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alanganes
07-10-2010, 09:18 AM
One of our sons has a neuro-muscular condition that limits his mobility. He can walk and get around on his own, but his muscles tire, weaken, and hurt before very long. When we go out to a museum or someplace similar that requires a lot of walking, he uses a wheelchair, but even propelling himself in that wears him out. And of course the wheelchair is not very good once you get off of reasonably hard, flat surfaces.

So one of the things I've been working on is an electric scooter for him to to get around on. Yeah you can buy them, but no 11 year old wants to cruise around on an "old lady scooter" (his words...). Plus most of them are heavy/bulky and don't do so well off of hard surfaces. We finally got to do some extended road trials yesterday:

A pic of it:

http://img.photobucket.com/albums/v479/alanganes/Ray%20scooter/ray1.jpg


And a couple of (sorta large) videos:

http://img.photobucket.com/albums/v479/alanganes/Ray%20scooter/th_MVI_2336.jpg (http://smg.photobucket.com/albums/v479/alanganes/Ray%20scooter/?action=view&current=MVI_2336.mp4)

http://img.photobucket.com/albums/v479/alanganes/Ray%20scooter/th_MVI_2335.jpg (http://smg.photobucket.com/albums/v479/alanganes/Ray%20scooter/?action=view&current=MVI_2335.mp4)


Not bad for a first outing. Still needs some refinement (like brakes...) but it went great even on the grass. It will easily negotiate most of the trails that we walk down to go fishing.

This is still "prototype" stage, but am pretty happy with the result. It breaks down into smaller pieces without tools for getting into and out of cars and such. Going to invest some bucks for a much lighter battery pack that has equal or better capacity than the two sealed lead-acid bricks that are on there now. They near double the weight of the scooter.

Of course he also wants a built-in IPOD dock, and a winter camo paint job.

If we get any dry weather over the weekend I'm going to strap the GPS to it for speed and distance/charge tests.

It is hard to convey how thrilled he is with this thing. He just zipped back and forth across the park for over an hour, a big stupid grin on his face. Tooling along like that must be a great feeling for a kid who never was able to even ride a bike.

I can post some better pics of the scooter and how it breaks down when I get back out to work on it some more.

Thought some of you might find this interesting.

-Al

Ken_Shea
07-10-2010, 09:29 AM
Way cool Al,
Who wouldn't want one of those :)

Goes at a pretty good clip to, maybe too fast ?

DFMiller
07-10-2010, 09:59 AM
Cool work Al.
So what are the details on your existing batteries? How many AH? What's system voltage?
With that we can make some suggestions. For max energy density some form of lithium is in order. Once we know the details I might have some novel ideas.
Dave

Evan
07-10-2010, 10:01 AM
Outstanding! I know exactly how he feels. My condition has precisely the same effect.

I presume you are using a commercial motor controller. You can get ones that have a braking feature built in. Motor braking is very effective. edit: It looks to me that the controller has a braking feature.

It's 24 volt and the motor is 350 watts. The batteries are about 20 amp hour VRLA type.

gnm109
07-10-2010, 10:21 AM
That's teriffic! He looks like a fine young man as well! :)

I'd much rather have something that my father had something to do with, too!

Could you post the details about the motors? I presume that it's two 12's in series for 24VDC. I need to do some more work on a reverse for my Harley sidecar and what you have there looks like it would be perfect.

Mcgyver
07-10-2010, 10:48 AM
that is very nice, great build, way to go....like Ken said who wouldn't want one. Must have been a great feeling making such a useful thing for you son.

alanganes
07-10-2010, 11:34 AM
Thanks, guys.

I know Evan has spent lots of time researching this sort of stuff, he was pretty close on the hardware.

Some details:

Frame is 6061 Al rectangular tube, mostly MIG welded construction, thanks to the guys on the welding forum here. The three major parts interlock as it is assembled, so no tools or fasteners are needed to stow it for transport. The frame, motors and controls weigh a bit under 30 pounds. The present batteries are around 26 pounds.

System is 24V, two 12V, 18 AH SLA. They were picked up used (free) and are of unknown overall condition, but do charge normally and have decent running life. We have not run them to cutoff yet, so I do not know the ultimate range at this point.

Motors are two 24V 250W PM electric scooter motors. These are the ones:
https://www.electricscooterparts.com/ProductDetails.asp?ProductCode=MOT-24250B

These seem to generate plenty of power. It moves me around (at over twice his weight) without problems.

Correct on the controllers, Evan, I used these:
https://www.electricscooterparts.com/ProductDetails.asp?ProductCode=SPD-24250

I used one for each motor controlled by a common throttle signal.

Evan, I don't know if these controllers have dynamic breaking built in. I got them mostly because they were a cheap and expedient way to see how this thing was going to work. They do have a "brake" connector on them which I presumed served only to cut power to the motor when a mechanical brake is applied. I may have that wrong. Do you know any more about these? I'm certainly not adverse to switching controllers for better capability. Dynamic braking would be a much simpler alternative to mechanical brakes, though I have some ideas how I might implement them.


Ken, It is on the edge of being "too fast" perhaps, but he is a pretty sensible kid and not overly given to doing stupid/dangerous stuff. On the other hand, I believe it is not such a bad thing for young boys to have at least a bit of opportunity to push the envelope a bit, so I discarded my original plan to add a speed limiting to the controls. Of course once he got a feel for the way it ran, one of the first things he did was to race his little brother. :eek:

gnm109 - The motors are 24V units, so likely won't be so good for your project. Electric reverse for a sidecar sounds like a cool and unique project.

And thank you, you are correct, he IS a fine young man. He is in near constant state of pain and is often near exhaustion from doing nothing, has endured several years of very uncomfortable medical tests, but NEVER utters a complaint about anything. He is always in a good mood and very upbeat. In many ways he is one of the toughest people I know.

Thanks for the comments and any additional ideas, guys. Like all such projects, it is never REALLY done.

-Al

Bill McLeod
07-10-2010, 01:48 PM
I there was a contest for "Best Project" you would win hands down just because of that no so silly grin !!!!!!!!!

Black_Moons
07-10-2010, 01:58 PM
Awsome design, I really like how you kept most of the weight/stress over the back and front wheels, so that the frame could be minimistic.

Some of that wiring in the back looks like it could be secured a little better.. Any vehical has vibration issues to contend with loosening all the bolts and connectors.

Zip ties work well for the wires, As well as giving it a couple once overs with a wrench to tighten any bolts working there way loose (Usally, once tightened enough this stops..)

Arcane
07-10-2010, 03:00 PM
Next thing you know, he'll be wanting (and you'll be building) something like this...:D No "old lady scooter" stigma there!
http://www.sitbetter.com/blog/wp-content/uploads/2009/10/tank_chair.jpg

alanganes
07-10-2010, 03:22 PM
Awsome design, I really like how you kept most of the weight/stress over the back and front wheels, so that the frame could be minimistic.

Some of that wiring in the back looks like it could be secured a little better.. Any vehical has vibration issues to contend with loosening all the bolts and connectors.

Zip ties work well for the wires, As well as giving it a couple once overs with a wrench to tighten any bolts working there way loose (Usally, once tightened enough this stops..)

Thanks, I did try to keep the weight back over the rear wheel, as you note. The seat post is angled forward like that in an attempt to shift enough weight forward to reduce the tendency to do wheelies. Pleanty of low-end torque with these motors. That seems to have worked as planned.

That is a fair observation on the wiring, it will be done properly. This was just the quickie setup to keep stuff out of harm's way so we could test the overall concept. I plan on doing a much more integrated setup on the wiring once all of the details are ironed out.

Right on on the vibration too. There are not many threaded fasteners on this, and I used split lock washers and removable loctite on most of them. A couple that I forgot were on the bottom of the seat. The nuts vibrated off of two if those bolts yesterday...

alanganes
07-10-2010, 03:23 PM
Next thing you know, he'll be wanting (and you'll be building) something like this...:D No "old lady scooter" stigma there!


Yikes! I better hope he never sees that or I WILL be building one!!

oldbikerdude37
07-10-2010, 03:25 PM
Thats a nice scooter you made, im sure others will see it and want one.
Looks like if it could hold a fat old man and a set of golf clubs then I would like one.

Kenwc
07-10-2010, 03:28 PM
That's one of the coolest shop made scooters ever. I was amazed at the speed. I'd be interested to know the top speed when you find out. I use a power wheechair that's rated at 7.5 MPH (motors) and (batteries) for 30 miles on a 5% incline with a 250 lb person abord. I don't weight near that much so it runs forever.

I totally agree with him on the IPOD dock....it's a must have....

Evan
07-10-2010, 03:58 PM
Unfortunately no dynamic braking on those controllers. They will shut off the power when brake is applied. You can take advantage of that to rig your own dynamic braking by using the brake switch to operate a horn relay(s) wired to just one of the batteries for the relay coils. Use a separate relay for each motor. Wire it so that when it is closed it applies a resistor across the motor terminals. This will give pretty good braking and won't overload the controller if it happens to be in circuit when power is on. (shouldn't happen)

The resistors can be a couple of 55 watt headlamp bulbs. The motors will generate about half the rated 24 volts maximum so 12 volt bulbs shouldn't blow. They can be used as brake lights too. If the braking effect isn't enough just add another bulb in parallel.

I will have a look around online to see if I can find a reasonably priced controller with dynamic braking.

I didn't see the other motor or I would have revised my estimate of the wattage downward. I do think it goes a bit fast and he will probably flip it at some point, hopefully on the grass.

doctor demo
07-10-2010, 04:20 PM
I know You said it isn't finished yet and He's an eleven year old boy but You could at least make him a padded seat.

Steve

Black_Moons
07-10-2010, 04:25 PM
Evan makes a good point about fliping it, Tricycle designs suffer from being easy to flip if you simutaniously slow down and turn (When they have 1 front wheel), You should probley make sure he sees some morons on youtube falling off trikes :) they are not very stable.. Infact I think those where basicly banned here due to being too dangerious (Quads still allowed)

Insure he knows that high speed is only to be used on the straightaway and you won't tollerate him trying to turn at high speed because his first indication of turning too hard will be it fliping, not skiding.

Making him wear a helmet would'nt be a bad idea either. (Its law here that everyone on a bicycle even must wear a helmet) If you let him pick out the helmet to his liking he will be much more likey to wear it btw.

Hawkeye
07-10-2010, 05:05 PM
Cool Build!!

Here's some wheels w/sprockets and brakes for under $20.00.

http://www.allelectronics.com/make-a-store/item/WH-19/ELECTRIC-SCOOTER-WHEEL-W/SPROCKET-AND-BRAKE/1.html

gearedloco
07-10-2010, 05:11 PM
My wife uses an "old lady's" 4-wheeler made by "Pride." It's the smallest 4-wheeler they make. She previously had a similar 3-wheeler but she dumped it a couple of times and the results were not pretty!:eek: :eek: The fact that she's on warfarin didn't help.:(

The "front end" of the new scooter is pretty simple and quite effective. Essentially, the front wheels have axle stubs mounted to king-pin assemblies which in turn are mounted to a front axle. The front axle can pivot a couple of inches in a vertical plane to provide equalization. This works very well on uneven surfaces. It keeps all four wheels on the ground quite nicely. When the equalization range is exceeded, the inside front wheel will start to lift, but since the outside front wheel is outside the center of gravity, it can't lift very far.

The only tricky part of the design is the arrangement of the steering rods on the king-pin, needed to compensate for the fact that the inside wheel follows a smaller radius than the inside wheel does in a turn. I'm sure that there are others here that can explain it better than I. For some reason the term "Ackerman effect" comes to mind, but that name may be something I picked up in a Sci-Fi story sometime. I can take and post some photos if it will be helpful.

If he complains to much about having 4 wheels, add a couple of (smaller?) motors to the front end and make it 4-wheel drive. That should do it!:D

The mechanical brake releases when power is applied. I think the scooter may have dynamic breaking, but it's hard to tell. It can be manually released, but the drive is disabled when that happens. In the final form, a key switch would be a very good addition.

She used to complain that I walked too fast, but now when we go somewhere she's usually way ahead of me.

Again, that's great. I'm sure he appreciates it more than you can know!

-bill

DFMiller
07-10-2010, 06:53 PM
Have you ever measured the peak current on the motors in operation?
Dave

gda
07-10-2010, 08:03 PM
Good for you. I have a daughter with medical problems as well. It is great to be able to make or modify things for her.

alanganes
07-10-2010, 08:05 PM
Evan, great idea on using headlamps for braking resistors. I'll try that. I had a relay system such as you describe in mind, I'm interested to see just how effective the dynamic braking is in practice. I checked the controls and they do not brake, as you suspected. I really did not figure they would, what do you want for 30 bucks?

The stated cautions about top speed and flipping are appreciated and well taken. We have helmet laws here as well for bicycle riders. He will, for the near term anyhow, be using this only with supervision and will be held to reasonable speeds. As I said, he is a pretty responsible kid for his age and can generally be counted upon to do as he is told.

Dave, I have not yet measured peak motor current draw. I'll post it here when I do.

I know for a fact that it will hold a fat guy, have not tried with golf clubs yet, though.

And yep, Steve, the padded seat is coming. My upholstery skills are pretty weak though.

4WD and Ackerman steering!? Sounds like maybe "Scooter 2.0" in the making!

Again, thanks for chiming in and for all of the great suggestions and ideas.
-Al

Your Old Dog
07-10-2010, 10:07 PM
Great job on the lean project! I like it. Always been a big fan of simpler is better engineering and that looks pretty lean. I do hope you'll consider working on a 2 wheel front end for safety sake. Trikes were outlawed because of there horrendous track record. Now that you got something for him to use, he can use it while you build up the front end you want.

Really nice job for what appears to be a really nice lad.

I have the skeleton of the old lady type in the loft of my barn. I may be able to supply you with the controller you want. It was my Dad's old jitney and the axel housing broke on the motor so the controller should work fine. Might even have the key lock for it. If so it's yours, I'll get back to you tomorrow.

ldn
07-11-2010, 02:25 AM
Nice project, he sure looks happy. I like Evan's idea about using headlamps as braking resistors -- actual power resistors get really hot.

By the way, if you've never tried it, dynamic braking works astonishingly well... But it won't stop the wheels from rolling slowly, so friction brakes are probably still a good idea.

I hope you'll post again when it is complete.

I noticed a couple of people talking about working with DC motors and I wanted to drop this link here:

http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXLMV0&P=FR

I have the "Watts Up" meter and is it very useful when experimenting with DC motors. It will handle up to 100 amps and give you good data on peak current draw, amp-hours drawn, etc.

Evan
07-11-2010, 03:22 AM
Another easy way to measure current draw is to use a piece of 14 gauge house wire as a shunt for a regular digital volt meter. One metre of 14 ga wire has a resistance of almost exactly 0.01 ohms. If you run power through that and measure the voltage drop in millivolts across that wire each 10 millivolts equals an amp of current. You can coil up the shunt in a figure eight pattern and twist it together so it does't take up much space. By coiling it in a figure eight it also has practically no inductance.

Fireman11
07-11-2010, 01:25 PM
For "other" batteries take a look at:
http://www.batteryspace.com/
For example:
http://www.batteryspace.com/lifepo4prismaticbattery256v40ah1024wh100aratewithb alacingpcm.aspx
That would get you halfway across the country. Or more resonably:
http://www.batteryspace.com/nimhbatterypack24v13ahnimhbatterypack20xfforhi-powere-bikesorrobots.aspx
12#, $350, 13AH.
Nice job on the project. May I suggest a helmet.

alanganes
07-11-2010, 03:29 PM
Thanks for the links to the batteries and the "watts up" meter. That is a really nice gadget that seems to pack lots of useful function into a $50 device. I'll likely end up building one into this, it will make a great fuel gauge as well as giving some useful data on how things are working.

Good tip on the quickie shunt, Evan. I've done something similar in the past using steel pallet band material in calibrated lengths to make custom high current shunts for test panels at a place I once worked at. I had a low ohm bridge with Kelvin clips available to dial them in, made it much easier.

Once again, Thanks for all of the input.
-Al

ldn
07-12-2010, 01:50 AM
One metre of 14 ga wire has a resistance of almost exactly 0.01 ohms. If you run power through that and measure the voltage drop in millivolts across that wire each 10 millivolts equals an amp of current. You can coil up the shunt in a figure eight pattern and twist it together so it does't take up much space. By coiling it in a figure eight it also has practically no inductance.

Nice tip, I'm definitely going to use that at some point.

darryl
07-12-2010, 02:53 AM
Adding to the 'quickie shunt' idea- many of the little analog meters found in various older electronic items will go full scale with anywhere from 25 to 100 millivolts. I've checked some recently and found those to be in the 30 to 60 mv full scale range. A bit of math would let you set the length of the shunt for the amount of current you would want to keep an eye on. For instance, if you used the 60ma meter with Evans shunt, you would be reading 6 amps full scale. If you wanted that meter to read 60 amps full scale, you would cut the length of the shunt down to 1/10 of a metre. If you had a meter that gave full scale reading with 30 mv, and wanted to read 50 amps full scale, you would first figure that 30 mv would give a 3 amp full scale reading, then for 50 amps you would shorten the shunt to 3/50 of a metre, which computes to 6 cm.

You could wire that length of shunt permanently into the circuit since the most it would lose you is 30 millivolts, and that is at 50 amps. For lesser current draw, the loss of battery voltage would be less.

By the way, the length of the shunt is the distance between the points where the voltmeter leads attach. The high current connections must be made outside those points to isolate the voltmeter from voltage drops due to the high current connection points losses.

Most analog meter movements are non-linear, so you won't necessarily be getting a correct reading across the scale, even if you calibrate it for a correct full scale reading. A digital meter will work quite well for this and will be more accurate. The same calculations apply for shunt length, and it's actually easier because you can start by knowing what the full scale voltage requirement is- it's right on the meter at one of the dc voltage positions. I've got a really cheap digital here that has a 200 mv full scale setting. To use that, I'd make the shunt length to suit a 200 amp full scale, so the current draw is read out directly in amps. The length of the shunt between the meter leads becomes 10 cm.

There will be some heat generated in the shunt because you have current flow and voltage drop. Say you have 100 amps flowing- that's going to give a 100 millivolt drop on that 10 cm shunt. That works out to 10 watts, which will get that 4 inch long (10 cm) shunt pretty warm. I'd be inclined to use a larger gauge of wire, say 12 ga or 10 ga, and work out the length for that. It will take about 20 cm of 12 ga to equal the resistance of 10 cm of 14 ga, so that extra length would spread the 10 watts out, keeping the temperature of the shunt down. My example is for 100 amps flowing, but most of the time it would be much less probably, so the actual heat generated would also be less.

A final point for now- a digital meter may not read correctly if it gets confused by interrupted current flow such as might be created by a controller circuit. In that case you'd have to add an integrator circuit to the meter leads. That's nothing more than a resistor and capacitor, nothing to be intimidated by. The analog meter would automatically integrate the signal it's receiving and would have no such problems (and also not require a battery).

alanganes
07-13-2010, 05:27 PM
So we took this out again last night for a bit more testing. Went out to a huge open grass field nearby. Started out will freshly charged batteries, they measured about 27 Volts.

I attached my small GPS to the kid, and sent him off. We tried a straight run across the (flat) field, with a short straight stint at wide-open-throttle. GPS recorded a top speed of 11.1 MPH(!). That is pretty close to the calculated number based on the motor rpm, drive ratio and wheel diameter.

After that, he just drove about the field at moderate-fast walking speed for while, until he could just "sense" a change in the response to the throttle, i.e. the batteries starting to fade. Not very scientific, I know, but close enough for right now. At that point he had logged 5.3 miles and the scooter still had plenty of oomph left. I did not have my DMM handy, but a check with the old Triplett analog VOM said the batteries were at a bit under 25 volts.

We had to leave at that point, but at 24-point-something volts, there was lots of mileage still to go. Even at that, 5 miles would be plenty for a museum or fishing outing. I expect on a smooth surface, and with out the "speed trials" the range would be further improved.

So far so good.

Thanks for all of the input!
-Al

darryl
07-13-2010, 08:02 PM
'driving about the field'- that's probably a good test as it would at least be a little harder on the machine than a smooth surface like a bike lane or whatever. If anything is going to prove to be a weak link, it will be more likely to show up in this circumstance, or with some hill climbing thrown it.

You probably should give it a hill climb type of test, just to ensure that it can handle that as part of an average driving cycle. I'd keep an eye on the temperature of all the components that pass the high current, which obviously included the motor and controller, but may also include some switches or relays, and wire connectors, etc. Any connection that might seem to be getting warm is probably going to end up being a problem spot.

That's a nice little machine- it's what I always wanted as a kid and never had. Now that I can build it myself and afford it, I'm too busy with other things to get back on my own electric 3 wheeler project. I'm hoping I will find time soon- it's been three years in the works-

Dawai
07-15-2010, 04:14 PM
Next thing you know, he'll be wanting (and you'll be building) something like this...:D No "old lady scooter" stigma there!
http://www.sitbetter.com/blog/wp-content/uploads/2009/10/tank_chair.jpg


HECK... I want one of them with a 350chevy running a hydraulic pump.

oldbikerdude37
07-15-2010, 04:49 PM
Next thing you know, he'll be wanting (and you'll be building) something like this...:D No "old lady scooter" stigma there!
http://www.sitbetter.com/blog/wp-content/uploads/2009/10/tank_chair.jpg


HECK... I want one of them with a 350chevy running a hydraulic pump.


Make it a hayabusa engine and add wheelie bars.

WaveDude
07-19-2010, 02:28 PM
Make it a hayabusa engine and add wheelie bars.

And add one of these:

http://i587.photobucket.com/albums/ss311/roxoevil/minigun.jpg

Too_Many_Tools
07-19-2010, 04:29 PM
Evan makes a good point about fliping it, Tricycle designs suffer from being easy to flip if you simutaniously slow down and turn (When they have 1 front wheel), You should probley make sure he sees some morons on youtube falling off trikes :) they are not very stable.. Infact I think those where basicly banned here due to being too dangerious (Quads still allowed)

Insure he knows that high speed is only to be used on the straightaway and you won't tollerate him trying to turn at high speed because his first indication of turning too hard will be it fliping, not skiding.

Making him wear a helmet would'nt be a bad idea either. (Its law here that everyone on a bicycle even must wear a helmet) If you let him pick out the helmet to his liking he will be much more likey to wear it btw.

I strongly agree on the helmet...visit a head trauma unit someday and you agree.

They have some great looking bike helmets...let him pick it out.

Great looking project....your son has a great Dad.

TMT

Too_Many_Tools
07-19-2010, 04:33 PM
About replacing that battery pack with a lighter one...that change will affect the center of mass of the scooter and its stability.

Before you finalize your design, use the final battery pack or its equivalent weight to determine if you are happy with the stability.

TMT

alanganes
07-19-2010, 07:23 PM
I agree on the helmet, particularly for use outdoors. No need for the trauma unit tour. He is #5 of 6 kids, we have had our share of serious injuries averted by helmet use. In particular, his older brother bonked his head on the pavement in an amazingly unspectacular bike spill about 12 years ago. He was wearing a helmet, but still had the memory of most of what happened that day knocked out of him. They did a CT (or MRI, i don't recall ) scan at the ER as a precaution, there was no damage. He (we) would have had a real problem without the helmet.

This scooter will most often be used as a substitute for his wheelchair to get around at stores, museums, and such. So no high speed stuff there.

Good thoughts on checking the stability with a lighter battery pack. Will make a note to do that.

And we already told him, no miniguns until he is 16.:mad:

Thanks again for all of the input!

michigan doug
09-07-2012, 03:10 PM
If you leave it as a three wheeler, you could put tip over preventer wheels on little outriggers at the front corners.

Excellent project.

Please carry on,

doug

browne92
09-07-2012, 03:45 PM
Brakes? You don't need no stinking brakes. :D

All kidding aside, I like the suggestion of some sort of friction brake in addition to dynamic braking. Even better if you could put some sort of a latch on it, to make it a parking brake, incase you have to park it on an incline or if it tends to roll when he's getting off and on. Not sure how you've got the throttle working, but maybe a panic button or magnetic switch/magnet tied to his shirt to shut it off if bad things happen.

Of course, there's always an ejection seat, but he'd probably have way too much fun with that. :rolleyes:

Dr Stan
09-07-2012, 03:59 PM
Next thing you know, he'll be wanting (and you'll be building) something like this...:D No "old lady scooter" stigma there!
http://www.sitbetter.com/blog/wp-content/uploads/2009/10/tank_chair.jpg

Looks like a project for flyo. :)