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2011 MK3 Version

This 2011 Lithium 15 MPH BM3 powerchair evolution continues on from the original BM1 & BM2 powerchairs. Which started out life initially as a Sunrise Quickie F55s powerchairs.

It now has almost no original standard parts or any of the original layout or "positioning" of motors, seating, wheels, batteries C of G etc left.

A total re-design. This includes, motors, wheels, tyres, control and battery system, wheels, tyres, seating position C of G, etc. It is a TOTAL re-design using practically no original parts.    

More info:      BM3 Home
       BM3 Lithium battery
       BM3 15 MPH
       Charging Lithium
       Construction detail  
       Roboteq controller
       PDF Summary Printable
Current version 2010:      BM2 Powerchair
Original version 1998:      BM1 Powerchair  



Because its light, strong and adaptable and looks good. About the only "good" part on the original F55 powerchair! The rear light cluster is another.

Although that frame now has a huge chunk cut out of it to allow re positioning of motors and batteries.

BATTERY LAYOUT IS TURNED AROUND NORTH/SOUTH & replaced with a huge (3x more powerful) Lithium Ion Phosphate battery. Which sits in a totally new fabricated centre section, that is also the mounting point for the new more powerful / faster motors in a better position, footplate, and almost everything else! 

The batteries are turned around to allow the motors to be mounted some 3 inches further inboard too. For a very good reason.





Larger View

Here is a  picture of a partly completed BM4 power wheelchair sat on my kitchen floor!  >>>


This new layout/centre section allows 6 inch wide "fat" all terrain or turf tyres (tires), to be fitted for a bunch of very good reasons! (later!)

while keeping total width to 26 inches, because I want this chair to be OFF ROAD and OUTDOOR as well as totally INDOOR capable. Wider that 26 inches is simply too wide!!!

An extra inch here & it feels like a truck indoors. 26 inches is as narrow as any indoor powerchair with a fat guy sat in it can be!  And the same as most other inferior "Hi end" modern powerchairs with full sized "Group 24" batteries and "skinny tyres" can be...

It means the best of both worlds. Indoor width, and outdoor all terrain tyres for ride comfort and snow/mud/sand capability.

Most parts here are fabricated from scratch like this complex centre section, mentioned above and built to my own design. It puts anti tips, motors, wheels, and total length etc to exactly where I want them to be.  But it also has to be capable of 3 different lead battery configurations, and 2 different Lithium battery setups. While being "crash safe" as I drive a van from this powerchair. It also needs to ensure 4 inches of ground clearance, bigger motors, fat 6 inch wide tyres, and get the C of G in the correct place, provide mounting points for footplate, seating, vehicle tie down, correctly position the anti tips, look cool, and be easy to make at home! To produce a far better chair than the one the frame rail came from. Lots of very careful design and no compromises here. It defines the whole powerchair!

Some parts are replaced with other components, often from non mobility devices. E.G. the high powered high voltage Roboteq Controller! Or the quad bike wheels and tyres, or the Lithium battery. Or the mass of karting derived "rose joints" or industrial rod ends, & fabricated bars and footplates, etc. Or the motors from a different powerchair. Or the hobby based Hyperion Charger! etc.

I just polished its rear wheels...


With centre cap installed.


wheelchair tyresTYRES & WHEELS

REAR:  Winter, 145/70 - 6 (14.5 inch) all terrain tyres fitted to the 4.5J x 6 wheels for snow, mud, sand. £49 a pair delivered from eBay... all terrain wheels   

Summer, 15 inch 6.00 x 6 tubeless 4 ply puncture resistant Kevlar shielded "turf" tyres, for summer &/or pavement use.

Off road wheelchair tyres medium 
Off road wheelchair tyres large

Either of these tyres fit. Rims are 4.5 wide, and 6 inch diameter. Can be either the cheap kids quad bike wheels in steel, or the better alloy aircraft quality HEGAR split rim wheels.

BOTH are great absorbing the shocks our streets dish out at low running pressures and with huge sidewalls.

The one on the left here is great on sand, snow, or mud. But it wears very fast on the roads in summer time. Width of chair using these tyres is just - 25.5 inches.

The one on the right (fitted) is tubeless and also Kevlar "K Shield" reinforced like a bullet proof vest. So zero punctures!

The council use these turf tyres on mowing machines. They run over broken bottles at the road side all day long. They are puncture free in any normal use.

And they give a much better ride than the usual skinny hard 3.00 x 8 standard powerchair tyre. Also works great on most sand and mud in summer, but does not wear out. At least its damned near impossible!  These are the tyres I use most of the time. Width of chair using these tyres is 1 inch wider at 26.5 inches.

If you are worried about marking carpets, these are also better behaved than the off road all terrain tyres.  Both are HUGELY better in every situation than stock wheelchair tyres!

FRONT:  3.00 x 4 (9.7 Inch Diameter) tyres, fitted to lightweight 3 spoke 4 inch wheels, (EBay again) using 10mm (lighter) stainless steel axles, and stainless steel sealed bearings for zero corrosion and much better service life. And lower mass to prevent caster flutter at higher speeds.  F55 caster forks fitted with stainless steel bearings, and redrilled for through axle, to remove bolt loading forces.  Scroll down for pictures.


Roboteq Wheelchair ControllerCONTROL SYSTEM

Roboteq Controller separate page here!

The Roboteq Controller HDC2450 High Efficiency £406 (imported from the US and VAT free for mobility use).

No industry powerchair control system from any manufacturer has anywhere near enough power for 15 mph capability +  high torque.

All of them are limited to antique lead based 24 volts maximum systems.

Boring & slow and very inefficient and a peak of 120 amps "boost" for short periods of a few seconds at the very very best available. 

That's not even close to enough total Watts for a 15 mph powerchair!   Its not even really enough for a decent 6 mph powerchair. So I am not using a mobility system! Since they are stuck in the dark ages like the powerchair manufacturers.

I will use a Roboteq Controller  Specifically the 50v HDC2450 150A-300A High Performance (See Link) -- Running on 45 Volts for around 14,000 watts of power!  A True 150 Amps per channel (300A total @ 45 volts)  2.5x + the power output of any current existing wheelchair system. And it will be smooth, direct and very controllable once I am done!


A very steep ramp for wheelchair access!This is to be an ALL DAY use, long range, powerchair.  Even with its 15mph capability 45 miles is a reasonable expectation. The result will be masses of torque when required and great turn and acceleration on the 150 amp 50v controller. Lots of accurate control, No more suffering at 6 mph in the cold or travelling along a dangerous road looking for a ramp or curb cut while trying not to be killed!

Remember that Ohms law states that ANY motor (or resistance) will draw double the amps at double the voltage. And the groove motors draw well over 120 amps stalled or at lower speeds under load on just 24 volts...  So on double the volts you really do get double the power.

This means a huge potential 18.7 Hp (14000 watts) is available from the controller although less will be left at the wheels! Some gets wasted as heat.

I need this amount of power & the sort of torque and control really needed for ramps like the one opposite. As well as for off road or use, hills, or beaches.  The ramp here in in my local pub!


"Powerchair controllers" as fitted to normal mobility devices, just cannot do this ramp opposite in my local pub.  Even with sedate 6 MPH gearing or speeds of "normal" chairs. They really struggle with torque and either lose control or just stop.

I have never found any production powerchairs other than my own modified ones, that can properly climb this ramp with any real control. At least with a fat adult sat in it such as me!

Most cannot climb it at all.  And either get hung up on anti tip wheels or rear casters or simply have "stalled motors" and will not move without a "straight" run up. And there isn't room for that! You HAVE to turn as you get onto the ramp. NO stock chair can do that. 


To build a true 15 mph+ powerchair that can properly negotiate this steep ramp is completely impossible with existing powerchair control systems and old style lead batteries.

This is a true 14+ degrees.  14 degrees doesn't sound much does it? Looks even more impossible in real life. I am about 20 Stone in weight. Some chairs can "do" 14 degrees, but these cannot actually steer as they transition onto the ramp, so in real world conditions their specifications are meaningless.  There isn't a straight on access to this ramp.

I need to use this ramp at least 4 times daily as its the back entrance to a local bar where I go for a beer...  Nothing keeps me from my beer! But more importantly it shows up the shortcomings of conventional battery and mobility power systems.

Groove motors, wheel adapters for bigger wheels!MOTORS:


These are 8.5 mph standard powerchair motors as used on the fastest Quickie "Groove" powerchair.  Chosen for this project because they had more torque than any other 8 or 8.5mph powerchair that I tested. Most have very little -- these were great considering the gel batteries etc.

I tested a LOT of chairs!  But these will have much more torque AND speed with double the voltage! My BM3 chair is using a purpose built 45v Lithium ion Phosphate battery rather than 24 volt lead (gel) batteries, & 150 Amps per motor from a very powerful Roboteq controller rather than the 120 (peak) that is used on groove powerchair the motors came from..

When on my 45v system they will go 15 MPH (because RPM per Volt is a linear relationship) and have MUCH more torque.

So 15 mph will be the speed. And with 300 amps total to play with should be able to plough a field.  As long as they don't break or melt!  If they do then I will find some better motors. But initial testing shows no problems.



Some "Bounder" wheelchairs in the US can do 11.6 mph (claimed) but with just a 120 Amp controller and 24v old fashioned Lead Acid (Gel) batteries for power they struggle very badly for torque and control. Show one a hill or a beach and its screwed unless you are a 13 year old ballerina!  They are suitable only for very lightweight users and flat ground.  Mine will have MUCH more power! (around 2.5x more) compared to the "fast" bounder wheelchairs. In fact it should have more torque than ANY other mobility products.

Speed on a powerchair usually limits range. Due to taller gearing sucking battery amps. I will not have that problem due to the lithium battery and almost double the voltage. So its real world range will be a true 45+ miles with 3x as much stored energy as the usual pair of large lead acid (gel) batteries! 

Double the volts, with 150 Amps (250A peak) per motor... Is like comparing a 4 cylinder 2 litre engine to a 7.5 litre big block V8!



size="2"The shiny things (above photo) bolted to the motor let me bolt the cheap all terrain wheels I need for smooth ride and sand/snow to the Groove motors. And the summer Turf Tyres too.   Heree  for a zip with drawings and AutoCAD file etc.  THESE adapters only allow the cheap steel kids quad bike 3 bolt wheels to fit.

I actually made steel ones later on shown here to fit the better alloy Hegar 6 bolt wheels I ended up using.


THESE ones opposite (no drawing) allow the fitting of the better alloy aircraft quality HEGAR wheels shown further down the page. This is a pre powder coated picture and very hot! >>>



Here for a zip with drawings and AutoCAD file etc. 5 OR 6 MM STEEL ANGLE IS REQUIRED HERE, NOT THE 7MM SHOWN ON THE DRAWING. 




Motor mounting plates / brackets.  Soon to be WELDED ON to the centre section!

These allow me to mount the Groove 8.5 mph motors to the side of my yet to be designed battery box...  ;

They have bolt holes to allow temporary testing bu0t will be welded in place on the new fabricated centre section eventually








Lithium Ion Battery Pack separate page here

  • The SAFE LITHIUM battery technology used means this powerchair is SAFE. These don't burn or explode!
  • A huge 50lb lighter than if it had 2x group 24 Lead batteries. That's a HUGE weight loss!
  • 3x the range!  Or 3000 watt hours stored at hi-rate discharge means around 3x the power of a pair of heavy group 24 batteries.
  • Almost zero self discharge means they do not go flat if unused! And they don't care if left unused/discharged anyway.
  • EXTREMELY low internal resistance allows smaller capacity/higher voltage to be used for increased speed with NO LOSS OF RANGE OR TORQUE! So I use 45V for a "free" boost from 8.5 to 15 MPH! These batteries can handle it, lead/gel cannot!
  • 2000 cycles at 80 percent. Compared to around 300 for lead/gel real world. And with 45 miles range you may need to charge just once per week. That's 2000 weeks use. Or 38 years! No need to worry about battery life, they will outlive the chair and myself! 
  • They can be charged at 5C or about 20 mins should you want!

Fast long range lithium powerchair battery

Shown here temporarily fitted into my new home built centre section while under construction.

Link to my Lithium Ion Battery Pack page



Rather than buy a used donor chair to cut up as I usually do, I bought just an old main frame, and a basic seat frame. And the caster forks. The ONLY parts of the donor chair I actually use. And these parts are modified and cut up anyway as you will see..

The main frame for e.g. has to have a chunk cut out to allow me to fit my new longer thinner battery and motor mounting "part". Or rather a complete fabricated centre section. It replaces a mountain of Sunrise parts with one carefully designed simple one. It allows me to turn the batteries north/south, and move the motors inboard, shorten the wheelbase, increase ground clearance, and get rid if about 100 spacers, brackets, covers, and other useless heavy complex stuff.

The anti tips are re located inboard, higher up, and are much shorter and stronger. All in the interests of a more agile shorter chair while fitting wider low pressure tyres for off road and snow/sand capability..

This allows me to fit three lead batteries batteries (36v) or my new lithium battery. And my bigger faster motors and STILL keeps total powerchair size exactly the same as the tiny Mk2 version.

This allows the motors to be moved inboard, and the batteries to be turned around, and lithium batteries fitted longitudinally. Target width is still just 26 inches or less. Even with 11 inches of fat all terrain tyres. So that it is STILL compact and BETTER indoors than other less capable commercial hi-end powerchairs.

With that in mind I cut 179mm out of the used frame as seen in the following image.

wheelchair frame ready to cut

Freehand but carefully measured! 179mm to allow 1mm of filing to correct any inaccuracy. Nice colour! Soon be powder coated black...  I can cut straight. Most people cant so the bit below had some tape wrapped around it as a guide. I only did the first cut. My carer, Brain, did the second one....

Wheelchair frame cut

Done! This gap will be 181mm once tidied up. Why? Because that's the width of the battery, metal sides to the battery box / new centre section to be fitted, allowing for some free clearance, that I will make next! Its this size as the batteries need to fit EXACTLY with no free play or wasted space.

Frame cut, wooden mock-up of new centre section in position for new powerchair

How do I design the new centre section? Well its not going to be made from wood! This is 3mm plywood. The real one will be made from 3mm steel..

I think very carefully about the exact motor positions, how they will attach etc and required strength, as well as where the C of G will finish up. I look up the total MAX battery dimensions and weight of the lithium pack I will be using.

Other way around!

And I need to keep the caster wheels from hitting the new centre section, as well as the total wheelchair length as short as possible. (about 35 inches including footplate) And total width down to 25.5 inches or less INCLUDING the fat off road tyres to be used. So what looks like a simple thing actually really isn't... Its a lot of extremely careful juggling of figures in my head. And as a proof of concept its easier to build a simple ply mock-up to be sure I am happy with everything. E.G. the rear anti tip wheel height, was just changed too allow wilder wheelies! 

OK that took hours... Now I just need to order some 3mm steel and TIG weld it all together. Actually I just gave the plywood model to my local engineering shop with a full page of measurements to copy. Since I wanted two making and its hard work if you are doing this in a bedroom!. Remember its always cheaper and faster to do two at once. It is almost as cheap as doing just one.

OK two centre sections done! To match my beer mat drawings and copied from my plywood model..

Not bolted in but propped in place here badly!

Total width 26.5 inches with these tyres. And just 25.3 with the 145/70 - 6 all terrain tyres. Measurements are dependent on tyre pressures and actual manufacturer. But under 26 inches just as seen here!

Motor angle. Well almost this is just stood here on my bed and a drink can! But you get the idea.

From another angle.

There will be a steel block mounted by bolts or welded to the side here for strength.

For anyone following this build here are some beer mat engineering drawings for some more parts required.  I am building 2 chairs so there are double the quantities you will need here!


Falling off the bed....

Front view...

I don't build my chairs down to a price, like manufacturers do. Instead I build up to the best quality and finish as well as performance as I can. Yet still it always works out hugely cheaper. Depending on how well you buy your gear, how much you pay others for work and how much you can do for yourself. I am seriously cheap!

Cost estimate is considerably more than the MK2 6 mph version as the 8.5 mph motors alone are not cheap. And there is the Roboteq controller and lithium batteries, rather than two cheap lead acid (gel) ones to buy...  

The MK2 BM2 Chair cost around 1700 UK pounds total. The BM3 here when complete will be about 2700 UK Pounds finished to show standard.


Motors mounted, centre section mounted, mini bike 3 spoke caster wheels fitted with stainless steel bearings to modified F55 caster forks with alloy spacers and 10mm stainless steel axle. Axle now passes through the caster forks so that loads are not transmitted to the fixing bolts as per sunrise... Stainless bolts and bearings to prevent any future corrosion. Will be polished and fitted once everything is re assembled after powder coating.

Rear wheels are located further forwards under your backside for control, and for wheelies, and to allow use on soft ground without caster wheels sinking. They will be very lightly loaded on completion. As per the MK2 chair.

Getting there!

As usual, every inch counts. So the stock sunrise medical "canes" are shortened drastically. You do not need push handles on a powerchair. These will be powder coated, and a new plastic plug stuck in the end!

This is a standard seat frame. It is modified by cutting off the awful swing away footrest mounting points. They get in the way of my legs, stick out interfering with transfers, and are only needed with those awful "swing away" footplates that most chairs are lumbered with. They hit every doorframe. So a simple central one will be used. It will be powder coated and a plastic "moss" plug fitted to cover this remaining hole.

A new seat mounting plate with multiple holes allows the seat to be relocated up to 2.5 inches rearwards. This has lots of benefits. Including a shorter chair that isn't nose heavy like all the production chairs...

Seat mounting plates as used above that move the modified seat base back (to move the C of G rearwards by around 2.5 inches) are used. These ones are now available ready made on my forum by a guy that is making parts for other people to use. See Martin O Refurbisher...

Footplate fitted. Seat front edge is rubber mounted - see blocks here. The seat centre rear -- your C of G is free to pivot on its mounting. So the fat rear tyres give your backside an easy life. The footplate is connected to the seat front edge. So as a caster wheel hits a bump it rises up but your feet don't. Its the same as having front suspension. The seat and footplate stay smooth and level, while the casters and front of the chair bang about over bumps...  Every bit helps!

In order to fit the HEGAR alloy split rim wheels, I had to make new wheel adapters. I made four. Because I am building 2 powerchairs. These will be welded to the original Groove motors "hubs" (the black thing)

Like this!

Sprayed black, and fitted to the motors, ready for the wheels. (lower down!)


This is the chunk of metal to be welded to the bottom of the powerchair. It allows a strong short 16mm bolt (actually a tow bar bolt) to be screwed into the bottom of the powerchair in 3 different positions.


See below...


















The new centre section/motor mounts/frame mountings, and vehicle tie down are now TIG welded together forever. All the temporary bolts can now go in the bin.

There are NO unmodified Sunrise F55 parts here at all in the above pictures!  There are 54 "one off" fabricated "burgerman" parts, or other non powerchair parts here, (not including stainless bolts etc)

There is 1 set of Sunrise Groove motors. (About to be tortured at 45v...)

There WILL be no unmodified sunrise f55 parts at all when completed other than the arm upright bits, and the arm bottom brackets. The rest of the arms will be replaced.

There will be no industry standard controllers, wiring, batteries, on this chair at all.




Attention to detail. It matters.

HERE are stainless steel bearings so they don't do what most caster bearings do, they never corrode and fail!

They bearings on powerchair casters get human and pet hair / fibre wrapped around the axle and under the rubber seals. This lets water in. Water causes corrosion and the bearings die soon after. Stainless steel bearings do not corrode, so do not fail.

Also the lightweight 3 spoke alloy wheel is heavily powder coated. And the axle, spacers, and and bolts are also stainless steel. Assembled carefully with loctite bearings, and spacers checked for length and re machined as required.

Steel axles, steel bolts, steel bearings, thin paint, and so on just will not do here! The wheel is also carefully balanced. Before fitting to the caster fork. The caster fork is also modified and drilled to allow the axle to pass right through. Because the bolts should NOT take the load!

Everything is put together with this much attention to detail and with the best parts. My chairs do not fail or break, and look good years later.




We are now using HEGAR alloy wheels, and different wheel adapters. These are much better quality, and properly designed for these tubeless tyres. They are split rims, and sealed with silicone rubber in the centre. Here you can see the high quality gloss hard powder coating on every part. Every bolt is stainless steel, and every bearing also is stainless steel. There are 16 stainless steel bearings in this picture! As well as two stainless steel needle bearing hinges on the battery compartment door! And 10 rose joints...








Its also extremely short! When the deep footplate is fitted, it is still under 37 inches long... Shorter than all other hi end power wheelchairs.













No footplate, or mountings fitted yet. Later!

Its all here ready to fit. And uses another 12 rose joints, and two rubber anti vibration mounts for the seat.

We only use the best coatings, stainless steel or other non corrodible materials. And everything is built with real attention to detail. 












Notice the 12 inch floor tiles. This chair is still narrow even with a full 12 inches of shock absorbing low pressure high floatation puncture proof Kevlar lined tubeless tyres.















Very high, short, small anti tip wheels. And 3x the power of a normal hi end powerchair means I will be able to flip myself over the back at will. The throttle pedal goes both ways however...






ROSE JOINTS FROM http://www.mcgillmotorsports.co.uk/index.php?act=viewProd&productId=12

STAINLESS BOLTS FROM http://www.westfieldfasteners.co.uk 




With centre cap fitted in wheel.


Battery fitted above 7 pictures...

Added modified seat base, on home designed mountings, and home designed adjustable footplate... 

If a jobs worth doing its worth doing properly! There is now 18x 8mm Rose Joints on this chair!


>>> Larger images here <<<



What's the purpose of the pages about the MK3 chair and the earlier MK1 and MK2 chairs since I don't sell them? To embarrass the manufacturers into getting with the show, and doing some real development work. And to show other wheelchair users especially Paraplegics like me, what is possible. As such there are others now doing the same or similar, many are members of my Message board.

More info:      BM3 Home
       BM3 Lithium battery
       BM3 15 MPH
       Charging Lithium
       Construction detail  
       Roboteq controller
       PDF Summary Printable
Current version 2010:      BM2 Powerchair
Original version 1998:      BM1 Powerchair  


  • My NEW Lithium Battery Fast BM3 Powerchair (under construction) HERE

  • Or see the BM2 highly modified chair I have been using for 2 years HERE

  • Or the slightly modified BM1 HERE













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