What would you buy/build

[John Griffiths]

Hi folks, nice to join you.

I'm already a keen cyclist, I've been a mountain biker for over 20 years and also a bit of road riding. I've managed to pass my hobby, read obsession, on to most of the rest of my family, so my children (2 out of 3, the other will be clear in a minute) are bike bad and my wife has a crack now and then.

At 43 I'm still pretty fit and ride 3 times a week and even manage the odd cycling holiday. So the reason for looking to join your ranks is a bit different than most. Basically my oldest son is severely disabled and permanently in a wheelchair. For the early part of his life we have been able to use a normal kids trailer and I've been more than capable of towing him. But a few years ago he just got too big for them and as we live in a hilly area, was starting to get tougher for me.

Fortunately the trailer issue is about to be resolved with a great adapter become available in a couple of weeks to turn his off road 3 wheel wheelchair into a bike trailer. which is great, but is going to leave the issue of towing him.

I can probably still manage for a few years longer, although it will possibly limit our routes. His mum has no chance and as he is so poorly he has a care team, who have all expressed an interest it taking him out, but are not going to be able to manage it.

A few other point to consider, although towing Tom is above all my top priority it would be good to be able to use such an expensive item for other things, also some points I'm considering -

- my wife could follow me on some more challenging (longer, steeper) mountain bike rides.

- obviously I'm going to need a bit of power to pull him at 55kg, I know legally I'm restricted on road, but extra grunt for off road would be great.

- I was thinking a throttle may be a bad idea (I don't want to confuse the carers).

- but I was thinking proper hydraulic disk brakes would be a very good idea, as it's a lot to stop.

- my father (70) only lives up the road and has an expressed an interest in borrowing it to go back and forth when my mum has the car (he helps a lot with Tom)

- I wouldn't mind something I could enjoy now and again. My friends and I had a very quick go on a Hiabike at my local trail , we went from "that's cheating" to "I want one" instantly.

- a riding friend of ours has a long standing back injury that has stopped him riding 2 years ago. One of other friends has a fat bike (not electric) he uses mostly on the beach where he live, but we have all had a go and it's great fun off road. So he has starting looking at fat ebikes (he like the look of the new KTM one, I'm a secret fan of the surly one you can get in the states). So I've added them to my list. But it must not come at the expense of the main reason.

- reliability is high priority.

If it helps, I was (or am) a time severed Electrical Engineer, and although it was a while ago I still know which end of the soldering iron is the hot bit and as well as being pretty well mechanically minded, I have friends who are bike mechanics. So a DIY solution is not out of the question. Although time is aways a issue for me.

Price wise I was hoping to keep it around the £3000 mark.

So what would you buy?

Thanks in advance for any help offered.

John

 

[Deleted member 4366]

You need a very robust high-torque low-speed motor. I'd recommend a kit with the 201 RPM 500w rear Bafang BPM motor, 25 to 30 amp controller and a 20 aH 36v battery. The motor is not too heavy and has an internal free-wheel so that you only turn the wheel without power, not the motor. You can get them from a number of sources, but BMSBattery.com is the best one-stop shop.

The nearest equivalent in a ready-made UK kit is the Ezee kit, which is about the same size and weight, but a bit less torque due to the controller being only 20 amps.

There's som nice crank-drive kits from Bafang too. I think that their 500W BBS02 might be an option, but there will be a tremendous strain on the drive train when towing, which will make gear-changing difficult, and probably lead to early demise of your rear derailleur, chain and cassette.

You can also get a plug-and-play MAC kit from Em3ev.com, who have some nice frame batteries, but the pedal assistance control is not as good as the BMSBattery controllers like the S12S.

 

[trex]

I'd put a Woosh front BPM kit on a good bike. It'll pull anything.
http://www.pedelecs.co.uk/conversion-kits/front-bpm-kit/

 

[John Griffiths]

What's the reason for not going 48v or a higher watt motor?

I see what you mean the em3ev batteries seem nice.

What about hydraulic disk breaks, easy or not?

 

[Deleted member 4366]

It's fairly easy to make a switch for hydraulic brakes out of a magnet and reed switch.

Higher voltage is better for higher speed, but not necessary for higher torque. The lower voltage gives the opportunity to save a bit of weight. Having said that; if you get the 48v 201 rpm motor from BMSB, it's 15mph max, so it's a real torque monster for towing and climbing.. The Speed of A BPM is given by its code number stamped on it. They range from code 8 to16. Here's a table of speeds compiled by Jeremy Harris. 15 mph iss 201 rpm in a 26" wheel. You have to use the Kv, and multiply that by your maximum battery voltage (42v for a 66v battery) to get the actual maximum speed, which makes the 48v 201 rpm one a code 16. Always ask the supplier for the code number because it's important:



The code number is the number in brackets:
http://2.bp.blogspot.com/-N_-T--VV_qI/Uxo9H-vaV_I/AAAAAAAAAkA/vLDY-GBAtmE/s1600/DSCN5211.JPG

 

[D8ve]

I am thinking a tandem tricycle is an option.
As you are fit a legal build could work. But low speed high torque would help with carer,s.
Big amps and or additional plugin battery to get range.

Keep going and good luck

 

[jackhandy]

As he's been looking at Haibikes for fun use, I can't see this having too much appeal

 

[shemozzle999]

A small wheeled 250W crank drive bike with suitable gearing and a sufficiently sized battery should develop enough torque to pull your son around, abeit a a slow speed.

 

[Alan Quay]

I agree with others who have said BPM. I think you need to go 500w, and I suggest putting it in the rear. If your donor bike is more than 7 speed, then go with the Bafang CST instead (Cassette version of the BPM).

I often tow my lad on his bike behind my CST motored bike.

As far as £3000 budget goes, well that's easy. Build 3 of them!!

You should be able to get the kit from BMS for around £500-£650 (including delivery and import duty), and a half decent MTB for £200-£300.