Stutter at low speed forwards - but fine in reverse

[topherzee]

Hey there - I've been enjoying the forums. Doing a build with my kids and stuck on something:
* Motor jerks or stutters at lowest speeds going forwards.
* In reverse, all is smooth.
* If I lift the wheels in the air, all is smooth forwards and backwards.

Short video of problem:

I'm not sure if problem is mechanical or electrical.
There were similar questions in the forums about checking the throttle hall sensor.. but since its all working smooth when wheels are in the air - it seems to me that the throttle is fine.

Its strange to me that it works fine in reverse. Could it be the geometry of chain and gears? Are there some rules to follow there?

Battery is rated for 30amps continous. Its a my1020 1000w, 48v motor. I would have thought it has no preference for direction cw vs ccw, and in the air it seems happy in both directions.

Any ideas or suggestions?

Thanks, Topher

 

[EpsilonZero]

Can you list your motor, controller and battery specs? I have run into issues before with there being problems going forward vs reverse. They were voltage and controller configuration based.

 

[Functional Artist]

I can't tell from the video but, could be the motor be flexing a little bit upon forward acceleration? (with a load ie. on the ground, with a rider)
...& the chain is skipping over the teeth of the drive sprocket?

Try again & watch the drive sprocket closely
...or record it & re watch in slow-motion

 

[topherzee]

Thanks guys.

EpsilonZero here's Specs I can find:

Motor: From label:"ZY1020GD", 48 volt, 1000 watt, Input current 20.8A
Battery: 48 volt, Rated for 30A continuous
Controller: 48 volt, 1000 watt, (it came in a kit with the motor (yi-yun.com ?) I don't have much more info on it (https://forandor.de/drive/3980187-9...31c.html#/312-eigene_angaben_machen-1000w_48v)

Functional artist, I checked the motor - its quite rigid on the frame now.
Here's a slowmo video of the chain on the axel sprocket https://drive.google.com/file/d/1ovqSqeqOd6CEzbPjOT203b0S-fAiBdIm/view?usp=sharing
And here's the motor sprocket side: https://drive.google.com/file/d/1jmmHhiASC0rDyapJddCQNeWYzt2Pd82H/view?usp=sharing

Lighting is not ideal, but I confirmed that the chain is not skipping on either the motor sprocket or the axel sprocket. However there is some play on the attachment of the sproket to the axel and the attachment of the wheel to the axel, and a little play in the chain. So I wonder if the motor gets going in that little big of "play area" and then slams into the end of the loose area, giving the axel a push and then ... momentarily dying for half a second before doing it again?

I'll see if I can get the wheel and sproket more tightly attached to axel. And try to eliminate the play in the chain - though I guess the chain should not be too tight either.

 

[redflash]

what is your gear ratio ? I have an 1800 watt motor and needed an 8 to 1 ratio to get a 100 lb kid rolling. I also had to reduce my tires from 18 inches to 15 inches,,,,,had the same stuttering and puked that motor. Yeah these motors are cheap.......... yeah cheap. but thats about all you can say for them....as beginners we don't want to throw a lot of money into them. These particular motors ain't real good...the good and reliable motors cost around $500 each. between batteries, controller smaller chains etc...you can have $250 to $300 into these small motors and my experience is that a predator 212 is much cheaper and more reliable......to do a reliable electric your motor will be $500 and the controller will be $500 and then you usually need 60 to 72 volts which is a load of batteries. Don't mean to be depressing,,, butthats my experience !

Da Flash

 

[EpsilonZero]

Yes... fix the axle sprocket and wheel first. None of that should be slapping around. If it is still a problem, then continue to troubleshoot.

 

[topherzee]

Thanks RedFlash - the gear ratio is 100 to 11. I would have liked smaller wheels, they are 20cm radius. The thing that is surprising for me is that in reverse everything is totally smooth. So it seems like there is enough power. Also in forwards direction if you give it a lot of "gas" right away, then it zooms forwards. The stuttering is only forwards when you give it low throttle.

EpsionZero - Now we got the sprocket and wheel on fixed and the chain pretty tight. But the problem remains. Hmmm.

 

[topherzee]

We tried moving the motor from the left side of the cart to the right side (and flipping the axel too) So that the forwards direction of the motor is now the reverse. Essentially to test if its a problem in one direction with the motor.
The problem remains! Jerky forwards at low speed, reverse is smooth.

So I guess its more a geometry issue somehow.

 

[EpsilonZero]

You could try a larger axle sprocket, or a more powerful motor. 1000w is pretty anemic. I have had a similar issue before that was fixable with those two solutions.

 

[madprofessor]

I keep seeing movement in the drivetrain in my mind when considering this. A past experience with a gas engine's mounting plate being too thin and causing flex under load may have something to do with that train of thought.
Any time I hear of a power source having a problem in one rotation direction and not the other always has me looking at which way other factors in the drivetrain will try to move under load in opposite directions of force application. Like if a factor or combination of factors together can move things one way in one rotational direction and move things another way in opposite rotation. Swapping the motor around backwards with same results only tells you for certain if the motor bearings are allowing lateral motion or not. The rest of the drivetrain will have the same forces applied to it regardless of the motor rotation achieving your forward/reverse motion.
A lifetime of power transmission experience from small to huge tempers that line of thinking, and I've certainly seen where 3-4 small factors together can combine to make a single problem that's only affected by power source torque in one direction only. If a combination of small things like sprocket movement on a hub, or on an axle, or a worn wheel bearing, or squishy tires, or a flexing axle, or flexing mounting plate, or flexing frame are causing you any grief, then it will happen regardless of which direction you mount the motor.