is only 1.5 inches long, and will not be long enough for having a wheel( 2 inch wide hub) and supporting both sides, which will take up approximately 16mm( including bearing flanges). The axle is far too short for this purpose.

In regards to the wheels, while the load capacity maybe 120lbs you will experience a significant “ballooning” of the tyres, due to the high load that they will be under.

I would suggest contacting AndyMark to ask about the load-rating of the wheels, VEXpro rate their wheels as “Conservatively rated for use on 200 lb robots” and I’m not sure if AndyMark do something similar. There is a big difference between a FIRST robot which might have 6 of the wheels and weigh 120lbs and a robot that weighs 240lbs and has 2 wheels.

In regards to the hubs it will depend on what output shaft you order the Toughbox Micro with:

If you get the ½ hex output shaft you will need these hubs:

If you use the BB gearbox( which shouldn’t matter because you won’t be able to mount the wheel directly to the shaft :slight_smile: ) or the ½ round keyed output shaft you will need these:

I would seriously suggest using the JVN calc, it’s really helpful and pretty easy to use. It will save you a lot of headaches, time and potentially a lot of money later.

https://www.chiefdelphi.com/media/papers/3188?langid=2

One question about the JVN calc; the “Driving Gear” and “Driven Gear” fields take a custom value, but it’s not clear what the number that goes into them is. I’m assuming it’s asking for gear teeth, or is it something else? I’m guessing the driving gear is the one connected to the motor’s output shaft, and the driven gear is the one driven by that gear?

Yes it is the number of gear-teeth, the same applies for the number of teeth on sprockets or belts. You can also just type in the reduction that you want say 1:3 etc.

Some gearboxes have more than one stage, but take it as the driving gear is before the reduction and the driven gear is after, so the driven gear should be rotating slower than the driving gear.

Yes the driving gear in a single stage gearboxes is the gear on the motor’s output shaft

Here is an example of what it should look like for the reduction stages of a 10.71:1 Toughbox Mini or Micro(the stock ratio):
http://i.imgur.com/wBzjXGZ.png

Update: I think I’m going to use ToughBoxes. AndyMark’s 8" pneumatic wheels are out of stock. So are some of the parts that I could use to assemble them myself. How hard is concrete/asphalt on plaction wheels? If I go with plactions and TBs, would these hubs work?

If you’re not on carpet, there’s little reason to use treaded wheels over rubber wheels like the kit wheel. The hubs you linked work with any sprocket mount / bearing bore AM wheel.

Try 8" Colsons if you want a tough wheel that can be purchased easily and will handle concrete and asphault. The hubs can be purchased in a number of places like Vex and BaneBots. I also recommend the p60s with rs775s if you want to conserve space/weight and get similar performance. I used the same wheel diameter as you for this project linked below plus I was going through real simulated regolith with large jagged rocks in it. Before we had the fancy wheels with grousers we used Colsons as a prototype. The p60s will allow you to jam the wheel right onto the gearbox or it can accept most vexpro/AM products to get the right gearing.