Another motor question?

[mnm99]

OK. I'll start out finding a 10 tooth motor sprocket. I'm going to order ( 2 )the 19.3" Wheeleez tire. They require a 1" axle. I'll figure out the hubs and mounts. So to reduce my speed a little to start my drive axle should be what? The motor came with a 12" tire and was a little faster than walking speed. Whats considered walking speed? 3 MPH?

Calculator shows 19.3" tire , Circumference of circle is 61.2612. RPM at 150. So with a 10 tooth on the motor and a 20 tooth on the axle I should be at around 4.35mph right? Thats a 2.1 reduction


http://www.compgoparts.com/TechnicalRes ... ulator.asp

[JoeC]

According to Wikipedia, average walking speed is just over 3 mph.

If possible, I'd get sprockets for a range of reductions between 2:1 and 3:1. If they're not cheap, maybe start with the next standard sprocket larger than 20. The low speed will make it easier on the motors, the controllers, and the batteries.

[woodygb]

10 teeth was just an easy example ...you might not be able to get the required bore in a 10 tooth sprocket.

I'm sure you can do the math for 15 , 20 or whatever tooth motor sprocket and the corresponding wheel sprocket..

You need to sit and think about the physical sprocket sizes and driving the Wheeleez wheel.

[Burgerman]

I would use toothed belts where there was sand, chains dont like sand much! Much experience of ruined chains on motocross type bikes...

[JoeC]

Have a look here for inspiration:

http://www.endless-sphere.com/forums/vi ... aca5415d44

There are a few belt drives there. There are some smart contributors there who are conscious of budget and weight, too, so I watch it often as I think of my ultralight project.

[Burgerman]

Why not just use the motors and controller you have for now. Use toothed belt to reduce speed to say 3.5 mph as its a fraction faster than walking. Will give more torque than stock.

Then whay you can fit better motors and controller to increase speed without losing the torque you need?

[mnm99]

Why not just use the motors and controller you have for now. Use toothed belt to reduce speed to say 3.5 mph as its a fraction faster than walking. Will give more torque than stock.

Then whay you can fit better motors and controller to increase speed without losing the torque you need?

Ahhhh. I wouldn't even know where to find belts. Besides the chair won't be used all the time. Maybe once a weekend to get on and off the beach.

[Burgerman]

Belts, toothed sprockets, chains and chain wheels, and taperlocks to fit all are commonly available on every industrial estate. Or online...

At 1001 places...

http://www.bearingboys.co.uk/Transmissions-1001-c

First one on google.

EG http://www.bearingboys.co.uk/22-8M-20_T ... ey-21453-p

They do belts, taperlocks to fit motor and wheel shafts, chains. sprockets ( as used here on my robot http://www.powerchair-review.co.uk/imag ... tion_3.jpg ) as well as bearings, couplings, etc etc...

Almost ALL industrial estates have a bearing place that also does power transmission stuff too. Just go in and ask them.

[Burgerman]

http://www.powerchair-review.co.uk/expe ... hair-1.htm

It might help to read these few pages from one of my old projects. It shows taperlocks, sprockets (you can use timing / toothed belts instead) and shows how simple a powerchairs electrics/motors are too...

[mnm99]

http://www.invacare.com/cgi-bin/imhqprd/inv_catalog/partsPHII_home.jsp?s=0&pagePostCount=1&partsHome=searchCategoriesToParts&formNbr=01-220&categoryDropDown=4845~Model+R51LXP+only~4845.pdf&selectedModelID=4845&catalogDropDownBox=01-220&fromPage=searchResults&partNbrOrDescr=1086222&catalogTitle=Nutron%c2%ae+

Seems to be 6 mph with 12.5" dia wheels

http://www.1800wheelchair.com/product/7 ... wheelchair

Go with a 2-1 ...twice the number of sprocket teeth on the NEW big wheel as you have on the motor / gearbox drive shaft.

I ended up winning these for $125. How can I figure out the rpm's? Using the calculator to figure out sprocket sizes I need to know rpm...

[JoeC]

If you have a source of power like a 12 volt (or easier, a 6 volt) battery, it's not hard. Get a piece of tape and stick it on the edge of the hub. Give the motor a low voltage, start a stopwatch, and count how many times the piece of tape spins around in a given time. From there it's just a little math to figure out RPMs at 24 volts. The motor spins twice as fast at twice the voltage, if that wasn't clear.

[mnm99]

If you have a source of power like a 12 volt (or easier, a 6 volt) battery, it's not hard. Get a piece of tape and stick it on the edge of the hub. Give the motor a low voltage, start a stopwatch, and count how many times the piece of tape spins around in a given time. From there it's just a little math to figure out RPMs at 24 volts. The motor spins twice as fast at twice the voltage, if that wasn't clear.

I'll do it for 15 seconds and count how many times it goes around at 24 v. How do i figure it out?

[mnm99]

22x in 15 Seconds.

[JoeC]

You counted 22 times in 15 seconds with 24 volts input? That's 88 RPM.

[woodygb]

(rpm * tyre dia in inches) /336 = mph

(mph*336)/tyre dia in inches = rpm

Assuming the specs I gave earlier are applicable.... 6 mph and 12 1/2 " dia tire.

(6*336)/12.5 = 161 rpm

Edit ..
(88*12.5)/336= 3.27 mph

[mnm99]

24v at the motor when tested. I used a volt meter. This was using the controller. Should I go direct.

[JoeC]

If you measured the actual motor terminals at the output of the controller, not just the battery, then there's no need. If you only measured the battery, you can't be sure it was putting out the full battery voltage to the motors. It's possible with programming that the chair is limited to put out something less than 24V.

If there's any doubt, use a direct connection with one battery. It should be half as fast as what you got before.

[woodygb]

24v at the motor when tested. I used a volt meter. This was using the controller. Should I go direct.

YES!

You've no idea how the controller is programmed...it could be set @ 60% or something!

[mnm99]

OK just did it again. ( 9 ) turns at direct 12v from battery this time.

[woodygb]

If you measured the actual motor terminals at the output of the controller, not just the battery, then there's no need

Apologies ..Joe was correct your meter would have read the % width of the pulsed 24v supply ...thus 24v = 100% width or full throttle.

[mnm99]

OK just did it again. ( 9 ) turns at direct 12v from battery this time.

edit..

[JoeC]

Something is odd here. 9 turns in 15 seconds is 36 RPM, and if you double that from 12 volts to 24 volts, it would go to 72 RPM. That's how the math works, and it shouldn't be off so much.

Are you sure that the parking brake lever was disengaged when you did the direct connection? If it was dragging that could account for the difference.

It doesn't matter if the tape goes on the wheel or the shaft, it will go around the same turns per minute either way.

[mnm99]

Something is odd here. 9 turns in 15 seconds is 36 RPM, and if you double that from 12 volts to 24 volts, it would go to 72 RPM. That's how the math works, and it shouldn't be off so much.

Are you sure that the parking brake lever was disengaged when you did the direct connection? If it was dragging that could account for the difference.

It doesn't matter if the tape goes on the wheel or the shaft, it will go around the same turns per minute either way.

Give me a min. I'll check the voltage when I count the turns in 15 sec. Be right back. I'll do both motors.

[mnm99]

Yup 9 turns 12.9V on one motor. 9 turns at 13.1 on the other.

[mnm99]

OK voltage was taken at the batt connector. I used a 16ga wire 1 foot long for the test. I connected 1 foot of 8ga and now get 11 turns.


OK....Last try. I tied both batt together with a 8 ga wire. 24 volts it turned 24x...

[mnm99]

OK voltage was taken at the batt connector. I used a 16ga wire 1 foot long for the test. I connected 1 foot of 8ga and now get 11 turns.


OK....Last try. I tied both batt together with a 8 ga wire. 24 volts it turned 24x...

I guess thats 96 RPM. OK I"M DONE>>>>>>>>Stupid me......The motor says @ 24V 110 RPM MIN right on the sticker. Could have lower voltage or the motor is worn a little.

[ex-Gooserider]

I agree with BM about the virtues of toothed belts in the final design, but IMHO, chains might be better in the prototype. Tooth belts are not cheap and are not adjustable for length. Chains can have links taken out or added in order to match changes in the sprocket sizes. Another potential issue is small stones and rocks, which can easily destroy a belt if they get caught between a belt and one of the pulleys. Another potential argument in favor of the chain is the width issue. The belts I've had experience with (on a couple of belt drive Kawasaki's) are much wider than the corresponding size chain. While overall width is presumably less of an issue on a beach chair than it would be on one intended to go inside, I can still see virtues to a chain in keeping the width to a reasonable level.

(worth noting as well that as sensitive to dirt as chains are, I don't know of any dirt-bikes that use belts...)

ex-Gooserider

[Burgerman]

But not many powerchairs have 50 bhp!

[Martin O Refurbisher]

My concern about chains is the impact loading going up kerbs and thro' potholes, ruts etc.

Rambing, DAFodil varispeed belt drives, Hydraulic couplings? Don't think so ...............

Belts can be adjusted to a degree by idlers, either sprung or manually adjusted.

Best,

Martin

[mnm99]

That was my thinking. I've owned quads ,dirt bikes and Go Karts using 35 and 41 chain in many rocky, dirty muddy spots and never had one brake or ware down fast.