1 motor vs 2 motors electric go kart .. #2

Thread Starter

Nunkmolian

Joined Nov 10, 2020
3
My Dad's racing kart has 2 motors, one for eack back wheel. No live axel. It went really well. A live axel can work ok, but I would vote for one motor for each back wheel.
Then, as an extra programming excercise, monitor the motor speeds and limit the drive to the motor that spins significantly faster than the other. A Limited Slip Diff :)
So then if a wheel comes off the ground, it does no spin up.
Hello
Sorry am new to this
I just signed up today
But saw your thread and you sound like you have knowledge that I'm after
In regards to two motors, how do you have a split axle?
And where can you get them?
Or do you not use an axle?
And where can I get info on this topic
I have recently purchased Arduino
And am in the process of making a small go kart like buggy
And how do I programme a differential?
I have also read that you can have two motors at the rear wheels and just use torque inertia as a differential
Therefore not needing an electronic differential
Just after any info I can get
If you can help
Many thanks!


Mod: link to old Thread
https://forum.allaboutcircuits.com/threads/1-motor-vs-2-motors-electric-go-kart.152721/post-1311895
 
Last edited by a moderator:

jpanhalt

Joined Jan 18, 2008
11,088
I strongly believe that project-oriented learning is better than simply trying to learn something like programming from reading a book. However, based on your questions, this project may be too much of a challenge to start with.

Have you looked on the Internet for any answers? Presumably you want an electric model. One motor or two? Live rear axle like this or completely independent rear wheel power with a motor on each? As for programming the motors, have you heard of PWM? That is how you can use your arduino to control motor speed. You then need a speed sensor at each wheel (like anti-lock brakes cars) so the arduino can adjust power to each wheel appropriately.
 

shortbus

Joined Sep 30, 2009
8,464
Don't know how they do it today, but back in the day of gasoline engine karts, the ones powered with two motors had each engine driving it's own wheel. This was usually done by a sprocket and chain mounted to the wheel. Where a single engine used a live axle, the two engine used a dead, non rotating axle with the wheels having their own bearings. No differential was used at all in them, the wheels are such small diameter they didn't need one.
 

Wolframore

Joined Jan 21, 2019
2,249
yeah but we still know pitman steering and differentials are nice to have. I'm building a custom radio flyer frame for my grandkids and it's getting pitman steering. Hmm... not sure if it's necessary but it will turn much nicer. I might put in a camber to it as well.
 

strantor

Joined Oct 3, 2010
5,527
The reason why limited slip is a benefit to single-prime-mover vehicles is that without it, if one wheel slips then all power from the single powerplant goes that wheel. With two powerplants this seems (to me) a moot point. I don't think you would need to give much thought at all to preventing slip on one wheel or the other; nor would you need to worry much about turning radius. As long as both motors are torque referenced (as is typical for traction systems) the cornering should work itself out.
 

shortbus

Joined Sep 30, 2009
8,464
I might put in a camber to it as well.
Camber or caster? Caster usually is used to make it steer easier, and straighten out after the corner.

differentials are nice to have
The karts I was talking about were raced on asphalt locally and the single drive wheel alowed them to "drift" like the big guys in 1/4 and 3/4 midgets or the stock cars did.
 

Thread Starter

Nunkmolian

Joined Nov 10, 2020
3
I strongly believe that project-oriented learning is better than simply trying to learn something like programming from reading a book. However, based on your questions, this project may be too much of a challenge to start with.

Have you looked on the Internet for any answers? Presumably you want an electric model. One motor or two? Live rear axle like this or completely independent rear wheel power with a motor on each? As for programming the motors, have you heard of PWM? That is how you can use your arduino to control motor speed. You then need a speed sensor at each wheel (like anti-lock brakes cars) so the arduino can adjust power to each wheel appropriately.
Yes
Have studied Pulse Width Modulation quite a bit
And want to use two motors on the rear wheels each independently driving just one wheel each
Am just wondering
Is there some form of template that you use for the electronic differential?
I have heard of a calculation based on the speed and steering angle that determines each wheel speed
But am not sure how you would programme it
I imagine that there is some sort of programming template.
And am wondering what sort of axle system I should use if the wheels are to spin at different speeds
Or do I not use an axle
If not
What do I use
 

jpanhalt

Joined Jan 18, 2008
11,088
Aren't those decisions you should make after some study? The axle design I linked to in post #3 would seem simpler and less complex than doing without one.
 

Thread Starter

Nunkmolian

Joined Nov 10, 2020
3
Aren't those decisions you should make after some study? The axle design I linked to in post #3 would seem simpler and less complex than doing without one.
The problem with that axle is that the wheels cant rotate at different speeds
As will be needed when the vehicle is turning
I want a motor for each rear wheel
That can rotate separate from each other
But am not sure how its done
 

jpanhalt

Joined Jan 18, 2008
11,088
Sorry about that. I found a design with a fixed rear axle and independent motors driving each rear wheel separately. Imagine each rear wheel and its drive linkage attached by bearings to that axle. I figured the fixed axle would reduce sway and complexity of the rear suspension. There were pictures of the completed build, but they didn't show the drive clearly. I thought the eBay picture showed that type of drive but was obviously wrong. My apologies. I would envision attachment to the fixed rear axle somewhat like front wheels are attached on a tapered spindle to handle axial forces.

Maybe this link shows the concept better: https://www.diygokarts.com/kart-plans/plans-rear-drive-system.html It uses a single motor, but one could use the same concept to drive each rear wheel separately.
 

shortbus

Joined Sep 30, 2009
8,464
The problem with that axle is that the wheels cant rotate at different speeds
As will be needed when the vehicle is turning
In my opinion, from doing this type of thing as a teenager that didn't at the time know any better, your over thinking this. Do you know how many karts were built that didn't have a differential? I can assureyou it is many, many more than ever had one. Just the diameter of kart wheels is one reason they don't need or use differentials, then you get into the weight of a kart compared to a car or truck, that has one. Now you can argue that riding lawn mowers use a differential, but they are making a much sharper turn than you will be in a kart, and people don't like to see skid marks in their grass.

To put a more fine point on why they aren't need in a kart, start researching something called the Ackermann principle. While it looks like most of the Google searches don't address it now Ackerman also includes the rear wheels or did years ago. But if you study the Ackerman principle you can and will see that as weight, wheel base and tire diameter get smaller the need for a differential gets less too. https://what-when-how.com/automobile/the-ackermann-principle-as-applied-to-steering-automobile/

You don't say where your located, but if your dead set on a differential you could get one from a riding lawn mower and then modify it to fit your kart. By putting two sprocket on the ring gear to accept the drive of the two motors.
 
Top