Skid Steer Tadpole Trike

[gromike]

Lately I have been thinking about building an etrike to function as a glorified mobility device with a top speed of 25kph (planning for the future, so to speak).
It seems that a tadpole with two hub motors upfront might be the way to go. Then I thought you could steer it with the motors, like lever controls on a zero-turn mower (i.e. skid steering). That would greatly ease the design and construction. So, my question, is this a viable approach?

 

[gromike]

I just watched Grin's dual motor video and I might just have some mission creep going on -- a skid steer front loading cargo trike. It would be similar to a Christiana cargo trike, but all steering by the motors. If I don't add suspension it might be relatively quick, cheap, and easy. A couple of inexpensive DD hub motors and controllers, the back half of a bicycle for the de regueur pedal system, and pieces of iron and aluminum. Batteries, I got.

 

[Papa]

This would technically be rear steering. You'd need a caster wheel at the rear, which would eliminate the rear pedal drive possibility. I'm reminded of the long defunct Sidewinder, a rear steer tad.

Sidewinder Recumbents - Bicycle Man

Sidewinder tadpoles is one of the least expensive recumbents on the market at $1595 Its seat is higher than most tadpoles making it easier to get on and off

bicycleman.com

quote from above link, "This can be fun at slow speeds in a parking lot where there is no traffic but would be very dangerous on the road, especially at speeds over 5 or 10 MPH."

 

[gromike]

I was thinking of two hub motors up front and steering by varying the motors' speed. There would be no steerer other than that.
The basic configuration that I would copy is this:

I might by able to build it for about a $1000+.

 

[BicycleJoe]

OP, in your scenario, and correct me if I'm wrong, the rear wheel is locked in the straight ahead direction. I can only assume that the front wheels do freely steer themselves left and right because this trike would only go straight otherwise. The front wheels must be locked together on the same trajectory. That is a given. The motor torque, on one side or the other initiates the turn.

From my understanding of current technology, you would need a very rich uncle at NVIDIA or OpenAI to make this dream happen.

This is a legit aspiration. You might be on to something big.

 

[gromike]

After a night of sleep, I had an eureka moment. It will need a pivot point like on a christiana type front loader trike. Something I realized after looking at the picture in Papa's post. Steering control would be by a left hand and right hand throttles, functioning like a zero turn lawn mower. If advanced electronic control is needed -- then this dream dies.

 

[Chalo]

After a night of sleep, I had an eureka moment. It will need a pivot point like on a christiana type front loader trike.

If you've ridden a trike like that, you already know you don't want to go faster than easygoing pedal speed on one.

 

[gromike]

It won't be a speedster, not even close. My planned use would be a couple of miles to the ferry, a couple of miles after, then return.
I would like to transport tools, like a table saw, for work projects without relying on a car. The ferry is under capacity and traveling on four wheels is problematic.
I have been using, and using at this moment, an ebike with panniers (and backpack) to make the crossing, and need more freight capacity.

 

[Chalo]

It won't be a speedster, not even close. My planned use would be a couple of miles to the ferry, a couple of miles after, then return.
I would like to transport tools, like a table saw, for work projects without relying on a car. The ferry is under capacity and traveling on four wheels is problematic.
I have been using, and using at this moment, an ebike with panniers (and backpack) to make the crossing, and need more freight capacity.

You need a bike trailer a lot more than you need a self-upsetting crazy trike.

Here's the bigger of my two homemade cycle trailers from a period when I was getting everywhere by muscle power alone. I've hauled up to around 400 pounds on it.

 

[gromike]

Maybe a trailer is a better, smarter choice, but the cargo trike thing gives me something to think about.
No material commitment yet, though I'm tempted to buy a couple of motor wheels while we still can.

 

[Chalo]

Maybe a trailer is a better, smarter choice, but the cargo trike thing gives me something to think about.
No material commitment yet, though I'm tempted to buy a couple of motor wheels while we still can.

If you live somewhere that has a community bike collective, they probably have a bunch of hub motor wheels from dead donated e-bikes.

 

[gromike]

My community bike "collective" doesn't take in ebikes : (
If I could find a broken Rad Wagon 1 local for cheap, I'd play with that.
A skid steer trike built quarter size with eskooter wheels might be a smart way to test the concept, but I'll probably buy a couple of direct drive motor wheels anyway.
After all , it's like money in the bank ; )

 

[Chalo]

A skid steer trike built quarter size with eskooter wheels might be a smart way to test the concept,

"Skid steer" refers to four (or more) wheeled machines that have non-steerable wheels, so that only one side's wheels rotating at a different speed than the other side's will cause it to change direction-- with lots of skidding because none of the wheels are pointed in the direction of the turn.

I think the term you want is "vector steering".

 

[gromike]

I'm thinking of skid steer as what a zero turn lawn mower does. Yes, you vary the speed of the drive wheels for directional control. A low speed turn is a skid, but at road speed -- no, no noticeable skidding.
There is a pivot somewhere between the front two drive motors and the third wheel, just where I don't know.
Can't find a coherent definition of vector steering for this application.

 

[Chalo]

Skid-steer loader - Wikipedia

en.m.wikipedia.org

 

[gromike]

Have you ever driven a skid steer (i.e. tank steer) machine? Granted, this be a 15kph thing. There are issues, but it could work very well as a cargo hauler.

 

[Papa]

I'm thinking of skid steer as what a zero turn lawn mower does.

Wrong...

"Zero-turn" lawn mowers employ 'differential' turning with 2 wheels, Two caster wheels to support the non-drive end of the vehicle (usually the front). Most zero-turn mowers use a single hydraulic motor in each of the two drive wheels (the wheels are NOT mechanically connected). The Sidewinder trike I previously posted employs 'differential' steering with a single caster wheel on the rear. Rear wheel steering is strongly discouraged (for a number of valid reasons), on public roads at speeds much higher than 5-8 MPH.

"Skid-steer" usually employs 4 or more wheels (or two tracks). Initiating turns force the tires (or tracks) to slide sideways. If you use rubber tires on a skid-steer machine driven on asphalt, you'll grind the tread off the tires in v-e-r-y short order. This is just one of the valid reasons why skid-steer vehicles are NOT designed, or intended to be considered roadworthy on paved, public roads.

How you plan to electronically synchronize two wheels to smoothly initiate turns, is over my pay grade. But I have no doubt it can be done. Go for it.

 

[gromike]

My battery zero turn mower has a motor in each of the two back wheels, and two caster wheels in front. I would have two motor wheels in front and one "caster" wheel in the back. On most road ways you won't scrub the tires, we're talking about 10mph.

 

[Papa]

My battery zero turn mower has a motor in each of the two back wheels, and two caster wheels in front. I would have two motor wheels in front and one "caster" wheel in the back. On most road ways you won't scrub the tires, we're talking about 10mph.

Did you even read what I wrote in post #17 ??

Most zero-turn mowers are, in fact, rear drive, FRONT steering.... because that's where the casters are located. The Sidewinder is REAR steer.... because again... that's where the caster(s) are/is located... at the rear. Neither are considered "skid-steer" machines.

 

[gromike]

Yeah, skid steer was not the best terminology to use, so I'll just call it tank steering. I figure that wheel scrub would be a problem on tight turns, and not so bad driving down the road. My vision, at the moment, is a low speed (under 25kph) cargo hauler with a pivot point at the front axle. something similar to a christiana trike.
It's all just a concept that's living in my mind. The real trouble would start if and when I purchase a pair of suitable motor wheels.

 

[gromike]

In order to operate on the road I was planning on having pedal power to conform with ebike regulation, but I just found out about EPAMD (electric personal assistive mobility device) classification. No pedals required!
That is a huge simplification. Just two motor wheels , and a caster wheel or two, plus a comfy chair.
Now, it's time learn about systems that facilitate tank steering.

 

[AussieRider]

G'day people's, thought I'd chime in here.
A trike with differential steering & a caster wheel has it's centre of gravity between the drive wheels & the caster.
Ok. If the caster is at the front, corner force pushes the front outward causing under steer. Easy to control by holding steering input.
With the caster at the back, corner force pushes the back out, over steering & tightening the corner, until you spin out. Much harder to control.
Even correcting to keep a straight line at speed can cause a bad spin that will hurt!

AussieRider

 

[amberwolf]

Dymaxion car - Wikipedia

en.m.wikipedia.org

 

[gromike]

Thanks for the link Amberwolf.
I guess I'm getting a history lesson, and an education in this thread.
As pedal power is no longer a requirement my concept has been greatly simplified. Just two drive wheels on one end, and a caster wheel or two on the other end. The thing could be driven in either direction, and if I ever build it I could see what works best. Computer controlled drive wheels along with an azimuthing rear wheel would be an interesting rabbit hole to jump into, but this old man doesn't have the time.
So my concept, at the moment, is a cargo sledge. Two motor wheels mounted to a platform, castor wheels as needed that fits through my front gate. Top speed of 25kph, cargo capacity of several hundred pounds.

 

[Papa]

Dymaxion car - Wikipedia

en.m.wikipedia.org

From your link Amber...

"Fuller noted severe limitations in its handling, especially at high speed or in high wind, due to its rear-wheel steering (highly unsuitable for anything but low speeds) and the limited understanding of the effects of lift and turbulence on automobile bodies in that era – allowing only trained staff to drive the car and saying it "was an invention that could not be made available to the general public without considerable improvements."[9] Shortly after its launch, a prototype crashed and killed the Dymaxion's driver."