Tug build advice needed

[Bob Builder]

I'm running into problems while trying to build a small tug prototype. Hopefully someone can help me out.

My current main problem is the motor controller reverse. I figured to start as simple as possibile so I got 2 hoverboard motors, 2 kunray s6-25 motor controllers, 2 thumb controllers and 2 standard hoverboard batteries. I thought of just fixing the 2 thumb controllers side by side and coupling them physically.

Problem is, the motors spin opposite so the contraption just spins around. The controllers do have a reverse function when connecting 2 wires together. The problem is that the speed in reverse is significantly slower... Do I need other motor controllers or is there a simple trick? These were very cheap.

The goal is something compact that can pull up to 300 kg / 700 lb. Speed ideally walking speed. It can be slower while pulling up a slope etc. It'll be a 'co bot' in the sense that I will also pull it. So the tug doesn't need to do all the work. I will attach a stick and a handle to it so I can pull it.

Ergonomics are very important. That's why it has to be small. Ideally it can also spin freely so I can pull it while there is no load to pull by walking fast.
My question about this is, I'm guessing this generates electricity, is this a problem? Will this go back to the battery?

I'm also in doubt about the hoverboard batteries and the controller and the requirements. If each motor gets it's own controller and battery, will the battery be fine with this controller? As I understand it draws 17 amps at max from the battery. Or am I at risk of setting the batteries on fire?

BTW I'm probably not yet on the right path here. Ideally it would be geared and lightweight in the future.

 

[RunForTheHills]

If you reverse the order of the phase wires from the controller to the motor, you can reverse the direction of the motor. They also sell wheelbarrow electric motor kits that would probably be more appropriate for what you want to do than the hoverboard motors. You do need a separate motor controller for each motor, but could probably get away with one battery if it was rated appropriately for the current required.

Geared Wheelbarrow Motor, No Tire

 

[Chalo]

For your application, worm gear motors from an electric wheelchair will work better-- low speed, high output torque, no backdriving the motors when parked.

 

[Bob Builder]

For your application, worm gear motors from an electric wheelchair will work better-- low speed, high output torque, no backdriving the motors when parked.

Yes some kind of gear would be nice. Worm gears seem good but they can't free spin. I need something that can be powered but that won't come to a sudden stop when I release the throttle. I don't really need a brake. Maybe a hub motor with a planetairy gear.

I saw this one 4.5 inch slow speed brushless dc geared hub motor - uumotor
and some slightly larger ones; 6 inch drum brake geared hub motor - uumotor
6 inch hub motor disc brake geared slow speed - uumotor

That is something to explore once the prototype is working with the motors that I already have.

 

[Bob Builder]

If you reverse the order of the phase wires from the controller to the motor, you can reverse the direction of the motor. They also sell wheelbarrow electric motor kits that would probably be more appropriate for what you want to do than the hoverboard motors. You do need a separate motor controller for each motor, but could probably get away with one battery if it was rated appropriately for the current required.

Geared Wheelbarrow Motor, No Tire

Thanks that was a good tip. I've played a bit with changing the blue and green wire. It changed direction. It also has a 'learning' wire. Finally when I unplugged that it actually is working with the phase wires in the normal order. Strange enough.

I fixed it to some wood and it's strong enough to pull me up a slight incline when I stand on it. Fast enough. Both batteries don't hold full charge and one is just weak. The power is promising though. I'm very curious how it will work with 2 good batteries.

If the motors can pull 100 kilo I would have to pull the rest of the weight myself.

The plan is to cut away part of the tires so the wheels will be a bit smaller and thus will hopefully have a bit more torque.

Some questions still,
Am I at risk of 'overpowering' the batteries with this controller? I'm afraid of fires, thermal runaway etc....

What happens when the throttle is released but I am pulling it by hand or it is still in motion or going downhill. Will it generate electricity? Where will that stay? Is this a safety risk?

 

[Chalo]

Yes some kind of gear would be nice. Worm gears seem good but they can't free spin. I need something that can be powered but that won't come to a sudden stop when I release the throttle.

Well, if you can't pull the entire weight on an incline, you can't control the load if power fails on an incline. That's where worm gears win.

 

[Papa]

Am I at risk of 'overpowering' the batteries with this controller? I'm afraid of fires, thermal runaway etc....

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[AussieRider]

I'm with Chalo about using wheelchair motors. Plenty of torque & the right speed range. They can be be pushed manually if you release the (usually yellow) freewheel levers. These levers operate on electric brakes that lock the motor when power is released or lost.
Used, non working wheelchairs can be had for next to nothing & you get a matched 2 motor controller to boot! Usually the chairs don't work because they've been stored without charging & the batteries have starved. Easy check, a volt meter in the charge socket. Less than about 22v is dead & you've found a bargain.

AussieRider

 

[calab]

Used to be a surplus store online that sold worm geared motors of every type.

https://endless-sphere.com/sphere/threads/surplus-electronics-links.132/#post-1083​

Surplus Center link looks like thats what I was thinking of.

Electric Motors | www.surpluscenter.com

Electric Motors,AC Single Phase Motors,DC Motors,DC Gearmotors,AC 3 Phase Motors,Linear Actuators,AC Gearmotors,Electric Motor Mounts

www.surpluscenter.com

 

[amberwolf]

Geared hubmotors may help do what you want, but if you want to try something different, you can poke around for scrapped powerchairs at local repair centers for them, or thriftstore finds, freecycle, craigslist, etc. Might even find them for super cheap, if not free.

If using the typical brushed Invacare-type powerchair motors with angled gearbox, where the wheels bolt to hubs on the gearbox output shaft, you can get versions that have a clutch lever on the gearbox that disconnects the output gear from the rest of the gearbox so it can be freely rolled...but otherwise it stays engaged, which will prevent rollback of your load on slopes, etc (very important for loads that you can't move up or down the incline without the motor help, in case any mechanical brake isn't working).

Many of these *also* have a parking brake lever on the unit that manually engages/disengages a friction braking plate inside (most of these also have an electric solenoid you can use to do this, too, but that can be physically removed if desired).

These are randomly found google images of some of these clutched gearbox motors; the first one looks identical to one I used on a middrive for the early CrazyBike2 that had enough torque to (when chains derailed) destroy chainrings, wheels, axles, and even bend the frame....so a pair of them would probably have all the torque you might ever need.

 

[Bob Builder]

Those are great tips. The only thing is that it should be very compact. Tire diameter preferably under 7 inch. Will the speed not be to slow with such a wheelchair motor if I bolt it to a very small wheel?

I'm afraid the gear ratio is made for wheelchair wheels and those look to be a bit larger.

 

[Chalo]

Motor RPM is proportional to battery voltage, so you have some control over what the top speed is. With brushed commutated motors, there are limits to the upper voltage they'll tolerate (due to arcing at the brushes), but you still have a range to allow you to match wheel diameter and intended speed by changing voltage.

The kind of power chair Amberwolf is talking about tends to have pretty small drive wheels. Not 7 inches, but small.

 

[Bob Builder]

Motor RPM is proportional to battery voltage, so you have some control over what the top speed is. With brushed commutated motors, there are limits to the upper voltage they'll tolerate (due to arcing at the brushes), but you still have a range to allow you to match wheel diameter and intended speed by changing voltage.

The kind of power chair Amberwolf is talking about tends to have pretty small drive wheels. Not 7 inches, but small.

I already have an electric tug that is strong, has worm drive etc etc. But it weighs around 45 kg and it's just too big to work with in tight places. It's like this one in the attached picture. ET10 | Electric Tug – Custom Trolleys Australia
Way too cumbersome. It's like taking a US schoolbus through a 500 year old Italian city center. Since it has a worm drive there is nothing I can do to help it. Because you can't pull to make it faster. It goes it's own max speed and that's it. It's not intuitive. It's not working WITH the bot but letting the machine do all the work. It's a waste of my own human energy that can also pull at least 100 kg.

I'm really looking to make something very compact and light. Nimble, tight turning, small footprint etc. The 2 hoverboard motors are just 6,5 inch. They are very compact. They can pull up too 100 kg at least. And they are not even geared. So I'm guessing there is enough potential in those small motors. Especially geared.

Even electric skateboards / longboards with their tiny hub motor wheels can pull an adult human up a hill.

This is the sort of tug that I now have: Specs on paper are perfect. More then I need. But it's just too darn big.

 

[DaLanMan]

I have seen a smallish hub unit that had a centripetal clutch (centripetal? Centrifugal? either way, releases unless motile force is applied) Might be the solution to making sure it is free spinning as desired.

Sorry I don't have better detail on them. Saw them at a trade show, never did figure out what problem they were trying to solve.

 

[amberwolf]

Those are great tips. The only thing is that it should be very compact. Tire diameter preferably under 7 inch. Will the speed not be to slow with such a wheelchair motor if I bolt it to a very small wheel?

I'm afraid the gear ratio is made for wheelchair wheels and those look to be a bit larger.

Most of the powerchair wheels Iv'e seen are 10-12" or larger (because very small wheels don't handle non-perfectly smooth surfaces very well, and are uncomfortable at best to ride on, even at slow speeds, and at much beyond slow walking speed can be outright dangerous on rough surfaces, or with debris or holes, dependign on setup and conditions).

Most powerchair motors, if run at the usual 24v most of them are powered with, will give a speed of 5-10mph (depends on the specific motor and wheel size). Running them at higher voltage provides proportionally higher speed (with a bit more motor heating from the brush arcing, etc), so that is an option to get faster speed with a smaller wheel.


If you need torque more than anything else, I'd venture that there aren't many simpler ways to get it than these types of motors.


But, they are heavy, and not all that small. And while you can override the motor and gearing to pull it yourself, you are disconnecting the motor from the output to the wheel to do it, so you then have no assist at all--it's all up to you at that point.