Cart/Wagon Drivetrain Questions

[bj2386]

Hi all,

Over in the Electric Projects subforum, I posted my plans for a battery powered yard wagon (Thread Here) a few days ago. I have some questions related to the drive-train that are not necessarily electric-specific, so I am posting those in this subforum to perhaps get more input.

As described in my design thread, my plan is to build the wagon with differential steering (like a skid steer or tank). In this arrangement, the two rightside wheels are driven together and the two leftside wheels are driven together. An 800w electric motor will drive each side of the wagon independently. See below photos.





I really don't have any experience with drivetrains, sprockets, chains, etc. so be prepared for some potentially dumb questions ahead.

Based on some youtube videos, I was initially hoping to install a second sprocket on the motor shaft (it comes with one 11T 420 by default) and have a chain running from each of the two motor shaft sprockets to the front and rear wheel, as seen below.



Unfortunately, after having received the motor, I have determined that the shaft is not long enough to accommodate 2 sprockets. So the single sprocket will have to do for now.

The fallback option is to now connect the motor sprocket to the right (or left) rear axle and then from the rear axle to the front axle. That arrangement will look something like this…



I assume it is advantageous to move the motor as close as possible to the rear axle in this case, which appears as:



As of right now, this appears to be the direction I am heading. The only thing that concerns me is how low the chain is to the ground between the two wheels. Clearance may pose a problem. Does anyone have any suggestions to improve upon the sprocket placement and chain path?

Another question related to sprockets. I have read it is not preferrable to have a very small sprocket directly linked to a large sprocket. In my case, the motor shaft sprocket is 11 teeth and the wheel sprocket needs to be 60 teeth (to limit maximum speed). Would this jump be acceptable or will there need to be a stage in between?

Also, I don’t know much about chain tensioning. If the sprocket distances are short (from the motor to the rear wheel), there doesn’t have to be any tensioning device so long as the motor mount is adjustable? I assume there would be tensioning on the chain between a front/rear wheel, but unsure what that would look like at the moment.

Finally, the motor comes installed with a #420 chain sprocket. Is 420 chain sufficient for this application? I am not familiar with the various chain sizes and was just going to go with what was on there from the factory.

Appreciate any input folks have on this topic. Thanks!

 

[ezcome-ezgo]

If the motor has/uses 420, stick with that throughout. Adjustable motor mount, adjustable wheelbase will deal with the tensioning. 11 tooth and 60 tooth will work just fine, no need to overthink.

Allow me to do some assuming: This vehicle is intended to essentially crawl, not haul 4$$? Will it need to steer? That will complicate the drivetrain considerably.

 

[JimD]

If you haven't bought the sprockets and chain yet, move up to #40 chain but keep with the #41 sprockets. The heavier chain helps out when your sprockets are not perfectly aligned plus it is a much beefier chain. #41 and #420 chain is the same thing but the #420 has been prestretched. A #40 sprocket will ONLY handle a #40 chain but a #41 sprocket will handle the #41, #420 and #40 chain. Stay away from #428 chain. What is the diameter of the motor shaft, how long is it and what size keyway is on it (want to know width of keyway)???

 

[bj2386]

If the motor has/uses 420, stick with that throughout. Adjustable motor mount, adjustable wheelbase will deal with the tensioning. 11 tooth and 60 tooth will work just fine, no need to overthink.

Allow me to do some assuming: This vehicle is intended to essentially crawl, not haul 4$$? Will it need to steer? That will complicate the drivetrain considerably.

Motor mount is adjustable. Hadn't thought about making the wheelbase adjustable. Not even sure what that would look like. I will need to search for some examples.

Yes, this wagon is meant to travel at low speeds (max 5-6 mph). I generally have no need for it to travel faster than I can walk. Like you mentioned, traditional steering seemed like a major undertaking, especially with my inexperience, so I instead opted for skid steer (differential steering) movement. There may be unforeseen downsides with that approach but it seems sufficient for the need.

 

[bj2386]

If you haven't bought the sprockets and chain yet, move up to #40 chain but keep with the #41 sprockets. The heavier chain helps out when your sprockets are not perfectly aligned plus it is a much beefier chain. #41 and #420 chain is the same thing but the #420 has been prestretched. A #40 sprocket will ONLY handle a #40 chain but a #41 sprocket will handle the #41, #420 and #40 chain. Stay away from #428 chain. What is the diameter of the motor shaft, how long is it and what size keyway is on it (want to know width of keyway)???

Thanks for the tip. It was exactly these kinds of suggestions I was hoping to receive by posting here. I'll definitely go with #40 chain then.

This is the motor I purchased: MOTOR. It is a dual-flatted motor shaft (12mm x 17mm ID). Shaft length is 1.25 inches.

 

[JimD]

Set screws would have a cup like point on them, you want to hit them on the belt sander to get them nice and flat. Use some blue loctite to hold them in place. I would swap out the set screws for some good socket head cap screws so you can torque them down good on the motor shaft since they will get a work out on the steering.

Get the sprockets bore size smaller since you will have to open them up to fit the metric shaft. Only the teeth are hardened in most sprockets so boring them open is not a problem.