First build: ebike for bike polo

[Merj]

Hi all,

I've been reading through the forum for days now and wanted to get your input on how best to build a reasonably priced ebike that's durable enough to play bike polo. I had to stop playing bike polo a few years ago due to some health issues that limits my cardio output. Performance requirements are as follows: We play 4 vs 4 on a grass soccer field and use pairs of traffic cones for goals. Our style of play typically requires a sprint front end to end (maybe top speed of 17MPH) followed by hard braking and slow, intricate bike handling in front of the opponents goal. Lots of stop/starts with balancing in between. Someone once measured about 12 miles of travel on a typical game day (we play multiple games). I can pedal fairly hard as long as it doesn't require sustained effort. Almost everyone uses single speed hard tail mountain bikes to play......keeps our bikes simple to repair/less likely to break down. I use a single rear mechanical disc brake on my steel Surly 1x1 frame. I can't remember the teeth count on my front chainring and rear cog. Will post later.

Based on what I've read on the forum, I've made the following assumptions:

1. Rear Direct drive is probably best due to simplicity/durability even though I'll lose torque at startup and true freewheeling when not pedaling
2. I'd like for the rear hub motor to roll as freely as possible and be compatible with rear disc brakes
3. I've never ridden an ebike so I have no idea how well PAS or torque assist works. Since I'm riding with my right hand on the handlebar (mallet in the other hand) it would be nice to only have that hand worry about braking only i.e. no throttle but I'm not sure if that's realistic. Maybe a PAS system with throttle override for sprints?
4. I think a bottle battery (or frame mounted battery as low as possible) would help with bike balance vs a rack mounted battery.
5. I've been looking at Dillinger conversion kits but am willing to buy individual components and piece together a better solution if that's possible. I did this for my electric skateboard which uses two 5S lipo batteries from hobbyking and a controller/motor from Alien Drive/Power systems.
6. Willing to spend up to $1,000 USD

Would appreciate any and all input.

Thanks!

 

[docnjoj]

I used to play bike polo as a kid in our schoolyard. My guess is a fairly strong geared motor like BMC or MAC with at least 10-15 AH Hobby LiPo. Good acceleraton and freewheel so no drag. You will need more capacity/power than most bottle batteries offer. I never use Hobby LiPo because I like to charge in the house. They do have very high power/weight though. Oh yeah. I played this game in the 1950's.
otherDoc

 

[cal3thousand]

hub motor for sure. middrive is too much work for that activity.

I agree on the MAC motor suggestion. And I would recommend a 10T. It will give you just enough speed (20mph) at 36V while having some solid oomph to get you going quickly. It will also handle the slow speed stuff really well. This kit comes out to 935, but you need to pay shipping. It has an upgraded battery for $85 more, so you could lower the price by that much but lose a little range:


http://em3ev.com/store/index.php?route=product/product&path=45&product_id=179

1 x Upgrade Mac Kit with 36V Frame Battery (up to 40km/h/25mph)
- Battery Type 36V 16.5Ah Frame Pack, 2.5A Charger
- Max Speed ~32km/h (20mph)
- Controller Type 25A 6 Fet (36-52V, IRFB3077)
- Front/Rear Motor Rear
- Wheel Type 26" Alex DX32 CNC
- Spoke Type Sapim Upgrade (Silver)
- Throttle Type Half Twist
- Ebrakes HWBS Sensor (1pc)
- Disc Spacer 1pc 2.5mm Disc Spacer
- Torque Arm Rear Rev4 (1pc)
- Freewheel Without Freewheel
- Display Without Display

Sub-Total: $935.00
Total: $935.00
View Cart | Checkout

 

[waynebergman]

You may also want to consider a version 3 CA to go along with the mac 10t so you can have better slow speed control for all the stops and starts that you will be putting the system through.

I have not seen bike polo but it sounds like fun. I remember seeing a crazy soccer game being played by very skilled trials style riders on fixed wheel bikes I think if I am right. They did a lot of stuff off of one wheel and stuck the ball with the front front wheel, totally crazy.

Could you could post a video link on your thread here to show what the bike polo is all about?

Wayne

 

[MadRhino]

The advantage of a motor will be too much. All players must have one, or none.

Slow hub motor, lots of Amps for high torque, regen braking is a big plus on the grass...
I would build on a short wheelbase FS frame and adapt to 24" wheels, 3" low PSI mud tires, light on the front end with a fairly steep steering angle.

I don't know about bike polo, but if it is mostly like polo each chukka could be played with a fresh battery. I would use small lipo packs, just enough to deliver power for the 7 minutes of one chukka.

 

[Drunkskunk]

My friends and I used to play Moped Polo, which was more like Soccer. We used a deflated soccer ball and no mallets, but we called it Polo anyway. Don't ask, it was a beer fueled idea.

Anyways, the point is the amount of power needed is surprising. you're going to be constantly putting the power on hard, which will be hard on both the motor and battery. With the mopeds, we blew engines almost every match, shredded chains, and broke wheels. All this when a moped has less power and torque than an ebike.

From that perspective, I'd suggest 2 motors, one on each wheel. not for more power, but so the motors can share the stress and cut the heating by half for the motor. 2 MAC motor running 750w each would have half the heat and stress problems of 1 MAC trying to run 1500W.

As for Pedelec, it makes sense, but you'll need to run a torque based crank sensor like the THUN. the magnetic pickup type aren't responsive enough for that kind of riding.

About the only battery that's going to be able to handle what you need is Lipo. They are dangerous if mishandled, so you'll need to learn how to handle them.

 

[Merj]

Thanks for the input everyone. I have a few follow up questions and comments:

1. I like the ideas of a MAC motor because of the increased torque from a standstill. Having said that, I'm worried about the stress on the internal MAC gears. Am I going to be constantly breaking gears? Should I consider Direct Drive and give up torque for reliability?

2. Will 36V 16.5 amp hour battery be enough for the MAC setup above? I realize that it fits into my budget, but I also don't want to have to order a battery upgrade right off the bat.

3. I think 2 motors (front and rear hubs) will be way out of my budget. Plus the added weight will be tough to handle.

4. Are the EM3ev batteries lipo? I'm assuming they are the safe version (LiFePO4). I run RC airplanes, 1/10 scale trucks and my electric skateboard on lipo batteries from HobbyKing and am very careful when charging. I realize how dangerous they can be. I run two 5s 5,000 MAH batteries on my electric skateboard. Maybe I should checkout HobbyKing for full strength lipos. I'd have to build a frame mount, buy a BMS and wire together though.....

5. Torque based crank sensor sounds good. Is the THUN compatible with MAC motor/Infinion controller? Who sells them?

6. I already have my trusty old steel Surly 1x1 single speed polo bike that I'm used to. It's collecting dust now so that's what I will be converting to an ebike.

7. The way we play, each 'chukka' lasts until one team scores 5 goals. On a typical Sunday, we travel 12-18 miles and play ~2 hours. The number of players that show up determines how, long we play. It's a serious workout!

8. The Cycle Analyst sounds like a good investment. I will add one to my build.

I realize that I'll have an advantage on the field over non-ebikes, but I actually I started grass field bike polo here in Richmond 14 years ago and all of my friends are encouraging me to come back out with a an electric bike so that I can play. My disease is preventing me from playing at the moment. I'm hoping an ebike will let me get back out there. I will post a video of our game when I get back home from vacation.

Thanks for all the input. Please keep it coming.

M

 

[MadRhino]

Should I consider Direct Drive and give up torque for reliability?

You don't give up any torque with a DD hub.
Torque on a DD is at the expanse of higher power and some extra weight, but it is capable of much more torque than a geared hub because it is not limited by poor gear strenght or ridiculous clutch size.

Then, if you play a chukka until 5 goals score, I believe it could be very long. Maybe too long to carry the batteries needed for high power, or too long to give any chance to your system to cool.

 

[Drunkskunk]

Ebikes.ca Sells the Thun, which also requires the Cycle Analyst version 3, which they also sell.

 

[Merj]

A few more follow up questions:

1. If I decide to build my own Lipo battery packs, where would you suggest I purchase them from? I'm assuming I would need a BMS or would that be redundant if I use my current lipo charger?

2. I thought Direct Drive hub motors had a lot less torque starting from a standstill than gear drive hub motors. Is that true?

Thanks!

 

[MadRhino]

You buy lipo at hobby king, I don't use a bms and most who are using lipo don't, monitoring is a must of course.

A geared hub will give you more torque for equal power, but its power limit is much lower.
So, you can achieve much more torque with a DD hub, at the cost of higher power and weight.

 

[waynebergman]

I wonder if the starting point for motor choice should come from if the build is based on 72 volt or a 50 volt system. A 50 volt may be best with a 12t or 10t mac and a nice sine wave controller. What could be real nice with a 72 volt system is the DD hub with the proper winding and rear wheel mix for your needs and with the DD that could be really cool is the adaptto sine wave controllers that are starting to make an appearance. The reason I mention the adaptto is there is talk of them building the regen into the throttle so this could be very cool on the DD hub for something like polo. The throttle I have heard will actuate the regen braking by twisting past the normal closed position so no need to fiddle with brake lever if it works. The more you would twist past normal closed the more braking you would get. This being said I think its all talk at this point for this feature to be a part of the kit that would include a throttle, display and controller. I gathered this from the interview the maker of the adaptto did on a recent podcast. I mention this as if its something you like and you go for a DD hub you could add this feature to your bike down the road if and when it comes to market. I also think to go with a 24inch rear wheel on either motors could work in your favour.

 

[EV_Ron]

Merj,

Did you make a decision and purchase a motor kit for your bike? What did you get?

I installed and am currently testing a Q100H motor.

Thanks...

 

[Modbikemax]

Another project by Gunna.