Lightweight booster help please!

[gofaster]

Hi All,

I have been lurking here for a few weeks trying to learn so thanks for all the informative posts!

Unfortunately, I am still not sure what bits I should buy so I am hoping for some advice please.

I am looking for a kit to add to my wife's 700c road race bike to give her another few mph. We would like assistance for alpine climbs and also hopefully assistance on the flat up to at least 22mph. She is only 7 stone so I think 250 watts would be plenty. Also because she is light hopefully the kit won't add much weight. We would need it for our trip starting 12th July but could refine it in the future.


I have seen a few kits on ebay etc for around £400 but I am not sure if they are what we need.

Thinking the Tongxin motor sounds good but less available in the U.K. than the heavier 8fun.
Also thinking of a 9Ah bottle battery but also like the idea of modular RC batteries for lightness and the option of different capacities for different trips.

She is happy with a simple on/off switch and would like some kind of power cut off when she pulls the STI brake/gear levers.

Any advice gratefully received - thanks!

 

[KirstinS]

welcome

ok, first off are you pretty with bike mechanics and basic electronics ? (by which I mean simply testing voltages and a bit of soldering)

if yes then a kit could be a winner for you, if no then you could get a compy like Cytones to convert your wifes bike. Usually around the 1000 mark and they use tongxin motors. They have small 4ah battiers though using NiMH battery. Also they will make it to legal limit of 15.5mph

Part of your requirements is assiatnce up to 22mph. That is not legal in europe on the roads so you either need a kit that you tinker with to go faster I imagine a 36v 250w kit but run at 44.4v will get the extra speed you need. As i say - not legal though. You can get 44.4v either by using lipo RC battiers or by making a 7.4v booster battery to your main 36v one.

LIPO are light and modular but require lots more care to prevent your house burning down. You'll also need to make up or modify a harness to hook up the LiPo bricks into one battery.

i can tell you that an 8fun motor wont go into normall sized 700c road forks. I had to change forks to get mine to fit (Surly 29er MTB rigids)


also an 8fun kit adds about 8.5kg to bike, cytonex more like 5kg i belive

do you have money to throw at the project ? Whats your budget? And what do you want exactly ? a bike that has a bit of assist up hills but otherwise you pedal unpowered ?

I may be wrong but I think you will need to compromise a bit in either weight, assist speed or effect on unpowered ridind

Or maybe just go out and get a bosch powered bike and get a dongle to nobble the system so that it assists up to 22mph and more. Expensive but suits your needs perfectly without compromise

 

[KirstinS]

Hope you can make sense of post! Fat fingers, small touchscreen and a train to blame for endless typo's!

 

[Croxden]

Hope you can make sense of post! Fat fingers, small touchscreen and a train to blame for endless typo's!

I hope I'm never on the train you are driving.

 

[D8ve]

Hope you can make sense of post! Fat fingers, small touchscreen and a train to blame for endless typo's!

that post made sense to me. only additional note is the whoosh CD etc as option with D8veh mods applied..

 

[jackhandy]

Is a Woosh CD really an option for someone wanting a lightweight road-racer with light assist to 22mph?

 

[D8ve]

The whoosh isn't lightweight but with d8veh reprogramming it will do 20ish or use the crank drive on a converstion. Or persuade me to sell my BH race Delux circa 17kg and with rehearing 20mph plus. I think there is another in Uk someplace

 

[gofaster]

Thanks for the replies. Yes KirstinS I understood that fine I will try to answer you...

I am fairly good at bike mechanics and I used to do a bit of soldering in the past. I could get a meter to check voltages. So yes hopefully I can get the parts together and fit them myself. I hope I can manage it sub 6kg for under £600. If I had a big budget I would blow it on a Gruber (Vivax) Assist!!

Interesting that the 8fun wouldn't fit. I have found a Tongxin 36v, 190rpm built into a 700c rim. Only one available for £200. I guess that aint cheap but it saves waiting weeks for one from China????

Do you think I should get that quick - then sort out the battery & controller choices??

As we are going to the Alps on the 12th - 15.5mph would be fine for that as its all up or down 8%+! I could work on the flat 22mph ability later.

(I am a keen amateur racer on the road and velodrome - I train with a "powertap" power meter which displays the power I exert on the rear cogs. I experimented today with sitting at 250watts for long periods to mimic a hub motor. I was able to sit between 18-25mph depending on the breeze direction & slope being +/- 2% gradient. So given that I am 10 stone and she is only 7 stone and would add around 50watts of her own - I hope that she could match me comfortably.)

Cheers for now.

 

[103Alex1]

(I am a keen amateur racer on the road and velodrome - I train with a "powertap" power meter which displays the power I exert on the rear cogs. I experimented today with sitting at 250watts for long periods to mimic a hub motor. I was able to sit between 18-25mph depending on the breeze direction & slope being +/- 2% gradient. So given that I am 10 stone and she is only 7 stone and would add around 50watts of her own - I hope that she could match me comfortably.)

Cheers for now.

I'd be interested to see how correct your assumptions that rated power necessarily converts so readily to bike speed turn out to be.

If 18-25mph is the target cruising speed range, I'd be cautious of assuming that's easily achievable over long distances from a lightweight kit unless you also stick with your basic road bike frame & slicks. If you veer away to hybrid bikes as some suggest and expect that performance consistently (assisted), then a very limited range can be expected without a large battery to support the inevitable high power draw these bikes will likely demand to mirror a road bike performance.

All hub motors are not equal (especially as regards speed, since they vary in RPM, and there are very few times a 250W motor would actually deliver 250W - most of the time it would be a lot less or a lot more, depending on controller responses and rider input). Seemingly logical assumptions don't always translate into practice, for a whole host of reasons beyond weight and rated power.

Hub motors which readily deliver high road speeds (21-25mph) tend to be at the higher end of the RPM options. These same motors are typically not great at meaningful steep climb assistance (which requires low RPM motors preferably with a high peak power output). If your trip is 'Alpine' then average power consumption will likely be high ...

 

[Deleted member 4366]

I think you've left it a bit late, so your choices are very limited. An Oxydrive kit is about 6kg, and will give the speed you want. You just have to go into the settings on the LCD display to change the speed limit. It costs a bit more than your budget.

You could use the Tonxin, but 190 rpm isn't fast enough at 17mph in a 700c wheel with a 36v battery. It would be easier to get an 8Fun kit, which would be about the dame speed.

For 22mph you need a 250 rpm motor, which you can get from China, but it'll take at least 2 weeks to come.

Another option is to get any other kit that can normally go about 18mph and add a battery booster. Extra volts increases the motor's top speed. The idea is to add an extra two 3.7v blocks to a 36v battery to get a 20% speed increase. You have to order twelve 18650 cells and make them into two blocks of six. You can buy them on Ebay ready welded into 2s6p configuration, but again, you might be stuck for time.

An 8Fun kit is one of the slowest. You could ask Juicy, Alien and Cyclotricity about their motor speeds. If they use the same motor as their 26" wheels, you might get 20mph or morein a 700c. If you go for the Cyclotricity, it's worth paying the extra for the LCD display for the extra PAS levels.

If you're technically competent, you could get the Cyclotricity kit with LCD and without battery, and use 12S lipos from Hobyking, which involves a bit of wiring. That will run at about 48v, which increases speed by 20% from standard. Total cost for a 10ah battery, charger, connectors, etc would be a bit less than the equivalent normal battery, but you'd need to make an enclosure for it.


Sent from my GT-N7100 using Tapatalk 2

 

[gofaster]

Thanks for the options you have outlined. I am now looking into them.

Yes I also wonder how well my power meter numbers relate to hub motor performance. Unless anyone here has gone through this themselves then I will just have to try a kit to find out. I will let you know.

 

[gofaster]

Hi again - quick question...

Is it feasible to change the gears inside a Dapu (or other) motor for different uses?

(The battery booster voltage increase idea could be tricky especially on an Oxydrive with the battery holder/ controller being integrated...

Standard is probably good for an alpine climbing trip. However on a future tour across the flat Netherlands a higher top assistance speed would be handy for her to keep up with me in a tailwind)

Thanks in advance for any advice.

 

[Geebee]

My experience with the same human wattage versus motor wattage is that the human one will give noticeably better performance in the real world.

 

[Deleted member 4366]

Hi again - quick question...

Is it feasible to change the gears inside a Dapu (or other) motor for different uses?

(The battery booster voltage increase idea could be tricky especially on an Oxydrive with the battery holder/ controller being integrated...

It's not possible to change the internal gearing of a hub-motor. Instead, you can change the speed by using different voltages.
Whether you have an integrated controller or not, it makes no difference to add a booster battery. The controller still has two wires coming to it from the battery with connectors.

Buying an Oxydrive kit and adding a booster battery makes no sense. It would be much better to buy the right speed motor in the first place.