Help with gearing

[tomo256]

Hi Everybody
As you know have i finished our toylander ( green one in the gallery  OBT 123 ) but i am dissapointed with the performance on inclines, so i have sourced a few spare parts such as a pair of fracmo 24 volt wheelchair motors that do 113 rpm, and also a 24 volt mobility scooter back axle and motor with a diff that does 160 rpm, i am unsure as to which setup to use but i will have to go 24 volt and am going to use 2 x 12 volt 35 amp gel batteries . Has anybody used any of these in thier projects and if so can they advise me as to the performance achieved and also the gearing they used, i will use the standard real life toys wheel sprockets and wheels.

Many thanks

[multisync]

Hi
Considering the complete axle unit, not the wheelchair motors.
The basic answer is quite simple, but it may be a bit long when written out.
If the original wheels were 10 inch diameter, and you want to fit 15 inch, thats an increase in size by a ratio of 3:2. You must therefore gear the drive to decrease the speed at the road wheels by the same ratio. The overall speed, and power at the axle will then be as per the original buggy, and as the weight will be about the same, the performance will be about the same.
This is exactly what I did and my Toylander and an identical buggy to the one I dismantled, have virtually identical performance.

If you don't know the original wheel size, see below.( sounds like 10 inch to me).
 If we consider the motor/diff/axle unit.........I assume that it is the axle, (not the motor), that does 160 rpm. Are you measuring this with full 24 volt across the motor. In practice the speed controller may have been adjusted to limit the top speed to 4 mph.
It probably has, or had, wheels with an overall diameter of about 10 inches, which have a circumference of about 31 inches.
It would therefore do 160 times 31 inches per minute. Or 160 x 31 x 60 inches per hour. Thats 297600 inches per hour. There are 63360 inches in a mile, so thats 297600 divided by 63360 mph. Thats about 4.7 mph. Probably a bit less as these buggies are supposed to be limited to 4 mph, and the motor may slow a little on load. So from the figures you quote this seems about right.

If you gear down more, you will have lower speed and more power.
If you gear down less, you will have less power but more speed.
Just like a pedal cycle, you can either have speed or power, not both.

Sorry this is a bit long winded, but I hope it gives the info you need. Let me know if I havn't made sense.

I cannot help with the wheelchair motors unless you can give more info.
These two motors may be more powerful than the one in the invalid buggy, or the two together may only have the same power as the one in the buggy.
Were they driving the wheels directly, or via gears?
What size wheels did the wheel chair have?
What speed was it capable of?

Best of luck
hope this helps
message me if you want more info/help
Walter

[markh15]

Hi Tomo,
The choice of motors used is up to you. Both types have there merits and drawbacks.

Speaking from experience, I have used the Mobility Scooter option, and the main drawback with the differential is that, unless you have a 'Swinging' axle at the front, if the car encounters a slight uneven-ness of surface, it is very easy to loose traction at the rear.

This aside, mine performs very well, even on grass, and as Walter has explained, providing you get the gearing right, it should perform the same as the scooter.

Because I had finished mine before the forum was up and running, I had to 'Fly Blind' so to speak, and guessed at a ratio.
As it turns out, the final ratio is 1.3 : 1, so the car still does around 8 mph flat out (I can't keep up with it), but the scooter I used was a 4 - 8 mph model.

The advantage of two motors is, you get the effect of a 'Limited Slip Diff', so if one wheel is slipping, the other will still drive forward, so the 'Swing' axle is not as important.

The only fly in the ointment I can see, is that you already have the standard 'Toylander' wheels, which I understand have quite small sprockets welded onto them.
I would advise that you use the twin wheelchair motors, and work out the ratio in the way Walter has explained to save yourself alot of extra work (and down time for the car), converting to the Scooter system.

If you should decide to change the gear ratio, 'Technobots' (www.technobots.co.uk) are really useful for chain and sprockets.

Hope this has helped,
Regards,
Mark.

[tomo256]

Oh dear what a minefield,

Basically i will be keeping the toylander 15.5 inch diameter wheels which have sprockets with 18 teeth.
The single motor that i will be taking off does 150 rpm and has an 11 tooth sprocket giving a speed of 4 mph.
If i fit two motors that do 110 rpm obviously one to each wheel but i want a speed of 6 mph so can anybody tell me what size sprockets i need to fit to the motors to achieve this.

                                                             OR

If i fit the scooter axle which does 160 rpm and achieve a drive via the same wheel sprockets and fit sprockets to the axle ends, what size sprockets do i need to fit to the axle to obtain 6 mph. All this is a black art to me so any help will be appreciated, i am leaning towards the scooter axle as it was designed to push a scooter and its rider so i think it is more up to the job.

[tomo256]

Sorry guys forgot to mention.
 scooter rpm were checked using a full 24 volts. I have no reference label to refer to and no idea as to the wheel size as i got it of ebay.

wheelchair wheels were 13 inch diameter and has the rpm stamped on the motor and were bolted straight on to the motors. I don't know the speed of the wheelchair but none of them are very fast from what i have seen. They have 30 amp stamped on them in the reference section of the label and 7 amp stamped in the amp section of the label ( once again confusing me ). they also have an electro magnetic brake.

Regards
Martin

[multisync]

Hi
If you fit 12 tooth sprockets to the mobility scooter axle, driving the 18 tooth sprockets as supplied on the wheels, you will have the 3:2 ratio that I suggested in the previous post.
This will give you the 4 mph drive just as the scooter had. (and is exactly the setup that I am using).
It will take 3 revs of the axle, with the small sprocket, to turn 2 revs of the wheel, with the larger sprocket. (Thats the same as 1.5 turns of axle for one turn of the road wheel.)
If you want to go 1.5 times as fast, you will need sprockets to give 1.5 turns of the road wheel for the same 1.5 turns of the axle, so a ratio of 1:1 is required.
So thats 18 teeth on the axle.
However this misses out one very important point!
The power of the scooter motor, is such that it can comfortably move the scooter and an adult along at 4 mph. Thats how it is designed.
If you gear to get more speed, you will lose out on power, and find that it may not start off, other than on level ground, and won't go up even slight hills.
It's the same if you have your car in too high a gear, it won't start off on a hill!
And if you have a pedal cycle, then you will need low gear to start off.
Unless your motor /axle is from an 8 mph scooter, you will find you need to keep the top speed to about 4 mph to be successful.
If it is from an 8 mph scooter it will be wider than the Toylander anyway as these scooters are much bigger than the 4 mph ones.
I know it's a lot to plough through, but if you read through Gremlins build blog, I'm sure he says that he fitted wheels directly to the axle, without reduction gear, and now finds that he has a good turn of speed but is lacking in power.
Sorry for another long winded answer.

I hope this all helps
Walter

[dale]

The advantage of two motors is, you get the effect of a 'Limited Slip Diff', so if one wheel is slipping, the other will still drive forward, so the 'Swing' axle is not as important.

That's what I thought when I opted for a twin motor setup on Jenna's Toylander.  However, in reality, if one wheel starts slipping, the other wheel will stop, as electicity will flow to whichever motor offers the least resistance (the motor connected to the spinning wheel)  That's why I ditched the fixed front axle in favor of a swing axle so quickly after completing Jenna's Toylander.  When I spoke to Richard about a swing axle, he remarked that he'd suffered damage to a Toylander as a result of it continuing to run at full power with a spinning wheel.  Effectively all 24 Volts went to one motor, and it was too much for the gearbox!

[jimmyybob]

The solution to this to use a tacho feedback i have only just got into this subject so i cant offer much advice but if you search for 'quadra' he has used a tacho feedback on his, it also gives you very high torque at slow speeds but you cant use the scooter controller you will need a 4QD controller for it to work.
Basically the tacho feedback supplies more power to the motor that needs it most.

[tomo256]

Hi Guys.
Thanks for all the advice, i think i am going to use the scooter axle and try the 12 tooth sprockets on the axle first. All going well i will try  13 tooth sprockets and keep going until i find a happy medium between speed and power.

Regards tomo

[markh15]

Hi Tomo,
If you start with 12 and 18 toothed gears, (the same as standard Toylander)your ratio will be 1.5 : 1, roughly the same as mine (1.3 : 1) and should be sufficient in both Pulling Power and Speed.

I don't know what engineering expertise you have, but, depending on the size of the sprocket, you might struggle to mount a 12 tooth sprocket on the scooter axle.

Just a thought,
Regards,
Mark.

[tomo256]

Hi Guys.
I don't think it will be too difficult to mount the sprocket on the axle as it is only slightly bigger in diameter than the standard motor shaft, so it only requires a little lathe work to the sprocket. I was going to make it a really tight fit, apply some heat to the sprocket, slide it on and when it cools fit a roll pin    OR    use the woodruff keyway and make a woodruff key and make it an even tighter fit and use the heat on one part and the freezer on the other part method and then maybe i wont need to fit a roll pin and damage the axle shaft thereby keeping my options open.


All thoughts greatly appreciated as most of you have a greater engineering ability than me.

Regards Martin

[multisync]

Hi Martin
I fitted my sprockets by machining them to a close fit as you say, I then locked them in place with two grub screws through the boss of the sprocket, one locates in the track for the woodruff key, so helps with positive location.
No problem so far.
Best wishes
Walter

[tomo256]

Hi Walter.
Thanks for the advice, that is even easier than i anticipated and as it has altready been proven by yourself i shall just do the same. Did you drill any kind of recieving hole in the axle for the grub screw that was not in the woodruff key slot, i also take it for granted that you used a thread lock solution as well.

Regards Martin

 http://www.youtube.com/watch?v=ycS6GLPHhj0

[multisync]

Hi Martin
I didn't have any grub screws at the time so I used some short bolts that I had available. The one that fits into the slot has the end filed down slightly so that it locates better. The other simply screws down onto the axle.
I always intended to change them for proper grub screws so I havn't even used locktite.
Another job I must get done one day!!
Take care
Walter

[tomo256]

Hi Guys.
I thought it was going to be too easy ! first problem is the scooter axle is too wide by 20 mm and is fouling the tyres. It is my intention to clamp the axle to the bench, lock off one end of the axle with a mole grips thereby allowing the other end to spin freely by way of the diff coming into play, i am then going to hold a hacksaw on the shaft and let the spinning axle shaft do the cutting for me. The reason i am doing this is because the axle is made of stainless and is hard as hell to cut by hand. Can anybody see any problem with letting the diff work so hard for say 5 minutes at a time or will it be ok?

Regards Martin