Kawasaki Z125 Forum banner

1 - 9 of 9 Posts

·
Registered
Joined
·
932 Posts
Discussion Starter #1
Anyone know how many engine rotations occur for a single rotation of the rear wheel? I need to figure something out and haven't been able to check it myself yet, thought I would ask and see if anyone knows the answer.

Probably measured in 3rd or 4th.

Also anyone know the circumference of the stock sized rear tire? This one is easier to calculate, but again asking because I'm being lazy.
 

·
Super Moderator
Joined
·
1,875 Posts
I'll put down 10 bucks on ZAPH knows :cool:
 

·
Registered
Joined
·
804 Posts
Pumped some numbers into Gearing Commander, I'll do my math based on roughly 8k RPM since that's where my motor spends most of it's time.


Doing some quick math, I get about 10,690.9 revs per mile in 3rd and 8,602.15 revs per mile in 4th.

Cheated and used an online calculator to get tire circumference and thus tire revolutions/mile.


Final answer:
3rd Gear: 9.86 engine revs/tire revolution
4rd Gear: 7.93 engine revs/tire revolution
 

·
Registered
Joined
·
932 Posts
Discussion Starter #4
Hmm... There is lots of good info there that I can use.

OK, so it looks like there is around 1250 wheel rpm at around 10,000 engine rpm. And if I can get an 8 inch roller (roughly 25" circumference) then I have roughly a 1:2 ratio (wheel to roller) of around 2500 roller rpm. And many positive displacement pumps in the 20 horsepower range are going to fail a little bit above 3000-4000 rpm so I could probably use a 1:1 chain drive between roller and pump.

Now if I can only get a 6 inch roller (roughly 19" circumference) I'll have a 1:3 wheel:roller which would need a slight gear reduction to drive a pump, but still slow enough that bearings on the roller are not a huge concern.

And that's all for top gear, if I use 3rd then a 1:1 drive with a 6" roller is probably fine.

The question now becomes, can I successfully weld three 2 inch wide cast iron/steel wheels together to get a 6 inch wide roller (4 would be better and 5 would be best). And then can I attach a drive gear to the same cast wheels and keep the whole thing from blowing up at 3000 rpm and a 200 pound motorcycle strapped to it.

I have some 3 inch rollers, but I think the roller RPM will be much too high which will require really good bearings and a big gear on the end to gear it down to the pump limitations. I'll have to measure them again and see what I really bought those 3 odd years ago. Smaller roller means lower assembly height means easier to build and easier to break down to store.
 

·
Registered
Joined
·
804 Posts
How are you going to measure horsepower? I suppose I should google how a dyno actually works....
 

·
Registered
Joined
·
932 Posts
Discussion Starter #6
It is pretty easy with the pump and a valve. Close the valve creates more pressure, creates more force on the pump (pump can pivot). Then a lever arm to keep the pump from spinning and a force gauge under that arm (torque). I have a beginning post on my website that has a few links. To get power, you also need RPM, roughly torque * rpm / constant Power and Torque: Understanding the Relationship Between the Two, by EPI Inc.

The positive displacement hydraulic pumps/motors don't care if you use them as a pump or a motor, either way stuff moves through and the shaft turns.

Linky: DIY Dynamometer - part 1

I think I have a few more links squirreled away, need to get back to it. Finding the larger size rollers without costing a fortune has been the issue (well and other things). I'm fairly certain that the 3.5 inch rollers I have will place too much stress on their bearings when spun up around 10,000 rpm. I think a 6x6 roller would be better, and up to about 12 to 18 inches wide would be best (don't want the tires to contact the sides of the frame).
 

·
Super Moderator
Joined
·
291 Posts
I like where this is headed. Please keep us posted.

I wouldn't worry about the bearings. Go to a specialty bearing store and tell them what size, load and rpm you're expecting. It always amazes me at how little $$ a high end brand name bearing is when you buy it from the source.
 

·
Registered
Joined
·
932 Posts
Discussion Starter #8
Not sure this is correct yet, but here is one option for a pump:


$32usd is pretty cheap and probably a lot more pump than this rig will need or can handle. Pretty sure I asked the guys at the sensor logger manufacturer if that pump would do for 20hp, and I think they said it would be more than enough. Hoses and power control valve can be had on Amazon for not much money, make sure to uprate the hoses and connectors, 4000psi would be a good working pressure to start. The sensors and logging box are the expensive part, and not an area where I would skimp. In reality, you want to monitor the RPM of the engine and the RPM of the pump, need to make sure you don't over run the pump or bad things could happen and high pressure hydraulics are not to be underestimated, ever!

The roller is still the biggest hang up, $300+ for big rollers on ebay and no idea what kind of mods would be needed to make them work. Shipping is a big part, most are going to be VERY heavy and over $100 for shipping. That's what is really holding me back. Really need an 8 inch roller for anything that goes faster than these little guys can go, and then you'd want to gear them down pretty good to get there. I'm not confident that I can weld steel/iron wheels together to make a roller, welding cast or sintered is always an until it cracks solution.
 

·
Registered
Joined
·
932 Posts
Discussion Starter #9 (Edited)
I think I found something... We just had a roof put on the house, and parked in the driveway is this massive dumpster. A look at the dumpster shows metal "wheels" about 8 inches in diameter and about 12 inches wide. Ebay had nothing, but a quick google shows that there are companies that recycle parts off of dumpsters!


While that link says 8x6, the description shows 8x8 and says made of steel so it can be welded and machined to put a gear on it. Just need some decent bearings on one end or the other.

[edit] an ebay search in business/industrial for "ground roller" is yielding some decent results.
 
1 - 9 of 9 Posts
Top