500KG 4WD agricultural vehicle

[Kodin]

I'm looking at a project right now to build a four-wheel-drive agricultural vehicle with a target weight initially of 500KG, fully loaded. Wheels don't need to be very big, but it needs as high a torque as one can manage, with maybe a maximum speed of 10 MPH. Do hubmotors exist that could satisfy this requirement? Either geared or DD? Initially I thought about "scooter" style hubmotors-in-rims, (10-14 inch fat wheels), geared or otherwise, however it seems the stock windings still bring them to too high an RPM/V configuration. Any suggestions?

 

[dmwahl]

What do you want to do with this vehicle? Without knowing intended use and some actual wheel torque, pretty tough to give any recommendations.

 

[Kodin]

That's the problem; the only vehicle I have that's even close is a 300KG ATV. I'm thinking anything from agricultural spray machine to possibly even light-duty hauling tractor. Biggest issue though is I want the maximum speed to be 10 MPH. At least for the first build. I'll add this is going to be an autonomously controlled platform. Last thing I need is a prototype vehicle taking off in an unintended direction at high speed.

 

[dmwahl]

Probably most versatile to replace the engine with a motor, but that assumes you're using an existing vehicle to start with. Regardless, if you want a PTO then you'd either need a separate motor or one that can be decoupled from the driveline.

 

[Kodin]

This will be a from scratch vehicle. Thinking more along the lines of agricultural sprayers with long vertical columns for each wheel and a very high ground clearance.

 

[John in CR]

Wheelchair hubmotors are going to be the closest match.

The problem is that high torque geared hubbies don't exist yet. Direct drive's problem is that when you make them low rpm they become low power too, so the motors have to get unnecessarily big.

If you're just testing with plans for higher speed later, then go with low voltage to prevent a high speed runaway condition, not a special motor. Then when you get it all right, everything is already good to go and simply increase voltage for more speed.

 

[mistercrash]

Brushed motors from forklifts?

 

[IanFiTheDwarf]

Your best option is probably to use hydraulic motors mounted to your wheels with one electric motor driving the hydraulic pump.

Hydraulic motors tick all the boxes for torque, size, weight and durability. Your vehicle is going to need motors that won't burn out if a wheel jams up on a stray length of barbed wire or a big rock and that can be submerged in muddy water without worry.

Hydraulic systems can be efficient if set up right, the right motors and pumps can all be well over 90% efficient within there best operating range which you can keep them in by varying your pump motor speed. Rather than controlling motor speed with a bypass valve like in a forklift open and close your valves fully with a solenoid and control the speed of your wheels by varying the electric motor speed.

You also only need an extra hydraulic motor and solenoid valve to create a pto.

The only possible issue with hydraulic motors is that if one motor spins you will loose power to the other three but you can restrict the flow to all the motors so that they can each only pass a little more than 1/4 of your pumps maximum flow so all wheels will always drive.

You should also be able to find plenty of parts from old ride on mowers and small fork lifts and pallet trucks to keep the cost of a prototype down a bit.

 

[crossbreak]

[..]The problem is that high torque geared hubbies don't exist yet. Direct drive's problem is that when you make them low rpm they become low power too, so the motors have to get unnecessarily big.[..]

that true john. as long as we dont know the wheel size, we cant tell you anyting. all we know is that you will need a lot of reduction. like normal diesel tractors have, too. Diesels are in the 1000 to 2000 rpm range. so if you want to do the same with a motor that does the same rpm (like the midmonster JohnInCr uses for example, it's just like a Diesel) you will need the same reduction ratio.

I guess you will use something like 40" diameter wheel? You say "not very big" which means not 60" like tractor wheels, so 40" is about right? You will need at least 1000Nm at the wheels to be able to haul some cultivator. The midmonster JohnInCr has, might do about 100Nm efficiently at 1000rpm, so we talk about 1:10 reduction with such a 15kW motor.

I would not use an hydraulics gearbox, since it is low efficiency <80%. Gear reducers for 1:10 play in the 95%+ league. Another thing you might want to thing of: you may dislike hydraulics fluid on your agricultural field.

 

[crossbreak]

Hydraulic motors tick all the boxes for torque, size, weight and durability

nope. A gear reducer is more lightweight, more durable andmay have more torque in the same package

 

[Kodin]

[..]The problem is that high torque geared hubbies don't exist yet. Direct drive's problem is that when you make them low rpm they become low power too, so the motors have to get unnecessarily big.[..]

that true john. as long as we dont know the wheel size, we cant tell you anyting. all we know is that you will need a lot of reduction. like normal diesel tractors have, too. Diesels are in the 1000 to 2000 rpm range. so if you want to do the same with a motor that does the same rpm (like the midmonster JohnInCr uses for example, it's just like a Diesel) you will need the same reduction ratio.

I guess you will use something like 40" diameter wheel? You say "not very big" which means not 60" like tractor wheels, so 40" is about right? You will need at least 1000Nm at the wheels to be able to haul some cultivator. The midmonster JohnInCr has, might do about 100Nm efficiently at 1000rpm, so we talk about 1:10 reduction with such a 15kW motor.

I would not use an hydraulics gearbox, since it is low efficiency <80%. Gear reducers for 1:10 play in the 95%+ league. Another thing you might want to thing of: you may dislike hydraulics fluid on your agricultural field.

Holy crap no! More like 10" wheels to start. It's going to be the size of an ATV in the beginning to develop the control and steering system. After that I'll probably retrofit to some of my heavy machinery I already own.

 

[Bluefang]

Vertical colums for the wheels? Makes life pretty simple, get 4 mid monsters from John, mount them above the wheels, gear them down to your wheel size and speed requirements and done. Make it a nice simple chain connection thats easily repairable and cheap, use a pair of cheap controllers that john should be able to supply and you are done. The controllers will be happy to run off one throttle, just feed power from only one throttle and the output to all the controllers. If you keep it below 60V you can use the cheap RC power meters to make sure all the controllers are balanced(not needed but good to know if one controller is down) and a Cycle analyst for main power monitoring.

The above is only if you need to go stupidly slow with a ton of power, ideally you would just use the hubs as true hubs in a nice cushy 10" wheel. They will be more then strong enough for 500kg if you use the right controllers and maybe even add some ferro fluid to the motors to keep it simple and cool.

 

[agniusm]

I think will wind your motors to whatever speed you need at given voltage. Inquire them first and seesee, perhaps qsmotors

 

[sigimem]

I thought about a vehicle maybe similiar to the specs you told. For moving small trailers installing a winch etc.
I don't know your plan but I would go with big electric motors for every wheel mounted to che chassis not using them as hub motors but with reduction. Even if you use Hub motors like suggested you don't need to rely on the axles and bearings to support your load when you mount them to the chassis. Especially if you want to go skid steer think big in terms of electric motors and reduction.

This being said a hydraulic (hub)motor is probably still your best option since you get them in different sizes and rugged for your application. Also you can use the hydraulic power for every other motion just like most construction machines. I am totally with IanFiTheDwarf here.

However going for a full hydraulic drivetrain won´t be cheap.

Screw efficiency if you want to pull something you need weight what better way to get weight than installing batteries?