PDA

View Full Version : Rebuilding an Assistive Device using the HB-25



rjo_
03-18-2009, 11:17 AM
Hi guys,

I'm rebuilding a scooter for my son's Special Olympic Coach's son, Joel. Joel has Down's syndrome. The only things he can't do are read and talk.

The only problems with the scooter are that the motor won't turn, the Curtis motor control board is shot, and the micro-controller is fried. Other than that it is perfect.

The scooter started life with a differential drive, transaxle AMT Schmid motor, geared to about 300 RPMs... 24V about 15 Amps.

The question for tonight is whether the HB-25 can drive a 1 horse motor... which is about 800 Watts?

Thanks,

Rich

kwinn
03-18-2009, 11:29 AM
The HB-25 is rated at 6 - 16V at 25A continuous, 35A peak so I don't think so. It will handle the current but not 24V.

rjo_
03-18-2009, 11:43 AM
Kwinn,

I agree about the 24V. But I don't have to use the same motor... everything needs to be rebuilt anyway, so I am free to choose the motors. My intuitive sense tells me that a 12V motor running at about 20A would be adequate... and I can always use two motors... so if I can really only get about half a horse using the HB-25, I'll just use two motors.

The other issue is useful travel. My understanding is that 24V motors are more efficient... roughly twice as efficient as a comparable 12V motor... so that would mean that the useful range would be cut in two or that I would need extra batteries.

I'm not an engineer... so predicting what peak voltages, etc, etc... is pretty much like rocket science to me.

I kind of expect that we have some guys that know the exact answer... "yes do it" ... or "no... go the other way." Which would
mean getting a 24V controller.

Rich

rjo_
03-18-2009, 12:19 PM
Oops... it isn't rocket science.

20 amps at 12V gives 240 watts...and this is a trike, which means that I only have two wheels to work with, 480 watts:)
800 Watts at 300 pounds = 20 miles an hour... so, ideally, 480 watts should give 12 MPH... just about right?

Philldapill
03-18-2009, 12:32 PM
Rich, I can build you a spankin' motor control. :)

Does this need reverse or is it just a forward only drive?

EDIT: Super cheap, of course. Only the cost of parts, which should be minimal(~$20). Remember, I enjoy this sort of thing, plus I've already designed a couple high power motor controls for myself.

rjo_
03-18-2009, 02:01 PM
Phildapill...

I should have known:)

I will no doubt take you up on your offer... but before we do that let's see what the experts have to say. I want to make sure we are talking about the same thing. I not only need a controller... but I'm planning to use the prop to control it...are you talking the same animal?


I'm a little tired... and I should be in bed... so this is going to sound like I should know when to shut up...

Motor control is one of those subjects that just never seems to end. I'm real comfortable with my HB-25s...

It looks like there is a hobby type 24V 25Amp controller from Dimension Engineering (called the Sabertooth 2x25). It is not cheap, but it uses TTL signals etc. etc. I've seen a couple of posts here regarding DE's 2X10 unit, so there are some guys with fairly specific experience.

My main issue is making sure I can use a Prop. The controller is one of those things I almost understand but just not quite. I understand what a differential drive is... and I'm assuming that with two motors, and with independent control from a Prop, the right software makes a differential drive.

Then there is the issue of electromagnetic breaking... is this just a motor with special software... or does it have to be wired specially?

There are lots of safety features to be emulated... and of course, I have no intention of stopping with a rebuild... I'm going to add a Ping unit or two,
an accelerometer, vanity LED's etc.

AND with all that experience... I should know enough to get back to building a rideable dancebot:)

Tomorrow is another day...

Thanks

Rich

rjo_
03-19-2009, 11:19 AM
After studying this issue yesterday and today, it appears that all of the motors that I would want to use, fall out of the specs of the
HB-25. But in theory, I think the HB-25 should be just adequate, if I could find the right motors, which I can't:)

At the moment, I'm watching Ebay for a motor... after that it will be a matter of either finding the right controller or mostly likely asking Phildapil to build one:)

SRLM
03-19-2009, 11:35 AM
I saw an add for this company in Robot magazine, and it mentioned that they have controllers for 55V 70A and lower with Dynamic brake and clutch output.

http://vantec.com/

edit: Look at this one:http://vantec.com/rsfr.htm. It has 140 V at 320 A! I'm sure a couple of those with the suitable motors will really make that kid fly!

Post Edited (SRLM) : 3/19/2009 3:52:24 AM GMT

W9GFO
03-19-2009, 11:51 AM
I have a old electric wheelchair with two 24 volt motors that I want to make into a robot. I have been thinking of using the Vantec controllers, they are not cheap. If Phildapil can make one I'll be right on it!

Rich H

Philldapill
03-19-2009, 11:55 AM
DC Motor Controls aren't that complicated. Usually, they only consist of a high power H-Bridge for forward and reverse. For dynamic breaking, the H-Bridge is switched off, so that no current is flowing through it to the motor. The motor windings are then fed through a boost converter to step up the voltage so that the momentum of the motors/wheelchair can recharge the batteries, causing the motors to slow down.

Sure, I can build a high-power drive. I'm always up for a new design project :)

W9GFO
03-19-2009, 12:22 PM
Well if you do go ahead with it, here is what I would like;

FWD and REV
Dynamic braking would be nice, regenerative - even better, but neither a requirement.
30V Supply
30 amp Continuos duty

PWM control input

*I'd rather see the Accel/Gyro board first though!

RIch H

ianw
03-20-2009, 12:45 AM
Since it seems you haven't purchased the motor yet, have you considered a brushless design? Most of the parts are now cheaply available in the RC hobbyist community. I think the segway uses this, and several of the electric bike conversions are moving to this design too. Better efficiency, smaller motors, etc.. Throw in some LiFePO4 batteries and you will have a really nice and lightweight scooter. You'll probably want to limit the speed though : )
I've often thought an open source powered wheelchair that followed this design direction would make sense.
OSMC is an open H-Bridge design for brushed motors, but I've not been able to find an open brushless controller capable of 10A+

rjo_
03-20-2009, 01:06 AM
ianw,

In terms of open source wheelchair designs... there is definitely a need. Maybe that is what this thread will turn into:)
There is a general consensus that wheel chair designs are lagging behind the available technology. It seems that the way the world should be going is in the rare earth disc (hub) type motors. I'm doing this as a favor and I am trying to spend as little as
possible (since I'm not paying the bill:).

Phil,

Young man... everything is simple once you understand it. For purposes of this thread ... what you are doing is rocket science... OK? (Never hurts to Spin your public image:)

Rich

Philldapill
03-20-2009, 04:33 AM
Ha! Thanks, Rich. Oh, and thanks for the plug in your PropPhone thread! :D

ianw
03-20-2009, 08:10 AM
>It seems that the way the world should be going is in the rare earth disc (hub) type motors.
OK, I'm not sure I agree with this statement though - hub motors are not ideal for many applications, and they tend to be pricier and bulkier than the non hub varieties.

>I'm doing this as a favor and I am trying to spend as little as possible (since I'm not paying the bill:).
I've not done a detailed cost comparison, but I assume the cost is not too far off from a similar brushed setup. I have some wheelchair motors, and they weren't very cheap, likewise I have a few of the hobbyist H-bridges sold by robot-power and others and they aren't that cheap. The same amount of copper, FETs, etc. is used in brushless/brushed - so commodization based on large production numbers is the metric to follow. Currently there are a lot of brushless controllers and motors being pumped out of china for the hobbyist RC community. Hobbycity has good prices - I can find nice 25A controllers for <$15. And since the brushless designs are more efficient, more of that amperage is being converted to work instead of heat

I'm not familiar with costs for the larger brushless motors but they are coming down in price - I'm using much smaller motors ~10A and they cost $10-$15.
This guy did a nice brushless recumbent design using a belt drive instead of hub motors, but used all top of the line equipment so he could get quick acceleration and 30mph speeds (e.g. Castle Creations ESC's, and high end 4000 watt motors), I'm sure it was not cheap. Look at the size of his motor though, it's slightly larger than my fist but can handle 4000 watts and is 93% efficient at 2000 watts.
www.wisil.recumbents.com/wisil/shumaker/default.htm (http://www.wisil.recumbents.com/wisil/shumaker/default.htm)
you could do a slower handicap scooter much cheaper

LiFePO4 is still pricey, so probably stick with lead acid for batteries to cut cost

Anyway, just my 0.02

rjo_
03-20-2009, 11:03 AM
IANW,

I just jumped into this... absolutely no useable knowledge whatsoever. So any info you offer is news to me:)

You are right on price. The ball park estimate that I have seen is that brushed vs non-brushed is somewhere between 25-35%.
I can't seem to find any reliability info on hub motors... and I think they are going to be too expensive anyway.

I took a look at the recumbent bike and then went over to castlecreations.com...they have some amazing motors...
http://www.google.com/search?hl=en&client=safari&rls=en&q=AXI+brushless+outrunner+motor&start=20&sa=N
http://www.castlecreations.com/products/neumotors/nm2200.html
10,000 watts!!!!! and an 8mm shaft:)

I have no idea how to guess about the gearing... if you look at the final gear on shumaker's bike... it is just amazing. And he gets to change gears and pedal any time he guesses wrong. I think Joel could handle a gear shift... if I put a little LED to tell him when to shift.

We are looking for 10 mph tops with a total gross weight of about 350lbs + the weight of the motor. The trike has to be able to climb a hill because his house is on a bluff and the bowling alley is in the valley.

The other problem... I have a complete machine shop, but I've never used it...don't ask:)

And I'll remind you that some folks can study their entire life and still shouldn't use a lathe:)

We do have two jell 12V batteries that seem to hold a charge, so that is one thing we don't have to worry about yet.

I actually did find a 12V brushless motor that seems like it would do the trick... but couldn't find a price and then forgot to save
a link. Now I'm wondering if the HB-25 will handle a brushless motor... I would think so, but maybe not at 10000RPM's :)

Rich

W9GFO
03-20-2009, 02:36 PM
Brushless motors are three phase motors, they have three wires. Swap any two wires and it turns the opposite direction. The controllers have to sense which pair of wires to send current through based on back emf (I think) and what you want it to do. The HB-25 definitely will not work with a brushless motor.

Every motor has an ideal speed where it is most efficient. Generally that is pretty high rpms. Hub motors, as far as I know, are really only good when traveling at a certain speed. For a bike, probably ok but I think you want something that is efficient at around 3 mph. BTW, 10 mph is fast for an electric wheelchair. The two that I have had top out at around 5 or 6 mph and they were of the several thousand dollar variety.

Also, you might want to check craigslist. I have seen several electric wheel chairs offered for free, one of which is in my garage - apparently, as I was told, it is hard to donate them, the usual places either can't accept them or have too many.

Rich H

ianw
03-20-2009, 09:52 PM
Yes, a brushless motor is electronically commutated so no HB-25, this article would be a good place to start: http://en.wikipedia.org/wiki/Brushless_DC_electric_motor

>BTW, 10 mph is fast for an electric wheelchair.
I think he is designing a scooter though. A brushless motor system could be optimized for lower speeds too (i.e. wheelchair) - e.g. most people aren't driving their segway at 10 mph. Although some optimize their wheelchairs to be very fast if you look around on various forums.

>Also, you might want to check craigslist. I have seen several electric wheel chairs offered for free, one of which is in my garage
I'll keep this in mind next time. I bought a several year old model off ebay a few years ago, and after watching/bidding auctions for a few months, I still spent several hundred dollars. New they are $1000+

>went over to castlecreations.com...
castlecreations does have nice ESC's and motors but they are way over priced unless you really need every bit of power

Post Edited (ianw) : 3/21/2009 8:00:06 PM GMT